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MG MGA - Rear Axle Wheel Bearing

Could someone with knowledge of metals, coefficient of expansion of steel, etc., answer this one. I have just completed the replacement of a rear axle outer bearing on my 1959 Twin Cam, which was in poor condition, by following the workshop manual and, particularly, Barney’s site (plus a few emails to Barney also - nice man!) The damaged bearing needed driving out of the bearing housing by hammer and a drift – no problem there but, mindful of needing to reverse that process, ie. having to drive the new bearing back into the housing and wanting to avoid the potential for damage if it was a tight fit needing a lot of hammering in, I decided to put the bearing in the freezer overnight (-18 C) and warmed the bearing housing to a comfortable hand temperature (say, +30 C). To my surprise the new bearing (identical type and size as original) was then a comfortable finger-push fit into the housing. The question is, is this acceptable and will the fit be adequately tight, as was the original, now that the two temperatures have stabilised. And before someone asks, no I didn’t try knocking it out again to check the tightness of the fit, in case it was indeed a good tight fit and I ended up with the new bearing wedged askew half in and half out!
Anyone care to reassure me, or otherwise. Thanks in anticipation.
Bruce Mayo

Shrink fitting is used in industry to make assembly easier and to prevent damage to new bearings when being installed. Usually used on larger bearings where more force would be needed but no reason that it would not work on small bearings as well. It takes some time to do, so that may be why it is not usually done on automotive work.
Ed Bell

coeff of steel expansion is ~ 12 x 10^-6 per deg C
so this x 38 deg C differential x 3" = about .001"
Enough to make it pretty tight.
My recollection in pressing it in cold was it wasn't too hard to do.

Art Pearse

Thanks guys. I feel reassured! It's now all back together and I even put a speedi-sleeve on to be sure of the new oil seal doing a good job. It took four axle oil changes to get rid of the last bits of debris which hopefully is now all clear. All fuelled up and ready to drive down to the Le Mans Classic next week with an MG group from West Sussex.
Bruce Mayo

Gear oil is a bit pricey as a flushing liquid!!
Art Pearse

Art, true, but I had lots of old, various viscosities needing binning so just used them up. Also, it seemed that flushing with some light spirit would need a lot of flushing out too, so went for old gear oil!
Bruce Mayo

This thread was discussed between 27/06/2014 and 29/06/2014

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