Clem,Dick,Lockwood.Tom-Rod bearing side clearance

[John N.]

Rebuilding a 58 with a ground crankshaft. The specs call for a bearing side clearance of .008-.012. The clearances on the rebuild are .016-2@.020 &.022. Is this too far off for a restoration big brake car? How much oil pressure would you lose? Any other problems? Thoughts please.
Regards

[Tom P.]

Re: Clem,Dick,Lockwood.Tom-Rod bearing side clearance

John,
I built the 350 that's in my 51 Chevy 33yrs ago. Since then, it has literally been my daily driver to Tinker AFB and many other unmentionable places. I don't know the exact mileage on the engine, but it is in the range of 300Kmi. When I picked up the engine parts from the machine shop, I learned that the rod side clearances were in the .015-.020 range. Knowing that the specs for rod side clearance was in the .008 range, I was needless to say somewhat unhappy. The machinist (who was VERY reputable) assured me that the rod side clearances for my rods would be quite satisfactory. That assurance really didn't reduce my concerns. Well, I'm here to tell you that 33+yrs and 300Kmi later, that engine is STILL holding good oil pressure. So, 35yrs ago, I would not have put an engine together with .020 rod side clearances, today I would.
Oh ya, and since that engine, I have built many more engines with NONE of them having anything close to .008 rod side clearances.

[Jim L.]

Re: Clem,Dick,Lockwood.Tom-Rod bearing side clearance

John,

I would build that engine and not worry about the side clearance.

It's not going to cost you oil pressure. Think about it this way.... if the bearing clearances are, say, .002" and the side clearance is .020", which of these two is going to be the restriction to oil flow?

In some racing engines, and I believe NASCAR engines are this way, they use what are called "piston guided rods" which have side clearances that can be as much as .100". They do this to reduce big end mass and rev higher. If there were a reliability issue, no one would use this "trick".

It's certainly a fair question to ask, but I don't see a problem.

Regards,
Jim

[Clem Z.]

Re: Clem,Dick,Lockwood.Tom-Rod bearing side clearance

too loose will not cause any problems. too tight will cause problems

[Dick W.]

Re: Clem,Dick,Lockwood.Tom-Rod bearing side clearance

The only way you will every get the lower specs is with a new crank and rods. Maybe. I would not worry about running this clearance. I would not worry if I were going to vintage race it.

[Joe L.]

Re: Clem,Dick,Lockwood.Tom-Rod bearing side clearance

The only way you will every get the lower specs is with a new crank and rods. Maybe. I would not worry about running this clearance. I would not worry if I were going to vintage race it.

Dick------


I agree; it's the only way you'll ever get it and, maybe, not even then.

[John N.]

Re: Clem,Dick,Lockwood.Tom-Rod bearing side clearance

Dick------


I agree; it's the only way you'll ever get it and, maybe, not even then.

Clem, Dick, Jim, Tom, Joe. Thanks for the expert opinions based on your experiences, they make sense and will make my life easier. Joe I bought about five military surplus cranks and must have become in spec spoiled on them. I will have to become more tolerant of these 50 year old used parts.
Regards