The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: UncleD on 11.02. 2019 08:30

Title: Rotten clatter!
Post by: UncleD on 11.02. 2019 08:30
1958 Super Rocket.  At around 55mph I get a rattle that seems to be coming from the top of the motor.  It seems to diminish at 60mph so feels like it is within this vibration /harmonic range.   

I have checked tank and engine mounts and other possibilities for loose external fittings.

I rechecked the tappets and found what looked like fine metal fragments on the top of the right inlet valve stem .  The valve clearances were all a little tight but not overly so; I rectified these with little improvement in the rattle  (perhaps some or perhaps my imagination).  The noise does not seem isolated to the right side of the bike but it's a bit hard to tell at 55mph.

Not burning or using oil.  Compression is good.  Starts and runs fine.

I do have badly unbalanced points gaps (outside reasonable tolerances) and am getting a richer reading from the right cylinder plug (not overly so but not as lean as the left cylinder)...no pinking.

Could the points gap be causing a timing problem that is causing the valve noise / damage?

I am getting an experienced friend to help me with the magneto but am wondering if the rattle and points issues could be connected?
Title: Re: Rotten clatter!
Post by: lawnmowerman on 11.02. 2019 09:52
G'day D

I had a similar vibration at that speed and it turned out to be the tank. Do you have the strap fitted to tie the tank halves together?
I think my tank is an Indian made one and the gap in the centre is slightly wider so I had to make a longer strap - also, even with the rubber buffers fitted, the tank still rattled at that speed. The solution was to snug it round the frame with some foam pipe insulation taped in place which fixed the problem.

Jim
Title: Re: Rotten clatter!
Post by: UncleD on 11.02. 2019 10:07
Thanks Jim,
Yes I have the tank strap in place and some thick rubber tubing on the frame.

Of note is that although the sound of the rattle seems to be in the head, the vibrations can be felt in the tank, handlebars etc .  Probably notice this more now that I have replaced a broken head-steady bracket.
Title: Re: Rotten clatter!
Post by: berger on 11.02. 2019 14:01
mine had a really bad clatter that made me think the rockers were starved of oil and they were because I had put the pipes  on the wrong way *problem* *bash* , this was also added to with piston slap but this is a story that I covered some time ago. my next clattering came last summer on a hot day and I convinced myself the rockers were being starved so I checked and this wasn't the case *good3*, the bike has a rubber mounted honda tank and has carpet underlay wrapped around the frame. as I sat uprightish [ clip-ons fitted] it was terrible but as I leaned out to listen to the rockers it was ok. *bright idea* so I took the tank off and replaced the old mounting rubbers and underlay, this cured my rattle . I am not saying this is your problem but tank mounting is a thought *dunno2*
Title: Re: Rotten clatter!
Post by: duTch on 11.02. 2019 15:06

 I hear more rattles when I'm low on fuel..... *eek*

 
Quote
......... because I had put the pipes  on the wrong way *problem* *bash* , ........

   Which way is not the wrong way ?    *conf2*
Title: Re: Rotten clatter!
Post by: berger on 11.02. 2019 17:26
"which way is not the wrong way"---- well its putting the feed from the tank to the feed on the crankcase and not putting it to the return *bash*
Title: Re: Rotten clatter!
Post by: bsa-bill on 11.02. 2019 17:54
Quote
well its putting the feed from the tank to the feed on the crankcase and not putting it to the return

Whooaaa don't do any lottery or buy raffle tickets as you've used up all your luck for a decade or two
Thats if I read you correct "feed from the tank" might better be described as "return to the tank"
Title: Re: Rotten clatter!
Post by: RichardL on 11.02. 2019 19:48
I had a (maybe) similar rattle. The noise would be substantially reduced when I clamped my knees hard against the tank. Turned out to be the nut on the top head-steady bolt was contacting the tank. I've ground down the bolt length and nut thickness and all seems fine.

Richard L
Title: Re: Rotten clatter!
Post by: duTch on 11.02. 2019 20:49

 
Quote
"which way is not the wrong way"---- well its putting the feed from the tank to the feed on the crankcase and not putting it to the return *bash*

 Ooooh- a 'down there' issue... You tried to suck the oil *out* from the  return & rocker feed to supply the (air) pump..... *eek*  so, *bash* ...though maybe the oil tank had enough head to self-syphon some to the rockers (nah- only if overfilled)
     
 
Quote
Thats if I read you correct "feed from the tank" might better be described as "return to the tank"

 back to topic....

 
Title: Re: Rotten clatter!
Post by: UncleD on 11.02. 2019 20:54
Righto, as much as I think my tank is solid, I'm going to have a good look at this again. 90% of problems have the simplest causes.

But just to appease my negativity bias...
If in fact there were some fine metal splinters at the tappet of the right inlet valve (my eyes are not the best), what might cause this?  If it were just poor adjustment I would expect loud tappet noise all the time.  Could it be a problem with the valve spring?  What other indicators would be present if this were the case?
Title: Re: Rotten clatter!
Post by: RichardL on 11.02. 2019 21:52
With regard to the metal fragments, maybe take the adjuster all the way out and look at its tip to be sure the metal hasn't broken away at that point. That would probably cause some clatter. Also, it's not impossible to have simultaneous problems to add to the confusion.

Richard L.
Title: Re: Rotten clatter!
Post by: UncleD on 12.02. 2019 08:42
... it's not impossible to have simultaneous problems to add to the confusion.

Richard L.

Ain't that the truth!
Title: Re: Rotten clatter!
Post by: bsa-bill on 12.02. 2019 10:13
Quote
back to topic....

apologies - note to self, don't assume your on topic with a reply
Title: Re: Rotten clatter!
Post by: duTch on 12.02. 2019 17:19

 
Quote
Quote

    back to topic....


apologies - note to self, don't assume your on topic with a reply

  Bill-  I wasn't having a shot at you, just nipping it in the bud before it had a chance to go awry..... *beer*
Title: Re: Rotten clatter!
Post by: bsa-bill on 12.02. 2019 17:38
Quote
  Bill-  I wasn't having a shot at you, just nipping it in the bud before it had a chance to go awry

no problem Dutch, I dodge in and out the house when weather allows and don't always take as much notice as I should
Title: Re: Rotten clatter!
Post by: Scott and Jay 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....
Title: Re: Rotten clatter!
Post by: RDfella 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 ...
Title: Re: Rotten clatter!
Post by: bikerbob 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.
Title: Re: Rotten clatter!
Post by: groily 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. )
Title: Re: Rotten clatter!
Post by: UncleD on 07.03. 2019 19:37
I don't like the sound of any of this (excuse the pun).
Title: Re: Rotten clatter!
Post by: UncleD 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)?
Title: Re: Rotten clatter!
Post by: bikerbob 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.
Title: Re: Rotten clatter!
Post by: Swarfcut 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.