G: Gearbox (Single - Burman) Burman Box Again

brian gains

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Reassembled box and on selection of 1st it can be graunchy once engaged and not all the time, which is rather frustrating as at least a consistent issue can be dealt with.
What does happen is that once 1st is engaged the drive can be a little snatchy and only in first,

Can the internal gear on the layshaft be installed accidentally the wrong way around?

How crucial is the spring compression on the selector layshaftshaft pawl?

Does the issue sound consistent with not having the 'O' indicator marks on the selector layshaft and toothed selector quadrant incorrectly aligned?
 

chankly bore

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If you are getting all gears then the selector shaft is probably correctly aligned, (9 o'clock with gearbox vertical). All meshing gears add up to 54 teeth, so layshaft from kickstart end is 24 teeth, 34, sliding dog, 28 and 21 teeth. Note that the splines for the last mentioned 21 tooth gear are wider than the other end of the shaft. The sliding dog cannot mesh any other way because the fit of everything is determined by the 33 tooth output gear which is fitted first. Snatchy drive can also be caused by the outer clutch plate lifting beyond the drum slots. You may be able to cure this by fitting a thicker plain plate outermost, or fitting one less pair of plates until they bed in a bit. The spring pressure on the selector pawl is not critical.
 
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brian gains

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MartynG ; good to highlight those vid's, tremendously useful in orienting yourself around the box but needless to say on the assembly / dissembly vid' to take note teeth numbers are different on Comet application.
Chankly B'; so if all the gears are there all be it with an issue for 1st and allowing that nothing is bent internally , missing teeth etc it would be reasonable to turn to the clutch and I'm thinking that the amount of torque when pulling away in 1st is significant?.
I;ve run the clutch with no issues previously so am thinking have I assembled it incorrectly. There are two washers either side of the clutch rollers a thick and a thin with the thick one at the rear so there may be a possibility these have been misplaced. Al;so the clutch plates, I'm sure the last one in against the pressure plate was a plain one could this be incorrect? I think I'll review Richardson's then go back into the clutch to check things out.
 

chankly bore

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The first and last plates must be plain ones, but if the outermost is a thick one then there's less chance of the outermost friction plate going too far out and clearing the slots. It is a matter of transposing plates to achieve this state. Thicker washer innermost and rollers must be 6mm. wide not 1/4" of course. Check the plain plates for flatness and get the glaze off all plates. Some owners report that A.T.F. causes less "stiction" than engine grade oil in the primary. Lack of use is also a problem nowadays!
 

Martyn Goodwin

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Interesting information about the effect of ATF on clutch plates


Summary - DON'T!
 

Martyn Goodwin

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When assembling a burman BAP box as fitted to a Comet should the 3rd gear 24BA (which is free to revolve on the mainshaft) be pulled up hard and tight against the inner race of the small bearing by the kick start mech and the nut 70X on the other side of the inner cover?

I ask because I suspect that with my recent rebuild that the face of 24BA is JUST making contact with the inside of the inner cover when all is done up tight.

I have fitted a slightly thicker gasket (0.030") between the gearbox case and the inner cover but logic tells me that I should be looking at a shim twixt 24BA and the small bearing as this seems to be the only way to increase the clearance between 24BA and the inside of the inner cover??

Surprise is that the std METRIC wheel bearing shims are a great fit if needed.

Ta Martyn
Burman Pic.jpg
 

greg brillus

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Third gear should not be pulled hard up against the bearing, the input mianshaft should have some end float when all assembled, regardless of the thickness of the inner cover gasket used. Yes the wheel axle shims work ok in the area behind the starter ratchet.
 

chankly bore

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Metric wheel bearing shims are 20 mm. i.d. as is 6304 bearing on mainshaft. I've not tried standard wheel bearing shims, (nominally 3/4" i.d.), but they may well be a little tight. Suck it and see!
 

brian gains

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I have end float in the main shaft so 3rd 24T must be free to revolve freely. However on the last rebuild the gear cam shaft did not have the 0.002" end float and did not revolve so I fitted a 0.030" for this reason where as when I had stripped down initiallt there was no inner case gasket at all.

However it should be noted that inner cam steel bush had worn considerably and the PO had shimmed out with hardened? washers and no doubt also omitted the gasket to take up end play. This all being negated by the newly machined inner steel bush, it is worth remarking that there is notable hydraulic damping when the gear cam shaft is pushed into the steel bush and this has to be compressed to bleed out trapped air.

Reading around the issue and taking advice here I shall check the plain plates for flatness, all measure at approx' 0.06" thickness. The fibre plates are all approx 0.17" thick and I shall check for flatness, scrub up on coarse sandpaper and clean with petrol or acetone. If this doesn't cure the issue I see a big spend and m/c off the road for foreseeable future 8-(
 
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