I removed the 1st motion outer race from my primary gear housing with no real fuss, and while I was there I removed the roller bearing for the idler gear as well. I thought there was a new one in the gearbox kit I had from Minisport UK...(there was one unopened box left).

Turns out I have a spare needle roller mainshaft bearing instead (I think it's third, the non-split variety).

So that means I have to get a replacement needle roller. Now there was two sizes I think in Aust at least, a larger and smaller diameter version. Are there any other varieties that were used?

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Yes there are two sizes... early and late.

This is the type you need:
http://classicmotoring.net.au/cmos/index.php?main_page=product_info&cPath=1_43_153&products_id=519

The larger diameter was generally not found until A+ and some very late A series boxes.

Thanks Anto, was there a different one fitted to the gearbox side of the idler bearingv or did they share the same part number? I had the old one from the case and matched it up to the primary gear housing, it seems larger?

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

The idler gear is longer on side than the other, but the bearing is the same on each side as far as I am aware.

There were 3 different size idler gear bearings, one for the early 3 synchro (#88G302), one for 4 synchro (#13H7848) and then A+ (#TUK100320).

Need to check what you have and make sure the transfer housing suits the gearbox.

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Steve

Yep I stand corrected - I forgot the 3 synchros were different. 88G302 is indeed the one for them and is the same as the upper control arm bearing from memory (25.5mm OD).

Later 3 synchro boxes also got the same idler gear needle roller as the 4 synchro box.
IIRC the O/D is 1 1/16". The first type O/D was 1".
I'm not certain by any means but it may coincide with the introduction of the commonised 3 synchro gearbox housing 22A1288.
Edit: I think it may also correspond with the idler gear with unequal shaft lengths.
RonR