Self-adjusting primary chain!

[Lindsay S]

A subject that I see has cropped up in previous postings but I am sure it doesn’t hurt to mention it again!
I adjusted the chains on my on my ‘58 Flash and in ignorance, left the well worn gearbox adjuster in a position where it wouldn’t allow the primary chain to go slack. What I didn’t count on was the rear chain pulling the gearbox backwards despite the two gearbox bolts being done up good and tight!
The result; after a short test ride I re-checked the primary chain to find that you could practically play a tune on it whilst the rear chain was like a skipping-rope!
The temporary solution was to leave the adjuster in a position where it was, in effect, ‘pushing’ the gearbox forward so that it couldn’t be pulled back.
Ultimately, the real solution was to replace both the adjusting nut and the adjusting lug that attaches to the gearbox plate (part numbers 15-5664 and 275705 respectively), both of which I was glad to find available from Draganfly. Expensive little bits but the ones I received were a precision fit together, allowing absolutely no movement fore and aft on the gearbox when fitted.
I was quite amazed at the difference that about a sixteenth of an inch of slop in the adjuster could make to the front and rear chains but I suppose I shouldn’t be!

[Swarfcut]

  Yes, this has been mentioned before, in that the box is positioned as usual  by moving it backwards and forwards, but that adjuster is better set to prevent the box moving backwards, after the top and bottom mountings have been tightened.

 Treat it as a backstop, rather than an adjuster.  Could easily add another to the other side, belt'n braces.

 Swarfy.

[limeyrob]

Exactly.  The tension in the rear chain is never less than double that in the primary and often a lot more so the force is always to pull the box back.  The trick is to get it right, do the box studs up then tighten the adjuster hard forward and then lock it.

[Lindsay S]

Good to get rid of the knackered old adjuster I had though!

[Colsbeeza]

The BSA Manual describes the procedure attached. I found this out the hard way in 1969 with my A7 after the chaincase burnt my leg. The primary chain was red hot and stuffed, and I had to get a new chain and clutch chainwheel.
Col