You can get them regarded and like what has been said already. It will be the only option soon unless you buy a brand new one

Has anyone actually had a 20vt crank reground and treated successfully and had it last a reasonable length of time?

I remember a few stories of unsuccessful attempts over the last decade or so but can't remember anyone saying they'd done it 100% successfully.

Obviously getting a new crank was almost always the preferred option until recently (due to cost/availability) so there are probably very few who have even attempted a repair.

I have had cranks reground and re hardened and the ones that I've sold are still running well today. In fact I have one fitted in the track car which has taken some real abuse over the past 3 years and still looked A1 the last time I inspected the bottom end after my small error with an oil restrictor

I like many didn't think it was possible to re nitrate these properly until I was passed the details for a company that does this all day long. It's not cheap as they charge by weight, then you have the machine shop costs so presently either a known second hand crank or if you're lucky enough to find a new OE units is still the route to take.

^^ Interesting, thanks.

What is the typical cost of getting a crank re-nitrate joe?

Some good info here.

Is it safe to say damage to the crank only happens when the knock first starts? And if a low oil pressure engine but not knocking would benefit greatly from a new set of shells that's if the crank measures ok?

In reality, bearing damage occurs long before you can hear it. In this case the bearing being the interface between white metal bearing surface and hardened ground crank. It's just that the crank is so much harder than the white metal bearing surface that you can often get away with clean up/polish and replace white metal bearings (shells). The key to the bearings success is the layer of oil molecules between the two bearing surfaces. Once and if this is compromised damage starts to occur. You may not hear or notice it for a long time.

Having spent 20 years in the bearing industry, the last five of those with SKF, I know a little about bearings. As for polishing a crankshaft and refitting it; it's often done and gives fairly good service, but with bearings often the ground surface is used to hold oil molecules in the microscopic valleys. A polished surface prevents this, so I would not expect a polished crank to last as long as a ground crank.

Regrinding a crank, if done to the original manufacturers spec in terms of accuracy, concentricity, parallel and surface finish, should be as good as a new crank, again assuming that the nitriding is done properly. Of course, we find that sometimes the manufacturer's spec can be improved upon, but this is a specialist job and advice should only be taken from specialists in this field with a very good reputation.

Nitriding is by no means a new treatment. It's been around for ages and I would have no hesitation in using a nitride and reground crank, with two caveats.

1.) The aforementioned trust in the quality of the machinist/workshop.

2.) An acceptance that by grinding the crank I have reduced the diameter of the bearing and therefore the crank will have less strength than previously. Knowing that these cranks can be used with much more than the 220BHP standard power, means that this wouldn't worry me too much, but I wouldn't use it in a 600BHP monster Coupe. It's only a little less strength and wouldn't be an issue in a standard Coupe.

That said, Joe has such a crank in his track car and that's got a few horses.

Their price is based on a minimum weight of 100kg, I'll find out the costs after Xmas as the paperwork was 2011 so it's with the accountant.



Heat damages the crank so damage can occurs before the shell actually spins but it is however possible to salvage a crank if it knocks and is caught early, ie not driven/started.
Low oil pressure engines aren't always down to excessive clearance with shell bearings. As Simon's showed a knackered turbo will also reduce the pressure, then there's the pump, oil ways to the cam buckets etc etc.

Nice post Peter, very imformative

Hi Joe, is the company you use for nitriding your cranks called Longwear Nitriding in West Bromwich, thanks.