Model Engine Maker

Engines => Your Own Design => Topic started by: Roger B on November 14, 2021, 09:19:04 AM

Title: 20cc Four Stroke Diesel
Post by: Roger B on November 14, 2021, 09:19:04 AM
After having experimented with my two stroke diesel for some time ( https://www.modelenginemaker.com/index.php/topic,5545.0.html ) I have begun to wonder if I am getting some specific 'two stroke' problems  :headscratch: I think it has a tendency to run on excess fuel that gets past the piston rings and is then inducted from the crankcase  :thinking:

I know that I have enough compression to ignite the diesel fuel (pump diesel). I know that the bottom end is strong enough, it even survived the passage of an M3 grubscrew through the system.

The next step will be to convert the current engine to a four stroke. I can use the crankcase, crankshaft and conrod. The cylinder and head will be based on the horizontal engine with a chain driven camshaft mounted under the cylinder. The head and combustion chamber will be a challenge to fit the valves, injector and water cooling passages. I am looking at two options at the moment, The standard bowl in piston and the Lanova type figure of 8 around the valves. The Lanova type seems to result in masking of the valves but makes fitting the injector easier. The bowl in piston will require some interesting water passages to allow a reasonably central injector.
Title: Re: 20cc Four Stroke Diesel
Post by: Minh Thanh on November 14, 2021, 12:24:02 PM
Hi Roger !
 4-stroke diesel engine is easily determines the efficiency of the pump and injector
  Good luck !
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on November 28, 2021, 07:35:46 AM
Thank you  :)

The first step on this conversion was to arrange a suitable camshaft drive. Studying the catalogues suggested that a 12 tooth 6mm pitch chain sprocket would fit in place of the injection cam. The boss on the crankcase cover had to be reduced in size to give clearance to the chain and the sprocket had to be thinned down to 7mm wide.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on November 28, 2021, 07:37:33 AM
Finally I broached a 3mm keyway in the sprocket and put it all back together.
Title: Re: 20cc Four Stroke Diesel
Post by: Admiral_dk on November 28, 2021, 11:07:49 AM
Great to see that you are moving forward again Roger  :ThumbsUp:

I'm wondering about your pump placement - will it still be crank-driven and if that is the case, what about the fact that you only should have one injection per 720 degree crank rotation ?
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on November 28, 2021, 05:17:54 PM
Thank you Per,

The injection pump will be mounted on the non drive end of the camshaft (about where the vertical exhaust pipe is now). This will keep my fingers away from the drive chain in the early trials. I need to think about timing adjustment systems  :headscratch: I may keep the idea from the two stroke but with the pump mounted vertically  :thinking:
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on December 05, 2021, 08:33:05 AM
I worked out the chain length and sprocket centres using the standard formulae and then put the pieces together for a sanity check. 12T, 24T and 64 links.

The cylinder liner is made from a length of 40mm cast iron. 35mm would have been better but I could not find any at the time, just make more swarf  ::) The blank was trued up in the 4 jaw independent chuck and carefully faced (250rpm 0.1mm depth of cut) and centre drilled. It was then turned to size at 500rpm and 0.5mm depth of cut. Finally I turned a centring ring for the hole saw before cutting it off from the stock. The other end was then faced and the centring ring was cut.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on December 05, 2021, 01:25:34 PM
The centre of the liner was cut out using a hole saw. Much quicker than drilling and boring with lightweight machines and you get left with a useful core  :)  The liner was then bored out until the lap would easily enter but the plug gauge (from the 2 stroke diesel build) would not go in.

Next up I need to think about options for milling the cylinder block  :thinking:
Title: Re: 20cc Four Stroke Diesel
Post by: Admiral_dk on December 05, 2021, 05:08:10 PM
I really like how you get something useful out of the core, instead of just converting it to dust ....
Just a shame that it can't be used as a piston in the same cylinder  ;D
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on December 12, 2021, 07:39:10 PM
Hi Per, maybe a fine laser cutter would work  :)  ::)  :wine1:

Next we have some work by 'Dodgy Setups are Us'. I initially planned to flycut the cylinder block and head but I could not get enough travel without removing the tailstock and using the x axis so a 20mm roughing endmill worked.

I have a fairly soft camshaft from the 25cc horizontal engine that should work for the initial trials.

Boring the cylinder block is on the limit for the Hobbymat but seems to work. There is some vibration at 250 rpm however things aren't falling on the floor  :)  ::)  :toilet_claw:
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on December 22, 2021, 05:43:05 PM
The block was bored out to be a running fit on the liner. I found I was actually running at 500rpm, hence the vibrations. I started boring the water space with the insert bar and finished off with a HSS bar with a greater offset. This needed to be done at 250rpm to reduce the chatter with less rigid bar.
The O ring groove was cut with my homemade bar (made from a broken HSS centre drill). I then turned the block round, re-centred it, finished the other end of the water space and cut the recess for the liner.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on December 22, 2021, 05:44:38 PM
As the 4 jaw independent chuck was fitted I trued up the core from the liner read for reuse later.
Title: Re: 20cc Four Stroke Diesel
Post by: RReid on December 22, 2021, 08:16:30 PM
Quote
... (made from a broken HSS centre drill).
I've got one just like that!
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on December 26, 2021, 01:50:34 PM
 :) :) :ThumbsUp:

The next step was to drill the fixing holes through the cylinder block. As this is a modification of an existing engine rather than a new design it is easiest to have long studs passing through the cylinder block and head to clamp everything together. The holes were marked and spotted from both ends, started with a stub drill continued with a normal length drill from both ends and finished with an extra long 4mm drill.

