Intermediate shaft bearing wear

[Cabriolet]

I saw a thread a few months back about this issue. so, I luckily bought a new bearing for an M20 I'm going to rebuild next week. the engine has ~250k on it and the crank and rod bearings are in excellent shape for their age, (minimal wear). However, when I pulled out the intermediate shaft, I was greeted with a fractured bearing. the inner bearing was perfect and within tolerances. but as you can see from the photo, this outer was shot.

please be advised to check this bearing if you are rebuilding your M20. It's only like $10 from blunt and as you can see, needs to be replaced.


Intermediate shaft bearing worn out by Eric Berger, on Flickr

[Cabriolet]

Follow up.

took apart a second M20 with ~200k miles on it. same wear and slightly worse. Blunt was kind enough to supply me with a new bearing. 11-11-1-280-863
when it arrived it the ID of the bearing was far too small. apparently this is an issue with the new bearings from BMW. i took the new bearing and shaft to a friend's machine shop and he suggested honing the bearing. after a pass he realized that the ID on the bearing is not round so that when it is pressed into the block it becomes round. the then through it on a lathe and took off .01" this gave the correct spacing of .002"

many people rebuilding engines never check this bearing and fewer changed it. if you do changed it. you will need to have the bearing ID made larger.

[jlevie]

The bearing part numbers are:
11-11-1-280-863
11-11-1-264-196

Measure the IM shaft diameter, chuck the bearings up in a lathe, slow speed,
cut to initial size. Use a standard cam bearing installation tool and install
them in the block, they will crush and become smaller then the diameter of the
shaft. Hand finish with a brake cylinder hone, low speed and a little goes a
long ways. Test fit, finish sizing with green scotch brite. Oh ya, make sure
the front bearing lines up with the oil feed hole from the #1 main bearing
feed (The second bearing does not matter as it is fed through the shaft from
the front journal)

You want about .001-.0015" clearance, I would say .002" max Anything more then
that and you risk loosing too much oil pressure.

[LJ851]

Really? Honing a plain bearing?

This is a job for a reamer, the bearing is soft and going to absorb the grit from the hone, not good.

I know people do this but it is NOT the right way to do it.

[Cabriolet]

yup. that's exactly what we did.

[jlevie]

Really? Honing a plain bearing?

This is a job for a reamer, the bearing is soft and going to absorb the grit from the hone, not good.

I know people do this but it is NOT the right way to do it.

That is completely correct. Reaming is the right way to do it. The complication here is that the bearings are of different sizes and well separated. It could be done with two custom piloted reamers or two reamers and a bolt on precision reamer guide. I believe the factory did this in a jig using a single custom reamer.

Without the specialized equipment, honing is an acceptable substitute. If using high quality stones and flood coolant the chances of abrasive getting stuck in the bearing is pretty low.