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; Iíve been silently following this thread for a while now.  Itís 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 canít 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 30į 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 45į 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 180į 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.