The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Gearbox, Clutch, Primary => Topic started by: Peter Gee on 28.08. 2019 20:06
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Please see last post by me in this thread for my solution Sorry to revisit a dead horse... My A7SS rebuild in deepest Africa has gone very well-- and the bike as received had never been opened, so most parts were good to very good, considering. And it did not come in bits, but as a whole bike. Gearbox rebuild was a breeze, and works really well..... but for the dreaded kick start jamming.
Not sometimes!Every time!
I have followed various threads on here and Britbike. One guy recommended shaving down the first quadrant tooth a la Triumph. Others said "get a pointy ratchet pinion. Someone suggested rebushing the cast iron KS bush. Another suggested re-bushing the ratchet pinion.
Facts are simple. If they had jammed on the showroom, now a single A7/A10 would have been sold.
There must be an answer given this seems quite a common problem.
Any clues gratefully accepted as this bike is entered in a fast looming international show.
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Ist things first - the gearbox was rebuilt - maybe not such a 'breeze' after all. What new parts were fitted?
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Bearings, not bushes...all the rest seemed simply worn within tolerances, nothing graunched or sloppy. But maybe a combination of small errors?
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G'day Peter.
A worn pinion bush is mostly to blame. A worn k/start bush compounds it.
Cheers
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Although looking similar, the tooth profile of the quadrant and pinion were changed in 1955. So possible the box has been assembled with a pair of miss matched early and later parts, which differ in the tooth profile with either the so called pointy or flat topped teeth. Later quadrant is 42 3160, match with pinion 67 3376. Have a good look at the mesh and tooth profile of these parts. All standard quadrants have the leading teeth relieved to aid engagement.
Swarfy.
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Peter,
These bikes you "rebuild" for international shows, do you actually use them or are they just for shows?
I have not run into an A series gearbox that did not need a new lay shaft blind bush, and at least a good rub with an external hone to smooth out the corn cobs on the shaft itself.
I am just confused on the hows and whys of a show bike rebuild I guess. *conf*
Lee
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I actually do use them, after the show which is a competitive one....
The bush was actually in good condition so I left well alone...the box works great. I rebuild to work as good as new in all components needing it.
To finalize this bike I have had to source parts from Kenya, Sweden, the USA and Zanzibar!
I have driven her and it's my first A7SS, sweet bike is it.. really smooooooooooth and gentle.... very little vibration, gearbox nice, some leak probs but all in the Chaincase and oil tank unions... am fettling it now.... so the always jamming K/S
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On the way to solving the jammy KS, I found clues after re-opening the out GB shell and decided to blueprint everything:
* Ratchet bush 67-3169 IMO loose both on the KS mainshaft end , with is 0.750" a.n.a (as near as, since it has to push fit at least onto the KS end bearing) yet I am measuring bush ID at 0.738~41 giving between 0.0012~0.009" play
*Ratchet bush 67-3179 OD is also very loose on the ratchet, whose ID is 0.930" a.n.a. Measuring the bush OD at 0.0924 so that's 0.006" play.
Weirdly, it shows no signs of wear or grooving on the OD. Hence an important ? below
I am presuming these run a max clearance of about 0.001" on both OD and ID, giving 0.002" total? Anyone know the actual clearances of these parts?/color]
* KS Outer cover bush is in BSA factory figs (only just obtained from Dutch BSA owners club site) and ID 0.749~0.750. But my quadrant 42-3160 is 0.733~0734 on the outer (kick) end. Max 0.016" play
* KS Inner bush on factory figs is 0.561~0.563. But the smaller shaft of my KS quadrant is 0.550~0.552/ Max 0.011" play
Again, weirdly, the KS quadrant shows no signs of grooving or stepped wear at all.
Any one of these errors, maybe two of them, would not IMO lead to the dreaded "jamming" - but when added all up, they are quite something in terms of sloppy play.
Sadly BSA does not publish all sorts of figures that would help insofar as factory ODs etc...
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On the way to solving the jammy KS, I found clues after re-opening the out GB shell and decided to blueprint everything:
* Ratchet bush 67-3169 IMO loose both on the KS mainshaft end , with is 0.750" a.n.a (as near as, since it has to push fit at least onto the KS end bearing) yet I am measuring bush ID at 0.738~41 giving between 0.0012~0.009" play
*Ratchet bush 67-3179 OD is also very loose on the ratchet, whose ID is 0.930" a.n.a. Measuring the bush OD at 0.0924 so that's 0.006" play.
