20v crank re-grind - who's had failiures?

i see it advised against but has anyone actually experienced a failure? if so, what happened exactly?

(i don't need a new crank, i'm grinding for another reason)

JBT had a failure shortly after a regrind, but I'm not totally sure the failure can be totally atributed to the regrind, I'l let him comment, or it might be worthwhile speaking to him direct

cheers mate, i'll leave it for him to see here in case anyone else wonders

from memory, re-grinding take off the nitrate harding from the crank.

and i *THINK* it does not allow a propper oil film on the bearings which casuing the bottom end to fail.

i no of an engine which had a full re-build + New oil pump the lot.. and it failed due to bottom end knock.

The problem Is that you go through the nitride coating when you grind. It's only going to be a couple of microns thick.

The coating is like a case hardening process. I.e. the metal of the crank isn't particularly durable.

I can't comment on durability afterwards but it was coated for a reason.

An interesting conversation with a guy I knew (worked for bae with weapons, firing pins etc.) Suggested that there were nitride coatings that were nigh on indestructible. It may be you can find a metal improvement company that will take on a small scale one off? You would have it ground to size and then coated.

Have a look on Guy Croft's website for the reasons not to regrind.

http://www.guy-croft.com/viewtopic.php?f=3&t=2031

Had one regrind on my 2.0TS, polishing on 2.5 and 20VT - no issues.....BTW at least 60% of our used cars here have some kind of regrind, i saw few times an crankshaft that was regrinded 3 times and used for long with no problems with appropriate bearings.......well most of it was daily cars, not driven hard......But hope you understand the reason for that - here in the price of one new 20VT crankshaft i can buy 2 used MK1 Punto's in full working order.

i cant see the problem personally, a grind and rehardening

guy crofts article makes no mention or hardening after the grind. in theory it may produce different stress risers which may lead to cracking but this is different to the wear problems described in the forum advisory.

providing anecdotal examples of small samples of failures is not reliable, these could fail due to a multiplicity of reasons ranging from poor machining, poor build, poor components, or a multitude of other reasons....

Guy covers it some more here http://guy-croft.com/viewtopic.php?f=13&t=2746

It has come to my attention that somebody thinks my engine failure in my project thread is related to this thread, it is not. My failure was due to incorrect bore size for piston clearance. I have NEVER re-grinded my crank nor had a crankshaft issue.

I would strongly advise against re-grinding as suggested above.

So, nobody has actually experienced a bottom end failure that has been 100% attributed to a re-grind? ...but then by the sounds, not many have actually tried it either so...

the problem with the GC posts are a) I get the feeling he's mostly talking about the old skool twin cams which were probably subject to differing levels of nitriding depth and b)he's not said the failures he's seen are 100% attributed to a re-grind either.

i would assume the nitiriding layer on a modern 20v crank would be a lot thicker, as much a 40 microns but that's just speculation - need to measure it really!

thanks for the input

I went to GC's when my engine was being built with a new crankshaft. GC pointed out that this didn't have the nitridring on it and he demonstrated the difference between the 2.

He took a centre punch and a hammer and gently taped the non nitrated crank, this put a dent in it straight away, he then took an old crank with the nitrated layer, used the centre punch and used full force on the centre punch, the result? No dent.

For me, this was quite conclusive on which crank I should be using.

can you get a crank nitrated harded after the skim?

supposedly yes and as it's done at relatively low temps, shouldn't distort the crank or create stresses. however, GC has some warnings on it so some further investigation warranted me thinks.

Are 20vt cranks that rare where you can't source a good used on?

Original 20V and 20VT crank is NOT nitrated!
We did several investigations.
Therefore regrinding is absolutely no problem at all.

Juergen

You should ask Guy directly about the 20v cranks, this sort of thing is one of his pearls of wisdom.

I would like to suggest that the earlier cranks have a deeper nitride layer than the modern versions which would be a different procecss entirely. The original liquid nitriding I believe was banned due to some sort of harmfull chemical used.

Is there no treatment at all on 20v ?

now that's very interesting!

would you mind sharing a few more details of the investigations?

Please do.. im interested...

i wounder if Guy Croft will come on here to explain a bit more..

Apologies, appear to have totally missed that. So that's two saying no nitride layer on the 20v cranks.

Don't know about the rest of you but after 70k, my crank was still within std OE diameters - so if they're not nitrided, what's the deal?

Very simple test - make a hardness test (I think we did Vickers) with original crank, take a file and grind a bit of surface, repeat test.
If there are no changes in the result, there cannot be any nitride on it. We did not find any change.
Moreover I am quite sure that a grinding shop would realize a hardened crank, when trying to regrind it...
It is very very hard to regrind a nitride surface...
Juergen

Maybe if you look at my signature, you will notice that I don't have a 20vt and was talking about 16v cranks

what kind of arsey response is that? you're the one talking about 16v cranks in a 20v crank thread!

and you checked the journal diameters first to make sure they had not been ground already? did you test more than one crank?

Begbie is Mr Cranky

Pun intended?

Maybe take the time to re-read your own thread.

People were discussing about regrinds and the topic went onto nitrate on the crank. I was giving a real life example of the difference between a nitrated crank and a non nitrated crank.

well, might as well! it was not ment to be.. but Yer..

Maybe you should just be quiet now - you know, given you're supposed to be a mod and diffuse situations, not cause them.

to be fair mate, Begbie gave you a real life experience on how a none hardened (giggady) crank will dent with out a lot of force... and a hardened one will not.. giving you a good example of the safer bet.

be it a 16vt/20vt ect

the last thing you want to happen is build a N/A monster and shortly after have the bottom end rattling out.

in my experience, go for the best you can get, and in this situation, get a none ground crank.

the otehr main question is.. would you want to risk it?