The 'open' end of the cylinder liner needed to be chamfered to allow the line to enter the sealing O ring in the cylinder block and to ease the piston rings into the bore. Due to the flange on the other end the easiest way to mount it was in the Keats angle plate with some 2mm thick spacers to clear the flange.

Next up is the cylinder head.
Title: Re: 20cc Four Stroke Diesel
Post by: Craig DeShong on December 26, 2021, 07:38:46 PM
Roger; I’ve been silently following this thread for a while now.  It’s difficult for me to comment because I know nothing regarding diesels.  I must comment though, that I have to admire your tenacity in staying with this project.  This is reminiscent of my experience with my first Otto & Langen engine, where it was over a year and a half before I got it to run dependably.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on December 28, 2021, 07:29:44 AM
Thank you Craig  :ThumbsUp:  :ThumbsUp:   I think that the challenges you faced with the Otto Langren are much the same as I face with the diesel, you can’t scale nature or tolerances and you have to work out which details are critical.

Before I cut any more metal it was time for a quick sanity check, I removed all the two stroke parts from the engine and bagged them up for later experiments. The cylinder block was then rested in place and the positions of the camshaft drive and injection pump were confirmed. Finally I checked the position of the top of the conrod at TDC which was 12.3mm as opposed to 12mm on the drawing.

The cylinder head fixing holes were drilled 4mm and the valve guide holes were drilled 7.9mm and reamed to 8mm. The fixing holes lined up with M4 screws :)

Next up I have to work out the best way to clamp the cylinder block for boring the 16mm camshaft tunnel and sort out the lubrication system for non 2 stroke use.

Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on December 28, 2021, 07:40:06 PM
The set up to bore the camshaft tunnel was not easy  ::) The 50mm width of the block is the same as the quill stroke on the mill, the block was to big to fit on the faceplate and the M6 T nuts that I had would not fit the milling table. In the end I milled the M6 T nuts down to fit and used the mill. I started off with stub, standard and then long 2.5mm drills, dropping the milling head 1mm to ensure breakthrough. This was followed with a 13.5mm drill, again having to drop the head to get a breakthrough.
To get the full 50mm stroke with the boring head I found an additional sleeve for the clamp bolt, the usual one only allowed 40mm. Previously I had purchased a couple of cheap 8mm insert boring bars so I could cut them down to sensible lengths to reduce chatter.
The first cut seemed ok but this will take a little while at 0.15- 0.2mm depth of cut. I have 16mm reamer to finish off.
Title: Re: 20cc Four Stroke Diesel
Post by: Kim on December 28, 2021, 10:45:53 PM
Wow... you had to make a lot of 'tool adjustments' to get this one made.  But you found a way to get 'er done!
Enjoying following along, Roger!  :popcorn:

I didn't follow the thing with the 50mm (vs 40mm) sleeve and clamp bolt thing.  What does the sleeve do that allows you more stroke length? Is it a Proxon specific thing?  Or am I just not understanding in general?

Kim
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on December 29, 2021, 07:17:52 AM
Thank you  :ThumbsUp:

Its a Proxxon thing, a nut that fits the drawbar thread won't pass the top of the quill so it needs a spacer. I should really make a 55mm long spacer next time I am in lathe mode.
Title: Re: 20cc Four Stroke Diesel
Post by: Kim on December 29, 2021, 05:58:07 PM
Ah!  I get it now.  Thanks for the explanation, Roger.  Makes perfect sense now.  :ThumbsUp:

Kim
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on January 05, 2022, 07:54:59 PM
We went off for a while to enjoy some warmer weather and sun in southern Switzerland  :) Now back to some engine making. The camshaft tunnel was bored out to 15.8mm and then reamed to 16mm. The next step was the bores for the cam followers. these were drilled out to 11.5mm and then reamed to 1mm. Finally I milled a 16mm pocket so I could have a chance to press the bushings in place. Just a few more holes to go  ::)
Title: Re: 20cc Four Stroke Diesel
Post by: RReid on January 05, 2022, 08:22:26 PM
What a beautiful sunset shot! Even prettier than your engine work, which is pretty darn pretty.  :ThumbsUp:
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on January 08, 2022, 05:28:06 PM
Thank you Ron  :) Ascona is always a beautiful place however the mist over the lower part of the lake made that sunset special, some of the other pictures almost look like posters.

I have decided to keep the oil pump feed to the crankshaft bearings and will run a low oil level in the crankcase. This will keep the camshaft lubricated via a 4mm drilled passage. The previous crankcase drain will go directly to the inlet of the oil pump.

Having finished the camshaft tunnel I put the pieces together with a temporary shaft to check the chain centres. It is a little slacker than I would like, but not a real problem as the lower pass is the tension side. There is a little interference between the chain links and the oil pump body which can be easily solved.

The camshaft bearing supports were turned from a dog end of 30mm diameter aluminium. A piece of 10mm silver steel was a good running fit so all seems to have remained concentric and parallel.

Next up is the fixing holes for the bearing supports and some water connections for the cylinder body.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on January 13, 2022, 07:42:56 PM
The camshaft bearing supports were set up in the Proxxon RT to drill the fixing holes. The holes were then spotted through to the cylinder block and tapped M3. The fixings for the cooling water were drilled and tapped M8x1. Unfortunately I picked the 7.5mm drill rather that the 7mm so the thread depth is limited  :( but it will still hold.

