Hoffman Main Bearings

Rick.Edwards · Post by **Rick.Edwards** » Fri Feb 15, 2008 6:54 pm

Can anyone out there confirm levels of fit for the main bearings on AMC twins,we think that the factory used STD fit on assembly and C3 fit for replacments.At Kettering HQ today we found a bearing supplier round the corner that has Hoffmans exactly matching the originals,in a brass cage,but these are C3 fit.Any ideas or comments? cheers

itma · Post by **itma** » Fri Feb 15, 2008 8:02 pm

Go for the C3 fit

Rick.Edwards · Post by **Rick.Edwards** » Fri Feb 15, 2008 9:12 pm

Thanks Ken, we were hoping that you would say C3, even the bearing man thinks that they should be used but it is even better that you agreeTrouble is there are only a few left with these brass cages.Apparenlty they run quieter.......

itma · Post by **itma** » Sat Feb 16, 2008 10:17 am

Its the fitted clearance that matters.
The normal ones run too tight, and will fail rapidly,
A C3 bearing feels very slack before you fit it.
So when you get a bearing from one off the cheapo suppliers and ask for a C3 fit and he says "WOT??" just walk away.

Rick.Edwards · Post by **Rick.Edwards** » Sat Feb 16, 2008 5:08 pm

I think i got mixed up plumstead used C3 not std,which seems to be all that is available and like you say too tight,got a pair of these C3 Hoffmans on the way now for my 650 but they are expensive. this i suppose is why the factory peened them in then?anyway thanks Ken

GSAX1 · Post by **GSAX1** » Sat Feb 16, 2008 5:51 pm

The peening would have nothing to do with the C3 rating. They did that as an extra precaution against the outer race moving inwards during. This according to a discussion in "The Motor Cycle" with AMC's managing director and chief designer in the '50s.

C3 bearings should be used in normal applications when there is an interference fit both on the inner and outer races as in the AMC twin engine.

Michael

deshollier · Post by **deshollier** » Sat Feb 23, 2008 4:53 pm

JSL has now made a special purchase of the remaining stock of the Hoffman C3 bearing that Rick mentioned. As I am planning an overhaul of my twin in the not too distant future I thought that this was too good an opportunity to miss. Received my set this morning - only ordered them the previous afternoon! A beautifully made bearing, with a lovely brass cage, I may frame it to look at before I put it into use! Thanks Rick for the info. If you are also planning to overhaul your twin, get in there real quick as they are not likely to remain on the shelves for long. Part number 011543A

Biscuit · Post by **Biscuit** » Sat Feb 23, 2008 5:55 pm

I have just replaced them - Oh woe.