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Old Sep 01, 2009, 08:42 PM
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Converting Chinese 4 stroke to diesel?

Hi all,
I don't know if this is possible, but my question is would it be possible to convert a 4 stroke glow engine (like an asp .61 4 stroke) to diesel without spending too much money?

If so, how?

Thanks,
Lucas
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Old Sep 01, 2009, 08:50 PM
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Lucas, there is a good chance it will just fire up and run on Davis Diesel Fuel with no assist but there is also the likelyhood that it has too much compression. Greg may be able to give you some hints on making the compression adjustable enough to work. I have run Davis Diesel Fuel in a Saito .80, too much compression, way too much in fact, a Saito 1.00, too much again, an Enya .53, not quite enough to slow to idle but runs fine at full throttle, same with Saito .50.
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Old Sep 01, 2009, 08:53 PM
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So you don't need to change any parts? How would you lower the compression?

Lucas
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Old Sep 01, 2009, 08:57 PM
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In the case of a fourstroke you'd need a device called a Lanova Cell, (spelling) that screws in the place of the glow plug. You have twist somebodys into making one for you. Mr. Davis and Neil Tidy of LASER engine fame don't think that fourstroke Diesels are worth the trouble although LASER made an .80 that worked pretty good.
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Old Sep 01, 2009, 09:18 PM
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Ah, after a google search, I see what you mean. The screw on the lanova cell backs out to lower the compression. The next hurdle is getting the diesel for cheaper than glow fuel. It's probably more expensive with shipping.
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Old Sep 01, 2009, 10:57 PM
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Most four stroke engines are short on compression for diesel operation. I increase compression ratio on all conversions. My Saito .80 would not run on diesel fuel.

A four stroke diesel conversion generally requires milling or turning the head to increase compression ratio, shortening pushrods and pushrod covers, shortening the intake manifold, and installing a restrictor in the carb, and the Lanova cell. Some engines require more some less modification. The Sanye FS.61 is a clone of the OS FS-52 and should be fine.

We had a good thread over at RCU.

Greg
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Old Sep 02, 2009, 09:29 AM
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So you're saying that some glow 4 strokes actually have too little compression? Well, whenever I get a four stroke, I will have to keep compression in mind.
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Old Sep 02, 2009, 09:42 AM
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Thanks for comming in here Greg, my Saito is an early .80 with very high compression, if memory serves one of the testors calculated that the CR was 15.6 to 1 mechanical and 14.4 to 1 corrected for valve timing. As I have reported before I can't go beyond about 5,000 rpm with a 14x6 when it begins to sound like its going to blow the cylinder off. My Enya .53TN can run at full throttle on a Graupner 12x6 at 7,500 rpm but when lowered to about 3,500 rpm the comression is too low and it quits.
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Old Sep 02, 2009, 10:10 AM
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I'm pretty sure my FA-80 is also a high compression version though I have not measured it. Yes some engines make all kinds of noise until the settings are just right.

In my experience all four stroke engines have insufficient compression for diesel operation. I've measured CR in virtually every OS, and Magnum below 1.20 size, and quite a few other four stroke engines. Every engine I have converted required increased compression ratio. If you do not have access to machining equipment it will not be possible to modify the engine as needed.

A few, like Dave, have run glow engines on diesel fuel on the bench. However, none of these have flown. In my experience there is a notable difference in the settings required for a bench run and settings required for a successful flight.

This is one of my recent conversions.

Thunder Tiger F-75S Diesel Engine Conversion (3 min 0 sec) (3 min 0 sec)
Greg
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Old Sep 02, 2009, 11:09 AM
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You're very correct Greg, I've put more than one Diesel in the air and heard it hunting/burping as some call it, from leaning out as a result of the prop unloading. A Cline regulator will eliminate that problem real quick. I just love those things.
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Old Sep 02, 2009, 11:15 AM
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Impressive, that has about the same power as a .50 sized conversion with most turning a Graupner 12x7 in the mid nines. Yours is very smooth.
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Old Sep 02, 2009, 11:50 AM
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I was disappointed in the power output for the displacement with the F-75S, but it's inline with the glow numbers and the engine still needs break in time. The F-75S appears to be about as strong as the FSa-56. I haven't converted an OS FS-70 yet.

So many projects......

Greg
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Old Sep 02, 2009, 06:11 PM
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So, unless you have a high compression engine, such as one that runs on fai fuel, it won't have enough compression for diesel? I really don't have the tools to modify engines, so otherwise I guess I'm out of luck.

Can you mix your own diesel fuel? If so what are the ratios?

Lucas
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Old Sep 02, 2009, 06:51 PM
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We diesel users normally mix our own juice. On a ball-bearing engine, a 20/30/50 mix works great, being correspondingly, castor, ether and paraffin/kerosene/lamp oil. But if you'll be able to source each fuel component, that's another matter...!

BTW, every engine runs on FAI fuel, some better than others due to compression differences.
For instance, an ASP will run great on 0% nitro IF you remove a head shim (they usually come with 2), but it will still run on 0% nitro if you keep them both, though not as powerfully. I run all my engines on FAI fuel, even Saitos and none of them has complained yet!
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Old Sep 02, 2009, 10:03 PM
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As opposed to Pat, I run Davis fuel exclusively, Davis Plane Fuel in bushing engines and ABC mix in ball bearinged engines. Both are run perfect every time fuels. I have run RedMax a few times, they'll make it however you want it.
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