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Rich H · Posted: Mon Jul 28, 2008 10:34 pm Post subject: Crank grinding

Hello,

My "worrying noise" has propted me to get my spare engine underway, first thing it needs is a crank grind. Now I have found 2 places locally that will do it but one of them said they can't reharden it afterwards, is this required? I can't find any reference to it anywhere else.

Does anyone know for sure if it needs re-hardening after a grind or 0.30 mm (The bearings I have) Is it worth getting done anyway?

Ta
Rich
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1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

RC · Joined: 25 Mar 2007 Posts: 2637 Location: Australia

No. It doesn`t Rich.
Its a forged crank but regardless it is rare for a crank to require rehardening of the journals. Usually only on bike, outboard or small engine cranks that use roller bearings and are case hardened. Have had many cranks ground and never been asked that. Would be a bit sus of that shop myself.

Roger

Rich H · Posted: Mon Jul 28, 2008 11:40 pm Post subject:

Cheers RC,

To be fair he said he didn't know and would have to find out, he said they couldn't do it if it needed hardening and offered the name of another place not far off that could do it if it did.

both places I have tried said the same price (£80 +VAT) so I'll go to the nearest one. I just have to check the dims as my shells are .30 undersized ones. Also found a friend of a friend who builds formula ford engines who will balance it (If it will go on his machine) for £50 too

_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

Just have it polished after it's ground and you're set. They should be able to do that with no problem.
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1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet

miniver · Joined: 21 Jul 2007 Posts: 11 Location: Lodz, Poland

And by rehardening do you/ they mean nitridization or some related process?

http://en.wikipedia.org/wiki/Nitridization

I know an engineer who is an expert in the field and from what he says the process makes the crankshaft almost indestructible. When I replaced the camshaft I had it undergo a process similar to nitriding (a process which I don't know the name of in English, sorry).

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

I can't recall the details ATM, but when we were having our stroker cranks prepared, I inquired about nitriding, and our crank guy recommended against it. I don't recall why now, but we followed his advice and didn't have it done. I think you will be fine with basic grinding. Those prices seem to be roughly equivalent to prices I've seen here in motown.
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erstwhile owner of just about every 924 variant ever made

Rich H · Posted: Wed Jul 30, 2008 5:54 am Post subject:

Cool!

_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec