Where can I get my crankshaft hardened?

[Nambo]

So, I have a spare crank, it needs hardening, whats the current best form of hardening and does anybody know somebody in the south of England who can do it please?

Am I correct in thinking that hardening puts a few thou on the crank so it can be polished down to the correct size?
My crank is only on 20 thou, isnt really worn but must have some wear, be nice if it can be restored to as new 20 thou just be hardening?

[DJT]

Try Oselli. They Tufrided one for my old Stag many years ago, and may still do it.

[Nambo]

Try Oselli. They Tufrided one for my old Stag many years ago, and may still do it.

Cheers, though they look expensive.
So is tuftriding better than nitriding?

[Motorsport Micky]

A crank -20 thou under standard size is just that. Tuftriding or nitriding won't ADD 20 thou onto it but rather develop a harder and tougher surface finish to withstand grit and oil carried debris from excessively marking the crank ground surfaces. Cranks used for motorsport are prepared this way as a matter of course and reportedly the Stag cranks were hardened so that they could withstand a -10 crank without retreatment.

Having checked my engineering books and sources for definitions nitriding is a chemical process where the crank is immersed in ammonia in a furnace as a gas so it diffuses into the metal and forms nitrates with the various alloy elements in the steel. Tuftriding is a similar process but using sodium cyanide in a liquid bath, the advantage of the nitriding being the lower temperatures involved wont warp the crank (maybe not to the same degree) like sometimes happens with tuftriding and the hard layer produced is thicker with the nitriding.
I had a crank with a 10thou bend put into it after being tuftrided, subsequently straightened by the engineering firm with no discernable runout (apparently they belt them with hammers !) the trick is where you apply the blows.


Micky

[Nambo]

I wasn't expecting to bring my +20 crank back up to standard, just inquiring if nitriding would replace 10,000 miles of wear to bring it back to a freshly ground +20.
The reason I enquire is that it would be foolish to harden a crank that is partly worn, but I had good oil pressure on this crank and would be a shame to take it to +30 needlessly.

[Motorsport Micky]

The 10,000 miles wear should be almost negligible, why not just grease up the crank and store as is and if ever you need to use it you can make the decision at the time.

Micky

[Nambo]

The 10,000 miles wear should be almost negligible, why not just grease up the crank and store as is and if ever you need to use it you can make the decision at the time.

Micky

Engineering prices get higher by the day, skills get lost, if I ever needed it, I would rather it be there ready and waiting, if I ever wanted to sell it, who would want a soft crank?

[Motorsport Micky]

See what you mean,then if it was my crank I would have it nitrided and have the journals micropolished, if done carefully the journal size should not be markedly affected and the crank should be eminently usable.

Micky

[Paul Roberts]

Nitriding and Tuftriding surface hardening processes are, somewhat, limited to certain metal alloys. The processes are not automatically suited to any/all steels (it's loosely related to carbon content.)

It's possible that Stag cranks were, originally, induction hardened (high carbon steel) and are thus less well suited.

To save a great deal of research: does anyone on here know what material the Stag crankshaft was/is made from? EN number?

[wilf]

Both hardening processes involve heat and the potential for distorting the crank.

If this crank has only done 10k miles and always had good oil pressure, and has no scoring or other wear damage to the journals, and mikes up as not oval, I personally would protect it properly and leave it be as ......................."it ain't broke".

[richardthestag]

faversham classics have an engineering workshop near them that do it. I bought the whole thing from FC

I found that some supplier cranks sold as hardened werent.

[richardthestag]

reportedly the Stag cranks were hardened so that they could withstand a -10 crank without retreatment.

Mine wasnt, 10 thou mains and big ends, within 30k miles two mains and one of the big ends were like the surface of a 78rpm record.

[Paul Roberts]

Just for the record: Can anyone on here advise or confirm the original specification of the crankshaft steel?

I assume the crankshaft was forged and not cast?

The only, obscure, reference I've found alludes to EN16 (a relatively low grade material for such a component) and whilst this may well have been used in vehicles of a greater age than the Stag, I would be surprised (and a tad concerned) were it to be the case; even with the Stag.