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Death (and rebirth) of my Diesel

Old 05-06-2005, 09:17 AM
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mwright
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Default Death (and rebirth) of my Diesel

Been flying an OS 40FP DDD head conversion for a while now on my Sig Rascal 40. Last night I cranked her up and while letting it warm up at idle it just stoped. I go to restart and it just spins without compression. The crank is sticking out about one inch from the thrust washer!!! I suspect the crank is broke infront of the counter weight. I have a few gallons through it and was just starting to enjoy messing with it. I could turn 11x6 to 12x8 prop in the 9 to 8K region. I mixed my own fuel (43% kero, 22% ether, 33% castor, 2% AN). Anybody else have a problem like this? Any suggestion on a replacement?
Old 05-06-2005, 10:18 AM
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Default RE: Death of my Diesel

What blew up your engine was the 33 percent oil in your fuel. These old crazy formulas go back to the days when there were only one speed engines, you know, control line and freeflight not variable speed R/C. If you put that much oil in a glow engine the plug would simply go out when you went from idle to full power but what do you suppose happens when there no plug to go out and your trying to compress all that oil. If you know the theory behind hydrolics then you know that liquid does not compress.
Old 05-06-2005, 10:23 AM
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mwright
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Default RE: Death of my Diesel

I agree with you. It's was not worth mixing my own fuel. It's really messy and took time. I'll buy my fuel next time. I must admit that I enjoyed learning about the engines and the head worked perfectly.
Old 05-06-2005, 10:26 AM
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SGC
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Default RE: Death of my Diesel

The ether content in your fuel is on the low side to, needing higher compression setting to run.
Stewart
Old 05-06-2005, 10:34 AM
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ddd
 
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Default RE: Death of my Diesel

Your quite correct SGC. We make it a point on this website to not talk fuel formula's for many reason namliy liability. As you know we furnish formula with heads outside the country so people will not make unfortunate mistakes.
Old 05-06-2005, 10:54 AM
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SGC
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Default RE: Death of my Diesel

I dont know why people try and ring the last bit of power out of "Sport " motors, running high nitro in a glow is at the expense of higher fuel prices and shorter engine life, with diesels low ether and higher kero will give more power but at the cost of reduced engine life.
I beleave unless competing a milder brew gives satisfactory results with long engine life, if you havent enough power go up in cc. I learnt in my early yrs that high power fuels rock - but short engine life goes with it.
Stewart
Old 05-06-2005, 11:18 AM
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Default RE: Death of my Diesel

So now that we have established I have used a bad fuel mix. What about replacing the crank vs. buying a dedicate diesel? Any pros and cons?
Old 05-06-2005, 11:28 AM
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Default RE: Death of my Diesel

Only if you believe two wrongs make a right. I really don'y know why you didn't use the formula provided with our head in the first place.
Old 05-06-2005, 11:40 AM
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Default RE: Death of my Diesel

Didn't have a formula provided with the head. I don't think two wrongs make a right. Sorry if I have offended, I'm trying to learn and not repeat my mistakes. Just looking for some friendly advice.
Old 05-06-2005, 11:48 AM
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Default RE: Death of my Diesel

Sorry did't look to see your in NC and should be using made fuel not getting into trouble. Did not mean to offend i'm just mad at all those old bogus formulas out their. You just got caught up in this morass of mis-information on the internet.
Old 05-06-2005, 05:37 PM
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Jim Thomerson
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Default RE: Death of my Diesel

I have four Tower 40 cranks broken at the base of the crank web from running diesel . I think my problem may have been running a 2 oz heavy hub. I've put several hundred flights in glow with the same heavy hub and am still running the same crank (cross fingers) I am well convinced that the stresses in a diesel are distributed different than in a glow.

Jim
Old 05-06-2005, 06:33 PM
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Default RE: Death of my Diesel

Jim I do not have a tower 40 but most of my converted engines irvine, super tiger, mvvs the counterweight at the end of the shaft is rather massive at least 1/4 inch in thickness is the tower one thinner?? I never had any crank problems with them davis heads and davis fuel martin ( or any parts bending or breaking)
Old 05-06-2005, 06:45 PM
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Default RE: Death of my Diesel

I'll give the benefit of my experience with this problem:

1. The problem was partly low ether content leading to high pressure requirement for starting. 33% ether and 22% oil would have been much better - some how the precentages for these ingredients were around the wrong way in the mix you used.