Weirdly, it shows no signs of wear or grooving on the OD. Hence an important ? below
I am presuming these run a max clearance of about 0.001" on both OD and ID, giving 0.002" total? Anyone know the actual clearances of these parts?/color]
* KS Outer cover bush is in BSA factory figs (only just obtained from Dutch BSA owners club site) and ID 0.749~0.750. But my quadrant 42-3160 is 0.733~0734 on the outer (kick) end. Max 0.016" play
* KS Inner bush on factory figs is 0.561~0.563. But the smaller shaft of my KS quadrant is 0.550~0.552/ Max 0.011" play
Again, weirdly, the KS quadrant shows no signs of grooving or stepped wear at all.
Any one of these errors, maybe two of them, would not IMO lead to the dreaded "jamming" - but when added all up, they are quite something in terms of sloppy play.
Sadly BSA does not publish all sorts of figures that would help insofar as factory ODs etc...
Looks to me like you've answered your own question.
You've got a total of 0.045" wear in there. ( F****D). All the bush I/D sizes will be std inch sizes ie: inner bush I/d = 9/16"(0.5625"), outer bush I/D = 3/4". The running clearance ( which will vary according to the end purpose)was set buy grinding the shafts to suit ie: 9/16" minus 0.002" = 0.5605."
Same with all the others.
Your K/S shaft is definatley worn or a P/O has played with it. IF the shaft is round the full length of the wearing surface & NOT tapered you can use it by making undersized bushes. Simple. Same goes for the K/S ratchet bush but the inner of that one needs to jus be a sliding fit on the main shaft ie: + 0.0005" ~ + 0.001". O/D - 0.002".
Hope this helps
Ironhead.
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Thanks Ironhead..I have answered my own ? finally by tracking down the info and then measuring everything carefully
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finally by tracking down the info and then measuring everything carefully
Yep.
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So it turns out a number of problems with my KS mechinism, some relevant to jamming and others not, and finally solved.
1) Ratchet gear 67-3376: My actual ratchet-gear teeth are really worn down by like a millimetre. They look rough and slightly mashed about. I thought this would prove very relevant.
2) The ratchet bronze bush 67-3169 had a lot of play both on the mainshaft and between it an the ratchet. Talking of a combined 8 thou or so.
3) The Main KS steel bush in the outer cover, a b@tch to remove involving a stout press with simultaneous heat, also had significant play on the KS shaft. It's ID should be a thou max over of the KS shaft whose factory dimensions are 0.7455~.7500, It had about 10 thou play.
3) The least play was in the blind KS smaller bush, nominal ID 0.561~563. This was about 4 thou over, but being I did not have the correct blind bush puller, I decided to deal; with items 2 & 3, whilst awaiting a new ratchet gear from UK. Assembly with new KS large bush and new ratchet pinion sleeve bush might prove the problem was solved.
This proved the following:
1) My clapped out ratchet pinion teeth, though they looked bad, did not matter.
2) Nor did the small inner kick start quadrant steel bush.
All that needed changing was the ratchet bronze bush 67-3169 and the large steel KS bush 67-3153. In fact I had custom ones made then lapped and honed them manually to close tolerances on the quadrant shaft and mainshaft and between pinion and OD of the bronze bush.
It would seem these are the two key components to carefully blueprint, and the major cause behind KS jams.
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Great! It's very satisfying to sort a problem, isn't it? *smile*
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Congrats. & very nice when one takes the time to post detailed story of work and results. Thanks.
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G'day Peter, thanks for posting.
I have found the pinion bush is the main culprit but a new one will only last so long if the other bush's aren't addressed at the same time.
A while back there was a bad batch of pinions that needed a special bush to match. I can't remember if it was big or small.
Cheers
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I know this is an old thread but I seemed to have fallen into the same trap. After recently rebuilding the gearbox I paid little attention to the kickstart. After all is is only a kickstart. All was fine when the gearbox was on the bench. Now the engine is connected nobody will be surprised that the kickstart jams.
So I have the outer gearbox cover off and can replace the the pinion bush and the outer bush on the kickstart. Without taking the inner gearbox cover off I cannot change the inner bush on the kickstart. I am struggling to get the inner cover off.
So a couple of questions
1/ Do I need to remove the gearbox from the frame to remove the inner cover?
2/ If not, is there an easy way to separate the inner cover from the body of the gearbox?
3/ Do I really need to replace the inner bush as the previous entry seems to think the pinion bush is key followed by the outer bush?
John
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G'day John.
It's been a while since I did one but it would be easier with the inner cover off but I think can be done in place with an internal puller. (pic att)
To remove the inner cover the pinion nut, pinion, bush, spring and washer comes off. The cover comes off with the bearing. It may be tight on the shaft so may need a few taps on the shaft with a hide mallet and pulling on the cover at the same time.
Cheers
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These blind bearing pullers work well for bushings and needle roller brgs the other puller is for starter motor bushings but its come in handy on other jobs
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Removed the inner cover and replaced the inner and outer bushes of the kickstart and the gear change lever. Also changed the ratchet pinion bush and the problem has dossapeared.
John