G80 CP Burman mainshaft problem

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Re: G80 CP Burman mainshaft problem

Postby Duncan » Sun Nov 26, 2017 8:04 pm

hatrack wrote:It looks as if swapping the '49 shaft into the '47 box may not be an option anyway.
Looking at Draganfly's website and list of parts for the Burman CP gearbox, the mainshaft is a different part number up to '47 and from '48.
This might juast coincide with the change from grease lubed to oil lubed, but I cannot see how that would need a change to the mainshaft. Does anybody know this difference between the two years?


Sorry I can not confirm the difference, only to confirm there is one, from memory I believe it is around the bushes for the gears and the "steps" in the shaft to accommodate them.

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Re: G80 CP Burman mainshaft problem

Postby zwarts » Sun Nov 26, 2017 8:14 pm

The mention of a 'New Gearbox' suggests to me that the above quote is referring to the B52 box and not minor revisions of the CP box. Both main shaft and layshaft are considerably shorter in the B52. It was developed from the racing Burman 7R 50 box, as used on the 7R and G45.
Having said that, Duncan is quite correct in his thoughts that the later oil filled CP boxes had subtle differences in that some of the previously unbushed gears became bushed and this required other changes to accommodate them. Unfortunately I too have forgotten the exact details!

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Re: G80 CP Burman mainshaft problem

Postby hatrack » Sun Nov 26, 2017 8:32 pm

Ok. Thats helpful. Enough for me to avoid mixing '47 & '49 parts.

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Re: G80 CP Burman mainshaft problem

Postby SPRIDDLER » Mon Nov 27, 2017 12:15 am

I'm not sure if it's relevant or whether I'm over-thinking things but it has occurred to me (whilst I'm waiting to do a late family taxiing job) that if the mainshaft lengths differ between '47 and '49 then the clutch pushrod lengths could/should differ as well :?

From the Spares Lists:

Clutch thrust rod

1947 Pt. No. 28-X-5 length 10 1/8" (5 plate for 500cc).

1949 Pt. No. 28-X-57 length 10 1/16" (5 plate for 500cc).

Although the '47 thrust rod is only is only 1/16" longer than that for the '49 it might be a clue................?

The other significant clutch operating parts for the '47 i.e. the steel ball, plunger, lever etc. have the same part number as for the '49 except that the '47 parts have a -1 suffix. E.g. the 1947 steel ball is 67-X whereas the '49 steel ball is 67-X-1 I doubt that the ball dia. would have been changed between the two years.

The 'Nut, retaining kick starter driving ratchet to mainshaft' for the '47 is Pt. No. 70-X and for the '49 it's 70-X-1. I would guess that both nuts would be the same.
I poke badgers with spoons.

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Re: G80 CP Burman mainshaft problem

Postby hatrack » Mon Nov 27, 2017 7:27 am

Thanks again.
I am aware that there are different pushrod lengths, and as I have to use a lot of adjustment on the hex sleeve in the k/s case, I wonder if there is an even shorter pushrod from a 350 lurking in there. I will check on all of this, including nuts, balls etc when I have a garage to work in again.
Today is the day when I should hear how soon that can be!

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