Author Topic: GEARBOX PROBLEM!!  (Read 7069 times)

Offline unclemeat

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GEARBOX PROBLEM!!
« on: 28.06. 2007 19:21 »
Howdi folks,

I'm having problems selecting first gear on my STD plunger A10 gearbox, and when i can select, it jumps out under initial acceleration. The cam-plate plunger is ok and at the correct compression. The dogs seem ok with maybe just a little wear.

Any suggestions ?
BSA A10 GOLDEN FLASH 1954
CHANG JIANG COMBO 1968
TRIUMPH THRUXTON 2007

Offline unclemeat

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Re: GEARBOX PROBLEM!!
« Reply #1 on: 28.06. 2007 20:07 »
just had a thought...

I wonder if i'v got the ratchet spacer and the first gear lay-shaft spacer mixed up. They are different thicknesses.

Does anyone know the thickness of the layshaft spacer ?
BSA A10 GOLDEN FLASH 1954
CHANG JIANG COMBO 1968
TRIUMPH THRUXTON 2007

Offline dpaddock

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Re: GEARBOX PROBLEM!!
« Reply #2 on: 29.06. 2007 00:13 »
OK, here goes:
   According to the late John Gardner, Tech Officer of the GSOC UK, "There are four large hardened washers . . . , three on the layshaft and one behind the kickstart ratchet pinion bush . . .Unfortunately, the BSA Spares List illustration [Plate 5, A Group Plunger] does not show clearly the correct assembly.
   Working from the clutch end of the gearbox, the washers should be assembled on the layshaft in the following positions.
   Part number 42-3078 is fitted between the main gearbox shell and the layshaft fixed gear 'B'.
   Part number 67-3203 is fitted between the 'F' and 'H' gears.
   Part number 42-3079 is fitted between the 'H' gear and the middle cover.
   Part number 67-3161 is fitted behind the kickstart ratchet pinion bush."

The "Layshaft Thrust Washer", p/n 67-3203, located between the 'F' and 'H' gears, has the following dimensions;
     .093" (.115 ") thickness*;
     1.093" (1.248") O.D*.;
     3/4" I.D.
*The difference between the two numbers show the practical tolerance that I've experienced. The first number is John Gardner's, the other is what I have in my A-10 and/or Gold Star boxes.

   John goes on to say "Pay particular attention to the washer part number 67-3203 which is also used on the gearboxes fitted with bronze layshaft bushes. The bore of the washer often . . . has a chamfer on one side only. If this is the case, the washer must go onto the layshaft with the chamfer against the spline, to give clearance for the small radius on the shaft at the start of the spline."
   I hope this helps you, uncle.
David
'57 Spitfire


Offline unclemeat

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Re: GEARBOX PROBLEM!!
« Reply #3 on: 30.06. 2007 14:08 »
Thanks very much for that...very helpful. *smile*

Hope to have another look inside the box today...

watch this space
BSA A10 GOLDEN FLASH 1954
CHANG JIANG COMBO 1968
TRIUMPH THRUXTON 2007

Offline unclemeat

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Re: GEARBOX PROBLEM!!
« Reply #4 on: 30.06. 2007 17:29 »
Well, had another look and the layshaft spacer 67-3203 was correct but the chamfer facing the wrong way round.
Now facing the correct way round (with chamfer facing splines) 1st gear has improved; it doesn't jump out anymore. However, I still have problems selecting 1st. Almost impossible stationary, possible when rolling to a halt. Very frustrating !

(my spacer is t=0,093")

I wonder if one of those roller cam-plate plungers would improve things. Still, the original should work ok?.
The clutch is set up just fine so it cant be that department.

My selector forks have little rollers that fit to the cam plate. Maybe swapping for the normal stud type might change things?
BSA A10 GOLDEN FLASH 1954
CHANG JIANG COMBO 1968
TRIUMPH THRUXTON 2007

Offline dpaddock

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Re: GEARBOX PROBLEM!!
« Reply #5 on: 05.07. 2007 19:22 »
If your problem is selecting NEUTRAL with engine running whilst stopped, it certainly sounds like your clutch is dragging. It's a common problem with all wet clutches, so don't feel poorly about how "fine" you set it.

If you can't select first gear, then your clutch is REALLY dragging.

You can select all gears, yes?
David
'57 Spitfire


Offline unclemeat

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Re: GEARBOX PROBLEM!!
« Reply #6 on: 07.07. 2007 09:53 »
Totally agree with your comments, however...no clutch drag whatsoever.

The problem has now been solved albeit, taking much more work than anticipated.

