A10 SR/RGS Jumps out of 3rd gear

[Viking]

The gearbox on MY A10 SR/RGS 1958 works in general quit well. It is oil tight and with no sounds or problems, except, one issue:

In accelerating hard, it can jump out of 3rd gear and find neutral between 3rd and 4th gear.

Not ideal when overtaking a car etc.
If I only give it ½ throttle, it is ok. But working hard in 3rd gear results in jumping out of gear.

The gearbox was first rebuild in Laceby Lincolnshire in 1995 and later by SRM in 1998/1999
It worked with a side car for 15 years. Heavy load., and the issue of jumping out of 3rd I getting more and more often.

The cam plunger housing is adjusted to “1 ½ threat”

Cam plate, plunger and plunger housing, spring, bearings, all new bush bearings, seals etc. was renewed doing rebuild.
What can cause the issue of jumping out of 3rd gear ?

[beezermacc]

This is usually because the dogs on the sides of the gears are becoming rounded. The pressure on the gears forces them apart. The dogs are usually cut square so that the pressure cannot force them apart. Lots of gearchanges over the years causes the corners of the dogs to become worn away so the dogs get rounded and are no longer lying flat against each other so the rounded edges are no longer capable of withstanding lateral thrust forcing them apart. You will have to strip the gearbox, identify and replace the worn gears. At the same time make sure there is no endfloat in the shafts which can also contribute to this problem, but, from what you describe, the dogs are already worn. Sidecar work won't have helped!

[Viking]

It sounds like a compleate rebuild job for the winter....

I can imagine that fresh / new gears are not that easy to get hold of..

It is a STD box.

Hmm. sound like I well send it to SRM in Wales. 

[Viking]

A little update.

Gear box is removed from the frame, washes and cleaned with Swarfega Jizer and ready to ship to SRM Wales.
Getting fresh gears, is not the most easy thing in this world.

Getting a 5 speed box is extreme expensive (Would be nice, but it is the same price as a 1/3 of the bikes value !) 

http://www.novaracing.com/ProductBSAGoldStar.html

[Beeza]

Hi Viking, as a temp fix I have used a slightly heavier spring in the plunger detent unit. You will have to use the thumb and finger pressure tester to compare tensions, and it should get you by for a while, but a worn gear set is a worn gear set. Also the play between gears and shafts combined with worn dogs will add to gears jumping out. I have swapped 3rd gear sets (it's always 3rd) with varying success. Sometimes they don't jump out of gear any more but HELLO 3rd gear whine. Good luck, and after a few goes the gear box is quite a simple unit.
Always wondered why no one brought out a nice bottle of red named "BSA 3rd GEAR WINE".

Cheers Thomas

[Viking]

 "BSA 3rd GEAR WINE".       good one...

I´m really tempted to swap the internals to 5 speed parts.

The one thing stopping it is a hefty price tag of 1675£+VAT  uhhh   

But new 3rd gears, bushes, fresh main shaft and sims should cure the matter
For the next 20-30 years.   

[duTch]

 My Plunger Flash/Rocket jumps out of third under 'extreme' load, and I've been meaning to shed my theory... in addition to previously mentioned worn dogs/shafts, it's also worth considering the play in the selectors themselves, and more likely , the fact that as far as I can determine, when in second or third gear the selector fork 'roller' is held in place on a very small surface area on the lobes on the camplate , and if that/they is/are worn, or there is a maladjustment in the scheme of things, it's extremely possible it'll jump...as per pic
 I hope that makes sense...

[Viking]

Nice Picture, Worth investigating

The box has not been used a lot. Approx. 5-8000 miles.
Cam plate, bearings, bushes, spring/plunger/holder, to forks changes, but not pinions.

[nimrod650]

owens uk have gearbox complete with sprocket as it came out of the bike £180??

[BSA_54A10]

Find some one who actually works on motorcycle gears and get your dogs & gears undercut
I had this done to an A 65 many years ago and it works a treat.
Modern riceburners use this technique as do most race boxes.
Being slightly undercut  the doges "dovetail" into the gear so the more pressure put on them the harder they lock together.
The gear change becomes a lot more stiff and a lot more posative and well worht the $ 120 I paid to have it done.

[duTch]

"BSA 3rd GEAR WINE".

; yep I agree, go tune the local Whinoery...

..anyways,
 For what it's worth, the other day I pulled the guts out of the box I'm running to replace a kick-return spring and investigate other stuff that will eventually surface elsewhere, and as it turns out my camplate is as good as or better than I'd expected, so I think I've blown my theory (

.....when in second or third gear the selector fork 'roller' is held in place on a very small surface area on the lobes on the camplate , and if that/they is/are worn, or there is a maladjustment in the scheme of things.....

) up the $hitter...

 but I've I think confirmed as I've suspected that it's an early box, and some of the dogs are a bit different too, but while a bit worn, don't seem to be too bad, so now it's research time, but for now 'vocational pleasure' is interfering with my life....

 Trev, I thought of this, as the Gutzzi has this, but I can't figure how it can be done to (some/our)Beeza gears due to the dog configuraton....
 

Find some one who actually works on motorcycle gears and get your dogs & gears undercut
I had this done to an A 65 many years ago and it works a treat.
Modern riceburners use this technique as do most race boxes.
Being slightly undercut  the doges "dovetail" into the gear so the more pressure put on them the harder they lock together.
The gear change becomes a lot more stiff and a lot more posative and well worht the $ 120 I paid to have it done.

[BSA_54A10]

With a small diameter dove tail cutter on a mill.
Mine were done by Balmain Motorcycles but unfortunately Bob's shop got compulsorly acquired for the never to be built political bull dust diverson called the West Sydney Metro, so he called it quits and retired. Got stiffed big time by the then Labour government and the site has since ben sold for 8 times what he got for a housing deveopement, Smells real funny.

[Butch (cb)]

Find some one who actually works on motorcycle gears and get your dogs & gears undercut
I had this done to an A 65 many years ago and it works a treat.
Modern riceburners use this technique as do most race boxes.
Being slightly undercut  the doges "dovetail" into the gear so the more pressure put on them the harder they lock together.
The gear change becomes a lot more stiff and a lot more posative and well worht the $ 120 I paid to have it done.

So can you take your old gears with worn dogs out of the box and turn them down and bung them back in with some 'undercut'? As in obviously they will now be smaller, but presumably work OK? Could I do this on a lathe? (as in is it latheable, rather than do I have the skills required - ahem)

[chaterlea25]

Hi,

So can you take your old gears with worn dogs out of the box and turn them down and bung them back in with some 'undercut'? As in obviously they will now be smaller, but presumably work OK? Could I do this on a lathe? (as in is it latheable, rather than do I have the skills required - ahem)

In a word, No!!
John

[duTch]

 I think under-cutting these gears is a wee intricate, especially the early ones, maybe left for later ....

.... as a temp fix I have used a slightly heavier spring in the plunger detent unit. ....

 Is there any info on the standard free length of the original spring? My housing is wound almost full in (-1/2 turn), so I'm thinking the spring has sagged, I'll compare it and use the best.

 Mine jumps only sometimes, gears aren't perfect but not too bad.