Spun main and rod bearings

Discussion in 'Race 400/430/455' started by nitrousfish, Feb 22, 2021.

  1. nitrousfish

    nitrousfish Dave Fisher

    Tore my engine down for a rod knock and found number five rod bearing was squished out the side with hardly any damage to the crank,a nodular, then pulled the girdle to find number two and four mains spun.
    This the first time I’ve ever seen this and at first I blamed the vac pump for sucking oil off them at high speed,but not sure. What do you guys think. It’s iron block,Peterson oil pump mods, moroso pro mod vac pump,464”
     
  2. Bens99gtp

    Bens99gtp Well-Known Member

    The vacuum pump would pull the oil from the wrist pins long b4 I effect the bearings. Are the pins stuck or stinky....if not I would doubt the vacuum pump.


    How much vacuum where you running
     
  3. dan zepnick

    dan zepnick Well-Known Member

    I had a issue with my moroso pump i installed for the last race 2 years ago. I was only running 7 inches of vacuum. After 4 passes it took out number 5 also. Slowed down every pass. Installed a previous freshened engine and it was doing the same on 2 passes before I removed the vacuum pump. I had the relief valve on the passenger side valve cover. Pump on drivers side. I want to get a fitting to mount the relief valve on the pump. Im thinking its pulling the oil off the floor,uncovering the pickup. Starving the bearings.
     
  4. nitrousfish

    nitrousfish Dave Fisher

    I never was cognizant enough to watch the vac gauge but it runs up to 5 unloaded free revving. Another piece of info: I noticed the rings were stuck on all pistons along with a silvery substance in the chambers, the valves were also allowing air to pass by them (did a leak down).
     
  5. Jim Weise

    Jim Weise 1000+HP

    So how much of the giggle gas are we spraying? and how sure of you on the tune?

    Everything you've said so far can be attributed to overloading. Wiped out main bearings, "squished" rod bearings, collapsed ring lands.

    Likely from excessive N20 use, or Detonation, or some combo of both.

    I can't recall who first said it, but boosted induction is not all the same... where Supercharging or turbo charging increases cylinder pressure, but it does it across as much as 30* of crank rotation.. Chemical supercharging (N2O) produces a very distinct spike in cylinder pressure, over a very narrow range of crank rotation degrees.

    You could say that the affect on the engine with supercharging or turbo charging is a strong push, with N2O it's like hitting the piston tops with a sledgehammer.

    And most likely why your seeing what you are.

    JW
     
    D-Con likes this.
  6. standup 69

    standup 69 standup69

    I'll share an odd experience with my vacuum pump on my engine 11to1 compression I run on 94 pump fuel ..never heard or felt any detonation ever ...put the pump on and the odd time I can feel it tip into detonation if I'm not careful ..

    My theory is the low tension oil rings and thinner metric rings are now sealing up tight and creating more cylinder pressure ..the car actually felt stronger with the pump which was surprising to me ...

    That being said I would say no way a pump would cause bearing failure. pressure of oil coming through bearings wouldn't be affected by vacuum. Even the piston pin thing is getting debunked lately from what I've seen..I'm with Jim detonation would be my guess
     
  7. standup 69

    standup 69 standup69

    I hear that the relief on the pump is a much safer way than drawing through the engine like that also
     
  8. BQUICK

    BQUICK Well-Known Member

    Many motors with loud exhaust or open headers can detonate and you won't really know it....if you can tell then it's extra bad. It doesn't take much to pound out rod bearings. Like a sledge hammer hitting pistons. A guy I know ran nitrous on BBB and was melting spark plugs and eating up bearings. Setup was wrong. Needed to pull more timing out on big end. Would always smoke some thru traps...detonation rattling the rings. Ended up putting BBC in.....

    Usually rod bearings go first then debris takes out mains. Happened on my original 70 GSX motor. The guy was hauling rocks cross country with it....no lie.
     
  9. Stevem

    Stevem Well-Known Member

    Sorry to hear this , but before you throw stuff out could you post up some pictures of the split open Rods Bearing area without the bearings in on some of the Rods that did not spin there bearings?
     
  10. nitrousfish

    nitrousfish Dave Fisher

    It was 28n32f fogger 5.5 psi fuel 950 bp Timing was 38 taking out 11. Footbraking Plugs were decent looking
     
  11. bobc455

    bobc455 Well-Known Member

    No idea whether it was the cause, but have you tried pulling more timing? I think 28n32f translates to a "240HP" shot but I bet you'll see a torque increase if you take out more timing than that.

    -BC
     
  12. Bens99gtp

    Bens99gtp Well-Known Member

    Well 11 for 250ish is close to base rule of 2* for 50hp. But I think starting at 38 is up there......I've never had a bbb that liked that much.

    What was the clearances when built.

    How did the main caps fit??? I lost the center 3 main in 2 1/8mile passes from missing the center caps didn't have enough fit into block. Even after all the trash the rods all basiclly looked like the 1 posted.

    Things can go south fast, my first clue was idle oil pressure down 15psi, I bet the next pass would had been a very different result though
     

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