After having a block machined, is there usually a wide discrepancy in the main bearing tolerances? Say after having my block machined, and installing new main bearings, am I going to be ok using STD mains, or is there usually a need to mix/match + and - bearings to get proper clearances? (I know this depends on the maching, but in general?) This will be a very competant machine shop doing the work. Also when checking main bearing clearance, to torque the mains for plastigage, do you reuse the old stock main bolts and then put the new main bolts in for final assembly? I know the main bolts are torque to angle correct?

 

May as well switch to main studs and then do the align.

If you're looking for dead-nuts bearing tolerances, you're going to have to mix and match. We went through 18 sets on my block before finding the perfect combination to get just the right tolerances.

 

18 sets? Good lord. How accurate were you trying to get? Im looking for between .002" and .003" on the mains correct?

 

We were looking for .0015". We had the time and plenty of bearings, so why not.

.002" - .003" is pretty loose for a good build. Running tight is .0015" - .0020".

 

Alright this is going to be a street motor shooting for arounf 450hp. Tight tolerances are for race built engines more correct? Everyone I have seen around here reccomended .002-.oo3 on the rods and mains. I guess my question is, how often do people really need to mix/match bearings to get within that range of tolerance? Most people on here that I have seen just throw in STd bearings and they usually check within spec.

 

Tight tolerances will work for either. The main thing to worry about is the machining. It can take quite a bit of work to get these blocks square.

I'd put them in and then at least plastigage them. Dial is better, but plasti will work. Hell, most of an engines reliability is in the machining and the tolerances you're willing to accept.

 

So what is the main concern when machining? Align honing the mains and honing the cylinders with a torque plate?

 

Yup. Those are the two biggest. Keep track of the deck as well. Most of them need some work.