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#477696 - 02/19/13 8:06 pm pre-unit gearbox top mount/drawbolt sloppiness  
Joined: Nov 2012
Posts: 165
koan58 Offline
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koan58  Offline
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Posts: 165
Isle of Wight, UK
My pre-unit 650 gearbox top mount uses a 7/16" stud.

It is a very slack fit in the hole through the top of the gearbox, making primary alignment very vague and difficult when adjusting the primary chain.

I initially thought that it had been enlarged by "chattering wear" by the gearbox being loose at some time, but the hole seems to be fairly circular and uniform throughout its bore.

Were these a very sloppy fit from new?

Thanks Dave

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#477840 - 02/20/13 7:06 pm Re: pre-unit gearbox top mount/drawbolt sloppiness [Re: koan58]  
Joined: Jun 2007
Posts: 5,456
HawaiianTiger Online content
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HawaiianTiger  Online Content

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Posts: 5,456
Maui Hawaii
Should be a good fit, as in a clearance hole, not sloppy. I recommend sleeving the hole with steel for a better fit. Alternately, I have used grade eight hardware there and tightened it with all my strength. It's a pretty common issue with pre-units.
Bill


Bikes
1974 Commando
1985 Honda Nighthawk 650
1957 Thunderbird/T110 "Flying Tiger"
Antique Fans: Loads of Emersons (Two six wingers) plus gyros and orbiters.
#477843 - 02/20/13 7:59 pm Re: pre-unit gearbox top mount/drawbolt sloppiness [Re: koan58]  
Joined: Nov 2012
Posts: 165
koan58 Offline
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koan58  Offline
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Posts: 165
Isle of Wight, UK
Thanks HT, I couldn't imagine it was engineered that way, but it's been like that in my ownership for 30+ years! Just always a bloody awkward job when adjusting the primary, especially with only one-sided adjuster!
This time round I am doing what you suggested, having the hole sleeved, and also got an adjuster for the other side.
Just find it strange, the hole isn't ovalled at the ends and seems oversize all through, as though it was meant to have a larger stud than the 7/16".
If you're curious, the bike is on Britycle's customer bike site-Dave's triton thru the decades.
Cheers Dave

#477846 - 02/20/13 9:00 pm Re: pre-unit gearbox top mount/drawbolt sloppiness [Re: koan58]  
Joined: Jul 2010
Posts: 77
al jam Offline
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al jam  Offline
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Scotland
Lovely looking bike Dave, interesting rear brake set up, is it connected to the front brake lever?

Great photos in the snow and Africa too, not many Triton' s been there I'll bet, must have been a trip and a half.


Al


1958 Triton
1958 Triumph 650 Speed Twin
1958 Velocette Viper
1959 Norton 650SS bitsa
1961 BSA Bantam D1
#477956 - 02/21/13 6:54 pm Re: pre-unit gearbox top mount/drawbolt sloppiness [Re: koan58]  
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koan58 Offline
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koan58  Offline
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Posts: 165
Isle of Wight, UK
Ta for the compliment Al, though it doesn't look that great at the mo with bits all over house and workshop!
Got any pics of yours?

No linking of brakes, merely a home made cable operated rear.
I didn't like the way braking force altered over bumps, and having to bend the rod round obstacles.
The idea originally came from a mate's A10, I think it was, and I just copied the idea using an old honda cb125 rear cable and some fittings I made in my old school metalworkshop in the early 80's.
Also has a needle roller swingarm setup made at similar time.

Do you have anything to add on my original enquiry, I'm still curious!

Cheers Dave

#477983 - 02/21/13 9:42 pm Re: pre-unit gearbox top mount/drawbolt sloppiness [Re: koan58]  
Joined: Jul 2010
Posts: 77
al jam Offline
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al jam  Offline
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Posts: 77
Scotland


Since the gearbox mount' s hole is round, I'd probably turn a bolt to fit in the lathe then drill out the engine plates and gearbox adjuster to suit.

If I didn't have a lathe I'd probably see if I could get a good fit with something metric (maybe M12?) and drill the plates and adjuster. A little naughty I know but if it were a nice fit I could live with it.

Good luck with the rebuild.

Al


1958 Triton
1958 Triumph 650 Speed Twin
1958 Velocette Viper
1959 Norton 650SS bitsa
1961 BSA Bantam D1
#478024 - 02/22/13 4:21 am Re: pre-unit gearbox top mount/drawbolt sloppiness [Re: koan58]  
Joined: Jun 2007
Posts: 5,456
HawaiianTiger Online content
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HawaiianTiger  Online Content

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Joined: Jun 2007
Posts: 5,456
Maui Hawaii
Now, that's a proper Triton.
Cheers,
Bill


Bikes
1974 Commando
1985 Honda Nighthawk 650
1957 Thunderbird/T110 "Flying Tiger"
Antique Fans: Loads of Emersons (Two six wingers) plus gyros and orbiters.
#483077 - 03/26/13 2:08 am Re: pre-unit gearbox top mount/drawbolt sloppiness [Re: koan58]  
Joined: Sep 2008
Posts: 71
rohart Offline
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rohart  Offline
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Posts: 71
Twickenham, UK
My '60 bonnie had the lower stud loose in the gearbox. I machined up a new stud, pressed in brass sleeves each side of the box and reamed them to fit.

It transformed the bike. After six years of admittedly low mileage the primary hasn't needed adjusting, and the vibration of the whole bike is much less. The whole riding experience is much tighter.

I just hope the materials I used won't corrode together.

But I'll never use an adjustable reamer by hand again. Next time I have to do a similar job I'll mount the box in a mill or a lathe.


Richard
#483161 - 03/26/13 7:09 pm Re: pre-unit gearbox top mount/drawbolt sloppiness [Re: koan58]  
Joined: Nov 2012
Posts: 165
koan58 Offline
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koan58  Offline
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Posts: 165
Isle of Wight, UK
Thanks Rohart, initially I was thinking about focussing on the bottom mount, on mine the stud has some slop in the g/box hole and also in the engine plate holes.
However, I think my application is somewhat different to yours, where mine is T120 engine and gearbox in a featherbed frame, with adapting mounting plates.
So the bottom pivot is less of an absolute guarantee of parallelness of crank and g/box shafts, compared with your manufacturer's plates and mounting holes. Plus, I run a duplex chain, with a unit thrust washer type clutch, making the situatiion a little more demanding in respect of shaft parallelism and sprocket alignment.
I guess that's why Triumph were happy with only a right side g/box adjuster on all but the last pre-units, with simplex chain and a clutch drum that wobbled about quite a bit.

I've left the slop in the bottom mounting (I need that to permit shaft alignments using the top mount), and had the top hole sleeved closely for the new st/st stud, and aquired an adjuster for the left side.
This should enable accurate parallelisation of the crank and g/box shafts, then I will have to do any necessary adjustments/shimming at the engine sprocket, for final chain alignment.

I'm almost looking forward to primary chain adjustments now, infrequent as they were, for 30+ years they have involved levering the left end of the g/box about until getting both alignment and tension right, in combination with the right adjuster, then nipping it up, finding chain too tight/loose, doing the misery again, etc!!

Only now do I realise how much patience I have expended!

Cheers Dave


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