ET: Engine (Twin) Lipped Main Bearings

Bill Thomas

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How did you grind the outer down Ed, I have a set of lipped for my new Comet.
My Old Comet is waiting for a Ride and just fitted a "D" Centre Stand on my Ex L/ning, I would like to put a few miles on that too :) .
Cheers Bill.
 

BigEd

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How did you grind the outer down Ed, I have a set of lipped for my new Comet.
My Old Comet is waiting for a Ride and just fitted a "D" Centre Stand on my Ex L/ning, I would like to put a few miles on that too :) .
Cheers Bill.
I have a friend in Newark that made the big-end, sourced the bearings and ground them to size and fitted them in the cases. He has all the kit in his workshop and used to work in the bearing industry so he definitely know s about bearings.
 

Bill Thomas

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Some years ago , I was not thinking right, And bought the narrow Alloy Spacer !!, So I would not have to grind a bit off !, But that would leave the lip miles away from the rollers :) , Twit.
Yesterday I had to Steal ! ,One of my own Bikes, I have so many locks and keys, I couldn't find a key, So had to
Angle Grind the lock off, Don't think I have many Brain cells left !.
 

Bill Thomas

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I think the "A" type 1936 ish was better, That had bearings fitted in a steel housing then the steel was screwed into the alloy case, Drive side.
I think what I have is imperial, Standard Engine, 2 of RHP bearings, MRJA1J 3/4" wide, One has to have 1/8" ground off for drive side, After grinding it may need to be demagnetised ?.
 

Marcus Bowden

VOC Hon. Overseas Representative
VOC Member
Tipped tools will cut it off no problem but when fitting, ground end in first. If no tipped lathe tools machine undercut aluminium spacer so out race can move in an extra 1/8". If no lathe take an essential trip to Cornwall and I'll do it while you have a cupper sat in the garden looking at the view, brother Ron enjoyed it.
 

Pushrod Twin

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VOC Member
I think the "A" type 1936 ish was better, That had bearings fitted in a steel housing then the steel was screwed into the alloy case, Drive side.
I think what I have is imperial, Standard Engine, 2 of RHP bearings, MRJA1J 3/4" wide, One has to have 1/8" ground off for drive side, After grinding it may need to be demagnetised ?.
It will need to be de-magnetised if the grinding was done by holding it on the magnetic table of a surface grinder. However, if the grinder is reasonably modern it should have a "de-magnetising" function that reverses the magnetism back and forth a few times until there is none left in the component.

I turned the width off my bearing ring in the lathe. Start with a fresh suitable grade carbide tip and the 60 Rockwell C bearing ring peels away like butter and leaves a nice finish.
 

Bill Thomas

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Thanks , I see why now.
I was hoping to Grind it my self, By hand, A little at a time ??, So as not to get it too hot.
I have a few ways of holding grinding paper.
I don't think it has to be dead straight, Because the ground bit will have to face out of the case for the lip to work.
It's only an 8th of an inch :) .
You have now worried me about using the magnetic boring machine, To bore the Bigend hole,
Will the Flywheels become magnetic ?.
Funny thing is I am now too old to use the extra 60cc, It is just a silly dream I have been putting off for years.
But with the Wife stuck at home, Now may be the time to have a go.

Many Thanks Marcus, But you are a bit too far from me, I don't travel well, Don't know how I used to get down to Devon to Ron's, But the Silly Sod has now moved to London.
Cheers Bill.
 

Bill Thomas

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The fit of the main bearings in old crankcases is a common problem. When I took my engine down last year (or maybe late 2018) one of the mains had "walked" and was machining a big end nut. A new big end and lipped main bearings were fitted. Lipped mains, in my opinion, are going to help avoid the "walking" and I can see no downside myself but am prepared to accept a good argument suggesting otherwise.
I wish we were rid of the current restrictions so that I could be back on the road, wearing out my Rapide.
Just a thought Ed, I am wondering if I have to shorten the outer track ?.
I bet there is enough clearance if left at 3/4", Have you still got your old one, Can you see any marks on your old one ?, As to how far out it came ?, As it touched the Bigend nut.
I had one do the same many years ago.
There would be no need to stake the cases, Because of the Lip !!.
Cheers Bill.
 

BigEd

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VOC Forum Moderator
Just a thought Ed, I am wondering if I have to shorten the outer track ?.
I bet there is enough clearance if left at 3/4", Have you still got your old one, Can you see any marks on your old one ?, As to how far out it came ?, As it touched the Bigend nut.
I had one do the same many years ago.
There would be no need to stake the cases, Because of the Lip !!.
Cheers Bill.
Dear Bill,
I don't think I have any of the old bits, Brian who sorted thee big-end, etc probably dumped the lot. I don't really remember, maybe he gave the scrap back to me, next time I'm in the shed where I keep all my Vincent bits (read, "junk" you never know, it might come in for something) I will have look. I will have to clear a path first through the other accumulated ...... junk.
The case haven't been staked.
 

Bill Thomas

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Ok, I have heated the cases and removed the bearing outer races. Note how doing this has disturbed the metal at the stakes fairly proving that they were original bearings. Note also the outer profile of the outer surface of the bearing. One edge has a chamfer rather than a radius as is usual and is on the opposite edge.View attachment 34451View attachment 34452
The Mod' that was in MPH years ago, By our now "A" Man,
You use a standard width inner bearing, No Spacers It just puts the inner in a slightly different place,
As it does with a standard setup, The factory must get the outer ground down, They don't come from the bearing company like that ??.
I helped Big Bill Telfer, West London, Do it to His Twin many years ago.
 
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