Author Topic: Rotten clatter!  (Read 672 times)

Offline Scott and Jay

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Re: Rotten clatter!
« Reply #15 on: 07.03. 2019 01:35 »
Hi UncleD,

I had a similar clatter in my A10. It chimed in at a similar speed. It turned out that the small end bush wasn't a good interference fit in the conrod. In fact it had been put in (back in 1976) by knurling the inner diameter of the conrod - very substandard, and by a firm with a legendary name (here in NZ). By then, they couldn't have cared about BSAs....

Online RDfella

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Re: Rotten clatter!
« Reply #16 on: 07.03. 2019 10:39 »
Scot & Jay - what the hell sort of 'engineering' is that? If the fit lacks interference, you make an oversize bush. As for knurling an ID, the mind boggles ...
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

Online bikerbob

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Re: Rotten clatter!
« Reply #17 on: 07.03. 2019 14:46 »
I have a1956 A7 swinging arm model and had a clatter at 50-55mph but it seemed to go away at 60-65 but could have been road noise drowning it out turned out to be small end bush it had turned in the con rod reducing the oil feed.

Online groily

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Re: Rotten clatter!
« Reply #18 on: 07.03. 2019 17:37 »
Scot & Jay - what the hell sort of 'engineering' is that? If the fit lacks interference, you make an oversize bush. As for knurling an ID, the mind boggles ...

Yup, am well boggled!
Really MUST figure out how to do that, in case anything starts rattling round here. (Why not just ram bits of feeler gauge behind loose shells and bushes, same as everyone else? Sooo much easier . . .  and blends in well with all the sawdust and molasses. )
Bill

Offline UncleD

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Re: Rotten clatter!
« Reply #19 on: 07.03. 2019 19:37 »
I don't like the sound of any of this (excuse the pun).

Northern Territory, Australia

Offline UncleD

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Re: Rotten clatter!
« Reply #20 on: 09.03. 2019 04:58 »
I don't know if this is connected...

I was fiddling with magnieto today to try and sort out my irregular points gaps and as I turned the engine over (plugs out/in gear) noticed air leaking out of the top of the outer timing case joint (through a point in the gasket, above the tacho drive/pinion area).   I actually heard it squeeaking like one of those old fashioned teddy bears when you squeeze them).

I removed the tacho drive and with my hand over the hole could feel air being drawn and expelled as I turned the engine over.  Should the air movement caused by the pistons be felt in the timing case or do I have a problem somewhere (rings)?

Northern Territory, Australia

Online bikerbob

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Re: Rotten clatter!
« Reply #21 on: 09.03. 2019 08:41 »
I think you need to take the timing case cover off then the inner cover  it looks to me that you have a problem with the crankcase breather, pressure in the crankcase is relieved by a timed breather which is located on the end of the camshaft there ae different thickness cork seals part numbers 67-134,135,136 137. these are all different thicknesses.

Offline Swarfcut

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Re: Rotten clatter!
« Reply #22 on: 09.03. 2019 09:31 »
UncleD  The crankcase in effect breathes via a keyhole in the timing side casting just above the oil pump. The keyhole also allows oil to drain from the oil pump cavity back to the crankcase.  There is free air passage between the crankcase and the area around the timed breather, so any change in crankcase pressure will affect the pressure within the timing covers, relieved when the breather opens.

  The timed breather bush is sealed against the camshaft drive gear by a cork washer, available in various thicknesses, (or  make your own) as outlined by esteemed member bikerbob, of a thickness which eliminates end float on the breather bush and camshaft without the bush binding too tightly against the inner face of the timing case. The cork should be just lightly compressed enough to give an air tight seal.
  The rotating breather bush opens a passage which runs across the back of the engine, to exit amongst the dirt and muck above the gearbox sprocket. So if the cork appears in order, check this breather air passage is clear  by blowing through with the air line. The inner cover will have to come off, so only worth doing if you suspect it to be obstructed or blocked, or the existing cork is allowing float on the breather bush. In theory you could seal the airline against the bush and rotate the engine in small increments until the breather opens and listen for leaks or free airflow. A bit tedious, but saves  dismantling. The system should hold pressure until the breather opens.
  What you describe is normal, as the breather only opens for a very short time, and a twin cylinder  engine with pistons moving in unison is a very effective air pump, hence the rise and fall in crankcase  pressure until the breather opens.

 If you decide to remove both covers, check for slop in the idler gear bushes and that the timing marks on the three gears are aligned correctly. The small cork washer behind the large dynamo drive sprocket crudely controls the idler gear end float, by being sandwiched between the back of the sprocket and the front face of the inner cover.


 Swarfy.