Advice needed on rear main bearing

[wkelley70]

While replacing the rear main seal on my 2006 LJ with 4.0 engine i discovered that the PO got RTV on the main cap on places it should not be. I cleaned up the rear main cap using Super Clean witch etched the bearing.

Should I replace all the main bearings or only the rear? At 145000 miles will i likely need to go undersize or stick with standard? I know I will need to measure the journal diameter but am not able to measure at the moment.

 

[Chris]

While replacing the rear main seal on my 2006 LJ with 4.0 engine i discovered that the PO got RTV on the main cap on places it should not be. I cleaned up the rear main cap using Super Clean witch etched the bearing.

Should I replace all the main bearings or only the rear? At 145000 miles will i likely need to go undersize or stick with standard? I know I will need to measure the journal diameter but am not able to measure at the moment.

Considering your mileage and the condition of the other bearings, I would recommend replacing all of them. That way you know when they were all last replaced.

As for going undersize, it really depends on the condition of the journals. Measuring them is crucial. If they’re within spec, you can stick with standard bearings. But if you find any wear or damage during your measurements, you may need to look into undersized options.

Once you have the means to measure the journal diameter, that will help you make a more informed decision.

 

[macleanflood]

I'd find the numbers on the bearings and order accordingly. Note that I've rarely seen a randomly different sized bearing in an engine but it does happen.

I'd probably do rod bearings and an oil pump at the same time.

And quite honestly if you're going this far pulling the head and pistons will let you check for cracked skirts.

-Mac

 

[wkelley70]

New main bearings are inbound. I would like to polish the journals as well. From the picture below you can see the "etched" surface from the Super Clean as will as a radial "grove" from something that got between the crank and the bearing at one time.

What grits of what sanding media should I use? Do I start at 400 and finish up at 1000?

 

[Jeepster09]

Considering your mileage and the condition of the other bearings, I would recommend replacing all of them. That way you know when they were all last replaced.

As for going undersize, it really depends on the condition of the journals. Measuring them is crucial. If they’re within spec, you can stick with standard bearings. But if you find any wear or damage during your measurements, you may need to look into undersized options.

Once you have the means to measure the journal diameter, that will help you make a more informed decision.

Get and use Plastigage for which bearing size to use. It depends on how much clearance is there. Going undersize without checking may be to little clearance left for oiling.

https://www.amazon.com/Powerbuilt-648441-Plastic-gauge/dp/B002INTX3C?tag=wranglerorg-20

 

[JKP]

The FSM has a section on replacing the bearings, how to read the factory paint codes on the crank (if still present), etc.

Download it from the Resources section.

 

[Daryl]

What grits of what sanding media should I use? Do I start at 400 and finish up at 1000?

I’ve always used 400 grit emory cloth to polish cranks.
https://www.amazon.com/dp/B005TQ2RY2?tag=wranglerorg-20