I think maybe you should take a bit of the advice you're so freely issuing here Nedge! I've read this whole thread and while I agree Begbie was a little short with his reply, it's you that now needs to show some restraint.

Back on subject now please guys.

hence the whole reason for the thread

NONE RELATED TO 20V CRANKS:

My 2.0 TS Suffered from a HUGE crank failure but didnt crack... re-ground 20 though' and used appropriate bearings to suit, 10k miles to this day and all driven hard, no isses.

good to know, cheers

Odd test tbh, besides which unless you used tool steelm, hardened or similar i find it hard to see how a proper whack with a centre punch wouldnt leave an impression at all. If that were the case rockwell measurements would ne very difficult to carry out without an impression to measure!

A conventional way to identify surface hardening is with a blunt file on a non bearing journal surface. Simply put unhardened 'grips', hardened slips.

Could you elaborate on your "another reason"?



How did you come to that conclusion?
Could you elaborate on the test results what HV did you obtain? Did you do a Rockwell test? Did you test all five journals? Was the crank tested brand new or used?

Just read this. lol
That's NOT a Vickers test, that just sounds like you you scraped a file across the journal and saw no marks so it will be ok. Hardly an "Investigation". If somebody wants me to test a 20V crank i can put in in our metallurgy department, don't expect it back in working order.

Neither ACL nor Mahle/Vandervell do race bearings for the 20v engines. Glyco are fine for the mains but not for the ends - not sure about the OE ones but unless they're cast tri-metal, not trying them.

The plan was to use C20XE +0.75mm bearings and have my rods made to suit - crank would have needed a polish but thats about it. As it turns out, they only go to +0.50mm which leaves me short so I'm considering grinding about 0.3mm off the end journals and using Audi 5-pot bearings.

Anyway, with the XE bearings, imagine I would have been fine. With the Audi's, will need re-hardening.

actually it is, granted not vickers or rockwell but the file scrape will tell you if it is hardened

With respect talk like that warrants digging deep into your pocket for a custom crank.

Aftermarket parts were never made for this engine because there was never a racing series with a Fiat 5 pot.

Why do you want "race bearings"?

You would risk grinding your crank to buy shells to protect your crank sounds like a paradox

I think you are treading on thin ice "frakenstiening" an engine together.

Nevertheless good luck

Equotip / Niton tester will let you know....

Equotip is invasive, Niton tester is not.

Cheers, will look into that.

All in good time.

Right, found another bearing that only requires polishing 0.0013-0.0017" off so even if the nitiride layer is, as suggested by GC for the twin cams, 0.005" thick, that's more than acceptable

I'd suggest OE bearing will be absolutely fine for what you are building, needing only a good lubrication system regular oil changes, clear galleries and oilways, radiused oilways, correct oil, correct oil/engine running temps and constant oil feed will be the items which ensure that metal metal contact won't occur.

TurboJ i'm with you on that one, sounds like the chevvy bearing fiasco in 4pots.

it's 1-2 thou, it's fine. if it goes bang, shit happens. i'd rather try something new than stick my head in the sand.

Had 2 engines fail within a thousand miles of having them built by a local engine builder.

Regrinding of the cranks is a grey area but is widely used as a good solution to an expensive problem.
Average grinding cost is around £100,average crank is around 10 times that.

The failures i had were down to the fact the company used top limit shells on a bottom limit crank.
So the oil gap wasnt big enough.
In static rotation on a bench you can use very tight shells and the engine will turn over nicely.But running in the car its a different story.

Grinding the cranks on these has always got people in to trouble but in my opinion grinding the cranks doesnt cause failure.
The shells are hard to come by these days so most people will risk whichever Fiat or OE parts supplier send them.

A ground crank may significantly reduce the life of the crank in terms of the wear rate but it would still do circa 100k easy enough even without the Nitri-coating.

+1......

I just spoke to Farndon Engineering who manufacture steel cranks and do nitriding, regrinding etc

They nitride to 0.6 mm depth and say their cranks can have three re-grinds before needing re-nitriding. They said that nitriding done by an OEM would be a typically be at least 0.5mm. Nitriding can be upto 2mm thick if desired.

Good news is, Farndon will regrind AND re-nitride your crank for typically £175-£200. Much cheaper than a new one.

There is only one F in Farndon

???This procedure was supposed by the metallurgist in my laboratory, a professor for metallurgy...
A quick method to detect a surface treatment anyway.
This test was done with a precise hardness test machine.
The Nitide surface has a size of max. 100um, according to my prof.
Therefore we grinded away some of the surface in an inconsiderable area and repeated the test, result no changes in Vickers...
In my eyes a very good test!

That must have been a re-ground crank already? That's 0.001mm / 0.00003937"!!

Anyway, cheers for all the input guys, will all be worth it in the end

(sneaky peaky...)

haha, so it is, dunno where i got that from!

I had a brand new crank on top limit,and Joe 78 had a ground crank on bottom limit.We got them both hardness tested and they were identical.So i agree with Stichl.
I cant quote figures as it was two years ago.

cheers jbt

like what i've done with your manifold btw?

Nedge didnt realise your a L,boro chap.
Have i seen you before?

yeah i came round to grab those manifolds off you after the welding cock-up with my vis one. 20vt ones turned out to be a much better suit

Ahhh thats right.The inlet ones for your 20v n/a.

yep, got the bodies mounted nicely now - 10 injectors here i come

Yikes,shell will love you.