Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board BSA A65 Rocket Gearbox

Hi all

Just rebuilt the bike over winter to clean out sludge trap, crank reground and new bush and main bearings. When putting the gearbox back, shimmed it to get the just perceivable movement on the lay shaft, confirming with a DTI gauge . When running it goes in and out of the gears fine, however when selecting up, there is a slight ratcheting sound in all gears. Resigned to the fact that I’ll have to strip it down again, but could this be due to too much shimming - the gap about 0.07 mm?

Its more likely that the clutch is not freeing properly, or another thing to check is the mainshaft nut, shim, and spring in the kickstarter mech, if the nut is loose, or the spacer shim is left out of the rachet you may get funny noises. Presumably going down the box is fine? 0.07mm = 0.0028 ", which is pretty much spot on for the nominal 3 thou.

dont u mean MAIN SHAFT not layshaft ?

if is shifting fine what is the problem? its not a Honda

The complete clutch is new so sticks a little. Will look at the kick start. The problem only occurs when the bike is moving and when selecting up, for example, when in 4 gear and continue to select up the ratchet sound is there.

Unfortunately I’m an ex fast jet tech and as such the machine needs to be spot on. There was no noise before I stripped the engine down completely. If there is an unusual noise then things are not right and could lead to failure of a key component.

Check your chain runs, maybe the final drive chain is rattling off something when unloaded

Ratcheting continuously as the lever is held up or just during transition? If continuous, rev the engine to determine if it is engine speed related or road speed.
Does this engine have the speedometer drive off the layshaft?

It’s all assumption until it’s either been gone through again or more description is given.

With the shims, did you note that you have the one with a thickness of .113” -.115” on the trapdoor side?

If you’ve only done a couple of miles it might not show up, but I would look at the cam selector plate wear, and ensure that the plunger isn’t digging in (though I don’t think this would give an audible noise) but check also that the selector forks haven’t got hot and started turning blue. If they have then there is too much loading against them.

There could also be nothing wrong with the box and your hearing the same noise the rest of us hear, an oil additive (I used to use Lucas oil, which made for a very slick and quiet box) or louder exhaust silencer will also work. 😉

Well mystery solved and how embarrassing. The gear lever was higher than normal, resulting in the heel of my boot pushing down on the kickstart causing the noise every time I selected up a gear. Just goes to show, the simplest of solutions are sometimes the answer. Gear box now silky smooth.

Yes, when we are testing an expensive re-build for the first time, anxiety can over-ride rational thought when unexpected noises are heard!

Glad to know it's just that, you will now sleep with a smile on your face tonight.

That’s so true, my hearing isn’t great and I do have some issues but when it comes to BSA’s I seem to be able to fine tune it and hear everything that I would rather not hear…. Especially as you say on a new build etc.

that sure would have made enough noise to warrant a look ... My apologies for thinking OMG non issue . Glad u found the problem before it was in bits hahahah