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B40 rattles/grinds under acceleration #773968 05/17/19 2:31 am
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LandoLando Offline OP
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My 1964 B40 (its got a a 62 motor in it with the points on top of the case) started making an awful noise on a short ride last week, and I've since parked it and begun dismantling it. The noise sounds like the gears are throwing a loose bolt or other hardware inside the primary. So I pulled the primary cover and everything looked fine. I pulled of the pressure plate and the clutch nut was still installed underneath and the clutch fingers looked tight in the grooves on the ID of the clutch ring. I haven't dismantled the clutch any further, because I am waiting on the extractor tool.

Because I wasn't sure that the problem was with the clutch, I decided to peek inside the inner cover. Nothing out of place there either. Any idea what could be causing such a terrible racket?


Last edited by LandoLando; 05/17/19 2:33 am.
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Re: B40 rattles/grinds under acceleration [Re: LandoLando] #774015 05/17/19 5:35 pm
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LarryLebel Offline
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I had a similar rattling sound on my B44R which turned out to be a loose alternator nut.

Re: B40 rattles/grinds under acceleration [Re: LandoLando] #774168 05/19/19 8:03 am
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BSA_WM20 Offline
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Remove the chain tensioner and take it for a short run.
They can be really noisy.
Some glue/rivet rubber / nylon / teflon on the working face to quieten them down.
Apparently cheap thin chopping boards work reallly well, unless she catches you cutting her nice new board into thin strips.


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Re: B40 rattles/grinds under acceleration [Re: LandoLando] #774200 05/19/19 5:02 pm
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I agree with the above but will add more info as I just finished a C15 and a B40

The primary chain has to be adjusted properly. I have found (even on A50 / A65) that a loose primary chain will cause all kinds or rattling noise, especially under load or acceleration

Does the noise tend to go away over a period of time? - perhaps piston slap

The only thing that can get loose is a rotor nut or a main-shaft nut. (also also the inner hub of your rotor)

Grab the rotor nut with a vice-clamp and rock back and forth and perhaps up and down

You can remove your primary cover and start the bike, make sure all the oil is removed and cleaned prior, perhaps that will help you isolate the sound



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