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Gas-to-Diesel conversion on single-cylinder engine?


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  #1  
Old 04-14-2010, 02:24:05 PM
Oberon67 Oberon67 is offline
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Default Gas-to-Diesel conversion on single-cylinder engine?

So... I was wondering if it could possibly be feasible to take an iron-block flathead single-cylinder engine like a Clinton or Kohler, shave the head to raise compression, put a big flywheel on it, put a mechanical fuel injector in the spark plug hole, and have a one-lunger diesel engine.

Just an idle thought, really... but if it's possible, I'd bet someone here has tried it.

-Oberon67
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Old 04-14-2010, 04:02:02 PM
Skip Landis Skip Landis is offline
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Default Re: Gas-to-Diesel conversion on single-cylinder engine?

GM did it with the 350 cid engine. not a great success.
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Old 04-14-2010, 04:24:15 PM
Oberon67 Oberon67 is offline
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Default Re: Gas-to-Diesel conversion on single-cylinder engine?

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GM did it with the 350 cid engine. not a great success. GM did it with the 350 cid engine. not a great success.
True... but in this particular instance, "...the wonder is not how well the bear dances, but that he dances at all." After seeing the home-brew HVID engine, it seems to me that nothing's impossible for this crowd.
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Old 04-14-2010, 06:03:38 PM
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John Newman, Jr. John Newman, Jr. is offline
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Default Re: Gas-to-Diesel conversion on single-cylinder engine?

If I were to attempt such a project, I believe I would start with a good stout Wisconsin engine since they are made with lots of heavy cast iron and most have a roller bearing crank. Look for one with the longest stroke possible compared to the bore. Watch your valve to head clearance. You may have to make a custom head to get the compression and clearances you need.
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Old 04-14-2010, 08:43:57 PM
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Default Re: Gas-to-Diesel conversion on single-cylinder engine?

I think a Kohler K series would be a good base, most if not all of them had roller bearing cranks.

Unfortunately I doubt you will ever get the compression you need with a flathead. You would definitely need to machine your own OHV head.

Kohler did have a K361, which was basically a K341 with an OHV Head. It has 9:1 compression (from what I remember, +/- .5 compression points). If I was looking for a small engine to convert to diesel, I would probably start with one of those.
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Old 04-14-2010, 09:10:58 PM
John Schwiebert John Schwiebert is offline
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Default Re: Gas-to-Diesel conversion on single-cylinder engine?

An old diesel man told me at least 50 years ago the reason all diesels are overhead valve is, you can not decrease the volume of the combustion chamber enough in an L head engine. You need to remember when rebuilding diesel head 0.015 difference in valve height makes a difference in starting the engine. Also a babbitt bearing will hammer out in short order.
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Old 04-15-2010, 09:43:31 AM
Oberon67 Oberon67 is offline
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Default Re: Gas-to-Diesel conversion on single-cylinder engine?

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An old diesel man told me at least 50 years ago the reason all diesels are overhead valve is, you can not decrease the volume of the combustion chamber enough in an L head engine.
I had wondered about that. I was trying to think of ways to reduce combustion chamber volume in the L-heads I'm familiar with, and the best I could come up with was to turn the entire face of the piston into "squish area" (minimum clearance, or essentially zero volume) and relocate the injector over the valves. I still wasn't sure this would be enough, and to judge by what the old diesel man told you, it would not.

I suppose it would be technically possible to build a low-RPM L-head diesel from the ground up, given sufficient stroke, but that's a different animal entirely.
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Old 04-15-2010, 11:21:56 AM
vern0n vern0n is offline
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Default Re: Gas-to-Diesel conversion on single-cylinder engine?

"GM did it with the 350 cid engine. not a great success. GM did it with the 350 cid engine. not a great success."
That is not actually true. There is almost no part that can be swapped from the gas engine to use on the diesel. It is true it was based off the Olds 350, but almost nothing interchanges. The block is differant, the heads are differant, the intake is differant, and the pistons are differant. I don't know if the crank and rods are differant. It just wasn't a very good design.
You could make a diesel out of a Briggs or a compressor, (using overhead valves), but don't expect it to last long.
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Old 04-15-2010, 11:38:06 AM
Oberon67 Oberon67 is offline
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Default Re: Gas-to-Diesel conversion on single-cylinder engine?

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You could make a diesel out of a Briggs or a compressor, (using overhead valves), but don't expect it to last long.
I agree. However, I also think the Kohler with the roller bearings might be a viable option, especially if you were to sleeve it undersized to reduce the thrust against the mains.

It would be a serious undertaking no matter which way you went with it; not something to do with a working motor. As I don't have a machine shop, I won't be having a crack at it in any event.
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Old 04-15-2010, 12:35:09 PM
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Default Re: Gas-to-Diesel conversion on single-cylinder engine?

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Originally Posted by vern0n View Post
../There is almost no part that can be swapped from the gas engine to use on the diesel. It is true it was based off the Olds 350, but almost nothing interchanges. The block is differant, the heads are differant, the intake is differant, and the pistons are differant. I don't know if the crank and rods are differant. It just wasn't a very good design...
Actually there were some interchangeable parts. The 350 Olds Diesel block was beefed up quite a bit and made a very strong 'building block' for putting together a high compression, high output 350 or could be bored & stroked a fair amount and still be a good strong block. I don't remember what all was involved in the conversion, but there was an aftermarket company that supplied a kit for converting the Olds diesel back into a gas burner. Pistons, Cam, Intake manifold, Distributor instead of injector pump, and a few other pieces, but overall it wasn't much different than any other rebuild swapping in new parts for old. Of course it was a whole lot cheaper to simply swap in a complete motor from a donor car when the diesels died with a broken crankshaft or other problems, and we did several of those swaps in my Dads Garage putting 350 & 455 Olds motors in pickup trucks, and then a few years later I swapped out a diesel for a 403 Olds in a big Pontiac station wagon for an old family friend in Rockford IL. When I did that swap I was able to hook up just about every sensor, switch, and gage in the wiring harness so he was able to take it to the local garage and plug it in to the diagnostic computer. Pretty impressive to watch a full sized 4 door wagon smoke the tires for a block and a half. And just because I could, I put the diesel valve covers on the 403 gas motor just as a conversation piece. Same valve cover, just a different shade of blue paint. Power steering, alternator, air conditioner, even the exhaust bolted back on with no changes.

As for raising the compression enough in a flat head, I think you can get the compression ratio up high enough with a domed piston going up into the chamber in the head, but the limiting factor would be the airflow, especially if you mill the head and don't carve out larger pockets between the valves and the cylinder.
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