Author Topic: 20 cc Horizontal 2 Stroke Diesel  (Read 40146 times)

Offline Admiral_dk

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #255 on: January 03, 2019, 10:01:29 PM »
Just thinking out loud. How many things (should) prevent overshoot here ?
I'm guessing a spring and the injector nozzle  :thinking:  and if I remember right, you loosened the spring on the injector to get a good run. I would guess that this also has an influence on the marks shown.

Online Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #256 on: January 04, 2019, 02:51:15 PM »
Thank you Per  :ThumbsUp:

After I had written this I went back downstairs for another look and think  :headscratch: I think that the overshoot is happening when the inlet port is exposed again for the end of injection and the pressure in the system suddenly drops from 10s of Bar to zero. I could increase the size of the return spring but that would also increase the total load on what is already a fairly stressed cam follower. Chamfering the ends of the bronze bush in the tappet guide and thinning the two pivot nuts down from 2mm to 1.5mm will resolve most of the actual problems.

The next problem I found was that the plunger had come loose in the rectangular tappet that fits inside the rack gear. This is the reason for the change in phasing between the rack and the helix  ::) The M2 thread was originaly locked with a medium strength screwlock as I thought I would probably have to dismantle it again. I don't know if this failed due to the shock loads or due to the various fluids (petrol, diesel, alcohol, lubricating oil) that it has been surronded with. I will try some Loctite 648 next and if that fails I will have to work out a mechanical solution.
Best regards

Roger

Offline Admiral_dk

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #257 on: January 04, 2019, 06:43:34 PM »
I suppose that there is no space for a second short spring - might be at the end of the first one - with a much higher force factor to absorb the shock and prevent the damage ?

Online Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #258 on: January 05, 2019, 02:17:36 PM »
I have thinned the nuts down which greatly increases the available clearance for overshoot. I think that this overshoot could have been responsible for pushing the original E clips off  :headscratch: To minimise the impact damage at the pump end of the tappet I have adjusted the clearances so that the roller is always in contact with the cam. This makes the little ball race work harder but it should cope as the load is minimal for most of a revolution.
After reassembly and priming I took some more volume measurements:

Stop was zero

In the previous 'working position' about 0.2mm3 per rev.

Full open about 0.4mm3 per rev.

The theoretical max volume required for a full charge of air (which won't be the case on a two stroke) is 2mm3 per rev. As you can't expect to use all the air and with the likely reduced air charge these figures seem reasonable.

The R and D dept. is currently closed due to snow so the next trials will have to wait.
Best regards

Roger

Offline Admiral_dk

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #259 on: January 05, 2019, 08:12:02 PM »
Glad to hear that you got yet another step forwards  :ThumbsUp:

As for the R&D department .... You could argue that It looks pretty and cold ... Brrr .... Her we had close to 10C and a nice sunshine almost all day  :cartwheel: .... But do see delays in the Test Report  8)

Offline Art K

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #260 on: January 05, 2019, 09:15:01 PM »
Have to admit that it's abnormally warm here in Wisconsin. The thermometer says 50 degrees F outside
Art
"The beautiful thing about learning is that no one can take it away from you" B.B. King

Offline Dave Otto

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #261 on: January 05, 2019, 10:52:23 PM »
R&D Department Closed!
I see a little spot next to that yellow watering can where you could work.  :lolb:

Dave

Online Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #262 on: January 06, 2019, 03:04:51 PM »
Thank you all  :ThumbsUp:

Following on from Per's suggestion for a second spring I think I can fit an O ring in the space between the end of the rack pinion and the injector body. The theoretical gap is 1mm and a 5x1mm O ring should fit inside the spring. I only have a 5x1.5mm at present so will have to order some.

I then went on to measure the output of the oil pump. According to ETW the design was suitable for engines up to 30cc. The system is set up so that I can tilt the pump away from the worm and turn it with a 4mm hex socket on the end of the shaft. A it was set it would empty my 5ml oil tank in a couple of hundred revolutions  ::) Not only too much fuel but too much oil as well  :facepalm:

I found some reasonable settings with direct drive and will then try again via the normal worm drive (20-1) in case there is a speed effect. 550rpm with the battery drill is equivalent to the engine running at 11 000 rpm  ::)
« Last Edit: January 06, 2019, 07:54:20 PM by Roger B »
Best regards

Roger

Offline AlexS

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #263 on: January 07, 2019, 08:36:02 PM »
Good to read that you have made good progress in this project.
Hopefully the engine will soon run a stable speed.

Can I ask why you add oil to the fuel?

Alex

Online Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #264 on: January 08, 2019, 11:10:22 AM »
Thank you Alex  :ThumbsUp:

The lubrication on this is based on the Field Marshall tractor system as is the rest of the engine. There is a separate oil reservoir and pump feeding the crankshaft and the cylinder. Initially I am running it as a total loss system although I plan to add a return system from the bottom of the crankcase. The pump has a variable output, the initial setting was just a guess, resulting in much too much oil which was then ejected via the exhaust.
Best regards

Roger

Offline AlexS

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #265 on: January 08, 2019, 08:47:15 PM »
Ah right! Thanks for your explaining.

Offline Admiral_dk

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #266 on: January 08, 2019, 09:38:34 PM »
Old Suzuki (197x) two-stroke multi cylinder motorcycles had one way valves and small diameter pipes running from the bottom of the crankcase to the inlet of the neighbouring cylinder - this "flushed" the crankcase from excess oil earlier than waiting for full throttle and a big smoke back out .....

Offline AlexS

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #267 on: January 13, 2019, 01:22:18 PM »
I like that oil system on the Suzuki GT models.
Coincidentally my father has a GT 380. Especially when the engine has been stationary for a while, it produces a lot of smoking when it starts. I drive a Yamaha RD myself, where the oil is only sucked in at the carburetor. With this engine the smoke is a bit less. Also at full load. But I use a different oil. And use it in the summer as a daily transport.
I do not have that much experience with two-stroke systems for diesel engines.
« Last Edit: January 13, 2019, 08:21:16 PM by AlexS »

Offline Admiral_dk

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #268 on: January 13, 2019, 04:41:45 PM »
Quote
I drive a Yamaha RD myself

OK, now I'm almost back to my youth, as my first (official) road bike was an Yamaha R5F (the last model before the RD350).
I LOVED two-strokes, but that bike cured me from that  :noidea:  Had it been one of the later water cooled models, things might have been very different - but then again, I prefer to ride more than to repair them  :shrug:

Don't get me wrong - if money was no object, I would love to have a big two-stroke bike with great steering + braking to take for a short spin from time to time. Oh and like wise - I would get one of the new fantastic eBikes to run to a from work and other daily errands - driving + environment  :)

Online Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #269 on: January 13, 2019, 05:23:19 PM »
The Field Marshall had a similar oil return system with a one way valve in the bottom of the crankcase and a small bore pipe back to the oil tank. When I have some idea of sensible oil flows I will have to make some experiments.
Best regards

Roger