BSA A10 primary chain tensioning

[Davidohyeah]

Gents,
I have been trying to tension the primary chain on my Swinging arm A10.
Now for some reason the tension changes when the chain/engine is in different positions,
is this normal?
The doesn't sem to be anyting obviously out of line, and I checked sprokect alignment before
installing the chain.
I plan to put a dial gauge on the crank and clutch basket to see if anything is untoward, but
as you know It is difficult to hold a dial gauge (even with a magnetic base stand) still enough
to tell me anything useful.
regards
David

[mugwump]

Its quite normal, as the sprockets are not perfectly concentric. When tensioning the chain ( same applies to the rear chain ) set the tension when the chain is at its tightest spot. When setting the primary chain tension you need to re-check the rear chain tension too .

[chaterlea25]

Hi,
If you pull in the clutch and operate the kickstart, does the chain tension change as the gearbox rotates?
I have seen more than a few bent gearbox shafts

John

[Davidohyeah]

Thanks Gents, Much appreciated. I 'm pretty sure nothing is bent. I've rebuilt the gearbox with new bearings, I'm reasonably confident nothing is bent.

[duTch]

 I have a similar thing with my Plunger A10, suspected bent mainshaft but  checked it out and seems as ok as it'll ever be 

[chaterlea25]

Hi,

I 'm pretty sure nothing is bent

A couple of thou bend on the mainshaft will cause a noticable difference in chain tension
The gearbox will still assemble  easily when the outer end has a bit of run out
DAHIK

John

[Davidohyeah]

Dear Chaterlea25,
I intend to try and determine what if anything is bent using a dial gauge, but I'm finding it difficult to hold the bike, and gauge
still enough to get anything sensible to astablish anything.
I've spoken to a couple of seasoned A10 owners (if you interested Facebook BSA singles and Twins), all of them describe 'a tight spot'
I think you are correct that it would only take the tinyest of differences in concentricness to make a massive difference to the chain.
I think when you consider the 'bracketry' between gearbox and engine, I think it would be lucky if it was perfect.
Currently I have something approaching a 'best average'. I'm going to run her up gently and observe through the inspection cover and deside my next move from there.
Many thanks for your help.
Regards
David

[mikeb]

I'm finding it difficult to hold the bike, and gauge still enough to get anything sensible to astablish anything.

have you got one of those magnetic holders for the dial gauge? like this: http://www.ebay.com/itm/Adjustable-Magnetic-Base-Stand-Holder-for-Digital-Level-Dial-Test-Indicator-Tool-/161373121941
even one of those cheap ones can stick quite firmly to something (even steel bar on a clamp to footpeg) and make the measuring job quite easy

[chaterlea25]

HI David,
I get a piece of flat steel and drill a couple of holes in it  that correspond to holes in the inner case
Or clamp a piece of flat or angle to a convenient part of the bike

John

[atkin]

 Worn sprockets and a new chain can cause tight spots .