Burman B52 moving backwards

[56G80S]

As part of my prep for the IJR Luxembourg I've been going over the Matchless. I posted on the IJR 2024 thread about adjusting chains. I went for a shortish run out, 10-12 miles, earlier this afternoon just to be sure that all was well.

On return I noticed that the gear change had got clonky and thought about the primary being possibly being too tight. On inspection it was really quite tight despite me leaving it in a very slightly slack position as, from experience, I anticipated a little backwards movement.

I recall that the instructions I remember on this job included easing the bottom pivot nuts and retightening them but I never do this as there's no way to get to them With the AMC box in place I used to use both the "between the engine plates" mechanism and a version of the Burman set up but then back in the day I was pulling a sidecar.

I also. having used the Search and seeing a pic from Spriddler, realise that I fitted the adjuster in the right place but with the positions reversed but don't see how that would make a difference although I will swap round so the two adjusting nuts are at the rear and not the front, as I have them. Perhaps the torsion/compression factor makes a difference.

Cheers

Johnny B

[bjork]

The rear chain will tend to pull the gearbox back, if the box is able to move. It's best to load the gearbox/primary chain adjuster so that it is pushing the box forward, rather than set the box position and tighten the top fixing then finally lock the adjuster.
Use the adjuster to first pull the primary chain tight, then the same adjuster to push it forward till the correct slack is achieved, then tighten things up. Basically the lower pivot bolt and the top mounting bolt will not keep the box from moving, no matter how tight you wellie them up. The adjuster has to be used as a hard stop to avoid the box being pulled back.

[SPRIDDLER]

A propos of nothing in particular, John.........
I long wondered how it was that the primary chain could be of lighter construction than the secondary chain when they both transmit the same power. I happened to mention it to Thrifty Peter (who is a professional in matters of engineering physics) and it's because the primary chain travels faster than the secondary chain, therefore it's handling less torque than the secondary chain, which is why the gearbox tends to be pulled back by the secondary chain rather than forward by the primary chain.
But I expect everyone else knew that already.

[56G80S]

Thanks, Bjork (and Sprid).

Back when I got the G80S it had an AMC box but no adjuster. The primary remained in place somehow but when I fitted a sidecar I also fitted the correct "between the plates" adjuster plus, on advice, an "outside the plates" adjuster like the Burman one. This remained the case after the sidecar was removed, I had acquired the GB/B52 together with other parts and refurbished it and fitted it plus an adjuster. After a couple of amendments the primary chain was fine for a few thousand miles before I had the engine out and put the AMC back in because it was slicker. It was also tired. So later, the Burman went back in.

I'll just have to keep an eye on it, but on a short run out Wednesday there was no movement. The plus element is that there appears to be no tight spot at all in the chain run.

Thanks again

Johnny B

[limeyrob]

The rear chain is up to 4x (very roughly) the tension of the primary, especially pulling a chair in first. When I had an outfit I would leave the gearbox bolts half tight then force the box forward on the adjuster before fully tightening. This was a BSA but the set up was not dissimilar.