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bearing clearance/chiltons manual is killing me

arhiney

NAXJA Forum User
Can anyone please tell me the bearing clearance for the rod and main bearings. I know I need to invest in a FSM!! Just can't afford one now. Putting in new rod and main bearings and need to know the clearance when I platigauge them.

95 xj 4.0

Thanks
 
Generally you want to be in the 0.0015 to 0.002 clearance range.Allowable range is 0.001 to 0.003 in. .
Wayne
 
95 xj 4.0

Ok, just plastigauged all my existing rod bearings. Although very worn, they were all within .0015-.002. (more towards .002) Does this mean that the rod bearings were not the cause of my knocking noise? What else should I check? The main bearings don't create a knocking noise when worn do they? They all plastigauged within specs also. I have also checked the bolts on the flexplate as Eagle suggested in a past thread. The knock was definetly from the bottom of the engine and towards the rear. Someone suggested that my oil pump may be bad, but my pressure was never low. He said that I might have good pressure but bad volume. ??? I'm not sure what that means. Any help woud be appreciated. I won't know if the new rod bearings will solve the problem until I start it up of course and wanted to make sure I got everything else before I button up the oil pan.

TIA
Adam
 
One thing that is puzzling me is that when I plastigaged these bearings they showed less clearance on the most worn part of the bearing i.e. the portion showing copper. How is this possible. I thought I would see more clearance in this area than the rest of the bearing. I also had a hard time getting all the oil off the crankshaft before platigaging. How much oil is too much when plastigaging? I am doing this with the engine still in the vehicle and as you know it's a pain to get all the oil off the journals. The mains showed very little wear at all. Is it worth changing them anyway?


TIA
Adam
 
I believe any oil is too much, when you're talking such thin clearances. However --

Check the flex plate very carefully. They tend to crack in a circle around the reinforcing ring that the bolts go through. I'm just finishing up replacing a cracked flex plate. Makes a terrible racket that sounds a lot like rod bearings. In fact, the kid from whom I bought the XJ had done rod bearings, and it didn't fix the problem so his father decided it needed a new engine and told him to get rid of it.

If you remove the inspection cover at the bottom of the bell housing and push and pry on the ring gear in various directions, you should be able to see if there's a crack -- but it won't be obvious unless you look closely. Once you see it, you'll wonder how you ever missed it.
 
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