ET77 Main bearing distance piece

[Big Sid]

This quickie tip is helpful in a pinch where a costly repair is impossible , or beyond reach .
Where you find an outer race has lost its fit , not firmly gripped in the case . Two criteria are set . Where its just able to be turned with ones finger tips but no actual wobble can be felt . And where it can just be slid into the case but no movement is possible , no spin at all . With ALL surfaces super clean , case and race truly degreased . Hands clean . In the first instance , race can be turned round , --- a light smear over both surfaces , the od of the race and the alloy case both wetted with high strength Loctite , it's quickly slid fully in and let sit 24 hours . The other situation , everything clean as described , the loose race is entered all the way . A bead of Loctite is applied round the entire joint , a small hammer or other tool is tapped lightly around the nearby metal surface to set up vibrations , promote the wicking into and around the joint . Watch for this and apply a bit more to maintain the bead around the joint .
It is the absence of air that sets up the hardening process . For what it's worth , this has worked for us several times , acheved a permanent fix . Sid .

 

[Howard]

Way back in my younger days I fitted a main bearing with Loctite. I can't tell you what engine it was in, but it was a ball bearing and I'm fairly sure it wasn't a Vin engine. I had to heat the cases to get the old bearing out. As belt and braces I heated the case, cooled the new bearing and smeared it with Loctite before fitting it in the case. When the case cooled the bearing wouldn't turn - strong stuff this Loctite.

H

 

[Big Sid]

A further note on Loctite . If the really snug race had been smeared first then inserted it can suffer from distortion , TOO much of it can cause this where the fit is very close . Allowing it to wick in lets it go to where it's needed , filling wider voids but not where it would be extremely close . Seems to be self limiting . Seems so to us . Sid .

 

[riptragle1953]

I seem to remember a time when a proper fix was impossible..... machining an 1/8" deep recess in the outside of the alloy E19 scroll spacer so a full width 3/4'' wide race could be used for more purchase.

 

[clevtrev]

Craig, The bores are offset by 1 1/4"

 

[Bill Thomas]

Hello Craig,The main bearing I was talking about is R and M MRJA1, Three dot if you can get it, The outer track has to be ground back to 5/8 of an inch, Then demagnetise. It has a lip on the inside of the outer track, Fitted to the outer side of the cases, If it were to come loose it can't walk in because the rollers would stop it. I would like to know what Trev, Sid and Rip Think about it !! Cheers Bill.

 

[Howard]

Hello Craig,The main bearing I was talking about is R and M MRJA1, Three dot if you can get it, The outer track has to be ground back to 5/8 of an inch, Then demagnetise. It has a lip on the inside of the outer track, Fitted to the outer side of the cases, If it were to come loose it can't walk in because the rollers would stop it. I would like to know what Trev, Sid and Rip Think about it !! Cheers Bill.

That's too easy Bill. I don't know why no one else does it (assuming they don't) - maybe because we assume the race won't walk out?

One point, you seem to suggest 3 spot (or C3 clearance) is preferable - I think it's compulsory at crankshaft speeds with interferance fits.

H

 

[timetraveller]

OK Craig. I will try to describe the items. If you can handle either .dxf or .dwg files I could send you such a file but for reasons explained below it might not be very useful. The reason for the caveat is that not all mainshafts are the same diameter and hence any drawing of the items will not necessarily fit others. The standard mainshaft is 1" but people who raced sidecars, and some solo riders, started to use 1.125" diameter shafts for extra stiffness many years ago. If light series bearings were used then the outside diameters were the same as standard but inners fitted the larger shafts. More recently some of the later bikes (Eglis) have been built using metric mainshafts, 30 mm diameter which is even larger than the 1.125" size. Because of this the bearings and the final dimensions of all the parts will depend upon what you are using.

The idea goes back to Dan Smith as far as I know, about 30 years ago. I will describe what is needed and it might be easier to understand with a copy of your drawing to hand. ET92, ET19, ET77, ET91 and both circlips are discarded. The mainshaft housing is machined out both on its internal bore and on the outer face. A hollow 'top hat' housing is made which has an inwards facing spacer in the middle of it, machined as part of this bush. The flange is made large enough to take six countersunk holes with a diameter to match that of the outer part of the original bearing housing. The thickness of this flange and the amount machined off the outer (chain) side of the housing have to be matched so that the total length of the housing is the same as the original hole. The holes in the outer flange are there to take six counter sunk screws which hold the whole thing in place and prevent any chance of it rotating. The outer diameter of this top hat bush is made to be an interference fit in the opened out and newly machined, trued up housing. The idea is that a taper roller bearing outer is fitted into both ends of the new steel top hat housing, both pushed in so that they are tight up against the inner boss. The both have their wider ends facing outwards from the centre of the new housing. The central part of the inner bearing buts up tight against the flywheel, possibly with a shim to centre the con rods in the crank case mouths. Another loose spacer is required to fit between the two taper roller inners. The thickness of this spacer has to be such that there is about a 4 thou nip on the bearings when everything is tightened up. The outer end of the new steel housing has a left hand thread machined inside it to take a screwed in anulus which carries an oil seal. This oil seal carrier has four 'pin holes' in it's outside face in order to allow it to be screwed in with a pin spanner(wrench). The outside of the sprocket has to be machined and polished to fit inside this oil seal. (As with other main shaft oil seal systems).

I hope that you can see now why I have not given dimensions. It will depend upon the exact sizes of the bearing as to the thickness of the machined in central spacer and the loose spacer which goes between the two taper roller bearings. If this is not clear enough I could do a sketch but I have already put one in the Forum a couple of years ago but am not sure what words to used to search the Forum to find it.

 

[riptragle1953]

You will become tired of my saying this but a bearing, especially a thin outer race main, is as only as accurate as the bore into which it is fitted. When any bearing race has been found to have come loose this also means you are
dealing with an oversize, unround, tapered bearing bore. Anything you do that doesn't reclaim the bore to perfection is creating an oversize (radial clearance), unround, tapered bearing. Gee, the bearing companies go to immense
trouble to create a perfect bearing ..... they are more than willing to provide fitting specifications, and everyone comes up with some plan other then doing it right.
Just because a machine runs does not make it right. I repaired a Comet once that ran well.... but the inner main was seized in the race and the shaft was powering the machine by spinning in the inner race bore!
Keep in mind as well that the outer race with a .0001 dial indicator on the inside can be squeezed several thousands out of round with your fingers.

 

[Bill Thomas]

Hello Howard, Last time I wanted one of these bearings, I was told you can't get 3dot, You had to have what they had !! You know bearings, Was he having me on ? Cheers Bill.