The bushes were then pressed into the bearing supports and faced off to length. A quick trial assembly showed enough clearance and the cam lobes were fairly central. A little off centre is good as it forces rotation and even wear  :)
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on January 17, 2022, 05:49:24 PM
The next step was to make the camshaft sprocket fixing and fine adjustment. I was prepared to mount the sprocket in the 4 jaw independent chuck to open out the bore but a quick trial in the 3 jaw was true enough, no visible run out, so I used that. I drilled 9.5mm and again no visible run out so I opened out to 9.8mm and then reamed 10mm. The jaws were changed to the external (???) set and the sprocket boss was thinned down. A bush was then turned from a dog end of mildish steel and parted off. The 2mm keyway was cut using my bench drill as a press and the bush was then moved to the Proxxon drill for drilling and taping 2mm for the grub screw. If there is a key I prefer to seat the grubscrew on that as it does not mark the shaft. The bushing was then transferred to the RT to drill the ends of the adjustment slots 2mm.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on January 17, 2022, 05:54:41 PM
The sprocket was then drilled and tapped M2 with the RT in the same position. The RT was moved to the Proxxon mill, centred, and the slots were milled with a 2mm endmill at 11 000 rpm in 0.5mm steps. The trial assembly seems to work and will allow easy setting of the cam timing. I now need to make a similar bush for the injection pump cam and mill some keyways in the camshaft. The cams will be fixed to the shaft with Loctite.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on January 27, 2022, 05:10:44 PM
A little bit more on this. The tappet bushes were turned and reamed from bearing bronze and as they are deeply recessed I made a mandrel for pressing them in place. The injection timing adjuster was made in a similar way to the camshaft one except the slots were made completely in the Proxxon mill rather than starting in the drill and moving to the mill.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on January 27, 2022, 05:13:36 PM
The last picture of the injection cam drive and a start on the tappets. These are made from 10mm silver steel with the camshaft end carefully polished with a fine diamond file and the pushrod hole drilled 6mm. These will then be hardened and polished again.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on February 07, 2022, 05:16:03 PM
With the Hobbymat back in milling mode I started on the injector seating in the head. It was clamped at 30° and centred on the bore centre pop. The seating was machined with a 14mm endmill in 1mm steps, hoping my drawing and calculations were correct. The injector hole was drilled from above and arrived almost on centre on the lower face.

The injector hole was opened out to 5mm followed by an 8mm bore for the O ring and a 10mm bore to clear the injector body. A quick trial fit suggests that the calculations were correct. The picture is with the sealing O ring uncompressed. It should protrude around 0.5mm more.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on March 05, 2022, 02:56:20 PM
I'm still doing some bits on this one. The tappets were turned from 10mm silver steel, hardened and polished. The ports and pushrod holes were drilled in the cylinder head and the block and head were cleaned in the ultrasonic bath. Next, I think, will be the valves and guides.
Title: Re: 20cc Four Stroke Diesel
Post by: propforward on March 05, 2022, 03:18:02 PM
Coming along nicely Roger! Some very fine and intricate work going on. I like how you go "all the way" hardening parts as appropriate too.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on March 12, 2022, 05:25:20 PM
Thank you Stuart  :ThumbsUp:

From my earlier trials I have determined that there are some high forces involved and try to avoid as many problems as possible (there are still plenty more out there  ::) )

The valve guides were turned from some 13mm bronze rod. The bores were reamed 3mm and then after they were pressed into the head they were reamed again. The bore collapses enough to allow a cut with the reamer.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on March 12, 2022, 05:30:50 PM
The valves are made, as I have done before, from stainless steel screws. The points are cut off allowing a little extra length and then faced and centre drilled in an ER collet. The blanks are then reversed in the collet and the bolt heads are turned down to 10mm. These are then held in a spring collet and the stems turned down to 2.9-2.95mm to allow a little clearance.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on March 13, 2022, 07:50:29 PM
Next the valves were held in the ER collet and the heads were faced and centre drilled. The seats were then turned to 45° and the under head was radiused. Finally the heads were turned to 1mm. This thickness is fairly critical due to the high compression ratio and the small clearances  ::)

Looking at the raw material and the almost finished valves, it is a bit like working with castings and seeing what is inside.
Title: Re: 20cc Four Stroke Diesel
Post by: RReid on March 13, 2022, 11:34:53 PM
I like your method of making valves, Roger. I think I may try it doing the valves for my current build that way.  :ThumbsUp:
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on March 14, 2022, 11:19:43 AM
Thank you Ron  :ThumbsUp:

I have also made smaller valves from M4 stainless steel caphead bolts. It all depends on what ss fastenings you local hardware store has.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on March 20, 2022, 07:26:40 PM
Next I cut the valve seats with a cutter I made for a previous engine. On trying the valves one was obviously not on its seat. A quick measurement showed that the valve stems were about 0.2mm out of true over the exposed length. As a first fix I pressed the valve guide out, turned it 180° and pressed it back in. The valve now appears to seat properly  :)
The next pieces were the valve spring caps, these are again a copy from the horizontal petrol engine. I reduced the recess for the E clip from 9 to 8 mm as I had a suitable end mill and that gave adequate clearance.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on March 20, 2022, 07:28:33 PM
The spring seat and parting off were made with my new Aplitec parting and grooving tool as I am still learning what it can do.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on April 15, 2022, 02:47:50 PM
Next up I drilled and tapped the remaining holes for the injection pump in the cylinder block and then moved onto the rocker support. This is held in place by the studs that go back to the crankcase. it was roughed out by drilling and hacksawing, much quicker than milling if you only have small machines  :)
The slots for the rockers were started with a 5mm endmill and then finished to width and depth with a 3mm radius cutter. The rockers will be made from 6mm x 10mm key steel like the horizontal petrol engine.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on April 15, 2022, 02:48:32 PM
The last pictures.
Title: Re: 20cc Four Stroke Diesel
Post by: propforward on April 15, 2022, 03:31:52 PM
Looks great Roger, following along and enjoying the process.  :popcorn:
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on April 24, 2022, 07:38:56 AM
Thank you Stuart  :ThumbsUp: I'm still slowly plodding along with this build. We've been enjoying some good weather recently so have been wandering around Switzerland.

