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Triumph5ta
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Gearbox cam assembly
#757263 11/27/18 4:14 am
Joined: May 2009
Posts: 348
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I finally got to ride my 1958 Square Four around my neighborhood for the first time - and never got beyond first gear! This is bike that had been partially restored by the p.o. I had been able to change from 1st to 4th while the bike was on the lift but then had to remove the outer gearbox to replace the kickstart spring. When I replaced the cover, I (stupidly) didn't run through the gears again until my ride around the neighborhood. I could select first easily and get to neutral but no further. I wonder if I must've moved the cam assembly (3705-52). When back on the lift I found the same thing - just 1st and neutral. I have removed the outer cover, again, and fiddled with the cam assembly but now do not know what position it should be when in neutral - e.g. With the centre of the three "pins" at 3, 6 or whatever o'clock. Could anyone please help me with that? Or have any other suggestions as to what I've done wrong?
BTW, the return spring works just fine, thanks.
TIA,
Paul


Paul

'74 Commando - Interstate
"74 Commando - Hi-Rider, possibly
'65 Atlas, mostly anyway
'15 R1200 GS Adv
'51 Vincent Rapide
'58 Ariel Square Four
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Re: Gearbox cam assembly
Paul Sammut #757269 11/27/18 6:12 am
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Paul, firstly I must admit my Burman experience is a little with CP and GB 52 as fitted to '50's Matchless. With these, a mark on the footchange rack should align with a marked tooth on the gear change camshaft pinion. Another thing to check, not readily apparent, is that overtightening the gear shift pedal on the hollow splined shaft can cause binding on the inner shaft that can affect footchange operation. But I would suspect the former.

Re: Gearbox cam assembly
Paul Sammut #757325 11/27/18 6:44 pm
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Hi Paul, Haven't had my Ariel box apart yet, but the box on my Panther is very similar - you'll see the markings that Triless was referring to in my photo - do you have these ?
Photo: https://drive.google.com/file/d/1bxFpqRDqthXjhf8-ZuJ_mFUmgVVfQcRf/view?usp=sharing

Also, remove the gear selector springbox cover and check that the springs aren't broken and the spring box isn't cracked - its made of quite brittle muck metal.:
Photo: https://drive.google.com/file/d/10VocAnG9oLNyA3Cr_0JdWOzFqNEEvA3p/view?usp=sharing

Cheers,
Bevan
ps
strongly suggest you join the AOMCC forum (no cost); http://www.arielownersmcc.co.uk/ Very active, and helpful people.

Last edited by BevanC; 11/27/18 6:49 pm.
Re: Gearbox cam assembly
Paul Sammut #757334 11/27/18 9:28 pm
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Hi All,
To the best of my knowledge the sq 4 has the later type Burman where the selector drum is inside the outer cover and linked to the two rods that carry the selector forks by pegs
These gearboxes have an external gear indicator on the outer cover, the gears can be changed by turning the nut holding the indicator arm on..
If the gears can be selected by turning the nut then the problem has to be with the "claw" that turns the selector drum
End clearance of the selector drum is critical to get a nice gearchange, as the detent spring and plunger act on the rear of the drum
A different gasket thickness or no gasket can make all the difference

John

Re: Gearbox cam assembly
chaterlea25 #757364 11/28/18 3:16 am
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My apologies - I had presumed that the bike had a BA box (I think they did up to 1955 ?); it appears it probably has a GB7. I am sure chaterlea25 is correct.
Cheers, Bevan

Re: Gearbox cam assembly
Paul Sammut #757371 11/28/18 4:16 am
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Thanks to all three of you. BevanC the gear change mechanism is indeed very different from yours and yes, as Chaterlea25 states, it does have the GB7 'box. My problem is that, with the outer cover off, turning the cam assembly by rotating the spindle that holds the indicator nut does not change gear even if I rock the wheel back and forth, so I cannot find neutral. The locator pins slide in the groove of the assembly, but I cannot change gear. I'm hoping this does not mean a complete strip down of the gearbox. Triless, I don't see the marks you mention.
Paul


Paul

'74 Commando - Interstate
"74 Commando - Hi-Rider, possibly
'65 Atlas, mostly anyway
'15 R1200 GS Adv
'51 Vincent Rapide
'58 Ariel Square Four
Re: Gearbox cam assembly
Paul Sammut #757388 11/28/18 7:37 am
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My mistake, Paul, as my limited Burman gearbox experience was a long time ago. The CP and BA types have the mechanism with the marks I mentioned, and shown in Bevan's pic. The GB is as Chaterlea says. I should have remembered this, sorry for the confusion !

Re: Gearbox cam assembly
Triless #757464 11/28/18 9:41 pm
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Hi Paul,
When the outer cover is removed the detent spring and plunger push the selector drum outwards
This "upsets" the position of the gears and will / may jam up the box
It is fairly obvious when you look at the outer end of the selector drum which way it should face so the claw will engage on the pegs
Its to the front, looking at this diagram
https://www.draganfly.co.uk/index.php/ariel/4-stroke/category/829-1952-1958-gb-gearbox

Its been a few years since I rebuilt a late Burman so my memory isn't as good as it used to be about details
That one was a PITA and I had the cover on and off more times than I want to remember before it just worked !!!!!

John


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