Need Crank - Reman or New?

My 540 suffered a significant overspeed last summer and it's just now working through the shop. Long story short, the overspeed event cracked one of the counterweight ears. Shop is giving me the option of an overhauled or new crankshaft - the latter at a substantial price premium.

The price difference is not a major problem, but certainly worthy of consideration. The main issue I'm now struggling with is whether the extra cash actually buys me any benefit. It seems obvious to go with new, but I've been bitten by the "improperly manufactured" crank AD once before, and there's a NEW one out currently. OTOH, a properly overhauled and inspected used crank has lived through the gamut of AD's and is likely to simply keep on truckin' until fatigue or wear finally takes it out of service.

Has anyone faced a similar choice or have any opinions that favors one or the other?

With the various shut-downs I've been hearing about, perhaps the one most quickly-obtained would be the way to go.

I wouldn't hesitate with the reman, assuming it was done correctly by a reputable shop. Caveat, I'm not an engine guy, just an old stress engineer.

Dave

Only thing I can think of is a potential issue at TBO. If the overhauled crank has been turned down a few times already, it may be at its limits -can't be turned down again. Can you find out the current dimensions of the used crank bearings?

Any crank that goes back in the engine will be within "new" standard tolerance - just like the "AD" crank that came out, and the reman that went in 3.7 hours ago to replace it (now cracked).

Certainly no expert here but I wouldn't have an issue either way. Running an overhauled crank in my 360. So far 370 hrs with no issues. The club uses reman cranks in their rebuilds and they go over 3000 hrs consistently. As long as it is done by a reputable shop should not be an issue. Haven't really heard about engines failing due to broken cranks unless they have been abused or have a manufacturing defect...ie. overspeed or prop strike with no bulk inspection after or an AD issue....

Used both new and overhauled in my hot rod days. Never had a crank fail...threw a couple rods though.... FWIW.

I went new...

My builder went with a new one, and I asked him to have it cryo-treated.

https://www.kitplanes.com/coming-into-the-cold/

Toobuilder said:

It seems obvious to go with new, but I've been bitten by the "improperly manufactured" crank AD once before, and there's a NEW one out currently. OTOH, a properly overhauled and inspected used crank has lived through the gamut of AD's and is likely to simply keep on truckin' until fatigue or wear finally takes it out of service.

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This is my current thinking. No current evidence to suggest age has any impact on potential crank failure, assuming positive NDT results. On the flip side, it seems many cranks produced in the last 10 years are suffering from failures due to manufacturing issues.

Seems there is little to no evidence to support the logic that new is better and some evidence to imply old, used is better. Your stated experience would seem to back that up.

Larry

Lycoming

lr172 said:

Toobuilder said:

It seems obvious to go with new, but I've been bitten by the "improperly manufactured" crank AD once before, and there's a NEW one out currently. OTOH, a properly overhauled and inspected used crank has lived through the gamut of AD's and is likely to simply keep on truckin' until fatigue or wear finally takes it out of service.
/QUOTE]

This is my current thinking. No current evidence to suggest age has any impact on potential crank failure, assuming positive NDT results. On the flip side, it seems many cranks produced in the last 10 years are suffering from failures due to manufacturing issues.

Seems there is little to no evidence to support the logic that new is better and some evidence to imply old, used is better. Your stated experience would seem to back that up.

Larry

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I don't think factory Lycoming cranks manufactured since about July, 2005 have any known issues, service bulletins or AD's against them. The current issues seem to be with aftermarket crankshafts.

Skylor

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I think it was early 2006 when the last crank SB was issued from Lycoming so you should be safe getting one that was made after that.

Unfortunately Lycoming SB 505B (corrosion inside hub) has taken a lot of otherwise good cranks out of service (one of mine included). The price of O/H crankshaft remains at a premium. Sold mine to the airboat guys for $500.

With a reman/OH crank hasn?t the metallurgy been somewhat proven?

Crankshaft Dilemma

I?ve built a few engines and this choice has always been an interesting dilemma. Usually price wins out, but in the current market availability may be the primary driver. Try to find any good used 0-360 crank in the current market, (Superiors issues ) your talking 4K used, if you can find any. I would stay away from the PMA?d world and go Lycoming factory new or used. At least Lycoming gave out crankshaft kits to replace their AD?d cranks in their last episode.

My question though is what was the rpm of your overspeed that caused the counterweight ear to break ?

I don't mean to imply that a new crank is "unsafe" - my main question really is: "What does the extra $4k buy me?" In my brain I can't come up with anything, and it seems this forum supports that.

Concerning the overspeed, it was in excess of 3800.

Not that it means anything but . . .

Toobuilder said:

I don't mean to imply that a new crank is "unsafe" - my main question really is: "What does the extra $4k buy me?" In my brain I can't come up with anything, and it seems this forum supports that.

Concerning the overspeed, it was in excess of 3800.

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Assuming the factory cranks are made on modern machinery and managed with current best practices quality control (air gauges, SPC, etc).

I would say a high probability exists for a better dimensional consistency and surface finish of bearings and proper nitride hardness/depth (along with a 100 more details). Basically a more precision piece. This makes for (typically) more reliable part.

But as long as the "rebuilt" crank had only ground surfaces, and re-nitrided with good inspection procures on each crank, then it would be just as good for its original purpose. And both sourced parts are still bound by the same TBO requirements.

You might want a mag and eddy current inspection just to be sure for sub surface inclusions that might have grown in service. They are not detected by mag inspection.

I think it kinda is how much money you want to spend for a little better "insurance".