G: Gearbox (Twin) Layshaft bearing problems

[oilyrag]

This week I fitted a new layshaft bearing and when the case cooled down the bearing has gone tight. ie. only turns very stiffly.
Also the layshaft has become a hard fit, you have to tap it to get it in. Before fitting the bearing it would rotate freely and slide on and off the shaft.
I have never had this happen before and I have fitted lots of bearings.
Your thoughts please?

Chris Tilley.

 

[chankly bore]

New or old crankcases? Is the bearing English, German, Japanese, Indian or Chinese? Have you access to a bore gauge, or can you try the layshaft in an old loose bearing? Have you a 2" micrometer to compare the o.d. with an old bearing, preferably English, German or Japanese.

 

[Robert Watson]

Was it a C3 fit bearing?

 

[davidd]

Yes, Sam Manganaro's Rapide had the same thing happen. Unfortunately, I do not remember what he did. I remember him taking it out. I think he worked on the bearing journal. I also remember that it was tedious work. It was also a C3 fit.

David

 

[greg brillus]

You will need to start again, the bearing will be destroyed removing it, at least it is not one of the expensive ones. Try the layshaft into the new bearing to see if it is too tight a sliding fit, if so you might need to linish the shaft perhaps a small amount until you are happy with it. You might want to check the same thing with the opposite end and see if the problem doesn't exist there also. This is not an uncommon problem, and i have found the small timing side roller ET 94 suffers the same result, luckily you can hone the outer race to give clearance, but not the other bearings. A lot of the newer bearings seem to have a much thinner outer race than the originals, and these tend to collapse more readily thus loosing the running clearance....... It can be frustrating, as it can catch you out when you would not expect it to happen.

 

[Black Flash]

Hello Chris,
Get a new bearing and be sure it's a C3 tolerance bearing. Try at least to buy it from a different source so you are more likely to get one from a different production batch. The bearing tolerance classes do overlap. So a tighter C3 bearing could well be sold as a standard bearing. Usually the bearing tolerance gets checked after manufacture and then bearings get grouped and the bearings stamped after demand. So if a manufacturer gets a big order for standard size bearings, they will get produced and those with more play will be be put aside and sold as C3 if there are orders coming in as well as standard.
Simply try another bearing from another source. Of course first measure your shaft and housing. In an big hefty alloy housing about 1 third to 1 quarter of the interference goes into the outer ring reducing the play, in a thin walled alloy housing it is less. On a steel shaft 80% of the interference goes into expansion of the inner ring, so you may need to lap your shaft.
These are proven rules of thumb.
Do not forget we are talking about microns when it comes to play in C2, CN, or C3 bearings.
But as I said before try a new bearing first before fettling with the bore especially
Cheers Bernd

 

[oilyrag]

Thanks for the advice. New bearing, C3, ordered.
The bearing I used came from the VOC Spares Co. and they told me on the phone it was a standard bearing.
Back with news when the new bearing comes.

 

[litnman]

Got luck and found this blind hole puller at a garage sale. Fit perfect.

 

[Roger Barton]

I use bread and a drift takes about 30 seconds and you get toast

 

[van drenth]

Be aware that the inner race is not against the blind end in the bearing hole.
Regards, van Drenth JC