Check this out to see if it is similar to your issue. Thanks.
LOOKING FOR IDEAS ON WHAT MAY HAVE HAPPENED. I have a 83 CJ7 with a 258 4.2, T5 trans, 4.10 gears and 33" tires. History: I had the engine overhauled due to a compression/leak down issue that I thought contributed to the engine dying as it came to a stop (often), but it would crank up fine to continue the journey. While at the rebuilder (a reputable shop in Bossier City, LA), the cylinders were bored .040 over and I decided to upgrade the cam to a Comp Cam X4254H Xtreme 4x4. I made sure to remind the engine shop that Comp had a kit and please follow all suggestions that Comp may have. After I reinstalled the motor into the Jeep, we had PROBLEMS! 1) Valve train rattle at all engine speeds. 2) Occasional "thump" noise coming from timing chain cover area, and 3) As soon as oil pressure developed after initial crank, black/blue/gray smoke would pour out the exhaust. I took the engine back to the rebuilder and there diagnosis is that the pistons had been "washed" by too much fuel. (I think this is a crock, as I did not make any changes to my Weber Carb from prior to the rebuild). Also they said the cam lobes were worn. All this "damage" was to have occured from the approximate run time since rebuild of 1 HOUR. It had one trip down the road for about 10 miles round trip to "seat" the rings as my mechanic thought it needed, no help. The other time was typical service bay time. Any ideas on how this damage could have happened? The rebuilder wants to blame me and I think he screwed up. Who could it be?