N99JH

My Feedback: (66)

Hi All

I have installed an old Davis M40 diesel head on a OS 40FP that I bought used on ebay. The engine fired right up and after about 5 minutes of fiddling with the NVA and compression, running a Top Flite 13-5 prop on a fixed venturi (CL application), I am reading 8000-8100 rpm. Is this adequate? should I expect more?
Thanks for any help I can get.

Best Regards
Joshua

buzzard bait

My PAW 40 delivers about 7500 rpm on a 13x6 Flo Torque, so I'd say your conversion is doing pretty well. By the way, it's enough to fly a VK Nieuport 17, 5 lbs 6 ozs, very well. I rarely even use full throttle.

Jim

N99JH

My Feedback: (66)

Thanks for the input Jim. While the numbers look good, on the 5th 6 oz. tank the engine quit abruptly, and, the spinner and prop flew away. Upon examiniation of the engine I found that the crank pin broke. Is this a pattern shared by other diesel users of the 40FP? Any input from users with reasonable length of time operating this particular engine is most welcome. I certainly hope this may end up as an anomally with my crank shaft only.
Joshua

buzzard bait

Oh sorry to hear it!

Hobbsy

My Feedback: (102)

I broke the crank on an Irvine .20, my fault, I didn't remove the afterrun oil before I tried to start it. Bad move.

N99JH

My Feedback: (66)

Hobbsy
How not removing the after run oil can lead to crank pin breakage? Also, are you flying diesel regualrly? If so, have you encountered any other mechanical failure other than the Irvine 20? I would like to hear more from regular diesel users - hopefuly, only good news

earlwb

I was running a 12x6 prop on my OS 40LA engine. It ran quite well with the 12x6 prop. I was getting around 8700 rpms with the 12x6 prop on it.
I never tried a 13x7 prop as I figured it might have been too large for the engine.
I think your 40FP is a little bit more powerful than the 40LA engine. Maybe it was just bad luck and you had a defective crankshaft in the engine, it was probably going to break eventually. The diesel conversion might have sped up the failure.
The OS FP engines have been quite popular for diesel conversions, and I do not remember anyone mentioning having the crankshaft or crankpin breaking on them before.

123Cat

My FP15 Diesel conversion did the same , I made a crank at 32 Rockwell and its good, about 20 flight s so far

an OS crank is 45 to 50

Recycled Flyer

From memory Ithink that Jim Thomerson used to run dieselised Tower 40's (a clone of the FP) and suffered crank web shearing off the shaft despite the fact that they have a radiused relief groove machined into that join. But he admitted to using a heavy coned prop nut for balancing the model so who knows what the the cause of the failure is really?

I tend to think they a lot of fliers over prop their diesels because ........... well they can! And suffer the consequences of a shorter engine life.

FP's were intended for higher rpm use than LA's anyway.

fiery

My Feedback: (2)

I agree. The OS 40FP as a diesel will turn a broad blade 10x6 or 11x6 propeller very nicely. Mine will acheive 12,000 rpm WOT on a Taipan composite 10X6 prop. No need to lug them down.

Hobbsy

My Feedback: (102)

Afterrun oil will not compress, that is only time I've broken anything in 22 years of running Diesels. My Diesel were all conversion until about 3 years ago when I bought a PAW .40, then a PAW .60 and .19. I have an Irvine .40 Diesel and about 20 conversions ranging from an LA .10 to a SuperTigre 4500. a couple of odd ones in betrween are a Tartan 1.34 with a Davis head and a Maloney 1.25 with an AJCoholic head. My favorite is my Fox .74 ABC conversion, it is the most run and most flown turning an Graupner 12x8 three blade at 9,300.

Recycled Flyer

Dave, how much, as in volume, of after run oil do you use?

Igenerally fill the venturi to the brim with ATF and draw it down by rotating the crank twice and then inject a few drops behind the prop driver to keep the front bearing happy.

That normally means that a few flicks of the prop with the exhaust port downwards will clear the oil inside nicely. (Often thought about flushing it out with neat kero though.)

Thanks mate.

Hobbsy

My Feedback: (102)

I don't know exactly, I just give er a shot with the aerosol can and guess. Obviously I over did it.

buzzard bait

Very interesting about the ARO. I put quite a bit in an OS 52 FS once and later found I could hardly spin it with the starter. After using the heat gun on it I got it going and it cleared.

Jim

N99JH

My Feedback: (66)

Here are some pictures of the failure. I plan on showing the part to a friend who is a mettalurgist and hope to get his analysis. It is a bit difficult to see the shiny spots on the fracture area but to the best of my knowledge they may indicate where the crankpin sheared. The grey area sometime indicate an area with a crack or imperfections in the casting material. I will report back what I find from my friend.
Joshua

N99JH

My Feedback: (66)

Guys
What I am most interested to find out at this point is: How many people use diesels A LOT and of those - how many experienced a mechanical failure. The reason I am asking is because it is naturally assumed that all of us on this forum love diesels and we are probably somewhat biased towards them. Do we therefore potentially gloss over some possible structural limitations? The reason I tried the 13-5 prop was because Mr. Davis cite as a performance example for the 40 FP a 14-6 at 8,000. That would be about equivalent to a 13-5 at higher rpm. I was quite happy with the rpm but of course not with the failure. I plan on rebuilding the engine and keep running the same prop to see if I can duplicate the failure.
Joshua

Recycled Flyer

I am not surprised that a fourstroke, if it had a flooded lower crankcase volume, may have been difficult to turn over!