Leaving the gearbox bolted to the engine and in the frame, i removed the clutch and primary drive. Then removed all gearbox internals including the mainshaft but leaving the drive gear with chain sprocket attached.

When i initially assembled the gearbox i noticed that the gears were the very early type with pointed triangular shaped dogs. These early gears cannot be swapped and changed with later variants as the selector lips are at a different distance from the gear. Not to mention the selector forks are also different : early ones seem to have a rib for strength but the later ones dont, and if you try to use an early fork with later gears - they hit !
I had a box with gearbox spares and after laying it all out, i managed to create a complete spare of the later variety. At first i was a bit nervous using this cluster with the early drive gear still in the gearbox but after looking closely i saw no reason why it wouldnt work.
Conclusion...perfect !!! it runs really smooth, good clean changes, no problem selecting gears at all.
Still cant work out why the original setup was not so good, maybe because it was the early design? it was improved on a number of times by BSA afterall.
Seems like the A10 gearbox could have a whole forum to itself!
If i get myself in gear i'll post some pics for ref.
thanks for the help.
BSA A10 GOLDEN FLASH 1954
CHANG JIANG COMBO 1968
TRIUMPH THRUXTON 2007

Offline dpaddock

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Re: GEARBOX PROBLEM!!
« Reply #7 on: 08.07. 2007 02:32 »
Wonderful! Those who toil in the A-17/10 vineyards are to be revered and will have their due reward! Many thanks for your work in this matter.
David
'57 Spitfire


Online bsa-bill

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Re: GEARBOX PROBLEM!!
« Reply #8 on: 08.07. 2007 09:19 »

Now I just got to have one of those A17s   *smile*

All the best - Bill
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline dpaddock

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Re: GEARBOX PROBLEM!!
« Reply #9 on: 08.07. 2007 20:59 »
There's a couple advertised on Ebay . . .
David
'57 Spitfire


Online groily

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Re: GEARBOX PROBLEM!!
« Reply #10 on: 03.09. 2007 08:53 »
While you knowledgeable folk are thinking gearboxes and their little idiosyncrasies, can I ask a new Q? Just back from a brief frolic in the UK from France where I live, and something of a struggle it was to make it home .  . owing to sudden decision of A10 box to start jumping out of top. Sometimes it found a false neutral, sometimes slipped back into top, other times went into 3rd. Occasionally stayed in gear for a few gentle miles. Roadside removal of the end covers on the right revealed no obvious faults in the gearchange assy etc, but I didn't take clutch off to get shafts and selectors out for lack of tools in back pocket. It seemed to engage all 4 very cleanly and positively. But clearly something amiss and I'll strip it down today. Do you wise people have a fund of 'jumping out of gear' stories with well-known common reasons for it? I'm assuming the dogs on the 4th gear pinions, or a selector rod/fork, are worn . . . (unless we are talking another missing/wrongly-positioned spacer or something). It has done 2000 miles in the 3 months since I bought it without any transmission (or any other) trouble at all, so we aren't talking about something that has been messed with.
Grateful for any thoughts you might have which would focus me in on the most likely causes .  .

Groily
Bill

Offline Beezageezauk

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Re: GEARBOX PROBLEM!!
« Reply #11 on: 03.09. 2007 19:20 »
Hi Groily, 

Before you start stripping your gearbox check the "Indent Mechanism".  The terminology in the parts book is the "Gear Control Camplate Mechanism".  You will find this underneath and towards the rear of the gearbox and it just looks like a blank tube about an inch long with a locknut on it.

When this is removed there should be a smaller pointed tube inside it and a small spring inside the pointed tube.  The idea of this is to keep a constant pressure on the camplate therefore preventing it from jumping out of gear into false neutral.  Sometimes the spring breaks or the pointed tube seizes in the outer tube, stopping the mechanism from working.

This may not be the problem but at least it is easy to check without stripping the gearbox.  If it is ok you will only have wasted less than 1/4 hour of your time.

Beezageezauk.


Online groily

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Re: GEARBOX PROBLEM!!
« Reply #12 on: 03.09. 2007 22:39 »
Ta very muchly Beezageeza, appreciate that tip a lot, and it makes 110% sense. In fact, I have checked that very thing and it was OK, in fact quite a fierce spring and plunger I thought - perhaps too far screwed in (plenty of signs of a nutter on the end of the squared shank with a worn out pair of mole grips). Maybe someone had already tried to sort out the same symptoms via the wrong route . . . 

