Reground Fiat TC 2 liter crank?

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vandor
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Reground Fiat TC 2 liter crank?

Post by vandor »

Ok, so due to some miscommunication my machines shop turned a 2 liter Fiat TC crankshaft 0.010" on both the rod and main journals. Guy, I know you say in your book not to turn 2L cranks. Is this because the hardening is thinner than 0.010"?
The machine shop claims that since there were 0.010" bearings available from the factory, it will be OK. Nice, but I am not planning on building a factory engine... Is there anything I can do to this to make it work?
Thanks.

Csaba
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pastaroni34
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Re: Turned Fiat TC crank

Post by pastaroni34 »

You are correct, the nitride layer is less than 0.005" thick (0.010" removed from the diameter). While the surface certainly isn't dead soft, it isn't ideal. There is now a major penalty in surface wearability and lubricity. This is ok for some people but if you're going to spend your time building it, you want it perfect.

You can send the crank to me, I'll cut it up to experiment with some lightening techniques. Otherwise, the thing is junk.
-Jason Miller
Miller's Mule Machine and Design Inc.
Houston, Texas - USA
Guy Croft
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Re: Turned Fiat TC crank

Post by Guy Croft »

"The machine shop claims that since there were 0.010" bearings available from the factory, it will be OK.."

yes, hard luck there Csaba, they always say that but it doesn't mean you can just go ahead & grind it, just as Jason says. Fiat and the aftermarket all offered oversize bearings for those brave enough to attempt the (re) heat-treatment indicated in the OE manual as being 'essential' for all the 2 liter cranks. Where, if you try it, have five cranks and hope to salvage one with the other 4 written-off due to micro-cracking and distortion. It is way cheaper to find another crank, trust me,

G
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Re: Reground Fiat TC 2 liter crank?

Post by robert kenney »

Since it has been declared suitable only for the scrap bin, I'd send it off for re-nitriding and have a close look at the surface finish. Nitriding is not that expensive. Nothing to loose really.

One caviat, to re-nitride, the original nitride depth (.005-.010" max) should be removed completely or as Guy stated there is risk of surface defects.
Robert Kenney # 111
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Re: Reground Fiat TC 2 liter crank?

Post by Guy Croft »

You cannot simply do that. The old crank would have to be stress-relieved as well or it will bend like a banana.

Heat treatment is always done by weight. Doing a one-off would cost a fortune. With all due respect to Robert, I would urge NOBODY ever to try and re-heat-treat one of these.

It is worth undertaking on a very big & very expensive commercial diesel (I have friends who do it a lot on Perkins engines) but not one of these.

G
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Re: Reground Fiat TC 2 liter crank?

Post by robert kenney »

We do it all of the time. Race cranks or just a hot street engine. $150.
Robert Kenney # 111
vandor
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Re: Reground Fiat TC 2 liter crank?

Post by vandor »

Thanks all. Luckily I have another crank, but I hate to loose one...
bye,

Csaba
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Guy Croft
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Re: Reground Fiat TC 2 liter crank?

Post by Guy Croft »

Not on EN40B forgings I bet Robert..

G
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Re: Reground Fiat TC 2 liter crank?

Post by Honza »

in my coupe I have reground crank, and believe me or not, its there currently almost 7 of wery hard seasons( the engine sees very often 8000rpm without problem - no signs of power loses, oil and compression pressure drops ...)
#100
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Re: Reground Fiat TC 2 liter crank?

Post by robert kenney »

Guy Croft wrote:Not on EN40B forgings I bet Robert..

G
No you're right there. Have done steel billet and steel forgings used in our 2000hp Big Block Chevy class. Suppose the cost to replace if a fair variable to consider, Eh?
Odd about the crank exibiting warpage.

This is quite an off topic engine but, right now I am in the middle of having an International four banger stroked .600" and this includes welding and grinding. It will be nitrided again after to add durability and strength. The grinder who I have chosen to undertake this project is not at all worried about warpage. He just plans to under size the journals .001 to compensate for the growth.
Robert Kenney # 111
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Re: Reground Fiat TC 2 liter crank?

Post by Guy Croft »

Respected members who want to run a reground 2 liter crank - listen:

The substrate material is EN40B which is tougher than mild steel but no way a suitable material to run against a hydrodynamically lubricated bearing of al/tin or trimetal composition.

Test the hardness on a scrap crank where the rear seal runs with a needle file and compare say with one of the webs that has been untouched since nitrocarburising. You will see readily how soft the core material is and you will also see how thin the infused & hard nitrogen/carbon compound layer is. The softer the bearing the more embedability and all bearing types will absorb micronic particles not filtered out and cut into the soft crank like abrasive.

Moreover without the compound layer you have lost the oil retention completely. In an over-fuelling situation a heat-treated crank will invariably survive a reground one will NOT and I have direct personal experience of this. The regrind will invariably require a regrind on the critical thrust faces which rely on drip lubrication and are easily undercut if the driver rides the clutch. Whilst these forged cranks are immensely strong in torsion and bending you have - incidentally - also reduced the fillet strength which is where a crank will fracture if it is going to.

