Any better or new hardening process for reground crank?

[alniki]

Wayne suggested in his engine rebuild book that worn crank better be replaced by a good used one instead of regrind because the original nitriding process is no longer performed for hardening after regrind.

Is that still so today? Any new process or source of nitriding for reground crank? Thanks!

[911pcars]

Not sure. Do an internet search for the following terms:

Nitriding
Tennifer
Tuftride

Many of these sources have disappeared due to environmental regs.

I've noticed gunsmiths use these same processes.

Sherwood

[Gary De]

Check out winberg crankshafts on the internet. The machine shop that i was working at did nitride this crankshafts.

[Steve@Rennsport]

You can still get cranks nitrided, but make sure its checked & corrected for straightness after such treatments.

[alniki]

Thank you, gentlemen! That would absolutely make a regrind more sensible.

[racing97]

Make sure that the shop that does the hardness treatment understands that the crank has aluminum plugs for the oil passages, and will need to be replaced or tapped for pipe plugs.

regards

[chris_seven]

Guys,

This one just keeps on going around and as an old-fashioned metallurgist I just can't help but being drawn to comment. One day I will find time to write a detailed article to try to unscramble some of the facts from myths and resolve some of the errors that have crept into almost every technical article on surface treatment that is published in automobile tuning mags. There are just a few basics that need considering:

I am confident that 911 cranks were surface treated using a 'Tenifer' process. This is also known as Tuftriding or Melonite treatment.

This process is more accurately 'ferritic nitrocarburising' and used to be carried out in a salt bath which used relatively toxic chemicals.

Many of these chemicals have now been eliminated from this process due to Health and Safety concerns, hence the belief that it is no longer available. This, however, isn't the case and there are many companies still able to offer this service.

Tuftriding can be carried out on virtually any steel and provides an improvement to surface hardness and hence scuff resistance. It also helps with lubricity and has a modest benefit to fatigue life. The thickness of the 'white layer' produced is around 0.0015" to 0.002" and it should not be removed.

Tenifer and all of the other similar process takes place at around 570 degC and if parts have been correctly stabilised before final machining shouldn't cause any distortion.

I think that some of the confusion results from the use of the term 'soft nitriding'.

In the sixties the industry offering this process decided to describe it as soft nitriding as a way of gaining a better acceptance of the process when compared to what I would describe as real nitriding. It was a bit 'cheeky' but did gain some acceptance as a name.

I do accept Tenifer treatments are useful and very cost effective but they do not compare with the genuine article in terms of surface hardness, fatigue life enhancement and case depth.

Nitriding in the Sixties/Seventies was generally carried out in a gaseous environment using Cracked Ammonia. (In recent times Plasma techniques which have other benefits have also been developed)

The steels used for nitriding have a very specific chemistry, the most famous being 'EN40B' which is still in common use.

It is conventional for these steels to be fully hardened and tempered prior to nitriding and this is an important part of the process.


Nitiriding also takes place at a relatively low temperature but case depths are typically 0.025"-0.040". Nitriding also produces a 'white layer' but in this case this layer should be removed before the part is used. This removal used to be carried out by grinding but now water jet treatment is quite common. As conventional nitiridng does cause a small amount of growth it was common to finish size the part prior to nitriding and then grind to remove the white layer and re-size.

The danger is that if a steel that is unsuitable for this process is used soft Iron Nitrides can be developed and these are likely to spall from the surface and cause untold damage.

I would never nitride an unsuitable steel and I don't believe that a 911 crank is made from a nitriding steel.

I have also seen many references to a process known as Nitrating, which I must say I have never heard used here in the UK and searches on the web seem to use it indiscriminately to describe either nitriding or nitrocarburising which also adds to the confusion.

The surface colour of both nitriding and nitrocarburising tend to be 'silvery' in appearance. I have never seen either of these treatments produce a blaqck colouration.

I have recently been told that the Rocker shafts produced by Porsche Motorsport are 'nitrated' as shown by their black colour. If I were a betting amn I wouldd say that they have been 'Parkerised' which is a surface treatment oftern used on camshafts. It is relatively cheap and quite effective.

Just to add a final note there is also a process known as Carbonitriding which is carried out at higher tempertaures of around 850degC. It is used an an alternative to carburising and gives better fatigue life but it is not suitable for treating cranks. It is often confused with nitrocarburising.

If you look on Wikipedia for these process there is some good information but also some tragic errors.

[alniki]

Thanks Chris, that's enormously informative and instructive and makes browsing Pelican forums a more rewarding addiction.

[Flieger]

So, what process has been carried out on these early 911S connecting rods?

I thought it was called "nitriding", which I always thought to be the molten salt bath treatment.

[chris_seven]

I think 2.2S rods were 'soft nitrided' which is ferritic nitrocarburising and the appearance is what "I would expect to see.

There are some new Melonite process such as Melonite QPC that give a black finish but this is still nitrocarburising.

As far as I know salt bath nitriding is also ferritic nitrocarburising and produces quite different results to gas or plasma nitriding

I do beleieve that these processes are beneficial but it is wise to differentiate to avoid costly errors

[djpateman]

Would any of the cryogenic treatments be useful for crankshafts or rods?
It does appear to be useful for bearings and brake rotors.

[chris_seven]

DCT - another process that will save the World

There are certainly benefits associated with this process and bearing materials and cast irons will certainly benefit from this treatment.

The type of steel used for cranks, however, doesn't really sufffer from the problems as the Retained Austenite levels are generally less than 2% and in any case many years of use is likely to have caused this metastable phase to transform.

Bearings can retain several percent and when the races/balls are loaded the Retained Austenite can transform and cause a volume change which disturbs the shape and conformity of tracks.

Cast irons are improved by other mechanisms and I am sure that the carbide precipitation repoterd in the literature is correct.

Many of the other claims, such as performance improvements in pure annealed copper and other alloys are unlikely to be proven and the industry uses great statements such 'although there is no technical explanation we have found....'

Where does that take us in relation to the question:

If I made a brand new high performance crank from EN40B or similar, I would probably use DCT prior to final grinding and subsequent nitiriding.

DCT certainly won't do any harm and may just offer some marginal improvement and as the process isn't very costly relative to the cost of a new custom crank. (Bit like an Aetheist hedging his bets).

If I had a used crank to grind I would turftride and not use DCT and I am sure it would perform well.

[911pcars]

Originally Posted by Flieger

So, what process has been carried out on these early 911S connecting rods?

I thought it was called "nitriding", which I always thought to be the molten salt bath treatment.

Not sure, but I could suggest shot peening to provide added strength at a relatively low cost.

Sherwood

[alniki]

Chris,

What about cams?
Cam grinders did not seem to mention any hardening treatment for reground cams.

[911pcars]

Originally Posted by alniki

Chris,

What about cams?
Cam grinders did not seem to mention any hardening treatment for reground cams.

My poor attempt at Japanese Haiku:
Unhardened cams soon experience roundness.

Sherwood

[alniki]

Found an informative old thread:

Crank hardening
Crank hardening

[alniki]

It's suggested that there are some questionable info in the above old thread, so read with a grain of salt as always on the internet