a good rule of thumb is to shoot for .001 inch per inch of shaft diameter. In the case of a generic small-block Chevy with a nominal crankshaft main journal diameter of 2.45 inch and a rod journal of 2.10 inch, that would have us aiming for clearances of roughly .0024 on the mains, and .0021 on the rods

 

fair enough, and good info..
one hole in the picture for me..

wouln't I have to put plastigauge on each side of the journal (180 deg from each other) then torque down to get a true clearence reading? is the .001" per inch of dia a clearenca all the way around, or the clearence on one side (with the 0 clearenc on the other side(180 deg out))?

 

ttt

 

you should only need to check one side

the plastigauge should have instructions

 

take the crank out and have it turned. you would be wasting your time if you didnt, the rough surfaces would just bite into the new bearings and it wouldnt have gotten you very far. this kind of work is ALOT easier to do on an engine stand i had to change an oil pan gasket after i put the motor back together and in the jeep, it wasnt too fun. since i had to do it like 3 times... that and i put new rod bearings in it and the oil pressure didnt improve all that much, didnt turn the crank when i had it apart

 

low oil pressure doesnt always mean bad oil pump....to much bearing clearance could be a factor.

 

where did you get oil pump from? i never said anything about the pump

 

I don't know where he got it from..

 

im just saying....since were on the topic of low oil pressure and bearings.

 

I have a 2001 4.0 L with 165k miles on it. Oil pressure drops to 10PSI when heats up to operating temp. Spun a rod bearing on Cyl # 4, just happens to be right next to where the catalytic converters are located on this vehicle. It has two mini converts mounted right off the exhaust manifolds in-line with the exhaust pipes. WOW, nice design,,,

I r/r motor today with a create motor from LKQ and when I removed the oil pan I found shreds of the rod bearing that looked like potato chips. What a mess.

Make sure you realize that oil pressure dropping when it warms up is a sign that main, rod, and/or cam bearings are worn and there is little journal left. Time for a new motor.

 

well swapped em out.. nois went away, fer ~ 15 miles.. oh well..

taking bets on how long it will run before it granades!

 

hey cptcliff? Any problems so far with the rod bearings?

Just wondering, I may have to do the same thing......

Let me know, ok?

Thanks,

J

 

I thought I had a rod bearing problem till I investigated it more throughly Turned out my flexplate was cracked. And the engine was fine.

 

My XJ 98 4.0...has a little rattle that can be heard from start (cold temperature) until it reachs operating temperature, after that no noise at all... i dont know if i can point it to bearings...but....if i go near oil pan the noise seems to be in there...any help on what to do?

 

mine is making the same noise but opposite. It runs great when cold but when it warms up, the knock starts. Checked the flex plate bolts already and they are all tight. Could this be rod bearings?