Author Topic: Crunchy nut cluster  (Read 856 times)

Offline Rusty nuts

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Crunchy nut cluster
« on: 16.07. 2009 10:55 »
Following on from Zitmans Bsa gearbox problem posted in May, some of you with early gearboxes may find the following useful.
Engineers, look away now!

 Thirty miles after rebuild of my 49 A7 plunger on the way back from  MOT, 4th gear goes "walkabout," acquires occasional gnashing neutral & downshifts are a bit too crunchy unless revs way low.

Next day after two miles fourth is back from walkabout but then obviously decides it forgot something & disappears again a few miles later!

 Gearbox was stripped on rebuild, fitted new bearings whilst it was apart & everything looked in good nick, but then it was the first gearbox I've ever looked at!

I have two extra gearboxes which came with my box of bits so plenty of other worn parts to play with!

First removed inner casing & jiggled it all about (as you do), examined selector arm claw & camplate which looked OK, offered it all back up & bingo 4 gears.
Feeling very pleased with myself went of to have lunch.

Return from lunch insert gasket, offer up & no gears! More fiddling & back to three gears

Notice one selector return spring is weaker than other one so pull spare box & use best one from that.
Better more positive shift but 4th is still occasionally otherwise engaged.
Notice spare box inner case mainshaft bearing has two shims fitted inside bearing housing, selector claw looks  marginally better
so offer up & bingo, four gears.
Would have to destroy shims to remove bearing & drive out claw pin so dunk whole inner in paraffin, bearing seems ok, clean up exterior & fit.

Gaskets are completely shot now, so lots of blue hylomar!
Outer case on, fill with oil, fire her up, kickstart return spring slipped or snapped on second kick!!!  tie up kickstart & go for a run.
 Much sweeter changes, all four gears present, downshift is noticebly smoother.

So sorted, in this case would surmise was mainshaft end float, but I suspect  60 years general wear of box  & all selector parts probably contributed!  
Changing selector claw (although visually same) definately helped &  changing return spring gives a much more postive return.

Not a very scientific approach but got there in the end!

Off to pull the outer cover & fix kickstart return spring now. Fun, fun, fun!

Wondering whether to investigate slight whine in 3rd at high revs but think will leave that for the winter & just change up earlier now that fourth has returned.

1949 A7 Plunger
1947 A7 Rigid Star Twin
1969 Triumph T120R
1972 Triumph T120V

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Re: Crunchy nut cluster
« Reply #1 on: 16.07. 2009 13:09 »
G'day Rusty, my '51 A7 has similar problems.I have trouble going up to 3rd and sometimes 4th. I found the claw had chips out of one side of claw. Replaced it and a bit better shifts but would miss now and then. I found by omitting the gasket between the main case and inner cover rectified the problem. I would think the teeth on the camplate are worn as well.
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Muskys Plunger A7