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Okrasa 82mm Crank - Nitride or Cryo?
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risk
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PostPosted: Fri Feb 05, 2010 11:13 am    Post subject: Okrasa 82mm Crank - Nitride or Cryo? Reply with quote

I have an Okrasa 82mm crank that has been ground .010" & .010"

I was told that the nitriding on the okrasa cranks only reaches a depth of about .010" , and running one that has been turned down can introduce the possiblility of breakage. Should I get the crank re-nitrided, or would cryo-ing it be a better option?.. or should i just run it as is?
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Unkl Ian
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PostPosted: Fri Feb 05, 2010 11:15 am    Post subject: Reply with quote

My understanding is that Nitrading doesn't stop breakage.
It is more for wear resistance.
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risk
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PostPosted: Fri Feb 05, 2010 11:44 am    Post subject: Reply with quote

It may not stop breakage, but it will increase resistance to fatigue and cracking to the depth of nitriding.. which is much less on my turned crank.. maybe only a few thousanths
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Jake Raby
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PostPosted: Fri Feb 05, 2010 1:04 pm    Post subject: Reply with quote

Not all nitriding processes are the same. I use Ion Nitriding and it does help with wear resistance, especially with engines that have high cylinder pressures.

Cryogenics has been employed in our thermal cycling process for 10 years now. It has proven to help realign the molecular composition of the component greatly.
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tncsparky
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PostPosted: Fri Feb 05, 2010 1:23 pm    Post subject: Reply with quote

Can you do both?
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Jake Raby
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PostPosted: Fri Feb 05, 2010 1:25 pm    Post subject: Reply with quote

Sure, they are not related. Its only money.
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risk
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PostPosted: Fri Feb 05, 2010 1:58 pm    Post subject: Reply with quote

So will the crank be ok or should i get it re-nitrided, cryo'd or both?..

The engine is a todd francis case, 94 bore, i'll be running the thick wall 92's and about 15-20psi max boost.
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1432
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PostPosted: Fri Feb 05, 2010 3:00 pm    Post subject: Reply with quote

Generally nitriding is only a .001"-.002" depth process for improved wear, always a good idea on these aftermarket regrinds, but crank should be checked for straight and polished after, cryo not so much I'd skip it
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PostPosted: Fri Feb 05, 2010 3:05 pm    Post subject: Reply with quote

Ion Nitriding is the highest pressure and highest temperature process. I have noted penetration of up to .012 with these processes in the past. Generally the best profile must be chosen from absolute material composition which usually requires destroying a like component.

Thats certainly not an option with this crankshaft!

Nitro carburize heat treating is a generic form of restoring surface hardness and it works well and is much more compliant with various materials.
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1432
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PostPosted: Fri Feb 05, 2010 3:33 pm    Post subject: Reply with quote

While deep nitriding does have it's place it would not be a good move on a VW crank, I'm concerned only with wear and anything thats worn beyond a normal depth of nitriding is unusable anyway, however the big negative to deep nitriding these "flexy" 3 main bearing cranks is the propensity for crack propogation from a brittle surface depth in the corner radius. I'd go with the basic process, it's all thats necessary and will most likely extend the life of the part.
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PostPosted: Fri Feb 05, 2010 3:41 pm    Post subject: Reply with quote

Yep.. It is easy to goo too hard and make for a brittle component. I've been turning three different IOn'd cranks extreme RPM for years of abuse. Two of them are in our road race engines seeing constant 6,500-8,500 RPM punishment for 45 minute races.

Another is in the Peanut Special Land Speed engine that makes peak power at 9,000 RPM. That engine has been together for 4 years since it's last rebuild with an Ioned crank and has set 4 records in 4 different classes since without coming apart.

The oil samples from it are as clean as they were when the engine only had dyno time on it..
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PostPosted: Sat Feb 06, 2010 12:45 am    Post subject: Re: Okrasa 82mm Crank - Nitride or Cryo? Reply with quote

risk wrote:
I have an Okrasa 82mm crank that has been ground .010" & .010"

I was told that the nitriding on the okrasa cranks only reaches a depth of about .010" , and running one that has been turned down can introduce the possiblility of breakage. Should I get the crank re-nitrided, or would cryo-ing it be a better option?.. or should i just run it as is?


Okrasa cranks have the best and deepest nitriding you can get . If you cut to first undersize you need no nitriding.

Udo
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1432
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PostPosted: Sat Feb 06, 2010 7:25 am    Post subject: Re: Okrasa 82mm Crank - Nitride or Cryo? Reply with quote

Udo.B. wrote:
risk wrote:
I have an Okrasa 82mm crank that has been ground .010" & .010"

I was told that the nitriding on the okrasa cranks only reaches a depth of about .010" , and running one that has been turned down can introduce the possiblility of breakage. Should I get the crank re-nitrided, or would cryo-ing it be a better option?.. or should i just run it as is?


Okrasa cranks have the best and deepest nitriding you can get . If you cut to first undersize you need no nitriding.

Udo


Udo,
That has not been my experience, back when VW midgets were big we used a lot of the, then new Okrasa 78.4 and 82mm cranks in that venue. they were either VW or 912 journal from the factory. While the original journals held up nicely with regard to wear the 1st under regrinds wore rather quickly on the bottom quadrants of the rod journals. It became standard proceedure to renitride and polish everyone we reground, one more thing I failed to bring up previously is the necessity to remove and replace the original oil galley caps with 1/16" pipe plugs prior to assembly, something that should be be done on any reprocessed crankshaft (nitride or cryo) with similar oil passages.
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PostPosted: Sat Feb 06, 2010 9:32 am    Post subject: Reply with quote

I have other experience . but you can get them gas nitrided if you want.

Udo
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Jake Raby
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PostPosted: Sat Feb 06, 2010 9:47 am    Post subject: Reply with quote

I once heard that the Okrasa cranks had .016 penetration from the factory.
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