D type rear axle pinion angular contact bearings

[Dave Mann]

Had a phone call query yesterday from an owner with a spare rear axle where there was a gap between the pinion angular contact bearing housing and the torque tube. I've not come across this problem, are these special narrow bearings?

[bystander]

They are.

 I believe 1/32" off the face of the outer race (i.e. similar idea to the AC front crankcase mains). RHP 8/LJT1 or Hoffman N1917 is the special bearing number - ideally should be a matched pair.

[Stuart Giles]

As bystander says, the A7 pinion thrust bearings are narrower on the outer track.

https://www.theaustinsevenworkshop.com/p...-ac-thrust

Should be possible to narrow down the outer track of the existing bearings using a toolpost grinder in a lathe. Some care would need to be taken to make sure they clock up true before getting to work in this case.

[Tony Press]

We had a specialist workshop turn 1/32" off the outer ring non thrust face on SKF ALS 8, RHP LJT 1" with a ceramic tool while still assembled. 

My list shows the original bearings were SKF W6898, R&M 3LJT 1". With the outer ring narrowed all other dimensions are the same. It is unlikely you will find a matched pair but the standard pair are usually acceptable. 

If you are keen, the standard bearings can be shimmed to give around 2 thou preload.

[Stuart Giles]

We had a specialist workshop turn 1/32" off the outer ring non thrust face on SKF ALS 8, RHP LJT 1" with a ceramic tool while still assembled. 

My list shows the original bearings were SKF W6898, R&M 3LJT 1". With the outer ring narrowed all other dimensions are the same. It is unlikely you will find a matched pair but the standard pair are usually acceptable. 

If you are keen, the standard bearings can be shimmed to give around 2 thou preload.

That's really interesting Tony. Do you know if they used CBN (Cubic Boron Nitride) tool? Can't think of anything harder for machining steel. I would have thought that the bearing race's hardness would be somewhere north of 60 Rockwell "C"

I used a CBN insert to machine this (non A7) pinion to make it fit in a different axle, even the CBN tool started to struggle a bit immediately behind the glass hard pinion gear.



I might try machining an old bearing race with the CBN insert if I can find where I put it -they're far too spendy to buy them in boxes of 10

[Tony Press]

Stuart, I don't know tool details and you are correct, SKF bearings are 60 Rockwell C.

[Stuart Giles]

We had a specialist workshop turn 1/32" off the outer ring non thrust face on SKF ALS 8, RHP LJT 1" with a ceramic tool while still assembled. 

My list shows the original bearings were SKF W6898, R&M 3LJT 1". With the outer ring narrowed all other dimensions are the same. It is unlikely you will find a matched pair but the standard pair are usually acceptable. 

If you are keen, the standard bearings can be shimmed to give around 2 thou preload.

That's really interesting Tony. Do you know if they used CBN (Cubic Boron Nitride) tool? Can't think of anything harder for machining steel. I would have thought that the bearing race's hardness would be somewhere north of 60 Rockwell "C"

I used a CBN insert to machine this (non A7) pinion to make it fit in a different axle, even the CBN tool started to struggle a bit immediately behind the glass hard pinion gear.



I might try machining an old bearing race with the CBN insert if I can find where I put it -they're far too spendy to buy them in boxes of 10

Stuart, I don't know tool details and you are correct, SKF bearings are 60 Rockwell C.

Resuscitating this thread as I had cause to use a CBN turning insert on another job today. Once that was out of the way, I fitted a wheel bearing from another (non A7) restoration project in the lathe chuck. It's a Nachi Ball race, was glass hard when tested with a file. Before and after pictures below.





Last one's a bit of a poor photo, but you can see the near mirror finish on the bearing face. The swarf comes off dull red! thankfully the (rather spendy) tool tip still looks like new.



Surface speed was about 300 SFM, manufacturer instructions are to machine dry with these tips; flood coolant is likely to cause cracking of the CBN tip.

[Charles P]

Good to know. I have the OD of a cam centre bearing to shave down and don't have a tool post grinder. Well I did have one and after 5 years unused in a box under the bench I got rid of it. Doh!