I've copied the timing adjustment from the two stroke version where the pump thrust is taken by a 4mm square bar in a slot.

The rockers are the next pieces to be made. They are generally milled from some 10 x 6 mm key steel and will be fitted with bronze bushes.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on May 14, 2022, 07:50:25 AM
The next step was to work out the positions of the keyways for the camshaft to give the correct alignment between the valve cams and the fuel pump cam. The two keyways were cut with a 2mm Woodruff key cutter. The camshaft was originally made for my 25cc horizontal engine and was replaced with one with more lift and opening period

The rockers were then profiled using the rotary table and cleaned up with a small sanding drum. The adjuster holes were drilled and tapped M4 and they were finished with a couple of bronze bushes. I decided not to harden the working faces initially as they are already fairly tough (C45K ~EN8).
Title: Re: 20cc Four Stroke Diesel
Post by: Admiral_dk on May 14, 2022, 09:02:33 PM
Nice to see that you still are making progress Roger  :ThumbsUp:

You mention the hardness of C45K and EN8 - are they hard to cut with a mini mill ?

Per
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on May 15, 2022, 08:14:17 AM
Hi Per, they cut ok with reduced speed and depth of cut. Getting a good finish can sometimes be difficult.

The next step was to dismantle the crankcase from the two stroke version to drill and tap the fixings for the four stroke cylinder block.

I will reuse the inlet trumpet although I will need to reshape the flange. The con rod carries the scars from an M3 grubscrew's passage through the engine. There is some scoring of the crankshaft where the flywheel and starter dog fit. The starter dog seatin has already been turned down and sleeved after previous problems.

The next step is to clamp the crankcase and cylinder block together and spot the holes.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on May 24, 2022, 05:25:19 PM
I was planning to use pieces from my milling clamp set to hold the crankcase and cylinder block together for spotting but the slots were not quite long enough. They were opened out in the mill using one of my recently won 8mm roughing cutters. The pieces were aligned and clamped together, the spotting was near the limit for my bench drill but worked. 80mm stroke was just enough. The holes were then tapped M4 and I cut some blanks for the fixing studs.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on May 24, 2022, 05:29:48 PM
I decided to thread these under power, but I know that at 250 rpm the Hobbymat has quite a long run on period so I couldn't use a fixed stop. A tool shank made a suitable aiming mark and all 5 were successfully made. The holes through the block were then opened out to 4.5mm and those in the head to 4.2mm. It all fitted together and allowed me to check the cam chain length and alignment. All looks OK  :)
Title: Re: 20cc Four Stroke Diesel
Post by: Brendon M on June 07, 2022, 08:45:34 AM
Hello Roger, I look forward to seeing this run :)
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on June 17, 2022, 08:09:15 PM
Thank you Brendon, you may have to wait a little while  ;)

The next stage was a slow lapping of the cylinder liner to the same diameter as the two stroke diesel. I use an Acro Lap and 40 micron diamond paste. I kept on until the plug gauge from the two stroke engine was a snug fit and then checked with the piston and spare piston rings from the two stroke fitted.

Next step is the piston.
Title: Re: 20cc Four Stroke Diesel
Post by: Admiral_dk on June 18, 2022, 11:03:23 AM
Great to see that you still make progress and nice piston ring to cylinder fit  :ThumbsUp:   :cheers:

Per
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on June 29, 2022, 05:57:29 PM
Thank you Per  :)

I decided to use the Keats angle plate to make the piston. It is set up so I can clamp a stub of 6mm silver steel in a collet and use it to align the Keats on the face plate. The blank was turned to around 0.5mm oversize, the bulk of the conrod space was drilled out and the skirt was bored. The Keats was then moved to the RT on the mill using the same 6mm centring hole and the gudeon pin hole was started from both sides. I have had problems with the drill being deflected by the conrod hole when working from one side. The hole was then opened out to 7.8mm and reamed 8mm.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on June 29, 2022, 05:57:58 PM
And one more
Title: Re: 20cc Four Stroke Diesel
Post by: Zephyrin on June 29, 2022, 07:03:57 PM
very nice angle plate you have Roger, very versatile piece of tooling !
although somewhat heavy on the face plate !

"I have had problems with the drill being deflected by the conrod hole when working from one side"
yes, the tip of the drill tip wander on the internal curve of the opposite hole, and both holes are misaligned.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on July 01, 2022, 05:39:42 PM
Thank you  :) I do like like that angle plate, it helps me to expand the capabilities of (overload  ::) )my relatively small machines. With that set up at 500rpm for roughing there was a little rocking at 250 rpm all was stable.

The angle plate was then moved to the milling table to cut the conrod recess. This was done with a 6mm end mill in 1mm steps. The same set up was used to drill the holes for the gudgeon pin fixing grub screws.

Next the angle plate was moved back to the faceplate to finish the piston diameter and cut the ring grooves. There was very little run out, some of which may be due to the relaxation of stresses in the CI blank.

jFr4XJ9ibto
The piston was then turned to the diameter of the plug gauge I used when lapping the cylinder.
Title: Re: 20cc Four Stroke Diesel
Post by: Admiral_dk on July 01, 2022, 09:30:02 PM
I can't say that it surprices me, to see the small amount off wobble in the short video - it is after all taken off the Lathe and put back on again .... it would require some rather expensive gear to be able to do that and have no run-out afterwards ...!

