Silverback

How can I tell what size my crankshaft bearings are?

I have a 2000 XJ with the 4.0. The factory service manual says, “The main bearing journal size (diameter) is identified by a color-coded paint mark on the adjacent cheek or counterweight towards the rear of the crankshaft (flange end).”



But there are no paint marks on my crankshaft!

The bearings themselves say “F-85 01 00” and “C-11” on them.

The crankshaft has a bunch of random stuff written on it, including “068-15” and “68010411.” Photos are attached.

I went through the whole 331 head replacement but I still have low oil pressure (verified by mechanical gauge).

Thanks!

bigbadon

I would pull a few caps off and visually inspect for wear first. I you don't see any copper then plasigage to measure wear. Rod bearings have only a slight effect on oil pressure....mains have much more. With a 0331 crack/leak most of the damage happens with the center 2 cam bearings which will have a dramatic affect on pressure. The reason for this is because UNDILUTED coolant from the crack pours directly into the lifter bores!
Bad news is the cam bearings are not easy to replace. The good news is even with the low pressure caused by the center cam bearing the motor can survive for a very long time. I have a 2000 that has been running with 4psi idle and 20psi highway for over 4 years and +40k miles!

Firestorm500

That's right. As we have said so many times before on this forum, simply replacing the 0331 head will not restore oil pressure.

DFlintstone

I like the plastagauge idea. If a number of the rods check OK, you just aren't gonna gain much there. I would assume the mains are standard. Never heard of the paint marks. Oversize inserts are stamped on the back. (oversize because the crank has been turned). Maybe the paint marks are to let you know they are oversize without pulling them. (not oversize, no paint). Best of luck!

That said, since it will likely be either a rod bearing or a piston/ring/cyl problem that someday kills it, slapping in a new set of rod bearing inserts is never gonna hurt. I've done that to a couple of engines just because I was there, but the machining and the oil was not as good then. What do you have to loose? About $30. Google Plastagauge. A cheap and easy way to check your rod wear/clearance. If your engine dies from low oil pressure, a rod bearing may well be the issue.

Firestorm500

Even a factory crank may have been corrected after machining by oversize (not standard) bearings.

Even though the engine has never been apart since new.

Jeep Driver

Correct, and there will be a code stamped on the passenger side of the block if that is the case.


OP,

You realize that you will not be able to drop the crank without pulling the trans, right? and all the rod caps?


And if you go that far........take it to the machine shop and have the crank turned or polished....whichever.......and the machinist will then tell you what size to order.


You ain't just throwing in new bearings in an afternoon.

Firestorm500

First mistake was just putting a head on an engine with low oil pressure.

Don't compound your mistake. Whole engine needs to come out to totally remanufacture/restore the short block. Should have been done from the get-go.