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MikeG
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#851448 06/12/21 2:40 pm
Joined: May 2021
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Z
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I've got a belt-driven primary section from N.E.B. on my BSA B33.

I ask my supplier for the correct belt tension.

They say you should turn is 90degr. in the middle of the belt between the front and back pulley.

So I did that and in principle, all works fine (except that I find it pretty loose).

I posted a movie (see below) on the BSA-OC-NL Facebook group and there some are saying it's much too loose,
it should be max 5mm up/downplay in the middle.

What is the truth?


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K
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Probably looks very different, i.e. tighter top line , when on the road and loaded, you're just ticking over over with no load and everything is slapping about, Instructions with my BNR belt drive were the same, i.e. be able to twist the belt 90 degrees when correctly tensioned, also when fully warmed up things will tighten up a touch more.
I'd take the manufacturer's advice over a Facebook group.

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Z
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Thanks Kev, it's not the manufacturer's but the supplier's advice. Should be the same I guess.

Waiting for maybe some more good answers....... thanks in advance !

Whats your bike you put the belt on ?

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Mine's a Bob Newby belt on a BSA A65, haven't looked at it running but the tension was exactly as advised and 1000 miles on it with no problems.
Admittedly it did feel on the slack side when not running/ being fitted but seems to work OK, on an A65 there's definitely some tightening up when the engine is up to temperature so you need to factor that in as well.

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Commando belt drives are much the same, 1/2 turn when cold but after a run will be much tighter as the engine etc expands. You have to take it for a run before checking again, too tight a belt will snap.

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Z
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Originally Posted by kommando
Commando belt drives are much the same, 1/2 turn when cold but after a run will be much tighter as the engine etc expands. You have to take it for a run before checking again, too tight a belt will snap.

1/2 should be 1/4 turn (90degr) I guess ?

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Originally Posted by Z900
Originally Posted by kommando
Commando belt drives are much the same, 1/2 turn when cold but after a run will be much tighter as the engine etc expands. You have to take it for a run before checking again, too tight a belt will snap.

1/2 should be 1/4 turn (90degr) I guess ?
Yes

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Hell, Z900

Did you have any trouble with getting the front pulley on? I am having a really hard time installing mine.

Jeff

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Z
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Hi Jeff,

I did, but when you make the pulley warm/hot then it should be easy !
Even (if it still won't go on) you can make the crankshaft cold with cold spray.


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