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Discussion Starter · #1 ·
Hi. I’ve got lots of T120/TR6 spares (including a complete engine) after doing my 1968 T120 restoration so I’m tempted to try and build a ‘special’ using a Japanese frame so that I can benefit from modern forks/suspension/brakes. However, I’m not sure which frame would work with a unit 650 engine. Someone once told me that a Suzuki GT380 frame would work but I’m not sure about that. Does anyone have any experience or reccomendations regarding alternative frames for a unit 650?
Thanks very much
Regards
Tony
 

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Discussion Starter · #3 ·
Hi GrandPaulZ. Thanks for your reply. I live in the U.K. and ‘spare’ pre-OIF T120 frames are very rare, that’s why I was tempted to go for a Japanese bike frame. If I could find a T120 frame, I’d still want to use Japanese forks as I find the stock T120 forks incredibly harsh . I only weigh 130 pounds - my weight just doesn’t seem to be enough to make the forks work on poor road surfaces - it’s like riding a bike with solid forks
 

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attaboy!

i have many projects in my foolish minds eye. one of them is parallel to yours.

consider something inexpensive and competent, such as a 2000s or so 250 ninja. that is what i am looking at.

alternatively, look to two stroke race chassis. thee are some very good possibilities there.

here is a mid 90s RGV suzuki 250 two stroke race chassis with an 880 A65



65 or so horsepower. it is very successful, as i am told.
 

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Hi GrandPaulZ. Thanks for your reply. I live in the U.K. and ‘spare’ pre-OIF T120 frames are very rare, that’s why I was tempted to go for a Japanese bike frame. If I could find a T120 frame, I’d still want to use Japanese forks as I find the stock T120 forks incredibly harsh . I only weigh 130 pounds - my weight just doesn’t seem to be enough to make the forks work on poor road surfaces - it’s like riding a bike with solid forks
Strange; I weighed 125# from about 1974 till about 2004 (I now weigh about 145) and I've never found decent condition, well maintained classic Triumph big twin forks to be harsh. The ones on my race bike have taken a beating and still feel the same to me (maybe I'm just not that sensitive).

Anyway, I've used ZX6, ZX7 & TL1000 forks on 3 custom Norton 850 Commandos, but they'd be WAY too much on a Triumph (in my opinion).

I did use a set of Yamaha XS650 forks on a Norton and they'd be a much better match on a Triumph (they came off a guy's '66 Bonnie that he wanted to return to stock, which I did).
 

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Someone once told me that a Suzuki GT380 frame would work
It would work particularly well if you had a desire for your bike to handle a supermarket trolley with one castor siezed.😊
 

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Yoo kno I cant spewl in USA langwige, I woz broout up in England😊

The GT 380 does not actually handle that badly after a few upgrades to twisty swingarm, soft suspension and tyres, it’s particularly sensitive to tyre pressures (tankslappers). Front brakes are bad also.
 

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thats why a more recent kawatrumphski might be a good sttarting point. this is a 2009 kawasaki ninja 250 EX



this tube frame uses the kawasaki engine as a stressed member, but it also means that you can fabricate several down tubes to complete a cradle for a T120 engine with maximum room for fiddling. plus. the japanese suspension and brakes are quite competent already, which means you dont have to start with something marginal and upgrade it. all your atenttion can be focused on fitting the motor with the chassis coming in as a package deal.

in america these machines can be found inexpensively. id be doing one now except i have three BSAs and a triumph in line in front of it.
 

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Hi,
frame uses the kawasaki engine as a stressed member, but it also means that you can fabricate several down tubes to complete a cradle for a T120 engine
Any reason not to use the T120 engine as a stressed member? Many years ago now, the British motorcycle magazine SuperBike featured an engineering degree student's project that was a sheet-metal monocoque with a T150 engine simply hung underneath it.

‘spare’ pre-OIF T120 frames are very rare,
What about an OIF frame? If you don't want a '73-on disc-brake front end, just modify your preferred Japanese front end to fit? IIrc, @Truckedup's done several? As I've name-checked him, next time he looks in, the Forum software should give him a link here.

Regards,
 

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i dont know about a stressed engone, stuart. im not any kind of an engineer. on a T120 the mounts would have to go to the head bolts or the central rocker box studs on later rocker box designs. certainlythey could hold the weight, but would vibration tend to loosen and misalign the head and valve gear?

on reflection the engine could be suspended in front from the single forward mount, using the rear mounts to steady laterally. i think that would trangulate sufficiciently against torque from the gearbox sprocket.

phil vincent did it after all
 

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Hi Kevin,
engine could be suspended in front from the single forward mount, using the rear mounts to steady laterally.
(y) I owned one of the Honda 400 twins some posters in the crank thread have been so scathing about ... Engine suspended from the pressed-steel backbone exactly as you've described - the cam cover was secured just by M6 screws, no more-substantial head bolts poking through it.

Regards,
 

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Hi Tony,
There is a lot of work in a conversion, usually the first thing to consider is drive sprocket alignment, a mag wheel will not usually give any easy adjustment to the left side. A spoked wheel will allow some compensation on the spokes to keep both the front/rear sprockets and wheel/frame centrelines aligned.
As with most project bikes, it will likely have more value to you rather than to anyone else, so do not expect to recoup the build costs.
If you have the upfront funds then it might be worthwhile considering a kit from these guys, expensive to start, but resale values are large.

Regards
Peg.
 

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Someone once told me that a Suzuki GT380 frame would work but I’m not sure about that
sounds a bit iffy to me in the fit department. I have no idea of actual dimensions, but.............. seeing as how the GT380 is a two stroke I would suspect the frame would not accommodate a tall ohv engine such as the T120.
 

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Engines used by manufacturers as stressed members are DESIGNED to accept the stresses imposed.

Classic Triumph engines do NOT have such inherent design considerations. Therefore, I STRONGLY recommend NOT doing so.
Hey, some people enjoy the "do it and see what breaks first" approach to engineering.
 

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Engines used by manufacturers as stressed members are DESIGNED to accept the stresses imposed.

Classic Triumph engines do NOT have such inherent design considerations. Therefore, I STRONGLY recommend NOT doing so.
paul, you are absolutely right that they werent designed to do it, so anybody who tried would be on his own. but i do stuff to my machines that they werent designed for all the time. not always successfully, i do admit.

id have to look at the 2009 ninja frame more closely, but it appears as if the engine cases are mostly only under tension, within the vertical plane. i dont think they have to resist twistinf forces-- that looks like it is absorbed by the twin frame rails under the tank. a later spar-type frame would take almost all the forces through the spar, and would be just as stiff without an engine at all, im thinking.

what might kill the idea of a T120 in a non-spar frame would likely be the rear motor mounts in the castings. these were certainly designed to accommodate pretty modest forces only in a single plane, and any twisting at all might crack em off.

but looping two tubes under the engine wouldnt be hard to do and might avoid any problems. or maybe just box the motor in front and back, like the preunits



just thinking out loud
 
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Isn’t this a solution in search of a problem? The jap frame I mean?
an OIF is a far better frame than earlier.
various rob north/ Rickman combinations are possible
or “Norton” (real or replica)

or stick with a pre 71 frame but improve suspension.
 
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