Rear Main Bearing Clearance

[Graham Barker]

I am well into a top end overhaul of my Ruby 3 bearing engine, but did not plan to overhaul the bottom end as it was allegedly done at a bit more than 1,000 miles ago, although that was some years back.  There is a little radial movement in the rear main roller bearing. When the crankshaft is pushed to one side, I can get a 2 thou feeler into a gap between the roller and track. How acceptable is that? Is anyone going to tell me that I can happily leave it alone considering that I do not expect to do high annual mileage's, just local Sunday drives?
I have read about acceptable clearances in roller bearings when measured with the bearing in free space and 2 thou is not too bad compared against these.  I have not been able to find references to acceptable clearances when the bearing is compressed into its housing.

[Chris KC]

Graham, I think the issue you need to consider is how slack in the rear main might affect the running clearance - perhaps 1~2 thou by design - of the plain centre main bearing shells.

[Graham Barker]

Chris, thanks for giving it some thought.  On further probing of the roller race, I realise that the 2 thou feeler was not actually going through the gap between roller and track.  This was at the bottom of the track (where greatest wear should occur) with the crankcase inverted so that the weight of crankshaft and flywheel would be pulling the roller away from the track.  So the gap is something less than 2 thou.  I tried at other positions around the track with the same resullt.
Plastigage of the centre main bearing shows a bit less than 2 thou.
So I am going to live with what I have.
Regards
Graham.

[Stephen Barker]

In the Essex Austin Seven Club website - EA7C.org is an article about centre main bearing shims and clearance.

Stephen

[Chris KC]

In the Essex Austin Seven Club website - EA7C.org is an article about centre main bearing shims and clearance.

Stephen

Each to their own, but in my opinion it's infinitely preferable to line bore the housing. 
The observant will realise that this means making a new housing, or at least upper segment (you can't machine air, and I've seen the consequences of people trying to do so...) 
Unless, of course, you are lucky enough to have one that was in line to begin with.

[Tony Press]

If I remember the original rear roller bearing mains may have had a special reduced inner clearance bur of copurse these are no longer available. 

The standard roller bearing SKF CRM 10 or RHP MRJ 1 1/4 may have slightly larger clearance but 2 thou should be OK - as mentioned the centre bearing must be line bored.

The standard slight rear bearing rumble is usual.