bearing removal

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bill.bottrill
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bearing removal

Postby bill.bottrill » Mon Jul 16, 2018 4:23 pm

I want to remove the leaded bearings on a sq 4 mk1,fitted in the offside crankcase which holds the crankshafts in place. Do I have to heat the crankcase up or will they just push out! how do I support the crankcase, (would a metal tube bigger than the bearing be the way to do it) Is there info on the forum somewhere. the aluminium case seems very fragile
I have just started rebuilding this mk 1 and the wear and damage it's been subjected too is quite something thanks bill

nevhunter
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Re: bearing removal

Postby nevhunter » Tue Jul 17, 2018 1:15 am

Heat it evenly away from drafts and press or carefully drift the bearing out. If you can cool it (the bearing) with a wet rag all the better. Always support the area around the bearing. Nev

bill.bottrill
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Re: bearing removal

Postby bill.bottrill » Tue Jul 17, 2018 8:56 am

SAM_0996.JPG
Thanks Nev,
That's more or less how I was going to tackle it,I enclose a photo of the bearing damage both bearings have this flaking at the bottom only. The photo overemphasises the damage I sent the cases for soda blasting and didn't notice anything amiss leaving the bearings in,I thought the blasting had done the damage but you can see the lead has been smeared away from it's backing so if the blasting hadn't lifted the lead I probably would have reassembled being non the wiser!
Bruce said this is very common and it usually occurs at the bottom,I have asked him to supply his drawings on making some bronze/lead bearings,Has anyone else used these,I don't fancy using the drags ones if this is what occurs.

john.whiting
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Re: bearing removal

Postby john.whiting » Fri Jul 20, 2018 12:57 am

Firstly ,it aint,or shouldnt be lead........it should be babbit...........but it was not unknown to repair bearings with plain solder back in the 60s and 70s .Ive even done shell bearings with solder in the days when $2 for a set of shells was too much,and the bits wernt available.............we used to use things like Austin A30 bearings cut down....I would never use plain bronze bearings,leaded or otherwise ,because you end up with a cut journal.One alternative Ive used is a aluminium shell with a hardchromed journal......but that was when Alan Chance was doing hardchrome in his backyard.........and I had a Landis grinder.

nevhunter
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Re: bearing removal

Postby nevhunter » Fri Jul 20, 2018 2:47 am

The babbit metal is supposed to be tinned onto the steel Whether it was or not the end result is caused by fatigue. The thicker the babbit layer the worse it is at taking load. White metal (another name for it) is very forgiving of a bit of muck and should have very small running clearances so it doesn't hammer out and it is low friction so doesn't need high oil flow to cool it . It was almost universal till the WW2 but on "slipper" bearings not straight in the conrod common just before the War..
The modern metals, Alutin and lead bronze (copper lead) need more clearance for cooling oil flow and don't like grit etc and should run on Hardened surfaces or some pretty dreadful things happen . The engines are generally a bit noisier due to the extra clearances.
Bill when I was a kid I had a BSA Z A7 and the RHS bearing didn't last long the way I rode it. I worked at an engine reconditioning place and I removed the bearing carefully and remetalled it about 3 times, over a period, and kept the fit in the case OK. I know a bit more now and would expand the steel bush if it got too loose, or just make a new one. If you flashed the steel bush with nickel (dull, not bright bath) it would tin better and last longer. If you make a new bush reduce the Babbit thicknes to 1/2 mm or a bit less if everything is on centre and the bearing will last longer as it doesn't fatigue as much when thin. The Chevrolet big ends had the whitemetal spun in molten and beautifully tinned. The layer was so thin you couldn't replicate it or you would inevitably strike the steel when on the conrod borer so the steel had to be bored out a bit more to give the latitude for twist etc The repair was never as good as the original in this instance. Nev


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