Recommendation for Crank Repair and Hardening

[Edwin Ek]

I have a 1973 car which needs crank repair. Recommendations please for who does a great job. Los Angeles - So. Cal. shops preferred, but shipping is fine too.

Thanks.

[ajwans]

Try these guys http://www.marinecrankshaftinc.com/

I've only heard good things about them.

andy

[Richardnew]

I hear good things about Scat. I know the work on Bugatti cranks. Actually they made one,

Here's more on crankshafts than you really need to know.

Richard Newton

[csbush]

Have you talked to Ollies or Walt at Competition Engineering?

[chris_seven]

Edwin,

What's wrong with the crank as this may have some influence on hat needs to be done to effect a repair.

[Jasper72]

+1 for Marine Crank

Also Armando from Custom Crankshaft & Repair is very good for nitriding crank, cross drilling, etc. His shop has moved to Texas though.

[raspy2point2]

Bruce Anderson's book on performance says if you need re grinding ,get another crank. Or send it to the factory for proper fix. Chris

[chris_seven]

I would be concerned about nitriding a standard steel Porsche Crank as they are manufactured from a relatively basic Medium Carbon Steel and the alloy content doesn't lend itself to traditional nitriding.

When you nitride these basic materials it is quite common that the results obtained aren't good. Nitralloy and other 'Nitriding' steels tend to produce surface harness levels of around 1000HV due to the presence to the nitride forming elements present in the alloy. The nitrides formed also produce significant residual compressive stresses which enhance fatigue life.

When plain carbon steels such as CK45 are gas nitrided the nitride layers formed tend to be much thicker, much weaker and not as hard with 600HV being quite typical.

When stressed these thick and relatively brittle layers can crack and 'spall' resulting in premature failure of the component.

It would be prudent to only nitride plain carbon steels to improve corrosion resistance and not to enhance their mechanical properties.

More recently a Plasma Nitriding which was developed during WW2 has become more commonly used and the manner in which the nascent Nitrogen is produced and diffused into the steel allows medium Carbon steels to be nitrided more successfully as the diffusion zone depth can be more easily controlled.

I have, however, still to see good evidence that a medium carbon steel that has been plasma nitrided provides the same level of performance as a gas nitrided Nitralloy.

Porsche Cranks were always subjected to a 'Tenifer' treatment which was commonly referred to as 'Salt Bath' or Liquid Nitriding.

This process is more correctly known as 'Ferritic Carbo-Nitriding' and involves the diffusion of both carbon and Nitrogen into the surface of the steel.

The depth of the diffusion layer is much shallower and the level of residual surface compression produced is much lower but in general it is effective and quite valuable as well as being very cost-effective.

The Process has several commercial trade names all of which tend to involve subtle variations an a basic theme and these are;

Tenifer - the original process, Melonite, QPC and of course Tufftriding.

Metallurgically I can see no reason not to re-treat a crankshaft that has been ground as long as the bungs are removed and the oil galleries thoroughly cleaned but apart for producing a hard layer on the journals there is little benefit.

It is possible that re-treatment may help to reduce the accumulated fatigue damage in the fillets of the crank and for a race engine being used at high speeds is probably a good idea but for a road car I am not sure the risk/reward benefit is worthwhile.

[Rick Cabell]

Raspy2, keep in mind Bruce wrote that book in the late 80's. A lot of technology has changed since then. I have many cranks ground and re hardened without any trouble after tens of thousands of miles, if not hundreds of thousands.

[drbooba1]

Melonite is available from Burlington Industries in Orange Ca.