Morris Minor Owners Club

Wow. That's no small difference.

If that solid spacer is the correct part then there must be an additional spacer in there. Something wrong somewhere!
Regards
Declan

There is. Think this photo may explain.
This is the pinion from my 3.9:1 diff. Between the crush spacer and the pinion inner bearing is another spacer. The crush spacer has been crushed to approx.19mm, and the two combined measure just under 41mm.
The solid spacer is marked 10/39 and BTA1225.

Cheers N

An additional spacer if you use a crush spacer? Surely someone must have had one apart, I can’t be alone in this? The distance between the bearing ‘seats’ is obviously fixed.

Edit. Mr Evans may have solved it.

PoolGuy wrote: ↑Thu Oct 31, 2019 9:47 am Edit. Mr Evans may have solved it.

That'll be a first!

I haven't actually had them apart yet, but it looks like there may be a shim under the solid spacer. Will report later today.

cheers N

Post deleted. Something went wrong!

The BMC manual does talk about using a washer of "known thickness" when reassembling. You then use the dial indicator reading & the markings on the pinion head to increase or decrease the washer thickness, in order to set the pinion height correctly.

Interestingly, the diagram in the the BMC manual, section HH, page 2, suggests that there is no shim between the solid spacer and the inner bearing, only a thrust washer between the inner bearing and the pinion head. Which is right?

Cheers N

Neil,
Look at item 29 on that page. It does show a shim.
Regards
Declan

This is how mine was, between the pinion head and the bearing, it’s 3.12mm thick and the inside edge against the pinion head has a chamfer on it.

The pinion head thrust washer (item 25) is between the pinion head and the inner bearing. Item 29 is the shim between the spacer and the outer bearing. The manual shows both.
Regards
Declan

Item No: 25 Washer Pinion Thrust is supplied in different thickness and dependent upon the thickness is given a specific BMC Pt No: ATA7048 to ATA7055. The shim item No: 25 determines the fore and aft meshing of the pinion to crown wheel,

Item No: 29 Shim Outer Bearing is also supplied in different thicknesses and dependent upon the thickness is given a specific BMC Pt No: 1G7261 to ATB7107. The thickness of these shims determines the amount of preload on the pinion bearings when a solid spacer (Pt No: ATA7046) is used between the inner and outer pinion bearings.

Right, I see now. Confusingly, my hardcopy of the manual shows the shim between spacer and outer bearing as item 27, but my electronic copy shows it as item 29!

Back to the spacers. I am a little unsure now. What I thought was a 21mm spacer and a shim between the crush washer and the pinion head, now on closer examination, appears to be just a change in shaft diameter. It is not shiny like the area under the spacer, and there is no discernible gap between the minor diameter of the shaft and the stepped area.
This implies to me that there are two types of pinion-one which has a step in diameter, like mine, and is intended for a crush spacer and shim, and one which is intended to take a solid spacer of approx. 40mm, plus a shim.

Either way, I don't appear to have a separate shim between my crush spacer and the outer bearing. Should there be a shim between the outer bearing and a crush spacer, or is the shim for solid spacers only?

(This is the 3.9 diff, not the 4.22, which I have tried to set the pre- load on. The 4.22 pinion is still intact in the carrier).

Edit:-new and old crush spacers side by side. The new one is 21.7mm, the old 18.9mm.
Cheers N

Just checked my box of bits and sure enough there’s a 5thou shim.

Where was it fitted? Did you have a solid spacer?

Between the thrust washer and bearing, it’s the one that Declan mentioned that sets the pinion height. Yes, solid spacer.

Ok thanks. So, the question is, am I missing a shim, or do crush spacers not need shims?

My assumption would be that the nature of the crush washer means that it doesn’t need a shim. But one of the learned members will give you a definitive answer.

It's annoying that the BMC manual only covers the solid spacer type. Well mine does, anyway.