Author Topic: 20cc Four Stroke Diesel  (Read 3058 times)

Offline Roger B

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20cc Four Stroke Diesel
« 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.
Best regards

Roger

Offline Minh Thanh

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Re: 20cc Four Stroke Diesel
« Reply #1 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 !

Offline Roger B

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Re: 20cc Four Stroke Diesel
« Reply #2 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.
Best regards

Roger

Offline Roger B

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Re: 20cc Four Stroke Diesel
« Reply #3 on: November 28, 2021, 07:37:33 AM »
Finally I broached a 3mm keyway in the sprocket and put it all back together.
Best regards

Roger

Offline Admiral_dk

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Re: 20cc Four Stroke Diesel
« Reply #4 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 ?

Offline Roger B

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Re: 20cc Four Stroke Diesel
« Reply #5 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:
Best regards

Roger

Offline Roger B

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Re: 20cc Four Stroke Diesel
« Reply #6 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.
Best regards

Roger

Offline Roger B

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Re: 20cc Four Stroke Diesel
« Reply #7 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:
Best regards

Roger

Offline Admiral_dk

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Re: 20cc Four Stroke Diesel
« Reply #8 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

Offline Roger B

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Re: 20cc Four Stroke Diesel
« Reply #9 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:
Best regards

Roger

Offline Roger B

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Re: 20cc Four Stroke Diesel
« Reply #10 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.
Best regards

Roger

Offline Roger B

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Re: 20cc Four Stroke Diesel
« Reply #11 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.
Best regards

Roger

Offline RReid

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Re: 20cc Four Stroke Diesel
« Reply #12 on: December 22, 2021, 08:16:30 PM »
Quote
... (made from a broken HSS centre drill).
I've got one just like that!
Regards,
Ron

Offline Roger B

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Re: 20cc Four Stroke Diesel
« Reply #13 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.
Best regards

Roger

Offline Craig DeShong

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Re: 20cc Four Stroke Diesel
« Reply #14 on: December 26, 2021, 07:38:46 PM »
Roger; Ive been silently following this thread for a while now.  Its 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.
Craig
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