Bolting gearbox to frame

[Russ]

I need to have a small frame adjustment done on my 51 A10 Plunger to the plunger mounts as the right side top mount is not perpindicular to the bottom mount.
My problem is that when I fitted a set of crankcases, with gearbox bolted on, into the frame to take to the frame straightener the mounting lug on the back of the gearbox is not flush against the lug on the frame which it bolts too. It is about 10mm apart. Also the gearbox sits low so the hole does not line up. The two mounting bolts on the bottom of the gearbox have had their threads poorly repaired by a previous owner and this is getting fixed now, however, this will not fix the alignent problem.
Has anyone had this problem before?
When the bottom threads are repaired I intend to bolt up the crankcases / gearbox as best can be and see what it looks like after the frame is straightened.
If necessary, can I simply put spacers under the bottom of the gearbox, to align the gearbox lug with the frame lug so the bolt will go through?
Next can I put a spacer between the gearbox and frame lugs to take-up the gap?
My thoughts are that in doing this the gearbox sprocket will not be lined up with the rear wheel sprocket.

Forgot to mention, when the frame is level the top of the crankcases are not level with the frame.

Cheers Russ

[duTch]

 Heya Russ, I had a similar issue that the top and bottom box mounts were put off square so I faced then up as best I could and packed them with stainless washers about 1" diameter.
  I'll have a better read when I get off this job

[Russ]

Thanks duTch
I have arranged to borrow another gearbox to compare with mine. I'll take a few more measurements, scratch the back of my head a bit more and see where it leads me.
Russ

[muskrat]

G'day Russ.
This is a real long shot. Is the bolt going through the down tube and the forging (the bit the box and footpegs mount to) still there? If that forging slipped down the tube you'd have a gap.
Cheers

[duTch]

 
 Hola Russ
 

........the right side top mount is not perpindicular to the bottom mount.

Not sure what you mean there, but I'm thinking perpendicular front top/bottom? , and think it explains itself below ☟↴

 

the top and bottom box mounts were put off square

That should read "the top and bottom box mounts were out of square "-( friggin phone spellchecker  )

 

.......the mounting lug on the back of the gearbox is not flush against the lug on the frame which it bolts too. It is about 10mm apart

 This can maybe be attributed to the "the right side top mount is not perpindicular/perpendicular to the bottom mount", if that is out of whack will maybe affect the other (the mounting lug on the back of the gearbox is not flush against the lug on the frame which it bolts too. It is about 10mm apart).

  I (think I ) decided to start with locating all the fixed points ie; top G'box lug bolt (assuming the interface with the box lug is centre, this is the bit that may need shimming, in conjunction with the bottom mounts to find a happy union )...I think the measurement from main inner g'box interface to frame lug is crucial, when/if I have a chance in the next couple of days(and remember), I'll do some measuring.

 Having done that, whatever doesn't line up in front, top and bottom is likely out of whack- was at this point that I realised my front downtubes were way out, and at that point decided I needed to go to the straightener (Dave Kellet).
 

[Russ]

muskrat the bolt you refer to is missing in my frame. I will be putting one in, however it looks like it has been missing for years and the tube is as tight as a fishes a---hole and hasn't moved.
duTch I am thinking along your lines and will set the gearbox in place as best can be then see where the cranckcases sit. I am thinking downtubes or bottom frame tubes out of wack.
Thanks for your help guys. Appreciated. Russ

[duTch]

 Even though my front down tubes looked straight enough, they were twisted to buggery which was really obvious when I set the front frame section alone on the floor, rolled onto the headstock and bottom bend and it lay over to one side.
 I was already resigned to taking it to the straightener, but this confirmed at least part of the problem.