Crankshaft nitriding

Discussion in 'Race 400/430/455' started by Bens99gtp, Dec 11, 2017.

  1. Bens99gtp

    Bens99gtp Well-Known Member

    Had a mishap on of our fresh rebuilt where it seems like the faulty msd grid is looking to be the blame of my.motor eating the main out but not the rods......but now my crank will need to be turned again. This will put the main down to .020 under the rods might not need to be turned but 100% the mains will.

    Thinking about having the crank nitride when they have it. It looks likes it's only about 100 more. Is it worth it.......what are some of the pros/cons for having this done
     
    Last edited: Dec 11, 2017
  2. 8ad-f85

    8ad-f85 Well-Known Member

    Are you talking about a cast or forged crank?
    I believe there are some process limitations with cast iron, but what does the company you are working with say about theirs and the bene's?
    It's more for surface hardness AFAIK, and a soft bearing might be good enough.
     
  3. Bens99gtp

    Bens99gtp Well-Known Member

    Stk crank
     
  4. 8ad-f85

    8ad-f85 Well-Known Member

    I suppose the answer more depends on the particular benefits you'd like to see for the money invested.
    For even a 100k mile deal I'd put money towards handling abuse rather than surface finish durability, but that's me.
    Fatigue life is drastically increased with cryo treatments and much of the crank's strength improvements come from a generous radius at modification time.
    Don't run grit through your engine! :D :D :D (pointing finger sternly)
     
  5. Bens99gtp

    Bens99gtp Well-Known Member

    Lol well I never would had guessed with only 3 passes, a couple of 1st gear 1/2 throttle pulls on the road for a grand total of about 2 hrs of run time my mains would look like this.

    Oil never got over 165* always had good pressure, 25 at warm idle 70ish when on it till the last hit which was an eigth mile pass and I lost about 10 psi at idle still had over 50 at 3000. Seeing that .020 is about as fair as anyone makes bearing for what I can see if it's the cranks last shot want to give it the best possible chance......but I don't want to make the crank brititle or anything either
     

    Attached Files:

  6. 8ad-f85

    8ad-f85 Well-Known Member

    Is it being suggested that nitriding would help the crank in this or any other situation?
    When you say faulty msd grid are you referring to timing, and that the rod bearings aren't damaged from detonation?
    This crank might be a candidate for stroking or heavy material removal if it isn't blackened heavily or cracked, other wise probably usable otherwise.
    I'm seeing some flexed main caps, some burning, the spring lost from the shells.
    With very little info, I'd guess a flex issue if there isn't a machining or balancing problem.
    Looks like the crank was trying to self clearance the mains and started wiping out the oil wedge.
    You might have the type of build that benefits from much lighter rods, block girdling, among various other things.

    Not trying to make this about more than crankshaft nitriding, just not seeing how that fits into what I'm seeing.
    What else doth the shop sayeth?
     
  7. 8ad-f85

    8ad-f85 Well-Known Member

    Honestly... if you are worried about the crank, I'd just set that one aside vs. putting more cash into it and think about the next build strategy.
     
    69GS400s likes this.
  8. Bens99gtp

    Bens99gtp Well-Known Member

    Shafttech just asked if I was wanting it when I talked to them... I know very little about the process.. just didn't know if could maybe help the crank last a little longer.

    My build is a stk rod 464, with a pistons girdle pan. This setup made 2000 passes in its first build, b4 the block got a pinhole in #4. Had another block done with a new set of stk rods, but the local shop did not do the oil mods so after a few hundred passes it damaged rod bearing 6,7,8. But no main damage. I reached back out to Mike Phillips who did the orbital build and he went through everything and did all the mods he felt it needed.

    The issue I had with the msd grid is what the techs called interference but adyer weeks of buying parts and trting every crazy idea msd had, I pulled the grid and the it's matching box and coil off pit an msd 6520 box on and my rpm issues went away. Pic is of the rpm trace issue I had with the grid.

    All the rod bearings look very similar to the attached pics. From what I can measure crank does have a .001 bend in it now....but seeing what it went through that's not bad and I would assume it wasn't there b4

    Thanks for all the input
     

    Attached Files:

  9. Bens99gtp

    Bens99gtp Well-Known Member

    The crank I have no doubt will be tunable at .020 on the mains.......the rods might be able to stay at .010
     
  10. 8ad-f85

    8ad-f85 Well-Known Member

    No criticism to the builders involved intended. :D
    Looks like the crank is whipping around. I'm guessing the 2 and 4 are worse?
    I haven't analyzed many 2 step crank problems leading to failures (like when people stand on the stutter forever!) but I can imagine a spark box problem beats the crap out of things in weird ways and may look like a crank whipping issue.
     
  11. Bens99gtp

    Bens99gtp Well-Known Member

    I'm hoping the crank isn't cracked......and when the box acted up it didn't sound like any 2 step I've ever heard. Of you look st the rpm graph, at 3500 is what the 2 step look's like. At 4000 it's clearly something different
     
    8ad-f85 likes this.
  12. Stevem

    Stevem Well-Known Member

    Get it cryo treated before you get it cut!
    Nitriding a crank can make different depth levels of hardening which can make it impossible to cut the Crank again should the need arise.
     
  13. 8ad-f85

    8ad-f85 Well-Known Member

    I see that on the graph, I referring to how intermittent firing or related problems beat the crap out of cranks.
    I see people stand on them for way too long end up with crank problems (engine failures) but haven't studied it very hard.
    I don't re-use those parts.
     
  14. MYBUICKS

    MYBUICKS Well-Known Member

    As far as I know, you can't nitride a cast crank. You can chrome it but pros and cons with that.
     
  15. sean Buick 76

    sean Buick 76 Buick Nut

    I would not bother... cryo treatment is a good idea though..
     
    8ad-f85 likes this.
  16. MN GS455

    MN GS455 Well-Known Member

    From the looks of it, the caps have not been indexed/cut and the mains linehoned.. is that the case? Pretty critical operation on a Buick. Even if they check out on size, alignment can be an issue as it’s a lightweight block and they move around over the years. That will give you funky shadowing on the bearings.

    The heat treat process on a cast crank is melonizing. It’s works great, really makes the surface strong. Gives it an eerie black finish. We used to do a lot of cranks before aftermarket replacements came along for the other brands.

    Note that melonozing and other heat treat processes will cause the crank to "grow" a little. A low limit grind us usually the protocol.
     
  17. Stevem

    Stevem Well-Known Member

    I would send a cast Crank out to be Cryo treated , not nitrided, this will provide overall more strength besides the jurnal ware resistance and not make the outer layer of the Crank more prone to cracking like the nitride does to cast iron!
     

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