so i never rebuilt an engine before and i had one of my friends help me who "has built tons of engines". we put a new 4.0 in my jeep that was a 97 block and 94 pistons out of another engine put in it. we did not do any machine work to block crank or pistons. all we did was hone the cylinders. i have been told by a few people its a ticking time bomb is this true? i put 7000 miles on her so far and i do have a knock on start up and shut off on cylinder 6. should i be worried?

 

Yes! 4.0L came from the factory with different size pistons in almost every cylinder. You have to look at the piston to see what size it is. Your best bet is to pull it back out, have it bored .30 over and then buy a new set of pistons for it. If you want to just hone and put new rings, always use same pistons and make sure they in same spot. If you have to replace just one psiton, you have to look at size to buy.

 

In 1993 and 1994 boring machines were off for the block, and each cylinder received different sized pistons as a result. None of it was documented. This came to a head in a 1995 class action lawsuit about piston slap. It was resolved in 1995/1996.

If you just built an engine and you have knock already, it's time to tear it apart and do it again, properly.