What Main and Rod Clearances for Street Engine?

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.

 

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.

 

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

 

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.

 

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

 

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.

 

SBB are tighter than BBB?

 

Smaller journals.

 

You should have the connecting rods refurbished/resized too.

 

If they need that, wouldn't the TA ones be better and not much more?

 

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

 

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?

 

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

 

Torque them down and bore gauge them. You should detect any out of round. Bore gauge everything.

 

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

 

Jim B. - educate me - why would the small block Buick (350) have tighter tolerances than the big block Buick(455)?

 

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

 

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.

 

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

 

Ok