2. With some converted engines, the crankshafts are weak due to poor material, and the bore for fuel mix being maxed out.

I had converted 1st generation ASP 46's that sheared cranks in front of the balance. The shafts were thin and made out of non hardened steel. Also, I suspect the steel to begin with was not top rate. You got what you paid for. I cannot speak for OS FP's as I have no experience with them.

3. Electric starters, a slightly rich condition after priming, will cause this to happen. Hydraulicing then - snap - windmilling prop!

Always try to start by hand. Only use a starter if you are sure the combustion chamber will not hydro-lock.

I learnt all these lessons the hard way, although I have never run less than 33% ether in any sport diesel fuel mix. A little more is often a good thing.

fiery

Old 05-06-2005, 06:52 PM
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Default RE: Death of my Diesel

To DDD:

Mr Davis, I have an MVVS .49 with your DDD head. I have had trouble accessing ether in Australia in recent years so have not run it.

I am now told that some better engine starting fluids can be used. What is your view of using John Deere starter fuid for ether, as it is reputed to be 80% di-ethyl ether, plus hexane? Are their any downsides?

I would love to get my diesels up-and-running again.

fiery

Old 05-06-2005, 09:46 PM
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Default RE: Death of my Diesel

John Deere starter fuid is just fine.
Old 05-07-2005, 12:02 AM
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Default RE: Death of my Diesel

Fiery you are really gonna like that MVVS with the davis head I have the 40 with the DDD head runs great lots of punch also the 61
although it came with the MVVS diesel head I elected to change over to the Davis head there was no way of locking down the compression screw on the original, At least for me the UK engines (Irvine) and the European made ones I think are a notch up
from their Asian counterparts and of course Fox (USA) on top also martin
I know you folks down under have made a few and top notch also (Burford comes to mind)
Old 05-22-2005, 05:12 AM
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Default RE: Death of my Diesel

If nothing else is broken, just replace the crank shaft. OR buy another engine from a different manufacturer upon which the head will fit, for just about the same price as an OS crankshaft.

There used to be several that qualified, but I don't know if they are still available. I'm sure Bob Davis knows.

I agree, it isn't worth making your own fuel. Use Bob's premix concentrate or some of the other manufacturers' fuel.

I wish now that I had held on to my Davis head and the OS.32F-H that it fit. That engine ran great as a glow and great as a Davis Diesel conversion.

I think I'll poke around over on Bob's site and see if he offers anything for the GMS .32 I just bought. Probably not. But that won't stop me...<G>

Ed Cregger
Old 05-22-2005, 08:51 AM
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Default RE: Death of my Diesel

Ed-- many of the Chinese engines are rips of the OS, the GMS 32 may be the same fit as the OS32 and 32SF give Bob a ring at
203 877 1670 and ask, -- He may ask you to send the head up to check, if not check with AJ
One comment on fuel. Davis stuff is available from Davis, Tower, and if your local hobby shop is on.
the ball they can get it fom Davis
the use of MEKP in the home fuel very dangerous one drop of this stuff gets in your eye permanent blindness, A
engines are replacable
eyes are not,
So Davis fuel here,(USA) Model technics in the UK and the Aussies may get lucky since they may have a maker coming
also Aerodyne is gone period in California martin
Old 05-22-2005, 01:40 PM
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Default RE: Death of my Diesel


I didn't realize that folks were messing around with MEKP as a cetane booster. Yep, too dangerous to mess with. Although, once it is in solution it shouldn't be that much of a problem.

I might still have a low time K&B .28 Sportster I could use, if Bob doesn't have anything that will fit the GMS. It is one that was made before K&B (or RJL) began using a bushing in the crankcase.