Looks like you're very close to having a new Piston for the Engine  :ThumbsUp:

Per
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on July 02, 2022, 04:31:34 PM
Thank you Per,

0.05mm TIR with such a simple setup is good  :) I had around 0.4mm to remove from the piston so plenty to play with. I turned the piston to the same diameter (as closely as I could  ::) )as the plug gauge I used when lapping the cylinder. The two piston ring grooves were cut with my 1.5 mm Aplitech grooving tool. There was a little chatter on the base of the grooves but the sides were smooth. I parted the piston off about 0.5mm over planned length to allow for cleaning up and the various tolerances in the system.

The piston is a good fit in the liner, unoiled it would take several minutes to drop through the liner with the end blocked. As soon as I unblock the end of the liner it falls straight through  :) This would probably be too tight for an aluminium piston but for a CI piston in a CI liner it should be OK. The parts that had been in contact with the diamond lapping paste were cleaned in the ultrasonic bath read to assemble the bottom half of the engine to confirm the piston length.
Title: Re: 20cc Four Stroke Diesel
Post by: Brendon M on July 08, 2022, 12:39:55 PM
Hello Roger

This is my first time seeing the Keats angle plate -- very interesting

It appears to allow you to easily move the workpiece between the lathe and mill attachment, if I have understood correctly?
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on July 08, 2022, 08:22:11 PM
Thank you Brendon  :ThumbsUp: The Hemingway Quick Set Keats has lots of possibilities. My build log is here:

https://www.modelenginemaker.com/index.php/topic,4275.0.html

I added the 6mm  locating hole to allow me to move between the lathe and the mill. It is being used here in yet another mode  :)

I rebuilt the bottom end of the engine and then trimmed the cylinder liner to give 0.1mm above the block for gasket sealing. As known from the drawings I needed to mill a couple of scallops from the liner to clear the conrod. This was done with the Keats in a different configuration and the rotary table. With a small mark I could remove the liner from the set up, try it and refit it.

When it was then assembled and free running I could check the piston height and the valve height to determine how to machine the piston crown.

4p1_Ib2BpzU
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on July 18, 2022, 08:26:03 PM
Looking at the combustion chamber I could see that I needed to reduce the size of the valves and slightly reduce the planned bowl in the piston to get a theoretical 20-1 compression ratio.

The piston was centred in the 4 jaw chuck and skimmed to length. I drilled a 6mm hole in the centre to aid the 6mm radius cutter and then milled the 6mm radius 5mm deep bowl. It all looks ok, the liner is 0.1mm above the cylinder block and the piston is 0.1mm above the liner.

I decided to reduce the valve heads to 9mm diameter (the ports are 8mm) so I could mill the clearances in the piston with a 10mm cutter. I also thinned the heads so they protruded 1 mm above the head before grinding in. Finnaly I parted off and then grooved the valve stems using my 0.5mm Aplitec grooving tool
Title: Re: 20cc Four Stroke Diesel
Post by: Brendon M on July 20, 2022, 01:02:35 PM
Seems like I won't be waiting as long as you think for this engine to run :)
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on July 20, 2022, 07:11:37 PM
Not sure , the problem at the moment is the good weather and the mountains  :)
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on July 20, 2022, 07:25:48 PM
The next step was to cut clearances for the valves in the piston crown. The Keats was used again to hold the piston and the cut outs were started with a centre cutting 6mm end mill and finished with a 10mm cutter. All went well and there is just enough clearance without the 1mm thick head gasket.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on July 31, 2022, 06:44:44 AM
The next step was to lap the valve with 20 micron diamond paste. I use a small drill chuck to hold the stems. The sealing O ring for the cylinder liner was then fitted, taking care the the clearance scallops for the cod rod didn't cut it.

The piston rings were spares that I made for the two stroke version of the engine. As the bore was lapped to the same plug gauge they fit nicely. I then realised I had forgotten to drill the camshaft oilway in the crankcase so I had to dismantle the bottom end again.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on July 31, 2022, 06:53:57 AM
The head, valves and crankcase then had a clean up in the ultrasonic bath and on with the assembly. The valve timing was set for approximately equal overlap at TDC. It can be finely adjusted later. I then saw that I couldn't tighten the grubscrew on the crankshaft sprocket so I opened up the chain. While I was typing this I realised that I just had to turn the crankshaft 90°  :facepalm2:
Title: Re: 20cc Four Stroke Diesel
Post by: MJM460 on July 31, 2022, 12:53:31 PM
More good progress Roger.  Still following along and learning heaps.  The detail really comes through in your pictorial posts.  Much appreciated.

MJM460

Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on August 01, 2022, 08:03:56 AM
Thank you, I'm glad you find it interesting  :ThumbsUp:

A few more bits. I am going to have to modify the compression tester to fit this cylinder head so a bit more drawing required. I started setting up the injection timing and found that I hadn't finished the replacement injection pump tappet. I probably left it until I could confirm the length. It was parted off to length and faced. Then came the fun task of milling the locating groove to keep the roller follower on track. The first version was cut with a slitting saw but the set up was rather complex so for the next one and this one I milled the slot with a 1mm end mill. The slot was taken to depth, 1.2mm, in 0.1mm steps at 18 000rpm and then opened out to 1.4mm in 0.05mm increments using a 1.4mm drill as a gauge.
Finally I cut the recesses in the M4 grubs screws used for the valve clearance adjusters with a 3mm carbide radius cutter.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on August 04, 2022, 06:04:18 PM
Next I started modifying the compression tester and making new clamp plates for it and the injector. Due to space restraints this engine has the fixing studs at 14mm rather than 16mm.

