Rear main bearing tolerances

[Bob Culver]

hi James
Deflections with sensitive eqpt can be confusing. Everythng deflects even under slight pressure. But a .005" clearance would be quite generous even for oil cushioned plain bearing. many rear mains have been replaced alone. Can try rolling over pieces of shim or card. To go further is not a huge job unless you find a cracked crank, cracks in be bearing metal etc. If you are not intending to drive to Peking, can risk a crankcase, and do not have a pile of spare money, often prudent not to look!
Many cars have gone long way on the spiral seal. OK unless worn. Slinger between flywheel must be present.

[Tony Press]

Hi all,

After a long time sitting disassembled, I've plucked up some courage, and am starting to sort out my engine (never having done one before).

The first thing that needs attention I suspect is the rear main bearing. There's enough slop in it that I can feel it, and something was very noisy in the engine prior to dis-assembly. 

Mounting a digital caliper to measure the vertical movement I can measure 0.12 to 0.13mm, depending on the rotation:
https://photos.app.goo.gl/eeqEfBmHLLUZtw71A

The only figure I've found re. play was that Jack French thought that 0.0013"  clearance was "quite acceptable" - in this case does "clearance" equate to play?

I am pretty sure that it needs changing, but figured it wise to check first!

On the assumption that it is shot, what are the replacement recommendations? Can one get a sealed bearing replacement?
The engine is a '34, two bearing.

Thanks!

James

The rear roller bearing for a 'light' shaft with 1 1/8" bore is RHP MRJ 1 1/8 or SKF CRM 9 with standard internal clearance. 

The rear roller bearing for a 'lheavy' shaft with 1 1/4" bore is RHP MRJ 1 1/4 or SKF CRM 10 with standard internal clearance. 

When mounted the bearing should have around  0.0006" (0.015mm) internal clearance. Internal clearance is 'radial play' or 'lif't'. 

Old stock inch series roller bearings are not available with seals and would not be used in this application.

Jacks suggestion of a maximum 0.0013" is reasonable  providing the bearing is a tight fit on the crank

[jamesheath]

A quick update - the bearing is out, without any damage to anything remarkably. It was tight in both the carrier and to the crank.
A long bit of 10mm round brass and a hot air gun heating the crankcase evenly to 65 deg C ish, and it drifted out very easily.
We then up ended the engine and supported the crank on a block of wood, then applied the drift to the inner part of the race and tapped that off gently - there are two notches in the crank that seem to be just for this purpose.

There's no clear deterioration to any of the visible surfaces of the roller or the outer - but there's clear air, just, between the rollers and the outer.
So I'll hunt out a replacement and hopefully find a lip seal too.

On to the next issue - the water branch studs..... but I'll start that in another post....

Thanks again to everyone!