Spun Bearing ...

[S14E30]

No this did not happen to me, but I figure I might as well know about it since it will probably happen some time in the future.

What exactly happens?
What goes wrong?
Can anything be done to prevent this from happening?
Are there signs that it will happen soon?
and what needs to be replaced?

And any other thoughts...

Thanks

[H a n]

I had a spun bearing, and did a swap/minor rebuild.

A rod bearing is basically two semi-circles that go between the crank journal and the connecting rod.
Here's a pic of the ones I replaced: http://www.salazar-racing.com/images...d_bearings.jpg

Oil is pumped through the crank, out of a hole right under the bearing.
This creates an oil film between the bearing and the crank.
When a bearing starts to wear, it becomes rough, and starts to flake.
Eventually, the crank will actually "grab" the bearing and cause it to rotate around the crank, that's why they say "spun" bearing.
Once that happens, the crank can be scratched or bent out of round, and the connecting rods will slap around the crank.

There are a few things that will lead to a spun bearing.
Oil starvation (ie. not getting to the bearing), detonation, and time.
To prevent it, change your oil often, wait until your oil is warm before driving the car hard, and be careful of intake leaks.

Symptoms will include a knocking noise, and flakes of copper colored metal in your oil.
My engine knocked REALLY bad, even at idle it was loud, but my friend's only made the noise >3500 rpms.

What needs to be replaced?
rod bearings (~$100)
rod bolts (~$100) they stretch when you torque them, so they can't be reused.
upper/lower oil pan gaskets (they break apart when you remove the oil pans).

[rich]

So with what you said, and knowing that our cars are known to spin bearings, does it make sense to replace the bearings as a preventative measure at some predetermined time?

Rich

[AlexMc]

When you spin a bearing often times the rod is badly damaged, in which case you must either replace it or repair it. We are one of the few shops that repairs the damage, new rods are something like $1600 a set! BMW does not sell them individually!

But there are different levels of damage depending on how early the engine is killed after it happens.. it can range from not so bad to a trainwreck.

[H a n]

Originally posted by rich
So with what you said, and knowing that our cars are known to spin bearings, does it make sense to replace the bearings as a preventative measure at some predetermined time?

Rich

I changed the rod bearings on my new motor, it had 100k, and was running great.
I just felt that since it was already on an engine stand, it would be such an easy job.
Looking at the bearings, I'm glad I decided to replace them.

[rich]

If the car is still alive this fall, I plan to do an inspection of the crank and related items, if ever thing looks OK I will go ahead and replace the bearings and oiling system.

Rich

[H a n]

Rich, Good idea.

Replacing the bearings isn't hard at all, you can even do it with the motor in the car.
Just get a few ratchet extensions, a torque angle gauge, some oil pump shims, and all the necessary gaskets.

[rich]

I have a few questions:
how does the torque angle gauge work?
are the new bearings keyed to a specific journal?
do you rotate crank after each bearing install?
where can I find the torque/torque angle spec for our cars?

Thanks
Rich

[H a n]

Originally posted by rich
I have a few questions:
how does the torque angle gauge work?
are the new bearings keyed to a specific journal?
do you rotate crank after each bearing install?
where can I find the torque/torque angle spec for our cars?

Thanks
Rich

- a torque angle gauge looks sort of like a protractor, it's really just a degree wheel.
you torque to a certain spec, and then use the angle gauge to turn the bolt a certain amount of degrees.
snap-on sells an angle gauge, it's about $60-70.

- the bearings are all the same, so you can use them on any journal.
but, make sure they point in the same direction (as the old ones),
and that you don't mix the rod caps or install them backwards.
the rods/caps have stamped numbers on the side to avoid this.

- I installed two at a time, rotated the crank, and installed the two others.

- lube the rod bolts (I just used mobil 1), and torque to 7 lbs-ft, then 22 lbs, then angle torque 60 degrees.

[H a n]

just pulled this out of the #3 rod last night. yikes.