Jeff N.

Any generally accepted idea on how long the main bearings last on a car that's had reasonable oil changes? How many miles will these things go?

Is measuring the end play in the crankshaft the best method to determine if the mains need replacement?

Slow Project 951

I am curious as well ? Going to have to replace the oil pan gasket and was considering replacement of the bearings as well.
Have gotten conflicting opinions . Some say these are all but bullet proof and question breaking the factory connection if they show no signs of wear . Others say while your there, prophylactic care ? Conflicted , thoughts ?

schip43

Well not an expert and if you have not tracked the car they are probably fine... but if you have the oil pan off, I would change them and do the Lindsey oil pan mod while you have the pan off, and etc,etc ...

Tom M'Guinn

I think Jeff is asking about the main bearings, which is an engine-out operation, unlike the rod bearings that can be replaced when the pan is removed. I don't know of any great way to check them -- maybe someone else has has some tricks? They seem to last a very long time in these motors, but if your end play is out of spec and/or you're getting low oil pressure for no other reason, then that might point to worn bearings. Oil analysis might also give some clues.

schip43

Oh your right I misread! I did change them on my 22r with the motor in place,same process but yeah that's a whole different kettle of fish!
Yeah I would not screw with those!

Jeff N.

Correct Tom. Do you know - is there anyway you can check the end play with the engine in the car and the torque tube still attached?

I haven't gone and read that section of the factory service manual; maybe it has some clues. Amazingly, clarks-garage doesn't have this procedure listed.

Tom M'Guinn

No, you need access to the back of the crank really. You might be able to come up with some way to check it in the front, but with everything hooked up, I can't see how you'd get reliable numbers -- you might be able to confirm it's bad if really sloppy in front, but any "good" reading would be suspect since there are so many things it could hang up on. Maybe someone's more creative/informed than me though....? What's prompting the question?

Jeff N.

Well, I have the car waaay apart at the moment - debating if I should just pull the short block out and do the main bearings as PM. Car has 190k and is being driven for DEs.

Of course, it's about a $500 decision to go after them between rod bearings, main bearings, gaskets, etc. My rods bearings were done about 40k ago or so by the PO so I'm thinking they are still likely OK.

Oil pressure when the pan temp is 230F is showing about 4 bar at 5k RPM. (Mobile One 20/50) I'd like to see it a bit higher but am also wondering if the lower pressure be due to pressure drop from my inline secondary oil cooler. An unnamed person of significant authority suggested that a setup like mine would lead to a pressure drop of about .5 bar.

Soooo, it would be nice to have good idea on the bearings before I just go to the work and $$ to pull and replace them. The cautious side of me says 'just do it', the work and $ side of me says get some more info.

schip43

Ok I see your point, that's a lot of miles. But still I have'nt heard alot of main bearings issues on these cars?
I'd do a leak down test and a compression test and let those numbers be a deciding factor.

Tedro951

I wouldn't bother with them until its time for rings (like schip43) says. If cranks were hard to come by, it might be different.

The way my luck works, I'd go thru the hell of doing the mains, then score a cylinder 3 days later..

Tim-C.

My $.02--I'd go ahead and do the bearings for the following reasons:

1) Your car is already apart. If you have a failure later, you'll have double downtime, but more importantly, unplanned downtime. DEs are generally non-refundable, no? In any case, time lost is absolutely non-refundable.

2) Ounce of prevention = pound of cure. In $ terms, penny of prevention = $.16 of cure.

Very interesting thread as I am sort of at the same juncture with my 951. Coolant in the oil, hence recommended rod bearings. Not to hijack the thread, but if the head is off the motor, how difficult is it to pull the short block? I know that would give easy access to the steering rack (plan to switch to manual) and motor mounts, but would it also give access to the clutch?

Good luck, thanks, etc.

Tim

schip43

Well we need pictures at this point, is the motor on a stand or still in the car?

Tedro951

Tim, if you pull the short block you'll have all kinds of clutch access....It's effectively part OF the short block, if you look at it that way.

Chris White

The face of the main bearing that supports the rod/piston load will last a very long time – almost indefinitely! The thrust face of the center bearing is another story – they can wear and fail due to a number of reasons – riding the clutch too much (don’t sit and the stop light with your foot on the clutch!) or a stiffer than stock pressure plate.

What is the hot idle oil pressure? That will tell you a lot more than the 5k prm pressure – the gauge is not very accurate up around 4-5 bar.

Jeff N.

Hi Chris,

Idle pressure seems like a little over 2 bar when ~180 or so. Less when hotter like 220ish. Mobile 1 20/50 oil with a VDO oil temp gauge.

Seems like I lost a little pressure when I added my secondary oil cooler and swapped over to the newer style OPRV (car's an 86). I put in a used new style OPRV with a new tip seal. Cold start pressure is about 4.5 bars whereas it was more like 5bar prior to the changes.

Is the only way to measure the crank play via pulling the clutch?