Author Topic: 20cc Four Stroke Diesel  (Read 5058 times)

Online Roger B

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Re: 20cc Four Stroke Diesel
« Reply #60 on: July 20, 2022, 07:11:37 PM »
Not sure , the problem at the moment is the good weather and the mountains  :)
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Roger

Online Roger B

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Re: 20cc Four Stroke Diesel
« Reply #61 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.
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Roger

Online Roger B

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Re: 20cc Four Stroke Diesel
« Reply #62 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.
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Roger

Online Roger B

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Re: 20cc Four Stroke Diesel
« Reply #63 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:
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Roger

Offline MJM460

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Re: 20cc Four Stroke Diesel
« Reply #64 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

The more I learn, the more I find that I still have to learn!

Online Roger B

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Re: 20cc Four Stroke Diesel
« Reply #65 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.
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Roger

Online Roger B

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Re: 20cc Four Stroke Diesel
« Reply #66 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.
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Roger

Online Roger B

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Re: 20cc Four Stroke Diesel
« Reply #67 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.
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Roger

Online Roger B

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Re: 20cc Four Stroke Diesel
« Reply #68 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:


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.
Best regards

Roger

Offline Admiral_dk

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Re: 20cc Four Stroke Diesel
« Reply #69 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

Offline Brendon M

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Re: 20cc Four Stroke Diesel
« Reply #70 on: August 12, 2022, 01:31:49 PM »
Doesn't seem like much longer now until it runs :)
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