Author Topic: 20cc Four Stroke Diesel  (Read 5055 times)

Offline propforward

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Re: 20cc Four Stroke Diesel
« Reply #30 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.
Stuart

Forging ahead regardless.

Online Roger B

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Re: 20cc Four Stroke Diesel
« Reply #31 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.
Best regards

Roger

Online Roger B

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Re: 20cc Four Stroke Diesel
« Reply #32 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.
Best regards

Roger

Online Roger B

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Re: 20cc Four Stroke Diesel
« Reply #33 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.
Best regards

Roger

Offline RReid

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Re: 20cc Four Stroke Diesel
« Reply #34 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:
Regards,
Ron

Online Roger B

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Re: 20cc Four Stroke Diesel
« Reply #35 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.
Best regards

Roger

Online Roger B

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Re: 20cc Four Stroke Diesel
« Reply #36 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.
Best regards

Roger

Online Roger B

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Re: 20cc Four Stroke Diesel
« Reply #37 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.
Best regards

Roger

Online Roger B

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Re: 20cc Four Stroke Diesel
« Reply #38 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.
Best regards

Roger

Online Roger B

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Re: 20cc Four Stroke Diesel
« Reply #39 on: April 15, 2022, 02:48:32 PM »
The last pictures.
Best regards

Roger

Offline propforward

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Re: 20cc Four Stroke Diesel
« Reply #40 on: April 15, 2022, 03:31:52 PM »
Looks great Roger, following along and enjoying the process.  :popcorn:
Stuart

Forging ahead regardless.

Online Roger B

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Re: 20cc Four Stroke Diesel
« Reply #41 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.
Best regards

Roger

Online Roger B

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Re: 20cc Four Stroke Diesel
« Reply #42 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).
Best regards

Roger

Offline Admiral_dk

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Re: 20cc Four Stroke Diesel
« Reply #43 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

Online Roger B

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Re: 20cc Four Stroke Diesel
« Reply #44 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.
Best regards

Roger