The hexagon was reduced to 8mm diameter, leaving a 2mm spanner flat. I also had to slightly chamfer the tip to clear the piston. There is around 0.3mm collision. The new clamp plates are made from 2mm thick bright strip. This raised a new problem as my spot facing cutters have recess above the pilot so the first attempt drifted off position. I was able to keep the second attempt on centre and finished them off with some filing buttons. This had to be done in two steps as the larger diameter is the same as the fixing hole centres.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on August 07, 2022, 05:40:34 PM
The new clamp plates seemed to fit so the next step was to make a punch template for the head gasket. This was made from a strip of 50 mm wide aluminium much as before. There are two 4mm dowels to keep everything in place and the two new punches ,4.5mm and 8 mm, were made from silver steel and hardened.  The 25.5 mm cylinder bore punch is case hardened steel from some earlier engine builds.

The injection pump tappet was hardened at the same time.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on August 07, 2022, 05:58:43 PM
The gasket template was set up on the faceplate to bore the cylinder hole. Every thing was deburred and cleaned ready for the first gasket which seems to fit  :)

With it all clamped together some problems appeared  :( The exhaust valve was leaking and the conrod was hitting the top of the liner  ::)  I took it apart again and could see the contact marks on the conrod and liner. I eased the liner with a little filling and also noticed that there was a lump of Hymolar in the camshaft oil passage  :toilet_claw:

The valve leakage was due to a tiny bit of something on the valve seat.

It was assembled once again and I made a couple of pushrods from 3mm music wire, cut with a disc in the Proxxon hand tool and profiled on the bench grinder. They may be a little short but will do for the first trials.

I fitted the compression tester and gave it a quick spin with the drill:

https://www.youtube.com/watch?v=Gu3i6eY_BXM

Gu3i6eY_BXM
It reaches around 22 Bar, 320 psi, with no lubrication other than a bit of rust preventing maintenance spray. OK for a start. There is still a little contact between the conrod and the liner, Maybe the liner is rotating  :thinking: it is not positively located.
Title: Re: 20cc Four Stroke Diesel
Post by: Admiral_dk on August 07, 2022, 11:09:44 PM
I see that you have made quite a bit of progress Roger  :ThumbsUp:

I'm sure you will find the last small details  :cheers:   Oh - and nice compression for first try  :ThumbsUp:

Per
Title: Re: 20cc Four Stroke Diesel
Post by: Brendon M on August 12, 2022, 01:31:49 PM
Doesn't seem like much longer now until it runs :)
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on September 04, 2022, 06:55:45 PM
A little bit more progress on this. There were a number of small problems to fix, the injection pump tappet fouled the camshaft bearing housing, the spacing between the follower and the cam was too much, the injectors needed chamfering slightly to clear the piston and the split link on the cam chain fouled the oil pump body.

The injector nozzles were held in a 6mm spring collet and chamfered 0.5 mm.

A relief was milled in the camshaft bearing housing with a 6mm end mill and 1mm was milled from the injection pump guide. The injection tappet clearance can then be adjusted if required by putting a shim under the guide.

The injection pump seemed to assemble properly so I moved over to the oil pump. Two small recesses were milled in the body with a 6mm end mill and it was cleaned and refitted.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on September 04, 2022, 06:58:08 PM
The next steps are to make a temporary mount for the oil tank from the two stroke and make a chain tensioner for the cam chain. The oil pump will just by used to feed the two main bearings and big end. The third outlet will be blanked off.
Title: Re: 20cc Four Stroke Diesel
Post by: Admiral_dk on September 04, 2022, 10:35:05 PM
There is a big amount of small details that really matters a lot more than a superficial glance would give a clue about .... and some of them you never know until something went wrong first .....

I believe it's called Experience  :old:

Godd to see that you are making progress again Roger  :cheers:

Per
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on September 10, 2022, 02:59:31 PM
The chain tensioner arm was sawn and filled from 2mm bright steel.  A 10T sprocket was thinned down to remove the grub screw hole an opened out to 8mm. Two Oilite bushes were slightly thinned down so they just met in the middle.

The shaft was turned from 4mm silver steel with a groove for a retaining E clip and silver soldered into the arm. It is held in place using one of the M4 holes that used to fix the injection pump.

The oil tank is supported by a bracket from the bits drawer. Together with the pipe it should be stiff enough for the first trials.
Title: Re: 20cc Four Stroke Diesel
Post by: Kim on September 10, 2022, 04:54:16 PM
Nice work on the tensioner arm, Roger!  :popcorn:
And I like the gas tank bracket - very functional. And from your spare parts!  All the better  :ThumbsUp:
Kim
Title: Re: 20cc Four Stroke Diesel
Post by: RReid on September 10, 2022, 05:17:33 PM
Looking forward to the last bits and the first start, Roger. :ThumbsUp:
The highest compression I've ever turned over by hand is 9:1. Can't quite imagine what 20:1 must feel like! Do you still have to make up a starter, or do you already have something suitable?
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on September 12, 2022, 07:22:39 AM
Thank you both  :)

Ron, I have a mains powered electric drill I use as a starter.

The next piece was a flange for the exhaust pipe. I made four as this size is also used on the horizontal engine and I have a couple more experiments planned for that.

The blanks were cut from 3mm thick brass bar with the Proxxon table saw. The fixing holes were drilled with a simple jig and two blanks were clamped together with 6mm and 12mm filing buttons. A little bit of filing and ready for use.

I am waiting for some 8mm elbows to complete the exhaust so next up is a few studs.
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on September 24, 2022, 09:47:54 AM
The studs for the injector and exhaust flanges were turned from 3mm stainless steel and the nuts from 5mm brass hex. A quick trial with the compression tester showed a clearance problem so a redesign is needed. To fit the injector and the valves in the head I reduced the stud spacing from 16mm to 14mm so there is no clearance for a spanner for the 8mm body of the tester. The 6mm body of the injector is no problem.

