Gearbox Noise

[Mick D]

Hi Simon

I think I would concentrate on the free movement and correct centring of the selector shaft, something causing the shaft to not centre and thus biasing the mechanism resulting in interference, (weak spring, gummy pivot etc.).

Regards Mick

[simon.holyfield]

There's probably 0.5 mm of longitudinal movement in each of the selectors. Some of it comes from here:

There's no perceptible movement in either of the ball bearings. They've only done 5000 miles.

Fifteen minutes work with various micrometers revealed this:

• Layshaft 2nd bush 1.061” gear 1.065” 4 thou

• Layshaft 1st bush 1.062” gear 1.0653” 3.3 thou

• Mainshaft 3rd shaft 0.786” gear 0.788” 2 thou

• Mainshaft sleeve shaft outer 0.931” 0.940” 9 thou

• Mainshaft sleeve shaft inner 0.928” bush 0.941” 13 thou

I'd say the clearances are all OK apart from the sleeve gear?

[Mick D]

Hi Simon

I'd replace the sleeve gear bushes as a matter of course if only to reduce oil passage. Not sure how to rationalise near zero axial on the mainshaft small bearing and 0.040" end float on the shaft, was the clamping to the bearing inner removed when measured?

Replacing the dowels would be a 'no brainer' followed by careful inspection of the selector assembly during re-build.

Regards Mick

[simon.holyfield]

Not sure how to rationalise near zero axial on the mainshaft small bearing and 0.040" end float on the shaft, was the clamping to the bearing inner removed when measured?

No - I hadn't dismantled anything bar the clutch at that point. I'll put the mainshaft back in without the rest of the cluster and have a look - it should be a bit more obvious without grease everywhere.

[simon.holyfield]

Here's the mainshaft end float Mick, you can see the gap under the nut.

Light bulb moment - the mainshaft doesn't pull up against the bearing, because the end float is needed to allow mainshaft third to spin.

[Mick D]

Hi Simon

Are you sure? that would mean the shaft was free to rotate in the bearing inner. I've not refurbished a BAP gearbox before but what is the function of PN 3118-48 pg 53 of the Draganfly catalogue?

Regards Mick

[paul.jameson]

2 questions:
Has the nut on the kickstart end of the mainshaft got a large internal chamfer on the side which should abut the kickstart ratchet?
Is the mainshaft bent?

[simon.holyfield]

2 questions:
Has the nut on the kickstart end of the mainshaft got a large internal chamfer on the side which should abut the kickstart ratchet?

No. There's a small chamfer, sufficient to clear the bottom of the thread on the shaft. I'll turn a shallow depression there, 0.5 mm deep, to reduce the end float a touch.

Is the mainshaft bent?

Don't know yet - there's a dead generator preventing me getting to the lathe! Anyone want a 25cc engine with a dead alternator attached? Auxiliary Power Unit for the SQ4 perhaps, or has Bennet cornered that market?

[simon.holyfield]

I'm on the home straight with my SQ4 gearbox now. In what may be the second to last trial assembly, I have 1.11 movement on the sleeve gear, gearbox in top, sprocket not tightened up. I'm now ready to make the spacer to move the sleeve gear inboard. I've currently got 2/3 of the sleeve gear spline length engaged with the mainshaft sliding gear splines, and can improve that a bit

What's a good number to aim at?

[nevhunter]

That sprocket seems to have been running too far out from the gearbox case. Is the big race in the correct position in the case? Nev