Tight Gearbox

[adrian.hannam]

Hello all, regarding a BA box, when I tighten the big nut on the clutch centre, the clutch centre becomes hard to turn by hand. It is free to turn when the nut is loose. The mainshaft has about 1mm endplay. The result has been that it is very hard to push the kickstart through (even without the clutch assembled) and the kickstart doesn't return by itself. I had it all apart to change the engine sprocket. I have been doing the big nut up dead tight, tight as I can with a long brace and then a couple of hits with a rattle gun. I didn't forget the thrust washer. What could be the problem? Thanks, Adrian

[paul.jameson]

Something is binding, and probably in the clutch rather than the gearbox. Have you fitted extra locking washers to the 6 bolts holding the clutch basket to the sprocket or something like that? Could the tab on the outer end of the needle roller race have moved out of its slot? Is something binding on the primary cases?

[adrian.hannam]

Thanks Paul, I will examine the clutch side first. I have been using lockwire for the 6 screws in place of a tabwasher, and no washer at all. I will try an extra thrust washer (temporary) to pack out the centre, see what results. The primary case, when tightened to the engine, sits out possibly 10mm from the frame lug at the rear. I have put a packing spacer in there. Possibly the primary case is skewed from the gearbox enough for something to rub. The basket and chainwheel seem to be ok, I can turn this by hand with centre nut tight (and spark plugs removed - 1948 KG).

[Simon.Gardiner]

... The primary case, when tightened to the engine, sits out possibly 10mm from the frame lug at the rear.

That seems a lot to me, have you got the right chaincase inner?

SG

[adrian.hannam]

Hi Simon, no I'm not sure the primary case is original. I packed out the centre by about 2mm to make sure it is not rubbing on the basket, still hard to turn with nut tightened. Sprocket/Chainwheel/Basket/Centre are not rubbing on the chaincase. I have notices that the larger splined diameter of the mainshaft is not visible, the thrust washer tab is not locating. It seems that the chain wheel is not sitting deep enough. This will give me something to investigate.

[john.davies]

I had a similar problem when putting the clutch together on my SQ4. It turned out that the faces on the back of the clutch centre where the main shaft splines butt up to it had worn allowing the centre to sit a bit further back on the main shaft and therefore rubbing on the basket. A little skimming in a lathe sorted that one out. Thanks to Paul Wirdnam who had the same problem and told me what to check.

[adrian.hannam]

I have taken the basket off, looks like not enough mainshaft is protruding? tighten the centre and mainshaft is hard to turn. That's all I have time for this week. Cases coming off again next week.

[adrian.hannam]

Did I put the chainwheel inside out? You can see the shiny bit where it looks like it has been rubbing on the primary inner case oil flinger, I think. Which side is the basket supposed to screw to?

[alan.moore]

Adrian
Flange to the outside (top pic). That's how mine is fitted, primary chain lines up spot on and clutch/gearbox are both smooth and precise.

To tighten the big nut I sandwiched an old friction plate between two old plain plates, drilled through all three and bolted them all together with three bolts. Two of the bolts are used to attach an arm (spaced out to clear the clutch basket) which is wedged against the bench. This allows the big nut to be properly tightened.

(Please ignore the schoolboy error in the attached photo...the outer chain-case needs to go on before the clutch basket is fitted.. )

Cheers
Alan

[adrian.hannam]

Thanks, Alan. That is the way I had it. The primary case doesn't fit properly. When tightened to the engine, there is a gap at the rear lug. When I tighten the centre, it presses the chainwheel against the flinger. Could be the wrong primary case, or maybe the frame is bent, or the engine crooked somehow.