The exhaust elbow was silver soldered to the flange and installed pointing down to avoid the 'clag fountain' of the two stroke version.

Next I primmed the oil system. By removing two of the pump fixing screws it can be tilted out of engagement with the worm and spun with the cordless drill. By blocking the pipes in sequence it is possible to force oil through the crankshaft and the feed pipes to remove any air.

The starter dog showed some signs of abuse so I skimmed most of the damage off.

The final step was to check the injection system and confirm that the zero fuel position was really no fuel and that there was good atomisation.

https://www.youtube.com/watch?v=YBNC1RCqSJQ

YBNC1RCqSJQ
Title: Re: 20cc Four Stroke Diesel
Post by: Admiral_dk on September 24, 2022, 10:24:03 AM
Yes - that is a very tight squeeze ...!

The rest looks very functional now - getting close to first Pop  :ThumbsUp:

 :cheers:   :popcorn:

Per
Title: Re: 20cc Four Stroke Diesel
Post by: Brendon M on September 24, 2022, 12:51:50 PM
Yes getting very close :D
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on October 08, 2022, 03:51:36 PM
I modified the design of the compression tester. It's not perfect but can be assembled. When I was dismantling the old set up I found a crack in one of the fittings which have been part of the cause of the leak off. The compression was over 30 bar when cranked with the electric drill so I packed it all up and took it to the welding bay at work for a trial.

After various injection timing adjustments it started to fire but still blows unburnt fuel and oil out  :( Then it caught and ran for a short while and would respond to the fuel rack  :) The next attempt after the short video clip produced no results at all, the fuel injection cam had fallen off  ::) I am happy with that run as it confirms my thoughts that the two stroke was running on fuel that had blown past the piston into the crankcase. Now I think I need to work on better atomisation from the injector. You can see the fine puddle of fuel and oil under the exhaust.

https://www.youtube.com/watch?v=8NKiJ2hAi3c

8NKiJ2hAi3c
Title: Re: 20cc Four Stroke Diesel
Post by: Kim on October 09, 2022, 05:40:56 AM
That looks like a very successful test run, Roger!  :popcorn:

Kim
Title: Re: 20cc Four Stroke Diesel
Post by: Brendon M on October 09, 2022, 07:32:23 AM
Fantastic! The moment we have been waiting for :D

It sounds like it will run great once you get the cam issues sorted
Title: Re: 20cc Four Stroke Diesel
Post by: Admiral_dk on October 09, 2022, 12:29:09 PM
You are still in a very small group of people that has mannaged to construct, build and run a true model Diesel Engine  :praise2:  So I would consider this another succesful test if I was you  :cheers:

I agree with Brendon - that the Cam issue should be manageble   :cheers:

Per
Title: Re: 20cc Four Stroke Diesel
Post by: RReid on October 09, 2022, 02:56:04 PM
Congratulations Roger!  :ThumbsUp: :cheers:
Title: Re: 20cc Four Stroke Diesel
Post by: MJM460 on October 10, 2022, 09:56:38 AM
Great result Roger, it proves you have all the primary elements together..

Minor component failures show the importance of these parts which possibly experience greater forces than we might imagine, but I am sure you will overcome those issues with your persistent and thorough approach.

Your thread is an inspiration to read, I always read each new update.

MJM460

Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on October 15, 2022, 12:17:44 PM
Thank you all for your interest and support  :)

I refitted the cam and checked the timing by removing the delivery valve and turning the engine until the fuel flow stopped. This was around 20° BTDC which is more than I was expecting.

The spray pattern from the injector looks good but I think that it could be smaller so I will make a couple more injectors with a smaller cone angle. This will be documented on the fuel injection thread:

https://www.modelenginemaker.com/index.php/topic,10603.0.html

The camshaft I am using is not the best, there is about 15 degrees of negative overlap and the inlet valve closes around 40° ABDC which does not help the compression pressure at cranking speed. It was a reject from the 25cc horizontal engine but was enough to prove the principal. I have started make a new one with a reduced angle between the lobes. It can't have too much overlap due to the limited clearance between the piston and the valves.

I will also need some cooling for longer runs. I think that thermosyphon with a computer cooling matrix will be enough initially. I can always add a pump if needed.
Title: Re: 20cc Four Stroke Diese
Post by: Don1966 on October 15, 2022, 08:37:12 PM
Some great work Roger you are persistent. I Can everyone you that…… :Love:


 :cheers:
Don
Title: Re: 20cc Four Stroke Diesel
Post by: cnr6400 on October 15, 2022, 09:01:01 PM
 :ThumbsUp: :ThumbsUp: :ThumbsUp: :popcorn: :popcorn: :popcorn:
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on October 30, 2022, 06:56:37 PM
Thank you for your interest and support  :)  :)

I decided to use the larger radiator and used a mixture of already existing and new fittings. This engine is a bit of a 'Bitza'. The radiator support frame may seem a bit over the top but vibration is always a problem. With the cooling set up I took it back into the welding bay for further trials. After some more timing adjustments it would start immediately when warm with a good response to the fuel rack. It has the usual diesel problem that as the revs drop the injection quantity drops until it stalls, this is why all diesels have governors. I don't think that the atomisation from my injector is so good, I have a delightful term I learned from the Smokestack Forum of a wet pipe engine  ::)

https://www.youtube.com/watch?v=I0Yqmevrq50

I0Yqmevrq50
Bringing the engine back to the workshop there were, as expected, a few problems. In less than five minutes run time I had emptied the oil reservoir. As this was not in the crankcase it has been blown out somewhere. The two M2 nuts had fallen off the injection pump tappet roller but due to the construction the pivot remained in place. One of the soft soldered oil pipes had also cracked. Vibration is a problem.

