First gear pinion on mainshaft interchangeability

[KiwiGF]

My 56 STD s/a box for my GF has a few chips on the first gear on the mainshaft and I was looking to use a gear from a spare plunger box I have, which I think is a 49.

The 2 gears look the same apart from the plunger box has every other tooth ground down/relieved where it locates in the adjacent gear. I guess this may be to improve selection but it does seem to be at the expense of strength.

My questions are... is it ok to fit the first gear from the plunger box? Is one gear design better than the other? I'm not sure that either box has the original gears in it.

I could post photos if needed.

Thanks in advance.

[duTch]

Hiya kiwi,
            Not sure 'bout the 'relieved/ground down' maybe post a picture??
Seems the '49-'57 plunger and S/A gears(std 27 T) are same part#, maybe '49 is a crossover year and some reason a bit different , but can't see why it wouldn't work at least to get you out of trouble??

[KiwiGF]

Hi Dutch, I'll post a pic later today when I get home. The teeth are relieved/ground away much more on the gear from the 49 box, such that only half the teeth engage "inside" the adjacent gear. My concern is based around the fact that I've read that early boxes had problems and the design was improved by BSA as a result, and I don't want to use one of the components that needed to be improved!

[trevinoz]

Kiwi,
          The gearsets from the early boxes are completely different to about post '51 boxes.
  Trev.

[KiwiGF]

Thanks Trev, I am interested in whether its a late or early plunger box mate might want this box for his longstroke. From what you say it's a late box and it won't be any use to him. I got the idea (probably wrongly) it was a 49 box from a part number on the selector forks being 67-3118 as opposed to the later 67-3204. From my experience to date of my bike and the parts it came with I would not necessarily rely on any part being what it seems at first.....the plunger box might have the wrong selector forks (or gears) in it!

The plunger box I have has a splined not keyed mainshaft (clutch end) the selector mechanism is very different design to the s/a box as well. The output gear is different on plunger box, but a couple of the other gears including bottom gear look like they will fit the s/a box - hence my question regarding the bottom gear.

One of the other plunger box gears I have already swapped over as it was identical to the equvalent s/a gear, other than what I think were material spec. markings "EN" versus "V".

[duTch]

Hi Kiwi,
          I think I know what you mean, the 'dog' part of the gear, it being similar to the sliding gear at the sprocket end that engages with the mainshaft sleeve gear?
   My info was looking at a spare Plunger gear cluster I have-(less mainshaft w. 1st gear), and as per parts books, and probably Trev is more able to help here, as I've had nothing to do with the earlier boxes, so'll quit whilst ahead...ish... ...

   Cheers,duTch

[bsa-bill]

List of parts and pinions here http://www.draganfly.co.uk/shop/pi1445653175.htm?categoryId=686
From the list you can see what is compatible

[KiwiGF]

Pics as promised. Oddly both boxes have forks with 67-3118 on them, maybe that's a casting number as it does not line up with my parts book or Draganfly.

Anyway hopefully the pics show the difference between the 2 bottom gears, hopefully someone will know if the gear in better condition (on the right) is OK to fit in s/a box.  

In the "exploded" pic the plunger box is on the left.

[duTch]

Yo Kiwi,
I see what you mean,much as I thought, but more pronounced. Can't see why they won't work, put em in and see if they make funny noises on the bench???? then on the road??

I know the RRT2 gears are totally different,and you'll see why if you have them, and maybe scramblers?

 Shifter forks are listed as part #67-3204 for s/a & plunger 49 on,so whatever they're stamped maybe as you you say(cast #?) and if they fit and do the job....?. Spare ones I have are also stamped 67-3118 and do the job.
 Otherwise see what others have to say????

cheers for now

       

[KiwiGF]

Thanks everyone, I had a good look at all the gears again tonight in the knowledge the part numbers were largely unchanged between the boxes and have come the conclusion the differences in design is just another of those little changes bsa made over the years and not related to the early box issues I'd heard about

One of the other gears had similar differences to the bottom gear, and the dogs were also altered in shape on one other gear as well, all with the same part numbers.

Overall I'll be better off with the plunger bottom gear I reckon so that's going in.

Its not a huge job to swap out the gears if the changing is no good!

Thats assuming i can figure out how to put the clusters back in, it looks like one of those "knack" jobs...easy .....once one works out how to do it.

[BSA_54A10]

While the cut on the teeth changed you can mix & match provided that you do it in pairs so you put both the plunger main shaft & lay shaft gears into the swing arm box.
As Trev noted earlier they are different so a plunger gear on the main & a SW on the lay will give you grief.
Also have a close look at the dogs .
When I have made an almost acceptable box from a bunch of buggered ones I some times need to play with thrust washers thicknesses or take a bit off the end of some dogs so that they can engage fully.

[KiwiGF]

Thanks Trevor, I will be fitting both gears it seems to make sense for a number of reasons but I'm stumped to see a noticeable difference between them other than the dog part of the teeth!

I'm just glad I could could get some use out an old box which I think is one of parts one can call "sale proof" in nz.

[chaterlea25]

Hi Kiwi,
Been away for a week or so,
In my opinion/experience  ????
The early gears have half the number of dogs to take the drive the later have long and short , this helps with  gear selection, and then the short provide more strength when fully engaged

I'm guessing BSA found a need for this on the bigger cc bikes as they continued with the early type gear on the 250cc models fitted with the heavyweight box (or maybe use up remaining stocks??)

I have also found that later boxes have gears stamped EN36 and earlier?? V18 or VIB
see this prevoius posting
http://www.a7a10.net/forum/index.php/topic,4817.0.html

Hope this helps
John

[KiwiGF]

Thanks John, there's more to the interchangeability question than I thought.

But the box build is on hold due my own stupidity! I ruined the Rh end mainshaft thread after the shaft got stuck in the smaller ball bearing in the inner cover, when I was trying to fit the inner cover after getting the mainshaft and layshaft all in place. The shaft was far to tight a fit in the bearing especially as the inner appears to be clamped by the nut and kickstart mechanism on the rhs end anyway. Should they be a typical interference fit?

I'm not sure if the bearing was at fault or the shaft but I'll test fit them together next time and once I have found a new mainshaft. Expensive mistake on my part :-(

Another question ......is the best way of assembling the box to fit the inner cover/bearing once the mainshaft is in position in the box? or fit the cover/bearing to the shaft, and then fit the whole lot together?

Hope that makes sense!

[chaterlea25]

Hi Kiwi,
Bummer about the shaft
OK heres another of my ?0.02 worth
The shaft should be a light press / tap fit in the bearing, the outer ratchet nut MUST NOT be over tightened as this will distort the ratchet bush
I fit all the innards before fitting the outer cover (works for me!!)
HTH
John O R