Anyway, went ahead after that and other checks on the bits we can all get at . . . but no dice. So took the whole thing down this pm, and found what I as a BSA novice thought were interesting things .  . (after I'd washed the outside enough to see the allen screw (why is mine metric-headed?) and figure out how the darn selector fork rod comes out of the casing, that is!)

. . . to wit - mainshaft pinion as wot locks the sleeve gear (top gear) into direct drive was having the trouble of a drunken Lothario achieving any degree of satisfactory penetration . . . unnatural practices had led to unnatural wear on the extremities of the engagement dogs. Nothing much else looking too knackered, including the mainshaft selector fork . . . except for the fact - and here I have no idea what the parts should look like not having as much as a simple exploded view of a BSA gearbox to hand - that the sleeve gear bushing was weird. Are there meant to be two bronze bushes, or one; are there meant to be two of equal length or a long and a short; or just one long one? Whatever, the combined length of the 2 bushes that were in this sleeve was about 1/4 inch longer than the sleeve itself . . . so some loony had hammered the end of the bush that was sticking out on the g'box sprocket side in a bid to try to make it flush when doing up the final drive sprocket . . .  net result, inner of the 2 bushes (if there are meant to be 2) on this sleeve was protruding well into the recess on the 'dog' side of the sleeve gear pinion and preventing more than about 30% engagement, in depth terms, of the 2 pinions. Ergo it had lasted a while, then the dogs had fretted enough to make a poor connection worse.

Remedy, if I can get the bits, is a decent sleeve gear and adjacent mainshaft pinion, plus new bronze sleeve gear bushes if they can be had. Or even a full set of main- and lay-shaft with pinions in decent nick.
 
If the bits can't be got - and I understand from this pm on the web from deepest France that pinions are tough to get - then I'll just turn up new bush(es) and see if the thing will work for a bit while pondering where to go next to replace the pinions. Haven't a clue whether, ref other comments here about washers and spacers etc, I'm also missing any bits completely - but the only washer or spacer in the entire box inboard of the inner right hand end case was one between the outermost layshaft pinion and the first of the splined ones operated by the layshaft selector fork . . . no idea how good or bad that sounds to them as knows about these things.

The only other sleeve gear I've had apart in recent times was on a Burman - in which there are 2 (more substantial) bushes, spaced apart and a decent press fit in the sleeve. If anyone has the dimensions for cutting new bush(es) to ensure a good fit in the sleeve that would be great . . .otherwise it'll be measure and make and fit and refit and ream on the inside till it all goes together just so . . . 'Course, if anyone has a reasonable second hand box they don't want from which I could make a decent hybrid or indeed just swap out the guts, my gold awaits . . .
The good news was that many of the other parts weren't at all bad, bit like the curate's egg. Plus, natch, I've enjoyed myself and learned a lot. Way to go!

Groily
Bill

Online groily

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Re: GEARBOX PROBLEM!!
« Reply #13 on: 27.09. 2007 18:37 »
On 3/9 I was moaning about knackered s/arm g'box and bemoaning lack of parts etc . . . just to say for those who are faintly interested in these things that I did manage to find a pinion and sleeve gear with decent dogs on, bought a new sprocket with an extra tooth, managed - with EXTREME difficulty in a small lathe (gimme a bigger one!) - to turn the clutch end of the mainshaft down about 12 thou all round - say 24/25 thou off the diameter (VERY sharp tool and very fine feed etc etc and lots of polishing afterwards - and not through the hardening so far), made new sleeve gear bush with reduced internal diameter out of a suitable lump of phosphor bronze I'd bought for doing the same and similar things to another box (and a reamer, adjustable but OK, at modest expense from RDG tools in Yorkshire England), and that by mid-month it was all back together. Feels like new and I hope all's as good as the feeling I had when it stayed in 4th, changed smoothly etc. Can't hear it even as it goes into 1st - which is nice - and the whole thing is just great. Gets neutral much better after messing with the clutch (a 4 spring in this case, which was missing one roller on the chainwheel and had been a bit wobbly before). Luckily have loads of rollers lying around and think I used one from a 1950s Sachs 2 stroke 98cc big end, which was spot on for diameter if a few thou short on length. So that's a hassle solved and a happy punter. Did me about 90 quid all in, including sprocket and lump of bronze . .
Groily
Bill

Offline db133

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Re: GEARBOX PROBLEM!!
« Reply #14 on: 23.01. 2011 16:51 »
I have been using the BSA Service Sheet 311 Dismantling and Re-assembly of gearbox's

With a view to the previous posts.....thrust washers and spacers etc........

Is the 311 Service sheet correct for STD Gearbox?s?

Is there any more information on Rebuilding STD Gearbox's ?