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Crankshaft limits and experimental a/c

P

pilot2512

Well Known Member
I know in the experimental world we don't always use certified parts. I have my crankshaft at the machine shop and it failed for the flange thickness being to thin by 0.005. The machine shop believes it came from Lycoming that way since they were the last to overhaul the engine and that Lycoming has different limits than field shops. If that was the only thing wrong with the crankshaft and everything else passes, can I decide to use it without a yellow tag? What are the regs on this? I plan to use it for my own a/c. Curious what others have done.

Thanks,

Jay
 
Crank

Is it a crank with flange lightening holes?? If it does not have lightening holes in my opinion it is better than a perfect crank WITH lightening holes. Also you do not state which engine. Some of the older engines I believe had thinner flanges, I know a lot of the older ones had lightening holes. I do not like the lightening hole cranks except for a wood fixed pitch prop.
What prop do you plan to use.
Some 0 360 and o 540 and maybe 0 320 aerobatic cranks have much heaver flange and they still have a history of flange failure with metal constant speed props when used for aerobatics. The composite and wood composite props seem to eliminate these failures. I know of one that failed at around 300 hours on a factory new 540 with two blade Hartzell.
Be ready to get flamed on this forum for using any engine part that is not certified/yellow tagged. This apparently does not apply to ignitions and fuel systems, high compression pistons etc. Mostly reserved for non 505 compliant cranks which have been used successfully with wood props for many years.
 
If it came that wAy from lycoming, I certainly would not be concerned with it's reliability. I recall the flange being around 3/8" and .005" thin is insignificant at that thickness in my opinion. I don't believe you are required to have yellow tagged parts, but that is not my expertise. Keep in mind that the shop will red tag the part. I would confirm that your insurance company will not have an issue with red tagged parts in case you have a claim due to engine failure. It's one thing to buy non certified parts, it is another all together to use a part declared as non airworthy in the legal world. To me, it has negligence written all over it. I would get the shop to write a note indicating the exact reason why it is red tagged with the dimensions. You could then show that it is in spec from lycomings perspective.

Larry
 
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engine is an 0-320D3G Wide deck. Crank is hollow but is post SB so it is PID stamped. By the time I put pmags and airflow performance fuel injection on it it won't be certified anyway. And a Catto prop.
 
pilot2512 said:
What are the regs on this? I plan to use it for my own a/c. Curious what others have done.

Thanks,

Jay
Click to expand...

There are no FARs in this regard for an aircraft with an experimental airworthiness certificate so you are free from regulatory prohibitions to fly the crank if you wish. It is up to you to decide if you have personal reasons for not using the crank.

What have others done? Twenty odd years ago it was common for experimental aircraft to have engines that came from the airboat community (any old-timers remember Pemberton in Florida?). Those engines were mongrels with parts that had been rejected for airworthiness reasons. Some builders got good service from those engines and some didn't. The logbooks were often a joke because the engines were assembled from pieces of several engines. But they were legal for use in an experimental aircraft.
 
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Another thing to think about is aircraft value, if you ever decide to sell the aircraft, the value will be less with an engine assembled from rejected parts.
 
The 0-290G the Lycoming GPU had a thin flange because all it had to do was drive a pretty much immovable alternator.

When John Thorp started converting the GPU for the T-18 project he advised fabricating a 1/4" thick aluminum plate that restored sufficient stiffness to subject it to propeller related gyroscopic forces.

Don't trust my memory on the thickness, Everything is packed away from a move, but it's available in the "old" or original newsletters on the T-18 forum

FWIW
 
Flange

The 0 290G used an 0 235 crankshaft. Those engines were rated at 100, 108 and 115 horsepower. The G's in homebuilts in many cases were run at fairly high rpm. Cut down metal props were also common in that era which made things much worse. Some G's were modified to 0 290D2 or D2B configuration which also greatly increased the stress on the 0 235 flaange
 
That pdf (an O-290G conversion manual) contains a Lycoming service letter that says the G engine's crank is not compatible with any a/c engine. I guess that might be because of bolts in the flange instead of drive lugs, but there it is...
 
Years ago, I had an O-290-G, and the crankshaft flange beef-up recommended, I believe by John Thorp, was a machined 4130 steel piece. I had to buy the two halves and install them. I don't recall an aluminum part, but as aluminum has about 1/3 the material stiffness of steel, doubt that such would be effective.

Dave
 
The 4130 part was a safety piece. If the flange failed, it kept the propeller with the aircraft. The spacer was used to stiffen the flange as an assembly with the intent of not needing the safety piece.

FWIW
 
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