Gearbox Noise

[simon.holyfield]

This picture is merely here for looking at! The part built FH has to come off the bench to deal with another problem.

Starting up the SQ4 this afternoon I was dismayed to hear a horrendous noise. This bike has been in service all last season without missing a beat, and yet when I go to start it it tells me vociferously that it doesn't want to go out again until it's been on the new bench.

On starting, after running for 2-3 minutes it makes a harsh rattle for a few seconds; the rattle stops after a few seconds and then it will do it again. This is intermittent and irregular. Initially I thought perhaps I had partly put it in gear - it sounds like poorly engaged dogs; the gears select nicely in both directions (the selector spring box is relatively new).

I wondered about timing chain, but this sounds more like it's coming from the gearbox, though I'm sure it's from the timing side. Another option might be the kickstart ratchet? Moving the rear wheel, it rather feels like the gearbox sprocket is loose, so perhaps the mainshaft nut is backing off.

It will go on the bench in the next few days, but if this sounds familiar to anyone, I'd love to hear from you!

[Mick D]

Hi Simon

It sounds, (sic), like it could be due to an increase in temperature, possibly gearbox oil warming up, does pulling in the clutch have any effect on the noise? Have you tried the 'stethoscope' test with a long screwdriver?

Regards Mick

[paul.jameson]

My money (but not a lot of it) is on the gearbox grease being stiff due to colder weather. Add an egg cup full of gear oil to the box and see if that makes a difference before you go taking things apart. (I am assuming that you have a BA gearbox, not a GB type).

[simon.holyfield]

A bit more diagnosis suggests Paul Jameson's comment regarding cold gearbox grease my be pertinent. At 28 seconds, into the video (link below) you can hear the noise I'm talking about - which is very similar to the noise you get when going into gear. It sounds like the dogs spinning against each other, and doesn't appear when it's in gear.

I fancy it reduces as the gearbox warms; I haven't added any extra oil yet, but I will.

My clutch is dragging a bit, but the noise diminishes to nothing when you pull the clutch in, as the mainshaft slows. I have a new AOMCC clutch centre ready to fit, as the splines are not brilliant.

VID_20240108_115907.mp4

(172.22 MiB) Downloaded 70 times

[will_curry]

I wonder how much end float there is on the gearbox mainshaft?

When you pull the clutch in not only will the mainshaft tend to slow down
it will also be pushed over to the drive side as far as the endfloat will
allow.

[simon.holyfield]

I wonder how much end float there is on the gearbox mainshaft?

When you pull the clutch in not only will the mainshaft tend to slow down
it will also be pushed over to the drive side as far as the endfloat will
allow.

Good question. I'll have a look when I get it on the bench.

Thanks Will.

[Mick D]

Hi Simon

Further thoughts based on your findings:

The noise reducing to zero as the main shaft slows when the clutch is pulled in suggests contacts either from the clutch or the gearbox, (have you tried putting a screwdriver onto them and your ear on the handle / can you identify the source?

The noise becoming apparent after a short while suggests it's facilitated by the grease thinning, adding oil will, in my opinion, render the issue more prevalent, though that may help diagnosis.

If the source is collisions at the drive dogs the cause is misalignment of the dogs, probable causes: excessive float on the main, lay or selector shaft, wear or 'sticktion' in the selector mechanism. The noise reducing as the main shaft slows tends to suggest it's not float in the main shaft, (easy to confirm by removing the dome and giving the clutch a wiggle).

I think my money would be on the selector mechanism.

Good luck Mick

[simon.holyfield]

Thanks for your reply Mick.

The screwdriver test suggests gearbox - you can really hear it from the timing said. I've not been inside the gearbox for a number of years, probably 6-7, though I've had the clutch apart in the last six months.

Bearing in mind that I have a GB to rebuild as well, do we have a handy source of tolerances for the various bearings and end floats in the gearbox? I've not been able to pin that down though I think Waller has the data scattered about. I might have to write something!

[paul.jameson]

Mick. My gearbox started being noisy one cold winter's day. Addition of the egg cup full of gear oil solved the problem for the rest of the time I used that gearbox. Hence my suggestion but it may well be worthless when tried in this case.
Simes. If you talk to AOMCC gearbox spares I suspect you will find he can tell you what you need to know if you can't find it in Waller.

[JohnnyBeckett]

hi. if the oil and grease is old in the gearbox i find the grease drys out , i use a oil/grease that's is used in the land rover axles it comes in a plastic tube /bag and it is easy to squeeze into the gearbox