SRQFlyer

My Feedback: (17)

I have a dieselized FP 40 (RJL head) in an Escapade (pictures in Escapade thread - about 3 or 4 weeks ago). After some experimenting, I found that it liked a TF wood 11-8 (old pattern prop) best. Mid 9's if I remember right. Pulled the 5 lb. plane around just fine. A 13-5 should not be too much prop for a REAL diesel. I had an Irvine 40 that liked a 12-8, but those are really beefy. I know I'll be careful with the FP from now on!

Jim

qazimoto

My Feedback: (1)

In the control line domain the conversions break all the time in my experience of watching various club members over the years. I'm surprised that so many r/c fliers have so little trouble with shaft failures. I suspect that a few are "internet fliers" only. I might add that most people I fly c/l with use diesels 50% of the time.

Model engine Crankshafts aren't normally cast, and your shaft has the classic pattern of a brittle fracture (Look it up on Wiki). You're likely to find that any replacement will also break using the diesel head.

There seems to be some truth in the suggestion that they last longer running faster, but doesn't that negate the supposed advantages of a diesel conversion?

The OS 40 FP runs very well as a glow, why not leave it that way and buy an out of the box diesel?

Ray

fiery

My Feedback: (2)

Hi Ray

I did a back-to-back comparison of my FP 40 on glow and diesel.

FAI glow fuel, home brew, 10x6 prop - 11,500 RPM WOT

www.youtube.com/watch?v=eFa407riGj8

Sports diesel fuel, home brew (25% castor oil), RJL head, same prop, straight after the glow run - 12,000 RPM WOT

It throttled well both ways. I'd say it is a practical power plant as a diesel. Just don't over compress

Recycled Flyer

Ray, would it be fair to say that a solid hardened steel pushed in crank pin would fair better in the majority of model diesel engines?

It just seems to me that the crank journal should be rather soft (to absorb the diesel thump) and the pin much harder (to wear better against alloy rods or bushes) and most cranks that I see in modern engines simply use the same grade of steel right through, some flame hardening (bluing evident) around the pin.

2walla

My Feedback: (10)

I would venture that most crank pin failures on model engines are from electric starter abuse rather than from running time.. Lots of guys hit wet engines with starters running full tilt.. I am amazed that they hold up as well as they do.. Since the motor was used you never know how it was treated..

fiery

My Feedback: (2)

Following on from Ray's comments. I wonder whether poor service reliability of converted glow engines in C/L has anything to do with stresses to the crankshafts and crankpins, following the sudden "one point landings" that are a part of "fly by wire".

We are drifting from the OP's topic. Perhaps this subject is deserving of a new thread

qazimoto

My Feedback: (1)

The diesel is probably running at a higher compression ratio, hence the extra 500 rpm.

TWIUI out of the box glows have a deliberately low compression ratio typically.

I believe this is so they can cope with the nitro methane fanatics who will run 30 right off.

If you carefully set the compression ratio and the squish clearance you will get an instant impressive increase in performance on relatively low
nitro fuels.

Witness the writings of the lamented late Lance Smith on the topic in ACLN.

As I said above it's a mystery to me why some break and others don't. Maybe it's the not over-compressing!

Both the FP 25 and LA 25 made excellent high speed team race engines, and I'd guess the FP 40 would as well if there was a class for it.

The FP, LA 10's, 15's all break as diesels even though they run very well beforehand. They are run very fast though.

Ray

N99JH

My Feedback: (66)

Hi Ray
I tend to agree with you that the failure looks like a brittle fracture. As far as I know, machine parts such as crankshafts are made from alloys such as 4130, 4140 steel, case hardened typically to a depth of about .030" and than ground. The crankpin fracture sure looks like it was through hardened and became brittle. I suspect that you see 50% failures in CL aerobatic flying, perhaps due to the fact that the airplane flys with engine wide open all the time and experience routinely 15 -20 Gs. Normal RC sport flying is usually done at half throttle and most manouvers are gentler.
My main interest is to substitute a light engine for otherwise a heavier one. I currently have a rather heavy stunter that flys with a Super Tigre 60 Blue Head. The engine less muffler weight 15 oz. and spins a 13-6 prop. IF I could substitute the 40 FP that spins a 13-5, the weight will be only 9 oz. That may be a worthwhile cause in CL world.
Reading this forum one gets an impression that there are thousands of diesel conversions happily humming all over the world but I am not convinced. I am definitely going to experiment more, but the funny thing is: I told a good friend who has been a CL modeler for more than 50 years with vast experience about my experiment with the 40 FP. He mentioned that in his experience he broke a few cranks. 10 minutes later his warning came true. Really makes me wonder?!
Joshua