engine knocking

[awigley]

Hello, I have a 99 grand cherokee limited with a 4.7 v8 4x4. It started making a knocking sound. It was faint at first and slowly got louder. It never lost any power though. I finally took it to a local repair shop. they told me it was a main bearing and I need a new motor. on the way home from the shop the jeep died on me and would not start back. I decided to rebuild it myself. I took the motor out and removed the oilpan to check the bearings and dont see any problems with them. any ideas what else might have made the noise.

 

[SteelHeadz]

Welcome to Jeepz. How did you check the bearings?. Did you remove the bearing caps?. The best way to check if the bearings are bad if it's not obvious to the naked eye is to use a plastigauge and a micrometer. Another thing to check on both 3.7 and 4.7 jeep engines are the wrist pins on the piston. On the upper engine section, check the valves and the valve springs and the valve spring locks. I've seen the valve spring break and eventually the locks would fall off and let the valve drop inside the cylinder. Not a pretty sight when that happens. In rare occasions, the rocker arms would also slide off to the side.

 

[Jester32]

We've seen lots of rocker arms slide off and many a worn chain guides allowing the chain to jump and cause problems.

 

[Jester32]

And bearings may be good shape but the big end of the connecting rod may be stretched or miss shaped. Or crank may be under sized etc etc. Lots of cause of a knock.

 

[awigley]

thanks everyone Im gonna check your ideas and see if they help. I just checked the bearings by eye so I will check with a micrometer also. Thanks ill repost when I check them out.