What Main and Rod Clearances for Street Engine?

Discussion in 'Small Block Tech' started by knucklebusted, Jan 13, 2022.

  1. knucklebusted

    knucklebusted Well-Known Member

    I'm going to, hopefully, get my block and crank dropped off at the machine shop today or tomorrow.

    What clearances should ideally be set for the mildly warmed small block? I plan to run 5W30 oil if possible.
     
  2. Mart

    Mart Gold level member

    Greg, I ran 20-40 pennzoil racing since 76 here in cold MI all year long. Was my daily in 76. 3k oil & filter changes. At 96k miles, main & rod jrnls looked great, only needing polishing. With you in KY, I would run GM spec tolerances, .0007- .0015, especially if you are going 'down' to thin 5-30.
    You want good pressure at idle, I wouldn't go over .0015 imho.
     
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  3. Jim Blackwood

    Jim Blackwood Well-Known Member

    I spec .0007-.0012", I think any reasonably up do date shop can handle that. If they give any argument about it moving on might be a good choice.

    Jim
     
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  4. Mart

    Mart Gold level member

    Yep, Jim knows...
    If you're cutting main & rod jrnls, you have the perfect opportunity to tighten clearances up to where you want them.
    .001 mains are around, I have never found .001 rod bearings, in case you're only polishing things up.
     
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  5. knucklebusted

    knucklebusted Well-Known Member

    Good to know. I was looking at .002 or less but this is more in line with what I was after.
     
  6. Jim Nichols

    Jim Nichols Well-Known Member

    Find a crank grinder that will grind your crank. Off the shelf reground cranks are probably .002. I always ask for .001-.0015 rods and mains.
     
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  7. 12lives

    12lives You die once. You live every day.

    SBB are tighter than BBB?
     
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  8. knucklebusted

    knucklebusted Well-Known Member

    Smaller journals.
     
  9. Jim Nichols

    Jim Nichols Well-Known Member

    You should have the connecting rods refurbished/resized too.
     
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  10. knucklebusted

    knucklebusted Well-Known Member

    If they need that, wouldn't the TA ones be better and not much more?
     
  11. Thumper (aka greatscat)

    Thumper (aka greatscat) Well-Known Member

    I do on all motors except race applications .002" and .002" 10w40
     
  12. Jim Nichols

    Jim Nichols Well-Known Member

    Big end of connecting rods get oval over time. Resized round with increased bearing crush where ends meet. Even clearance all around crank journal. You do want your engine to last?
     
  13. Jim Nichols

    Jim Nichols Well-Known Member

    Capscrew rods are probably OK. The earlier nut and bolt rods distort. I use SBC 11/32" ARP bolts with those.
     
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  14. Mart

    Mart Gold level member

    Torque them down and bore gauge them. You should detect any out of round. Bore guage everything.:):D
     
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  15. Jim Blackwood

    Jim Blackwood Well-Known Member

    It really depends a great deal on how the engine was used. All materials are elastic and plastic to some extent but if properly engineered and then used within the design envelope no permanent deformation should occur. Thus the rods of a stock engine in average service should still be round if not abused. This can often be determined by the wear and contact patterns of the old bearing shells. Wear on the inside, contact on the outside. This is your first indicator for mains alignment issues as well. The greatest stresses on rod bearings come with increased rpm, so if the engine has never been run over 4800 rpm which is rather typical with Buick engines there isn't a lot to worry about there. By all means check it, but don't be surprised if they are fine.

    Also on the clearance question, yes Buick engines do run tighter clearances than Chevy and were engineered that way. Running Chevy clearances is a sure way to destroy any chance of having adequate oil pressure.

    Jim
     
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  16. 12lives

    12lives You die once. You live every day.

    Jim B. - educate me - why would the small block Buick (350) have tighter tolerances than the big block Buick(455)?
     
    Last edited: Jan 15, 2022 at 10:44 AM
  17. Jim Nichols

    Jim Nichols Well-Known Member

    If you change the bolts and nuts on the earlier rods to ARP the big end will distort.
     
  18. Tom Righter

    Tom Righter Well-Known Member

    Jim, I run .0028-.0032 mains and .0025-.0028 on 2.200 Rod journals also have grooved Main saddles to feed rods extra. I have no issues having adequate oil pressure. That’s with a TA cover standard gears.with all oil mods rear balance line. And yes I Read oil pressure from back of engine.
     
  19. Jim Nichols

    Jim Nichols Well-Known Member

    Stock 455 clearance is .002 mains and tighter .00075-.00125 for the rods.
     
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  20. Tom Righter

    Tom Righter Well-Known Member

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