Author Topic: 20cc Four Stroke Diesel  (Read 5102 times)

Offline Roger B

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Re: 20cc Four Stroke Diesel
« Reply #45 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.
Best regards

Roger

Offline Roger B

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Re: 20cc Four Stroke Diesel
« Reply #46 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  :)
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Roger

Offline Brendon M

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Re: 20cc Four Stroke Diesel
« Reply #47 on: June 07, 2022, 08:45:34 AM »
Hello Roger, I look forward to seeing this run :)
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Offline Roger B

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Re: 20cc Four Stroke Diesel
« Reply #48 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.
Best regards

Roger

Offline Admiral_dk

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Re: 20cc Four Stroke Diesel
« Reply #49 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

Offline Roger B

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Re: 20cc Four Stroke Diesel
« Reply #50 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.
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Roger

Offline Roger B

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Re: 20cc Four Stroke Diesel
« Reply #51 on: June 29, 2022, 05:57:58 PM »
And one more
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Roger

Offline Zephyrin

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Re: 20cc Four Stroke Diesel
« Reply #52 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.

Offline Roger B

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Re: 20cc Four Stroke Diesel
« Reply #53 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.


The piston was then turned to the diameter of the plug gauge I used when lapping the cylinder.
Best regards

Roger

Offline Admiral_dk

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Re: 20cc Four Stroke Diesel
« Reply #54 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

Offline Roger B

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Re: 20cc Four Stroke Diesel
« Reply #55 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.
Best regards

Roger

Offline Brendon M

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Re: 20cc Four Stroke Diesel
« Reply #56 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?
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Offline Roger B

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Re: 20cc Four Stroke Diesel
« Reply #57 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.

Best regards

Roger

Offline Roger B

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Re: 20cc Four Stroke Diesel
« Reply #58 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
Best regards

Roger

Offline Brendon M

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Re: 20cc Four Stroke Diesel
« Reply #59 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 :)
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