Im rebuilding a 302. I really want to avoid having to machining the crankshaft if possible. What are acceptable measurements of the rod and main journals. How much is too low?

 

I'm doing .010 under on my 428 crank and I asked the same question. I was told by my machine shop that .020 under is acceptable but not anything more. Don't forget to match up your bearings so that they are .010 or .020 under (over...what ever).

FYI most engine stores will sell up to .040 under, so .040 might be safe.

James

 

thanks. but im trying to use stock sizes if possible. i think my measurements are within 0.0010

 

production specs for journal clearances is on the order of 0.0008 to 0.0015 for rods and mains. if you say you have that now you just need std replacement bearings.
quoted from E how:
73 302 engine: The main bearings have a journal diameter of 2.2482 to 2.2490 inches and oil clearance of .0005 to .0015 inch. Shaft end play is .004 to .008 inch with thrust on piston number 3. The connecting rod has a journal diameter of 2.1228 to 2.1236 inches with oil clearance at .0008 to .0015 inch. Side clearance on the connecting rod is .010 to .020 inch.

 

Without turning the crank, I would stay with standard sized (or whatever sized bearing you presently have) on the crank. You really need to have the crank turned and proper undersized bearings installed to do the job correctly, however. Don't worry about how much the crank turning requires, as long as bearings for the specs are available. Bearings these days are good enough to allow more turning than was recommended in the past.
Best,
Al