Help with spun rod bearings in my 496 bbc

Discussion in 'PSI Superchargers Tech Questions' started by Kurtis500, Nov 24, 2009.

  1. Kurtis500

    Kurtis500 New Member

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    Just spun the rods in 3-4 and 6-7. Engine is a 454 .060 over 4-bolt with a forged crank, h-beam rods, 13.5:1 compression and a tunnel ram with a bird catcher on alcohol. The oil pump is the M77v mellings. Clearances are .030 and I run 40 weight. I ran this set-up with dual carbs and race gas at 12.5:1 before. I never had oiling problems before I switched to the hat and injectors so I'm a little baffled. I am not washing down the oil with alcohol since the oil is staying nice and clean. The mains are clean also. The strange part of this is I had 60 psi idling and 80 under throttle. The motor was well primed before ever starting.

    My only thoughts are that the rods are not dowel pinned or I should be using aluminum rods in this set-up... Maybe there are some chevy specific race-prep techniques I missed?

    Any thoughts or experience with this? I am used to my hemi which never has this problem..
     
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  2. SoDak

    SoDak Active Member

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    Sounds like those 4 cylinders are detonating, not enough fuel.
     
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  3. Dave Germain

    Dave Germain New Member

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    You mentioned clearances of .030. Is this the connecting rod to crank clearance? I would think something closer to .003 would be better. Did it just spin the bearings or were they burnt and then spun? You mentioned cylinders 3 and 4 and 6 and 7. Were the bearings on 5 and 8 ok? If 5 and 8 were ok it isn't likely it is an oiling issue so that leans toward detonation. Dave Germain
     
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  4. Kurtis500

    Kurtis500 New Member

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    Oops, yes it is .003 The rods did get very hot. They are nice and black on the big end and they are both burnt and spun. 5-8-1 and 7 are all ok. I am running an injector on a tunnel ram with the nozzles just above the intake on the heads. All are in facing the right way also. This happened all on the first pass too. I checked the pistons and all the tops look ok and the rings spin freely... All lines come from a single distribution block. Would it be safer to run the nozzles in the hat only? (if this is the problem?)
     
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  5. Dave Koehler

    Dave Koehler Member

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    Naturally you should check every line and hole in the injection but that doesn't sound like the problem. Distribution block isn't a problem unless it has a rag in it.

    All heated up black steel rods has to be lack of oil and/or clearance. As to why remains to be seen.

    Sounds like you just made the switch. Bear in mind this may have started with the carb setup and just now showed up enough to hurt.

    Dave Koehler
    http://www.koehlerinjection.com
     
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  6. Kurtis500

    Kurtis500 New Member

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    Additional info here now that I see where this may be going.... After the first pass I brought it back and let it cool between rounds. It didn't run very well with the tune-up I use, and that works, for the conditions. I did notice a certain smell after the run which I later ID as the spun bearings. When I fired it back up I had 60psi oil pressure at idle and it sounded good for a few seconds. Then the motor wanted to die while warming up. This is when I shut it off for good. Its possible the damage was done on the pass and the warm up was what got em hotter? It's hard to figure out that all the mains are good, rods 1-2 and 5-8 are good also but the middle cylinders are spun only on the rods...

    You guys are helping...Thanks so far..
     
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  7. boat754

    boat754 New Member

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    did this happen at phoenix?
     
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  8. Ron C

    Ron C Jr. Dragster

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    Just a thought, could this of happened after the finish line? Do you decellerate the engine after the finish line, if so what happens to the oil pressure?

    Blessing............Ron C.
     
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  9. Randy G.

    Randy G. Top Alcohol

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    What 40 wt are you running. If it's an over the counter oil that would be a good place to start. Over the counter oil is a no-go.
     
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  10. boat754

    boat754 New Member

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    Ron C

    I know where your going with this, and that's what I was leaning towards.:)

    At phoenix the long shut off typically mean you put your foot back into the throttle to get off the track. Sometimes if you don't wait long enough the oil is still in the front of the pan and then when you start to drive off the track the oil pressure is very low. The unpinned rod bearings are not very forgiving and can catch and spin easliy. I would go to a pinned bearing with .003 min clearance and try to wait until the oil pressure gauge shows 40-50 psi before putting your foot back into the throttle and driving off the track.

    good luck

    Vic
     
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  11. James D

    James D New Member

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    How did you pick up 1 point of compression? Any chance the pistons are hitting/kissing the heads?
     
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  12. Kurtis500

    Kurtis500 New Member

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    Yes I am. I'm using Valvoline 40wt. What is the difference and what would you recommend?
     
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  13. Kurtis500

    Kurtis500 New Member

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    This is a good idea. Cars can coast all the way off the track while the boats hit the brakes right away. I'll check that next time. Is there any better oiling system for the bbc than the mellings pump? I know dry sump and etc. is an option, but for internal pumps???
     
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  14. craig moss

    craig moss Member

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    system 1 makes a nice wet sump alum gear pump but then you must buy a custom olson pick up for $75.00
     
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  15. James D

    James D New Member

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    If you think it might be a loss of pressure in the shut off pick up an accusump. I ran one with my BBC and had it set to push oil back into the engine if oil pressure dropped below 40 lbs, worked perfectly.

    Forgot to ask, what type of pan are you running? I'm guessing a box style.
     
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    Last edited: Nov 27, 2009
  16. SoDak

    SoDak Active Member

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    One time my oil pump pickup fell off and it was either #7 or #8 that made a nice exit hole in the pan. :eek:

    If it was oil starvation, wouldn't it take out the rear con rod brgs first?
     
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  17. James D

    James D New Member

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    If it was oil starvation, wouldn't it take out the rear con rod brgs first?[/QUOTE]

    I would think rear main would be first to show signs of abuse. That's why I'm wondering if his pistons didn't hit the head and take up the clearance. I spun a rod bearing just that way. After we got it apart we could see that about 6 pistons had touched:eek: but only the one hole hit the head hard enough to push the bearing into the crank.
     
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  18. funnycarmike

    funnycarmike New Member

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    James is 100% correct here. An accusump is an absolute must with any wet sump engine. We like to call it the poor mans dry sump. Had one on my funny car (BBC) for nine years before going to a dry sump.
     
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  19. Kurtis500

    Kurtis500 New Member

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    After close examination of the pistons I noticed very slight marking where the exhaust valve has touched the piston. It's light enough to have not placed a dent in the aluminum of the piston dome but created a sort of polished looked. This probably explains why everything worked and went together fine, then idled ok and then torched the bearings on the first pass...
     
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  20. SoDak

    SoDak Active Member

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    Last year I let the ex springs on one motor get too weak and all 8 were bent/touched pistons and I had no rod brg issues. I would keep looking.
     
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