Putting my 326 back together. What is the connecting rod and crank bearing clearance supposed to be? I will pick up some plastigage for measurment. Thanks
You'll probably get several different answers but...anywhere between .0015(tight)-.0030(loose) usually has worked for me without issue. The number in the service manual is for brand new parts that you probably will never get(or want) on a rebuild.
Pontiacs came with fairly tight clearances. 67 rod and mains were 0.0005-0.0025/0.0002-0.0020. Some say the tight clearances were cause of overheating problems. I don't agree. Racing and hot rod guys think you should have 0.0035+. I put mine in the middle at 0.0025. I think that gives enough oil flow through the bearing/journals to cool, supply enough oil to maintain a good wedge and still have oil pressure at a red light in hot weather.
If you are getting ready to assemble and measure you must already have the machining done or are checking before reassemble. If you get clearances in the range Firebob stated you should be fine.
Just want to add that the same thing can be said about keeping lifters in the correct order when pulling a cam out. Obviously you can number them anyway you want as long as you make sure they go back in the same way. Occasionally cams and lifters are sold because someone wants to make a change and it's a real good idea that the buyer makes sure exactly how the seller numbered the lifters upon removal.
I would re-measure everything whether the machine shop did it or not. Preferably with a micrometer and a dial bore gauge if you have them or can borrow, but plasti-gage at a minimum. Machinists can make mistakes. My advice is double check every part even if you had no machining done and are just re-ring and re-bearing it. Believe me, I found out the hard way.
