[hurryinhoosier62]

Originally Posted by llwta76

I admit that the tighter the clearances you shoot for ( as in the example you state) the more critical diviation becomes. But I was referencing the OP and my own experiences in running .0025" +/- bearing clearances. I would be uncomfortable running any bearing clearances as tight as those you mention. After all we're talking about Pontiac street/ strip stuff here. Again... he states that there is NO deviation in journal diameter and no change shows up when using plastigage also. I do admit it's great to be able to machine to within 1 or 2 ten thousanths when doing bearing clearances but I have never found it necessary in any of my own experiences.

I follow the "Crocie rule" for Pontiac street engines...2/2 .002 on the mains and .002 on the rods. I see no problem opening that clearance up to .0025 on the mains of a street/strip Pontiac as long as you have good oil pressure and keep the bore sizes to the minimum end of the spec + .0005. Believe it or not, the bearing clearance for the main bearings on a 4.6 Windsor modular V-8 is .0008-.0018. Plastigage is the most inaccurate crap ever devised. It gives you a range, NOT an exact size. If you're not familiar with using precision measuring instruments, by all means use it or leave your blueprint specs to we professionals.

[GRX]

Retired ASE master engine machinist here as well. Have ground, polished, and balanced my share of rotating assemblies and have seen far worse than the above get by with just a polish job. As said a 010 re-grind won't significantly affect the balance. Factory assemblies are usually far worse than that. And let's not forget this is the street section.

[edit]
Maybe one of the worst cranks I fixed was a 400-N which came into the shop as scrap because it spun #5 rod bearing to the point of turning black & blue. Actually had 0.080" run-out at the center main journal. After passing a complete wet mag test I set out to heat & bend it back into submission with oven & hydraulic bender. Balanced then ground at 020m/030r that crank has been running in my 69 GTO for over 20 years now.

[hurryinhoosier62]

Originally Posted by GRX

Retired ASE master engine machinist here as well. Have ground, polished, and balanced my share of rotating assemblies and have seen far worse than the above get by with just a polish job. As said a 010 re-grind won't significantly affect the balance. Factory assemblies are usually far worse than that. And let's not forget this is the street section.

[edit]
Maybe one of the worst cranks I fixed was a 400-N which came into the shop as scrap because it spun #5 rod bearing to the point of turning black & blue. Actually had 0.080" run-out at the center main journal. After passing a complete wet mag test I set out to heat & bend it back into submission with oven & hydraulic bender. Balanced then ground at 020m/030r that crank has been running in my 69 GTO for over 20 years now.

You're a braver soul than I. If I had EVER tried to put a crank with that defect through our QA dept, I would have gotten a day off WITHOUT pay. I have seen severely spun mains and rod journals clean up @ .030 under on forged cranks (especially 6.9/7.3 IDI), but not too many that were cast cranks. Good job!

[Schurkey]

Originally Posted by hurryinhoosier62

I also realize the specs I use for balancing (less than .5 gram) is a little tighter than what most shops use.

Balancing to half-a-gram is an excellent exercise in self-control, precision, and perceived value. Does it do any actual good considering the moment that engine builds oil pressure, the crank gathers liquid oil in the crank passages and bearings. Add a bit of oil windage, that half-a-gram (a raisin is about one gram, so half-a-raisin) balance job is thrown out-of-balance.

I wouldn't be concerned about a "ten-under" crank grind affecting balance in the real world.

MAYBE a polish would clean-up the score decently enough; it's tough to tell via photograph versus in-person.

[hurryinhoosier62]

Originally Posted by Schurkey

Balancing to half-a-gram is an excellent exercise in self-control, precision, and perceived value. Does it do any actual good considering the moment that engine builds oil pressure, the crank gathers liquid oil in the crank passages and bearings. Add a bit of oil windage, that half-a-gram (a raisin is about one gram, so half-a-raisin) balance job is thrown out-of-balance.

I wouldn't be concerned about a "ten-under" crank grind affecting balance in the real world.

MAYBE a polish would clean-up the score decently enough; it's tough to tell via photograph versus in-person.

The .5 gram is the SAME spec MOST professional engine builders I've known use. Granted, the majority of these engines were for racing ONLY. Oil windage has nothing to do with balance since the oil is continuously shed from the rotating assembly. There are two forms of balancing: static and dynamic. Static balancing is matching all the components weight wise. Dynamic balancing is assembling the rotating mass and bringing up to speed to insure the mass is in balance. An engine CAN be in static balance, but fail dynamic balance testing. I saw an engine years ago that was within .5 gram static balance, but would nearly throw the crankshaft and bobweight off the balancer because the crank was so far off in dynamic balance. We went through 3 crankshafts before we found one that was near enough in dynamic balance to finish balancing the engine.

[llwta76]

Originally Posted by hurryinhoosier62

I follow the "Crocie rule" for Pontiac street engines...2/2 .002 on the mains and .002 on the rods. I see no problem opening that clearance up to .0025 on the mains of a street/strip Pontiac as long as you have good oil pressure and keep the bore sizes to the minimum end of the spec + .0005. Believe it or not, the bearing clearance for the main bearings on a 4.6 Windsor modular V-8 is .0008-.0018. Plastigage is the most inaccurate crap ever devised. It gives you a range, NOT an exact size. If you're not familiar with using precision measuring instruments, by all means use it or leave your blueprint specs to we professionals.

Thought I might get hammered on the plastigage thing. It gets you close but certainly not with the precision you're talking about. I just mentioned it because the OP said he used it and validated it w/a mic. I still say he's fine. Bottom line ... his call.

[Blued and Painted]

Looks like most of the machined surface is still there. I would hit it with a green scuff pad to knock off the high spots then assemble with new stuff. Sleep easy.
Lately I've been using the Lucas assembly lube.

[hurryinhoosier62]

Originally Posted by llwta76

Thought I might get hammered on the plastigage thing. It gets you close but certainly not with the precision you're talking about. I just mentioned it because the OP said he used it and validated it w/a mic. I still say he's fine. Bottom line ... his call.

Precision assembly is the way I was taught many years ago. Bud (my mentor) didn't differentiate between race or street engines. They were all built to a specific stardard. It was probably overkill, but I know of only 1 warranty "come back" that he ever had.