If nitrocarburising by whatever method was employed since 1st introduction of the 2 liter crank in 1973 you can be certain Fiat would NOT have used it as it is a complicated and time-consuming op. However it enable 2 liter engines to run to over 1/2 million miles with NO WEAR AT ALL which is by no means common with all automotive cranks.

Kindly understand that this kind of risky un-approved stuff gets thrown at me all the time and I see a fair number of reground cranks here and spend an inordinate amount of time trying to explain this. To read on this website that it is 'OK' because you have done it is not exactly helpful to the cause. I have prepped and installed hundreds and hundreds of these cranks and am constantly being told (quite stridently) that much of what I do and advise is 'unnecessary'. It is not.

By regrinding the 2 liter crank usd in Fiat/Lancia models you are eating into the longevity of the crank and at very least if doing this professionally you should brief your client on what I have said.

What other practices were employed BY OEM in the matter of crank production is neither here_nor_there as far as I am concerned.

GC
timinator
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Re: Reground Fiat TC 2 liter crank?

Post by timinator »

This discussion has got me confused. Some are describing traits associated with carbon nitriding. Robert is definitely talking about nitriding. GC did you mean ferritic nitrocarburising also known as tufftriding? They all are very different processes with different results.

I would assume that only the last two are acceptable for re-grinds since carbon nitriding is done at high temperature (warping) and produces a thin layer of case hardening.
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Re: Reground Fiat TC 2 liter crank?

Post by Guy Croft »

Hard to be specific.

I do know that when Fiat 1st introduced the process in 1973 for the 2 liter range (as opposed to induction hardening used on some of the earlier smaller engines) they did specify Tufftriding as such (note correct spelling with two of the letters 't' which I always have to look up). Beyond that not all the manuals are so specific. The functional depth of the compound layer here(nitrogen/carbon - tufftriding is a nitrocarburising process) is very shallow as you can read below.

From the website of the highly regarded firm Tecvac:

Tufftriding

http://www.tecvac.co.uk/heattreat05.php

Nitriding/nitrocarburising:

http://www.tecvac.co.uk/heattreat03.php

Tufftriding is a pretty specific process as are all products with a brand name (CNG from Kent Heatreatment was one I used to use on 1800 cranks and the EN 351 and EN24T billet cams I used to make): salt bath immersion and temp of around 500 deg C. Plenty high enough to warp a crank.

Nitriding and other associated (non-branded) methods like nitrocarburising are not branded products as such vary greatly and the depth of compound layer, diffusion zone and surface growth depend on what is specified by the metallurgist who lays down the process plan. And the temperature the part is exposed to is anything between 490 deg C and 580 deg C. So without direct access to that (OE source) it is unwise to second guess it.

Moreover to test the method used on a crank would likely mean sectioning crank 'A' on a journal which destroys it and there is no guarantee that crank 'B' will be the same. Why? Because you'd have to have production data and batch numbers for the cranks. Tufftriding may have been dropped at some much later point for a gas or non-cyanide salt-bath process on environmental or cost grounds, but as for the introduction date of a revised process and the type of vehicles it was applied to - who knows?

The OE manual released 10 years later in 1983 for Strada/Ritmo 125/130TC cites says that the crank was subjected to 'nitriding' but read on in the notes and they continue with, 'if the crank is to be reground a liquid nitriding process "Tufftriding" must be applied'. They also say that after the process the crank must be junked if it distorts which is noteworthy because if you can put a used crank thru 500 deg C without bending it you're a better man than me. And if you press to straighten it you are just overstressing the brittle compound layer and inducing unwanted stresses into the metal. A similar reference appears for the Croma 8V and other TC units introduced in 1985 - the specific word Tufftriding is dropped but 'liquid nitriding' is still there. By 1990 for the 1800 16v Tipo engine the word 'Tufftriding is back' and that is all the data I have. My firm view -reflected in everything I have written - is that the compound layer is very thin and that if you attempt to heat treat again you will be disappointed. It is hard to glean much from the net about 'microcracking' but I was warned about it when attempting the crank overhauls mentioned earlier and it indeed became apparent. As I said, I got one good crank out (I think) 5.


G
Brit01
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Re: Reground Fiat TC 2 liter crank?

Post by Brit01 »

Very interesting and informative links Guy.

Thanks.

Chris
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Re: Reground Fiat TC 2 liter crank?

Post by timinator »

Thank you GC, very good reading. Always impressive how generous you are with your knowledge and time. One small point about crank warp after nitriding. The best crank grinder I ever meet told me that if you try to straighten a crank in a press it will crack every time. He used a large hammer to straighten the crank. He repaired several expensive crankshafts for me over the years. I never had a chance to ask him at what limit he would not try to straighten a shaft. Like many of the best craftsmen I knew he is gone.
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