The BSA A7-A10 Forum

Technical => Clutch, Primary, Gearbox => Topic started by: shuswapkev on 06.11. 2012 20:48

Title: gearbox dimensions
Post by: shuswapkev on 06.11. 2012 20:48
 i have a plunger rigid type gearbox...and it must have gone to the moon and back with a loose bolt...on the upper ear..
i have cut it flat and square in my mill... but what is the thickness that bsa made it to???  i had to cut nearly a .100 to get down to good metal...
Title: Re: gearbox dimensions
Post by: wilko on 06.11. 2012 23:45
Just make some spacers to make up the difference. The original width would be the same as engine cases.
Title: Re: gearbox dimensions
Post by: Brian on 07.11. 2012 00:06
The gearbox area on the plunger models can be a bit of a pain.

I have measured a couple of mine and I think origionally they were 1 1/8". Most, if not all, have suffered from some wear over the years.

If the top mount on yours was worn chances are the bottom two bolts will also have worn so you will need to put some time into getting it to all fit properly.

First thing to do is make sure the bolt that holds the frame together just behind the gearbox is tight and there is no movement there. Next I would put the engine/gearbox unit in the frame and put all the front and the lower front bolts in, dont do them up just slide them all in. I would then shim up the bottom two bolts under the gearbox, you may need to put washers between the frame and gearbox. Its important to get to the point where the bolt in question will slide in. Depending on which side you have milled off you may need a washer between the frame and gearbox mount.

This whole area is not the best of designs because if the frame moves where it fits together behind the gearbox it puts all sorts of stresses on the gearbox mounts. I have seen these badly worn and have torn the two bottom bolts out of the gearbox. The mistake most make is to put the top bolt in and then do the two underneath up. With the two underneath done up the top one has to be able to slide in, if it doesnt line up you have to put spacers under the bottom two until it does.

Hope this makes some sense.
Title: Re: gearbox dimensions
Post by: shuswapkev on 07.11. 2012 10:25
thanks for does make sense..i generally replace all my frame bolts with new grade 8 bolts...ream out and bush if neccesary..
these frames really arent the strongest engineering and modern sticky tyres and smooth bitumen puts the stresses into play..

i have assembled bunches of old harleys over the years...and if the motormounts arent shimmed to the motor...generally a broken motor mount will be the result..

does this site have the frame dimensions...for 48 rigid twin????
the bottom bolt holes...threads look fine..was thinking about heli coil...but will take your advice and order in one...
Title: Re: gearbox dimensions
Post by: Brian on 07.11. 2012 10:37
This might be what you are after.
Title: Re: gearbox dimensions
Post by: wilko on 07.11. 2012 20:47
Oh, a plunger, sorry.
Title: Re: gearbox dimensions
Post by: shuswapkev on 07.11. 2012 23:23
thanks heaps for the frame is a rigid frame 650 that i am parting together..easier to call it a plunger so dont get caught up in some real old stuff... it is a 51 motor cases so more than likely original motor  (cases) were in a plunger frame
 so now i can bolt that thing to the concrete floor and start  measuring and get the jacks and chains out...start the bend...

i had a b33 plunger and wasnt particulary enthused with the way it worked...bounding along..
i have a rigid matchless that has it beat in every way...all the way down to the ground...
Title: Re: gearbox dimensions
Post by: Brian on 07.11. 2012 23:33
There are two rigid frames. The one in the pic in the previous post is the "one piece" type used up until 1948. That frame never had a A10 in it but the A10 unit will fit.

The frame the A10 used is the 49' onwards "two piece" type. Same front section but had either a rigid or plunger back half.

An just to keep the nit pickers at bay, yes I know there was a third type used right at the very start with the drop down centre stand.

Title: Re: gearbox dimensions
Post by: shuswapkev on 10.11. 2012 11:54
my frame is a one piece
 and..yes it will have an a10 motor...once i get it all straightened out
Title: Re: gearbox dimensions
Post by: duTch on 10.11. 2012 16:03

 Kev, I had a similar box mount issue and have done as Brian suggested-still to road test though, but should be better than before.
 Sounds like you're all geared up for the job of checking for straight, I ended up dropping mine into Dave Kellet (frame straightener)at Springwood, with the drawings, as my back end was pushed to one side a few mm, and front downtubes out of whack, which is why I couldn't get the wheels to line up.
 Good luck, I can give you Daves' number if you need it
Title: Re: gearbox dimensions
Post by: shuswapkev on 11.11. 2012 11:28

 thanks for that...maybe put his number thru for me...i have seen a sign there on a shop in springwood...frames straightened...
  i picked up a length of 8 inch channel iron make a bending jig...might have a go...looks like some simple bends....
 if not..i,ll take it to him...
 just got my crank done at crankshaft engineering ...browns plains...quite an enthusiastic bunch...says he still does ,m on a regular basis...even uses his cnc to make custom norton cranks...
 i reckon this thing will be oilin the roads of queensland in the next 6 months...
Title: Re: gearbox dimensions
Post by: duTch on 12.11. 2012 09:34

 'day Kev, Dave is at U3/46 Randall St, Springwood- (Parallel to Moss street ) up the laneway
 ph #07 3290 2811,
 (page 209 Brissy Business Ph. book under "Dave'- Dave's not here!! -Sorry couldn't resist that)

 i'm a bit confused though, you got a whole bunch of stuff to make a 'bending jig', I thought you want to straighten it???
 I guess I won't be following you if you're oilin the roads,(unless it's dirt) had a couple of diesel dilemmas that's enough *eek*