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British Bikes / Re: Notchy gearbox
« Last post by Oggers on June 08, 2021, 05:44:09 PM »

I stand slighty corrected. When on the main stand and in neutral, the rear wheel rotates quite quickly suggesting a little clutch drag. I'll try and adjust things further. Just took it out and I moved the gearlever a notch over the spline. Seems slightly better....   
British Bikes / Re: Notchy gearbox
« Last post by Oggers on June 08, 2021, 11:37:47 AM »

My poor description perhaps. Clutch nut  = clutch operating rod ajustment. The slotted rod held by locknut behind the cap in the centre of the outer primary chaincase.

It's not particularly difficult to engage first from standstill, nor does it move much with the clutch lever fully pulled back.

For sure it has a short gearlever, considerably shorter than my other British bikes - Ariel VB and Velo MSS - and indeed I did  think of swapping it for something longer. I just wished to clarify that there is not something I could do to improve things before I did so. Mine is also unit construction....
British Bikes / Re: Notchy gearbox
« Last post by iansoady on June 08, 2021, 10:56:44 AM »
I'm not familiar with the gearbox but this kind of problem is often caused by slight clutch drag. You seem to have done most of what would be needed however, although your descriptions are a bit odd - eg "Various adjustments at clutch nut - the one concealed behind the chaincase".

Is it easy to get into first from neutral at a standstill? When in gear does it feel as though it's trying to move off with the clutch fully disengaged?

Different bike I know but I briefly had a unit 500 Triumph and hated the short gearlever. If I'd liked the rest of it I would have lengthened it.
British Bikes / Notchy gearbox
« Last post by Oggers on June 08, 2021, 09:47:30 AM »

1966 Triumph T120 Bonneville is proving to be an occasional pain in the neck when changing gear - especially from 3rd to 4th. Here it basically does not engage into 4th and finds neutral instead. Compared the other bikes, the gearchange just does not seem positive in selection and seems over-light - for want of better words. The throw of the gearlever between changes is also very small, and finding neutral from 1st or 2nd is a very fine art. The delicate tap required at the (standard) gearlever to find neutral is almost imperceptible.     

Of course I realize this may be all perfectly normal and that I need to adapt my right foot to the circumstances, but it does seem a little "light"

Things I have done fairly recently

Fresh gearbox oil - to the spec as per the manual - filled with correct amount
Fresh engine oil - to spec
Various adjustments at clutch nut - the one concealed behind the chaincase
Various adjustments of the clutch cable at both the lever and at the gearbox ends
Cleaned up the clutch plates/basket
I change up at around 4000/4500 rpm with a slight whiff of throttle.

It may simply be an attribute of the gearbox - which I understand to be original - but all thoughts welcome, particularly from other T120 owners.   
Autojumble / Re: velocette gtp
« Last post by Rex on June 08, 2021, 08:25:50 AM »
I'm sure I read somewhere about someone utilizing a hub from some Jap trail bike (DT 175, maybe?).
Absolute heresy of course, but if it gets a bike back on the road..
Autojumble / Re: velocette gtp
« Last post by beardyimpman on June 07, 2021, 08:47:43 PM »
Autojumble / Re: velocette gtp
« Last post by Rex on June 07, 2021, 08:25:38 AM »
Best of luck with that particular search. Velo wheels/hubs from the 1930s seemed to be unobtanium when I was looking, and that was close on ten years ago now.
Autojumble / velocette gtp
« Last post by beardyimpman on June 06, 2021, 09:39:43 PM »
looking for front wheel or hub, buy or have gtp spares to swop, thanks any help greatly appreciated
British Bikes / Re: Contact breaker adjustment
« Last post by cardan on June 06, 2021, 05:01:31 AM »
Yep, 40 degrees BTDC sounds a lot, but, for example, the book value for a 1920s side-valve EW Douglas is 45 degrees BTDC! In an overhead valve engine the plug is right in the combustion chamber, adjacent to the valves and above the piston, whereas in a side valve the plug is usually way off to the side somewhere...

Certainly "points opening TDC fully retarded" will work on the side of the road. But keep in mind the Standard for magnetos is 30 degrees of adjustment at the magneto, which equates to 60 degrees on the engine. So for an unmolested mag "TDC fully retarded" will give a spark at 60 degrees BTDC with the a/r lever fully advanced. i.e. it will run best with the mag lever set about half way. Good enough to get you home.


British Bikes / Re: Contact breaker adjustment
« Last post by Rex on June 05, 2021, 12:31:36 PM »
40' sounds a lot for an old SV clunker running on modern juice though.
IIRC my old Bonnie was something like 38' on 5 star petrol, and down to something like 34' when unleaded etc were introduced.
On balance, I think for a bike like this I'd stay with the "set at TDC retarded" method and find the sweet spot with the A/R lever. These old girls run hot at the best of times and I wouldn't want to add to that.
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