Author Topic: Plunger gearbox mount  (Read 602 times)

Offline unclemeat

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Plunger gearbox mount
« on: 12.04. 2015 10:09 »
Hello to all - (has been a while since my last post)

Has anyone noticed a gap between the lower gearbox mount and the frame to which it bolts to with 2x 5/16th whitworths when bolting the complete unit into the frame. ie. lower engine mount in, front engine mounts in, top gearbox mount in, head steady in place and all nipped up results in an approx 1mm gap at the lower gearbox mount bracket. I put 2x thin washers in the gap to prevent any unwanted stress, mainly in the upper gearbox mount (I have seen these crack in the past).
Any thoughts or comments appreciated.
Unclemeat.
BSA A10 GOLDEN FLASH 1954
CHANG JIANG COMBO 1968
TRIUMPH THRUXTON 2007

Offline muskrat

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Re: Plunger gearbox mount
« Reply #1 on: 12.04. 2015 11:20 »
G'day Unclemeat.
I've never noticed that. I've always put all the bolts in loose then tighten those up first followed by the bottom engine bolt, top g/box bolt, front engine plates, head steady.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
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Online Brian

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Re: Plunger gearbox mount
« Reply #2 on: 12.04. 2015 12:08 »
That can be caused by a couple of things.

Wear on the bottom of the gearbox casting or movement in the frame where the bolt goes through just behind those mounts. If you loosen the large bolt that goes through the frame just behind those mounts you may find you can close that gap.

Offline duTch

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Re: Plunger gearbox mount
« Reply #3 on: 12.04. 2015 14:25 »

 Heya Uncle- I had exactly that too, and did what you did with a couple of ~1" O.D. stainless washers, maybe needed two each side ( *????*or maybe I made a single plate to do it  *dunno*)

 I also had to do same with the big top lug
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
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Offline unclemeat

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Re: Plunger gearbox mount
« Reply #4 on: 12.04. 2015 16:01 »
Thanks for the tips. I'll give that bolt a loosen..
BSA A10 GOLDEN FLASH 1954
CHANG JIANG COMBO 1968
TRIUMPH THRUXTON 2007

Offline unclemeat

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Re: Plunger gearbox mount
« Reply #5 on: 12.04. 2015 16:48 »
ok..removed bolt completely (bike on centre stand with rear wheel off ground so engine weight should load the gap closed) but gap stayed same. oh well…washers will go back in.

For info, the bolt is 7/16"
BSA A10 GOLDEN FLASH 1954
CHANG JIANG COMBO 1968
TRIUMPH THRUXTON 2007

Offline unclemeat

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Re: Plunger gearbox mount
« Reply #6 on: 12.04. 2015 16:51 »
I'm assuming 7/16" is correct of course.
BSA A10 GOLDEN FLASH 1954
CHANG JIANG COMBO 1968
TRIUMPH THRUXTON 2007

Offline duTch

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Re: Plunger gearbox mount
« Reply #7 on: 12.04. 2015 19:46 »

 Yep,7/16....and if two washer are not enough (one each bolt) and (in my opinion), you may be able to squeeze two in with the 7/16 bolt loose in place with up-pressure on the box, best if there's no interference with the under ones done up, otherwise you could be stressing the lug up or down
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Online morris

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Re: Plunger gearbox mount
« Reply #8 on: 12.04. 2015 22:46 »
Maybe gearbox from another bike? Mine fits perfectly up and down.
Don't think it's important though, just avoid stressing the lugs and check if the gearbox mainshaft runs well centred through the primary's oil seal or else the seal may wear rapidly
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