CB72/77 Gearbox mainshaft bearing

Phil-UK · Post by **Phil-UK** » Mon Mar 24, 2014 7:04 am

Hi

I queried the clearance for the gearbox bearings a while ago but this is about actual bearing dimensions.
The old parts books say that the clutch end uses a 6305 bearing 91004-259-000.
The CMSNL online parts fiche says Honda replaced this with 91004-438-003 which is what I got and used. However the bearing sticks out from the joint face of the crankcases because it is 17mm deep and not 16mm as per the original.
Checking various bearing suppliers here in the UK I cannot find a match for a 25x62x16 ball bearing with snap rings. SKF do one in 16mm depth but no snap rings.

Has anyone found a currently available bearing that has the correct dimensions and has the snap ring groove ?

I can use the Honda replacement but will have to remove 1mm from the back of the clutch to bring the primary chain alignment back to standard.

thanks

Phil

jensey · Post by **jensey** » Mon Mar 24, 2014 12:42 pm

Hi,

Grind it off 1 mm if possible (the bearing)

Jensen

malcolmgb · Post by **malcolmgb** » Mon Mar 24, 2014 1:19 pm

I believe it is possible to get the snap ring groove put in a bearing try http://www.vintagebearings.co.uk/ I know they will do dowel holes.

malcolmgb · Post by **malcolmgb** » Mon Mar 24, 2014 1:26 pm

I have found this http://simplybearings.co.uk/shop/p43118 ... _info.html although it doesn't say it has a groove the picture shows one, maybe worth contacting them.

Tinman · Post by **Tinman** » Mon Mar 24, 2014 4:39 pm

Phil,

I replaced both transmission bearings this winter, not realizing the difference in width on the 6305. I got the superseded Honda part# off of the CMSNLl website, cross referenced for size and assumed what I had bought was the correct bearing. My only concern when I installed it was if it was supposed to be of the C3 variety, which this is not, would be a problem. Now I may have another concern, which is premature wear on the primary chain or sprockets due to the 1mm width difference.

When I installed it, it appeared flush with the side of the case so I didn't give it any further thought. I have close to 300mi on the engine since reassembly and haven't noticed any difference in performance or any questionable noise.

However, I have noticed how touchy it is to adjust the clutch. It doesn't seem to take much in turning the adjustment cam to get the clutch where it should be. Perhaps the 1mm does make a difference on clutch adjustment.

Here is a link to the bearing I used and from the company in which I purchased it from. They do not list a 25x62x16mm snap ring bearing unfortunately.
http://www.vxb.com/page/bearings/PROD/N ... ng/Kit9950

Dennis

Phil-UK · Post by **Phil-UK** » Tue Mar 25, 2014 7:18 am

Thanks guys for the feedback,

I contacted Simply Bearings and they say that the 16mm 6305 they do doesn't have the groove. Also emailed another supplier selling them on Ebay and they said they could get a groove machined but only on a minimum order of 10.

So it seems the original is no longer available and the Honda replacement is not a true replacement. Luckily I have several clutch drums so I think I'm going down the route of machining the back of that ( easier than grinding 1mm from the bearing ). Can't see that this should have any other side effects but if there are I'll flag them up on the Forum.

Phil

jensey · Post by **jensey** » Tue Mar 25, 2014 8:18 am

Hi,

Maybe easier, but keeping the CB parts in one piece, a bearing is disposable, when I have the choice, I always change the disposable parts.

Grinding off a bearing can be done by a grinding machine, just 0,02 to 0,04 mm at once, takes an hour and no heat is generated. I have done this before, it works.
Jensen