G: Gearbox (Single - Burman) Burman BAP gearboxes

[chankly bore]

Dear folks, I have just been down the shed stuffing around with Comet gearboxes, and thought I'd pass on the following priceless information. (and since price is a function of worth, draw the inevitable conclusion). The proper gearbox is type G97, followed by a month/letter and year/numeral code. The correct mainshaft is 11.3" long and is threaded 5/8"x20t.p.i. at both ends. The boss at the drive end on which the clutch centre sits projects about .735" from the inboard shoulder. The 1/8" slots for the clutch centre go all the way through the shoulder . The bottom cast boss on the shell which takes the 5/16" CEI adjusting bolts for primary chain tension is 2 5/8" wide and inset about 3/4" from the outer face of the output bearing housing face. The top pivot lug is about 2 7/8" wide and is similarly inset 5/8". Large Panther gearboxes, type G42. are identical EXCEPT for the mainshaft, gearlever and kickstarter. Another gearbox I recently found has different offsets on the top and bottom lugs on the shell, but I should be able to compensate with a suitable lash-up. It seems to be type G10 A47, so I knew it couldn't be off a Vincent. This drivel is prompted by a recent ebay listing for a Comet 'box which obviously showed the wrong "new mainshaft"-at least as far as I could tell. The correct inner and outer casings have one more bolt below the kickstarter than the CP type. The correct casting numbers for these are 4-520 and 4-521.

 

[beatim]

Dear folks, I have just been down the shed stuffing around with Comet gearboxes, and thought I'd pass on the following priceless information. (and since price is a function of worth, draw the inevitable conclusion). The proper gearbox is type G97, followed by a month/letter and year/numeral code. The correct mainshaft is 11.3" long and is threaded 5/8"x20t.p.i. at both ends. The boss at the drive end on which the clutch centre sits projects about .735" from the inboard shoulder. The 1/8" slots for the clutch centre go all the way through the shoulder . The bottom cast boss on the shell which takes the 5/16" CEI adjusting bolts for primary chain tension is 2 5/8" wide and inset about 3/4" from the outer face of the output bearing housing face. The top pivot lug is about 2 7/8" wide and is similarly inset 5/8". Large Panther gearboxes, type G42. are identical EXCEPT for the mainshaft, gearlever and kickstarter. Another gearbox I recently found has different offsets on the top and bottom lugs on the shell, but I should be able to compensate with a suitable lash-up. It seems to be type G10 A47, so I knew it couldn't be off a Vincent. This drivel is prompted by a recent ebay listing for a Comet 'box which obviously showed the wrong "new mainshaft"-at least as far as I could tell. The correct inner and outer casings have one more bolt below the kickstarter than the CP type. The correct casting numbers for these are 4-520 and 4-521.

Hello, I'm wondering if you can give me a bit more advice regarding the difference between a G42 Burman and a G97. Do you know if it is possible to use the G97 mainshaft in the G42? Or in other words turn the G42 into a G97 for all intents and purposes.

 

[chankly bore]

Well, yes. I've a friend who is an instructor at a trade school. He machined the clutch centre splines of a Panther shaft back in to the shoulder and cut about 1/4" more thread on the clutch end of the shaft. Be aware, it is hard material all the way through. I think he used a tungsten tipped cutter. I had already machined the boss back to the dimension above. Two things to note. your adjuster threads, 5/16" x 26 t.p.i. are probably stripped or oversize. You may need to trim these bolts off, slot them and dress them with a file then remove them inwards to save the thread if it still exists. If they are really buggered I make up a correctly threaded 7/16" B.S.F. o.d. brass sleeve and Loctite it in. You can just fit a G97 mainshaft. I believe Maughan's stock them. I've quite a bit of BAP stuff. As you're a Kiwi I'll help you if I can. my email: hardarser(AT)outlook.com.