I need to make a few more tests on injection quantity and timing as well as some more development on the injectors. It's getting there  :)  :wine1:
Title: Re: 20cc Four Stroke Diesel
Post by: Vixen on October 30, 2022, 07:25:23 PM
Hello Roger

Well done   :ThumbsUp: :ThumbsUp:
That's a nice reward for all your hard work and dedication.  Some minor changes and adjustments and you will be there.
 :cheers:
Mike
Title: Re: 20cc Four Stroke Diesel
Post by: RReid on October 31, 2022, 01:18:41 AM
Congratulations Roger! You took on a real challenge and have good reason to be happy and proud to get to this point. :wine1:
Title: Re: 20cc Four Stroke Diesel
Post by: Zephyrin on October 31, 2022, 09:37:09 AM
all this thread is very fascinating...
the amount of tests and changes to get successful run are really impressive, congratulations Roger and thanks to share !
Title: Re: 20cc Four Stroke Diesel
Post by: Admiral_dk on October 31, 2022, 12:04:48 PM
Oil-Pipes - why not have a few strategicly placed 'Rubber-Hose Joints' in the places (or close to) where the Pipe usually cracks  :noidea:  It certainly works fine on my Suzuki DR350 - admittedly for Lubrication Oil.

The other possibility is a number of strategicly placed rubber grommed holders to 'Fix the Piping' to the Engine - as this should prevent the Pipe to 'Shake to a different Pattern' than the Engine. I remember seeing this on the First Golf GTI and it's mechanical Fuel-Injection - between the Pump and the Injectors, there where a number off combs, holding the Pipes.

I thought that the Guv'nor on a Diesel was to prevent Run-Aways .... but I can see it be useful in all RPM ranges.

Per
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on November 01, 2022, 08:55:20 AM
Thank you all  :ThumbsUp:

This was just a soft soldered joint in a lubricating oil pipe union that cracked. The injection pipe is silver soldered and has survived all the trials so far.

I need to decide what to do with the lubrication system  :thinking: The oil pump delivers a small quantity of oil at very low/zero pressure to both main bearings. The big end is fed via drillings in the crankshaft and the resultant spray hopefully lubricates the cylinder and little end. The oil remaining in the crankcase was planned to be blown out by the crankcase compression as in the prototype Field Marshall.

In these trials the surplus oil was thrown out of the top of the crankcase via the original inlet port (the reed valve was removed) hence the rag on top of the engine.

I could machine out the bottom of the crankcase to make sump or I could put the reed valve back in place and blow the oil back to a tank. Needs some thought  :headscratch:
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on November 20, 2022, 09:35:25 AM
The next step was to finish the new camshaft. The one fitted is a reject from my horizontal petrol engine which has negative overlap. The new one will have the same timing as the one now fitted to the petrol engine. The lobe assembly is made from 16mm diameter silver steel and hardened, the shaft is 6mm silver steel not hardened.

The keyways in the shaft were cut with a 2mm Woodruf key cutter. As before the lobes were milled in 6° steps using a DTI to set the depth of cut with each cut being ticked off on the table when completed. For this operation the lobe assembly was held to the shaft with an M3 grubscrew. The lobes were then polished, hardened and polished again. Next the lobes were (hopefully) correctly aligned with the keyways and the shaft was spotted through the grubscrew hole. I then filled a small flat on the shaft and the two pieces were assembled with some medium strength Loctite and the grub screw.

Finally a sanity check on the timing, with the drive side keyway on top the valves should be on the overlap (remembering that it is a horizontal engine) with the exhaust valve closing.
Title: Re: 20cc Four Stroke Diesel
Post by: Admiral_dk on November 20, 2022, 07:10:10 PM
Great looking Camshaft Roger  :ThumbsUp:

One option for the Crankcase is to install the Reed in such a fashion that the pressure can get out, but not back in. This princip has been used on some racing engines to lower pumping losses, but also to avoid Oil-spillage - that might also prevent it from (partly) running on the Lubrication Oil ....

Per                  :cheers:
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on November 24, 2022, 06:59:35 PM
Thank you Per  :ThumbsUp: I'm still pondering the oil system  :thinking:

I fitted the new camshaft. There is definitely overlap now and the inlet valve closes significantly earlier. I had to set the camshaft timing very carefully to avoid the valves hitting the piston and at the first test the compression pressure is 40 bar plus, probably too much  ::) The starter dog was slipping on the crankshaft. I may need to make some shims to increase the thickness of the head gasket. That is always reversible, machining things isn't.

https://www.youtube.com/watch?v=-P4Dor2e-B0

-P4Dor2e-B0
https://www.youtube.com/watch?v=g8y0zJQFtUU

g8y0zJQFtUU
Title: Re: 20cc Four Stroke Diesel
Post by: Admiral_dk on November 24, 2022, 10:15:45 PM
Don't forget that most starters are geared down - so maybe you aren't in the right gear  ;D

Per
Title: Re: 20cc Four Stroke Diesel
Post by: Roger B on December 04, 2022, 05:11:25 PM
I had a look at the starter dog to see why it was slipping on the crankshaft. This was a problem in the past when the clamp was only slit on one side but having slit it right across it seemed better. At the time I turned the end of the crankshaft down to 11.5 mm and sleeved it back to 12 mm. Removing the starter dog showed that the sleeve had given way under the load  ::) I decided to remove it completely and modify the dog to 11.5 mm bore. A quick shot through with an 11.5 mm reamer plus some filling of the faces seems to have solved the problem  :)

I need to do some more work on the injectors (in the Fuel Injection 2 thread) before the next trials. I will keep the compression where it is for the moment.

There is a problem with the links to my videos  :( I have repaired the recent ones but to fix it all will take some time  ::)