Hard chrome crank back to std/std?

[Mark Henry]

My 3.0 crank is sick and she's not going to polish out. I'm a bug guy so it will sicken you to know I'd usually just get my crank guy to cut it first under, $75 worth of bearings (that's main and rods, KS german bearings) and Bob's your uncle.

So now I need either a different crank or I can get most of my journals hard chromed and polished back to std/std.
Hard chroming, also known as engineered chrome, will cost me $600
A used crank from the classifieds looks to be about $700-800, plus shipping to Canada, plus brokerage fees, taxes...

So Henry, Steve, Tom, Wayne (Sorry I know I missed a few names) what do you guys think about this process?

[ix0ifan]

I wouldn't entertain using this process on a performance engine crankshaft unless it was a very rare part that couldn't be replaced.

Hard Chrome will significantly reduce the fatigue life of the crank. It does this by reducing the threshold stresses needed to cause crack initiation (I can easily believe that this will be between 20-40%) so it is much easier to initiate fatigue cracks which will then grow rapidly and cause a catastrophic failure that will completely trash the engine.

There are a few processes that are supposed to eliviate the reduction fatigue life but I don't think they are well enough established to take the risk for one off applications.

There are quite a number of shops that hard chrome cranks but these are usually for use in Industrial Diesel Engines or Industrial Compressors which have very limited duty in terms of rpm and torsional vibration.

It is also commonly used on really big Marine Engines where new cranks are a few hundred thousand dollars.

I would tend to re-grind and suffer the bearing cost of the undersized shells or buy a good used crank.

[Tim L]

Hard Chrome will significantly reduce the fatigue life of the crank. It does this by reducing the threshold stresses needed to cause crack initiation (I can easily believe that this will be between 20-40%

Don't do it, this is from my 911 hard chrome experiment!!

[kenikh]

whoa!

[Steve@Rennsport]

Totally agree. Hard chroming is never an option for a high-performance crankshaft that will see high (6K+) RPM.

I would either have it re-ground and nitrided or simply buy another one: new or used.

[tom1394racing]

Mark

I you decide on a new crank, I have a couple of std/std on the shelf ready to go.

[Mark Henry]

Dang, Figured as much. I almost feel like giving Tim L a paypal donation for showing me the results of that 'experiment" pic.

First I'll look around locally then I'll give Tom a PM and/or do a WTB.

Just for devils advocate what do you guys think about 1 or 2 OS main bearings on a crank.
Looks like the under size rod bearing are not too bad of a price, it's the mains that are the big nut.

Thanks.

[jwasbury]

How far out of spec is it? I had my crank nitrided and got a small amount of "growth" from the process. In my case the rod journals were smaller than the lower spec, but still larger than the wear limit. After nitriding and a mircopolish, they were back inside the specs.