Hey fellows. Can any of you tell me what the out-of-round tolerance for the bore in a 1968 6.4L 390? I think 0.0005" is pretty standard. Is this right?

 

At 5 ten thousands, you have nothing at all to worry about!!

Russ

 

How about 0.002"? Iremember reading that at 0.003" you don't have much choicebut to rebore. But at 0.002"? What do you all think?

 

Are you talking about the bore being out of round?? or are you talking about taper in the bore??

Because depending on who did the last bore..and How old there equipment was.. I have used bores with .0015 to .002" taper in the bore...But not being out of round that far...

I think the rings would have a hell of a time trying to seat....

Russ

 

0.002" out of round unfortunately. This engine was original 1968 with no rebuilt, first one and it sounds likeit needed it. I wasn't sure if it was on the borderline of a rebore, or not. Ithink your post gave me the answer. Thanks for your help.

 

Yep .002" out of round is not good!! At All...time for a rebore!!

Good luck on your rebuild!!

Russ