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MG Midget and Sprite Technical - Blood, sweat & gears..help!

Hi there,

I attempted to fit a new tail shaft bearing 2A3325 into my later type 1275 gear box tail shaft housing. First issue was that it wouldn't fit. I meausred 0.2mm interferance. Measuring the old part I noted less interferance. I sprung open the shell along the joint, and filed out what I thought was a reasonable amount to allow the shell to close up with a smaller external diameter. But I didn't remove a lot as I was concerned about making it too small and having the bearing spin, when the alluminium housing warms up in use.

I managed to get the interferance fit started, but it wouldn't budge after inserting about 1/2 of the length. I then used a plumbers gas burner to heat the housing, applied some grease and oil, then used a 6 lbs hammer and a piece of oak. Job done.

I thought to check that the tail shaft fitted and passed the assembly under the car and attempted to fit the tail shaft. It didn't fit, and when meaured the shaft came up larger than the inner bearing diameter of the bearing I had just fitted. With more heat I manged to drive the shell all the way throught the casting and remove it, but it's a bit chewed up now.

Qu.s
1) Is there some osrt of machine in situ process that I've missed? Reaming?
2) Has anyone else experinced this - how do we fix?

My plan this morning is to request a replacement part from Moss and measure the tail shaft, housing and shell and work out where it's incorrectly sized to see if I can do anything about it.

Help! Thanks, James Eastwood

James Eastwood

The bush does need reaming to size once fitted. The oil groove in the bush makes the reamer to tend to run off-centre, which is not helpful! An alternative is to get it machined with a boring bar.

I have fitted two Moss bushes recently, both were good for size and felt right for interferance fit in the press. You need to be careful trying to measure the interferance fit of a split bush, as the split is inevitably open a little, and trying to close it can distort. it
Paul Walbran

Paul,

Thanks, I hadn't realised it needed reaming, and probably wouldn't have attempted it if I had known. Also I could have left the one I had fitted in place (ouch.. 2nd wrong decision).

I may have to use another tail casting with the bearing still in place so as not to lose too much time sorting this out.

Regards, James
James
James Eastwood

Just spoke to Moss, direction is "..all split bushes need reaming after assembly.."

JE
James Eastwood

Paul,

I've ordered a new bush, sourced a hydraulic 25 Ton press to fit it, and some one to help with the reaming;

Qu.s;
1) What should I ream it out to? Or what clearance should I aim for between the bearing and shaft?
2) What load should I expect to see as it's pressed in? (Just as a guide).

Many thanks if you can answer,

James
James Eastwood

Clearance: The BMC manual has no specs on this, I use on a couple of thou and it seems to work OK.

Load: Our press is 12 ton, did it reasonably easily. No gauge, but you can feel the load (though the pump handle) needed to press the old bush out, the new one should be similar.

Note that old bush usually has a high peak load to get it to ove initially, age usually bonds things a bit. So the comparison is with what's nneded after that initial peak.
Paul Walbran

This thread was discussed between 13/04/2011 and 14/04/2011

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