Author Topic: A7 Timing case noises  (Read 195 times)

Offline Degsy

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A7 Timing case noises
« on: 05.08. 2022 16:29 »
Hi Folks

I recently completed the rebuild on the derelict BSA A7 Bobber I bought last year, but I noticed a whirring and knocking/clacking sound when it was idling and having bought the bike as a non runner, I am not familiar with how a BSA A7 should sound, the bike starts first kick and idles fine, so I ignored it at first but it is definitely not normal. 
Putting my hand on the engine I can feel it’s coming from the timing cover, not the barrel or cylinder head.

I need to take the timing cover off and hopefully the problem will be revealed and not too serious.

Degsy

……………………

Degsy
Scare yourself with a listening stick on the magneto drive end. Worn ATD units rattle and clank at low revs, so a good place to start. Missing cork washer under dynamo drive gear will allow float on the idler gear shaft. Cam should have next to no float. Dynamo chain also needs to be set up OK. Too loose and it machines away the inner timing cover.
Swarfy
…………………………


Swarfy – Thanks for the comments.
The bike has an Alton alternator conversion with a belt drive and removing the outer cover revealed black dust from belt wear on the lower non tension side of the belt somehow after just a few miles it has worn a small groove in the inner cover screw boss on the casting and the belt was showing clear signs of wear.  So I can only assume it was not tight enough, but at least that explains the whirring sound.

So what is causing the knocking?  The magneto is an electronic ignition conversion and the ATD unit is tack welded closed, so it can’t be that.

I have removed the inner timing case cover and turning the engine over on the kick start gives two distinct clicks quite close together and then it repeats after a gap as the engine is turned.

If I hold the smooth taper of the idler gear while turning the engine over I can feel the clicks coming through the timing gears.  Using a listening stick it sounds like the clicks/knocks are coming from the camshaft area.

There is about 0.7mm end float on the idler gear and I can’t detect any end float on the camshaft.  The teeth on all of the timing gears look OK and I can only just feel a very small amount of backlash in the gears.

I noticed in another older thread that Musky and Swarfy say “these bikes all make some noise from the timing gears”.  I must admit I did not notice anything on a brief ride up the road, but the knocking is distinct when idling.

I am glad it looks like it is nothing to do with the crank, given the errors I have found on this bike during my rebuild I feared the worse, the bike has been a strange combination of thoughtful upgrades and serious mistakes from its previous rebuild, one of which relates to the needle roller conversion.  I will tell the story at some length on this forum when I get the time.

A sticky Cam Follower? I do not fancy stripping everything down to access the camshaft and followers just to check.

Depending on your comments my inclination is to put things back together and just run it while keeping a close eye on things, if it goes wrong well at least that will reveal the problem.

Cheers
Degsy


Online Rex

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Re: A7 Timing case noises
« Reply #1 on: 05.08. 2022 18:10 »
I have removed the inner timing case cover and turning the engine over on the kick start gives two distinct clicks quite close together and then it repeats after a gap as the engine is turned.
Cheers
Degsy

Sure it's not just the valves clicking closed again?

Online slighthitchmitch

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Re: A7 Timing case noises
« Reply #2 on: 05.08. 2022 19:24 »
I helped someone out with a similar problem once, he had a knock sound on a swing arm motor.
This may or may not apply to your engine, I don't know how plungers differ from later ones.

The sound in a nutshell, was one of the front primary chaincase screws clipping the flywheel web as it turned because they screw into the crankcase and only stop just in front of it.
Unscrewing then one at a time found the culprit and a short term fix was a washer underneath but obviously it needed filing down a fraction.
Worth a try and no dismantling required for the front bolts.  You also have screws inside the chaincase to try as well if it's not them.

Could be? Who knows, not me that's for sure. *smile*  Good luck, whatever it is.

P.S. I notice you have allen screw bolts, they are notorious for being slightly the wrong length, that is what caused the blokes problem.
Portugal 54 GF, 48 B31, 72 A65T

Offline muskrat

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Re: A7 Timing case noises
« Reply #3 on: 05.08. 2022 20:52 »
G'day Degsy.
The click clack is more than likely backlash in the timing gears as I've described in other posts. Sticky lifters or valves can make it worse.

I have belt drive on both my dynamos  and had the same problem with the belts contacting the screw boss (previously damaged by a loose chain). My remedy was to cut off the boss and use a countersunk screw  *work*
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '78 XT500, '83 CB1100F, '83 GS850, 88 HD FXST .
Australia
Muskys Plunger A7

Offline orabanda

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Re: A7 Timing case noises
« Reply #4 on: 06.08. 2022 00:44 »
Also, check the tappet clearances.

Offline Degsy

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Re: A7 Timing case noises
« Reply #5 on: 06.08. 2022 15:38 »
Hi Guys

As usual great advise from you all.

Yeah noisy tappet was my first thought and I did the tappets again, but no difference.

Muskrat – Interesting you had the same problem with the belt drive, I thought I had the tension about right, I’ll try a bit tighter but I don’t want to overload the idler bearing.  If the noise persists I’ll get the Dremel out and do a bit of grinding as per your solution.

Mitch – Would never have thought of the primary case screws as the problem, you did well to solve that one.  Easy to check so I’ll have a look.

My gut feeling is it is something to do with the backlash in gears, sticky lifter and valves sequence, this engine has had less than an hour of running since I put it back together, so things might improve on running in.

The back story is that the engine was seized when I got it, due to part failure of the oil flow (a story for another time) so the piston was seized in the cylinder which is probably just as well, because on removal, both small end and big end bearings looked like they were going to fail in a big way, if the piston and barrel had not decided it's too hot and called a halt to things.

I replaced big end and small end bearings new pistons for a newly +60 rebored and unused barrel I by chance found locally.  I gently reground the valves onto their seats but reused them the guides and followers.  The followers were transferred over from the old barrel and I was concerned they might be a bit sticky, especially given those awful aluminium pushrods which I thought at first might be some homemade bodge until I checked. 

I probably should have renewed all the valve gear, given how much other work I’ve done on the bike, but I can easily do this at a later stage and I just wanted to get the bike up and running.

Cheers

Degsy

Online Joolstacho

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Re: A7 Timing case noises
« Reply #6 on: 07.08. 2022 00:50 »
I wonder if it could be a/the cam follower/s bottoming out on the locating screws (at the rear base of the cylinder).