That is just one method of hardening, With Induction hardening the components are heated by means of an AC current fed through an induction loop which gives an alternating magnetic field, this is done until the surface temperature is within or above the transformation range and then followed by dunking. The core of the component remains unaffected by the treatment and warping should not occur.

 

I rebuilt mine after a big end failure for £350 which covered a full gasket set, mains and big ends. You can get a rebuild manual off the web (think it was a URL on the GG website). Although it had spun No 3, on inspection the crank was ok. Has done 20k miles at 290bhp since no probs. I ported the heads and matched the headers while I was at it.

Be under no illusion about the amount of work in it though, you won't do it in a weekend and a popped piston would make me think about a replacement long engine if you can find a known good one as an engine swap is comparatively straightforward.

 

As well as maybe,Vacuum Heat Treating ,Atmosphere Heat Treating,Sub Zero Treating and Laser heat treating.

 

And uncle Tom Cobley and....................

 

It may be ok in the short term, but i feel you are on borrowed time. depends on how much they have taken off, and the finish/quality/geometry of the pin.

As normal APIdavid and Zen performance are right. Subaru Plasma nitride there cranks. It does leave a very thin hardness layer that is dependant on how long they are processed and gas mix etc, but judging by the cycle time they were using in the furnaces that i saw it will be very similiar to the cranks @ my place of work.

you are looking at around about 600 vickers (not especially hard, but enough) and this drops to around about 500 at 0.2mm depth.

so if you grind any more than say 0.3mm on diameter from the pin, you are seriously affecting hardness.

Plasma Nitriding steels will not have the carbon content (and there is other elements in there as well) to allow any kind of effective induction hardening of the ground pin. Induction hardening is a pain on cranks anyway, requiring pre stress relieving ops, and tempering and straightening ops after hardening.

The reason lots of jap cranks are made this way is simple - its very clean and controllable compared to more traditional methods.

The cranks are machined and ground (so are geometrically correct) before hardening. Plasma is such a comparitively low temp (520 deg) that no distortion takes place during hardening. Hardening is done in a controlled vacuum furnace, no mess/coolant/oil around.

As soon as they are out, a polish of the pins and mains to remove the white layer and you have a finished cranks.

The only japanese factory making cranks not using Plasma i have been to was a Nissan factory in Thailand. quite a few european manufacturers still induction harden though.

Carburising and nitride baths etc went out with the Ark for production, but still have there uses in the F1 and protoype industry.

In short, grinding a scoob crank is a long term recipe for disaster.

 

I knew that Just didn't know how to put into words.......

Well done p1mark that's clarified it all for me. Thanks very much

David APi

 

No probs David-i knew thats what you were getting at.

The depths and Hv figures qouted above are not subaru figures, but i know that they are using a simiiar material (A jap spec EN40B for the mettalurgist ***** ) an identical cycle time (26 hours button to button) and an almost identical hydrogen/nitrogen mix to the cranks i am familiar with. The cranks i saw being processed were EJ20 and 25 items.

I would hazard a guess that those hardness figures and depths are pretty close, but if you grind 0.2mm off and it fails dont blame me

If you use ANY heat treatment methods other than low temp (i.e you are changing the structure of the material and not 'adding' to it) on something as flexible as a crank you will get distortion, growth and/or inherent stresses added.

At Daimler/Cryhsler in Berlin, i witnessed some big diesel truck cranks - soft all over but with induction hardened pins/mains/spline having to be put through a CNC press that could squash a car flat. The cranks were run up between centres first. the ones i saw were up to 5mm TIR out. The production engineer responsible said they had to scrap up to 5% out that they could either not straighten or cracked after straightening.

Not much use to scooby lovers when all said and done but interesting nontheless IMHO

PS Lewis's post earlier in this thread about non-distortion pretty much shows what kind of an 'engineer' he really is

 

when you say another engine how many have you had?
martin