Ed Cregger
Old 05-22-2005, 02:05 PM
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Default RE: Death of my Diesel

Ed make the phone call to Bob sounds like you might have plan B--Bob has been making them, since 1975 and Fox and K and B around
about 50 years. Also the demand for the Davis heads has picked up overseas proof again that that things that work and work well
are always in demand, very nice to see products made in the USA going overseas, quality is recognized world wide.
Intresting bit of. history very briefly is that Diesel never went away overseas back in the early 50s C/L and FF use but constant one speed engines in the 70s RC started to come on strong resulting in the need to throttle engines and of course the glow engine to replace
the hassle of spark ignition a little before. Davis comes up in 75 or so with the variable compression compression head to spring in the .
coversion of modern RC throttle controlable engines.In all fairness, yes PAW was there but now a very wide choice of diesel conversions comes on the scene. I think the Aussies had a few down there but limited production and very few made it out to the rest of us, Last but not least there are a very few talented folks who have made their own engines and heads (AJ comes to mind) but 99% of use do not have the skills
for such an undertaking hence our reliance on the commercially available product
almost forget MVVS of course has always been there too with a few martin
Old 05-22-2005, 04:18 PM
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Default RE: Death of my Diesel

I've been flying model Diesel engines since 1962, back in my control line days. I can remember when nitro was banned in many parts of Europe and Asia Minor. If not by outright law, then by the economic aspect.

My first experience with a Davis conversion head was on an OS .90 that was mounted on a huge Nosen Citabria. The previous engine was an Enya .91 four-stroke. It just didn't have what it took to get the Citabria off of the ground reliably. Probably poor prop choice. It was my friend's airplane and engine, so I had no say in prop choice. 8^>

One day he began calling various club members to find out who had some Diesel experience - any model Diesel Experience. It turned out that out of nearly 100 club members, I was the only one. The OS .90 (.91?) was really easy to start and a Teddy Bear to adjust. I tried to explain the sound of being overcompressed, but, for whatever reason, my friend just couldn't hear it. Anyway, I had the job whenever he brought it to the field. Yes, the Diesel converted OS .90 did the job in a very scale-like manner, whereas when running on glow, the prop barely cleared the cowl. Naturally, it couldn't do much more than taxi on glow. This was a silk and dope covered model, so it weighed a ton.

The above occurred in the late seventies.

Ed Cregger
Old 05-22-2005, 04:42 PM
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Default RE: Death of my Diesel

Well put Ed. good luck on the head quest , Sadly the only ones who seem to have a handle on it are the guys down under, the

Brits and Europeans and the ones here who have been into it 20 years or more here (US and Canada) enough said
Sorry almost forget you guys Dar and Barkai martin
Old 05-25-2005, 08:09 AM
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mwright
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Default RE: Death of my Diesel

OK here's an update, got another OS 40 FP for my ddd head. I'll wait to buy something like a PAW 40 TBR when I get some more experience under my belt.

Fiery - you were right my ether and oil amounts were reversed. This makes sense because I have been flying my Rascal with the inverted 40 FP for a while with no problems. But a fellow club member was talking to me when I was mixing up the last batch of fuel and I got distracted. Also I wonder if running this engine inverted with too much oil was a factor. I could imagine that during warm-up any unexpelled oil could have pooled in the head causing hydrolic lock. Just a theory along with a low ether content making me overcompress for starting. So I'll use a premixed fuel and start it upright for while.
Old 05-25-2005, 08:49 AM
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Default RE: Death of my Diesel

I have been busy the last few days.

I bought a fellow's used Magnum .40 plain bearing engine and a new Thunder Tiger .15 plain bearing engine. I should be able to get heads for them. Now to buy just one head and give the fuel a try again to see if I can handle the smell. I'll probably go with the little .15 first. There is something about little Diesels that I just love. Besides, I like .15s anyway. A TT .15 Diesel powered Clancy Lazy Bee ARF should be quiet enough to fly in the neighborhood. Someone will smell the fuel and report a suspected meth lab in the area. [X(]

Ed Cregger
Old 05-25-2005, 08:51 AM
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Default RE: Death of my Diesel

I have been busy the last few days.

I bought a fellow's used Magnum .40 plain bearing engine and a new Thunder Tiger .15 plain bearing engine. I should be able to get heads for them. Now to buy just one head and give the fuel a try again to see if I can handle the smell. I'll probably go with the little .15 first. There is something about little Diesels that I just love. Besides, I like .15s anyway. A TT .15 Diesel powered Clancy Lazy Bee ARF should be quiet enough to fly in the neighborhood. Someone will smell the fuel and report a suspected meth lab in the area. [X(]

Ed Cregger

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