C95 bearing rumble

[Geoff Hastings]

Hi there, I rebuilt a pile of bits till it resembled a C95 as documented on this site two years ago. Since then it’s been a lovely little bike to ride but recently I’ve been aware of a slight rumble from the bottom end. The main bearings seemed fine when I was rebuilding the engine and so were not changed. I’ve just taken the side cover off and there’s quite a bit of play in the main bearing now so the engine is going to have to come back out and the bearings changed. Shame really as I’ve been enjoying buzzing it round the Surrey lanes. When I checked the price on CMSNL I realised why I’d decided the old ones would do. Oh well!

[Geoff Hastings]

I decided to double check the bearing number so partially stripped the generator side of the engine. I was surprised to find that the bearing appears to have no play in it but the crank is rattling around in the bearing. I’m not sure if this site will support a short video clip but I’ll try. If not you’ll just have to use your imagination.

[Michael Stoic]

At least it's not the bearing, but then what - did the ID surface of the inner race develop wear, where it contacts the OD surface of the crank?

Video: I am not sure whether the forum software can display video (I'll work on that), but post a youtube link, if you can upload to YT.

I always follow your reports with interest. Thank you for the updates!!

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Michael

[Geoff Hastings]

Thanks Michael,
At the moment I’ve not got room in my workshop to drop the engine and strip it completely but as soon as space is available I’ll start the autopsy. My only thought currently is did the bearing partially seize and spin on the shaft, when I bought the bike it had been off the road since 1978 and the cylinders were seized but the bottom end seemed ok. The main bearings seemed fine but of course all I could do was feel for play and smooth running and the oilways were clear so it’s a bit of a puzzle at to what went on. Certainly there were no unusual noises but I was aware on the last few rides of the engine feeling slightly harsh with a slight increase in engine noise which is not the norm for this bike.

[Michael Stoic]

...partially and temporarily seized is a reasonable supposition. Will be interesting to learn more when you get to it.

Those bearings are not available in a crossover by size?

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Michael

[Geoff Hastings]

If it turns out the shaft is a loose fit in the new bearings I’ll probably just try some Loctite bearing fit. I’m hoping to park a couple of my bikes in a friends garage next week so then I’ll I drop the engine out and have a look inside. I’m not aware of any differences in bearing size, I’ve just ordered a pair of original bearings but unfortunately they are at todays prices, £210 in the uk

[Geoff Hastings]

https://youtube.com/watch?v=pffY3tv95yg&feature=share

Possibly, I might have managed to post a link to the you tube video. It’s only 15 seconds long as a crank shaft moving is not that exciting but if the link works it will give you some idea of the amount of play.