tony27 Posted August 10, 2018 Report Share Posted August 10, 2018 I have my own story of small end failure. I was swapping the piston port top end on my CZ to a reed valve converted top end & got greeted by all this when I pulled the pin out, who knows how much longer it would have run before making a big mess. What probably saved me from a big blow up is the washers that centre the rod inside the piston kept the bits of collapsed bearing cage contained Sometimes we get lucky & avoid the big mess 2 Quote Link to comment Share on other sites More sharing options...
cornishflyer Posted August 11, 2018 Author Report Share Posted August 11, 2018 (edited) Well I tracked the source of the noise, but I still don't really know what the cause is. The tensioner bush is quite warn but the inner surface is pretty smooth. The rubber wheel is well aligned to the chain and round. The rubber is quite hard but I suppose it they are supposed to be? I don't think it's the additional tension putting pressure on the clutch bearing, all of the bearings in the engine are new, as are the seals. I'm pretty certain I've put the clutch and flywheel on correctly. I'm running 300ml of ATF, but that doesn't dull the noise. Has anyone seen this before? I could run it with the tensioner I guess, or just ignore it. Edited August 11, 2018 by cornishflyer Quote Link to comment Share on other sites More sharing options...
feetupfun Posted August 11, 2018 Report Share Posted August 11, 2018 34 minutes ago, cornishflyer said: Well I tracked the source of the noise, but I still don't really know what the cause is. The tensioner bush is quite warn but the inner surface is pretty smooth. The rubber wheel is well aligned to the chain and round. The rubber is quite hard but I suppose it they are supposed to be? I don't think it's the additional tension putting pressure on the clutch bearing, all of the bearings in the engine are new, as are the seals. I'm pretty certain I've put the clutch and flywheel on correctly. I'm running 300ml of ATF, but that doesn't dull the noise. Has anyone seen this before? I could run it with the tensioner I guess, or just ignore it. If there is looseness in the fit of the tensioner wheel then it might be precessing (not sure of this is the right word). What I mean is that the tensioner wheel could be wobbling. If it is, then it will wear the bushing rapidly and fail. I would suggest either leaving the tensioner off or buying a new one. I run a M49 without a tensioner since I rebuilt the motor about 4 years ago and have not had a problem. The tensioner probably helps the chain and sprocket teeth last longer than without having one, but there is always the risk of the tensioner failing and causing damage to the casing and clutch. Judging by the number of internally damaged Bultaco clutch casings I have in my collection, having things come apart inside that casing is not uncommon. Your video reminded me of a Bultaco M99 (325cc Alpina) I had when I was a kid. The chain was so worn on it that when the motor idled, the tensioner arm would tap against the inside of the casing. 1 1 Quote Link to comment Share on other sites More sharing options...
b40rt Posted August 11, 2018 Report Share Posted August 11, 2018 BSA's run a metal slipper tensioner, no spring, just adjust and once set seems to last forever, as does the primary chain. (also running in auto tran fluid) Maybe yours could be modified to suit ? 1 Quote Link to comment Share on other sites More sharing options...
scot taco Posted August 11, 2018 Report Share Posted August 11, 2018 (edited) My 74 pursang has no tensioner from the factory and I have been racing it since 98 with only one new primary chain in that time with no troubles.I had a 77 pursang that had a tensioner and even after fitting a new one still made noise.I talked to Hughs Bultaco about it and he said that year pursang always did have noise from the primary so I just ran it.My 199a has one but is quiet so I don,t know.I think I would take feetups advice and just run it with no tensioner. He are pics of my then new piston after it ingested the small end bearing.I keep it on the shelf as a reminder. Edited August 11, 2018 by scot taco 1 1 Quote Link to comment Share on other sites More sharing options...
bullylover Posted August 12, 2018 Report Share Posted August 12, 2018 Just put a new tensioner in there. In Motion have them and they are not expensive. Any high revving Bultaco engine it is best to not use a tensioner as they have a tendency to self destruct. On the slower revving bikes they smooth the switch from no revs to some revs quite a bit. Just makes them smoother. 2 Quote Link to comment Share on other sites More sharing options...
section swept Posted August 13, 2018 Report Share Posted August 13, 2018 (edited) That tensioner helps keep the primary chain in its ‘torque arc’ the centrifugal effect that makes the chain try to arc upwards as if following the crank sprocket but the clutch drum sprocket pulls it down. As you say smoothing the on off throttle but also helping to slow the wear on sprocket teeth and chain. That whirring sound is the engine humming to itself.....it’s the chain under tension and is normal on nearly all Bultaco with single row chain, the twin row or duplex primary chain is less noise prone. Edited August 13, 2018 by section swept 1 1 Quote Link to comment Share on other sites More sharing options...
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