Weight of the XS650 frame

[jaybar6]

Then there is the large bracket for the shocks. This could be removed and the pin moved between the top seat tube and the rising tube.

 

[arcticXS]

Wait a minute! I forgot about the TX750. That was a new frame and engine. The engine failed but the frame, along with all its cycle parts could accommodate the xs650 engine. Yamaha could of had two bikes, the new 750 engine and the old xs650. They could compete against each other. I know which one would win. Although cubic inches always has a draw. JayView attachment 327735
I wonder if somebody has done this engine swap? There cannot be much interest in the TX750, and thus low buying price.

I wonder how the TX750 handled, compared to the TX650? And frame weifgts? That 750 frame seems to have a lot in common with the RD350 frame, and the RD was known for decent roadholding. Also, that frame style makes it possible to play with longer intakes, even with linked carburettors. If I had access to a 750 frame like that, with papers, I surely would look into a swap.

 

[Grewth]

I wonder how the TX750 handled, compared to the TX650? And frame weifgts? That 750 frame seems to have a lot in common with the RD350 frame, and the RD was known for decent roadholding. Also, that frame style makes it possible to play with longer intakes, even with linked carburettors. If I had access to a 750 frame like that, with papers, I surely would look into a swap.

I'm not really familiar with anything about the TX750, I don't think that they were ever sold here in the UK, (prepared to be corrected about that), and the only ones to get here are "grey" imports, rare as rocking horse manure.
But the TX750 is a vertical twin with dual balance shafts, basically, it should be smoother than a four.
Unlike the 650 which has large out of balance forces trying to shake the engine out of the frame.
That's why the 650 frame weighs so much, to prevent excessive flexing around the engine mounts.
Anything that is flexing will eventually begin to break down after enough milage has been covered.
I've got a 650 Special who's frame split longways under the engine, hopefully the TIG welded repair has cured it.
I've got a set of hand held luggage scales somewhere, if they come to light I'll start weighing some of the frames I've got here.

 

[40north]

Of course removal of the sidecar brackets, must be 2lb, right there:
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Any frame engineered for a hack is over-built when the hack is not there. That said, the lighter the hack, the better! I ran a Kawi 440 with a hack, it killed the rear hub-drum...circular crack all round. Of course I abused it, but it was destined to break there eventually. A hack setup is planned for one of my XS bikes, if I ever get time...and rest assured, it will be a very light hack. For the body one of those stream-lined rooftop cargo thingies made for small cars...so just 1018 1" tube and a Honda 90 front tire...rubber-blocks for "springs and a shock from a quad...and perhaps swipe a fiberglass chair from the laundromat, throw away the metal, just the ol' bucket. Mostly to make runs I make now with the old toyota, shopping. The XYL (wife) is too stove up for bikes anymore, but not me, not yet.

 

[40north]

I'm not really familiar with anything about the TX750, I don't think that they were ever sold here in the UK, (prepared to be corrected about that), and the only ones to get here are "grey" imports, rare as rocking horse manure.
But the TX750 is a vertical twin with dual balance shafts, basically, it should be smoother than a four.
Unlike the 650 which has large out of balance forces trying to shake the engine out of the frame.
That's why the 650 frame weighs so much, to prevent excessive flexing around the engine mounts.
Anything that is flexing will eventually begin to break down after enough milage has been covered.
I've got a 650 Special who's frame split longways under the engine, hopefully the TIG welded repair has cured it.
I've got a set of hand held luggage scales somewhere, if they come to light I'll start weighing some of the frames I've got here.

"Anything that is flexing will eventually begin to break down after enough milage has been covered" Good rule, but there are plenty of hours if the "modulus of elasticity" is not exceeded. That's measurable. But it's non-trivial. See for fun film "No Highway" with James Stewart... Airplane movie... (Speaking of Boeing, hehehehe Two inspectors decided to die suddenly...)

 

[gggGary]

 

[gggGary]

https://www.xs650.com/threads/jims-speed-twin-build.54889/

 

[Grewth]

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Brilliant bit of engineering there.
But TBH, I'm not really sure that I'd want a XS650 with it's vibes surgically removed.
I actually like being able to feel those pistons moving while I'm riding it.
I'm sure that every XS rider has amazed other motorcyclists, by putting the bike on the center stand and giving it some revs.
Not to mention the quivering front end into the bargain.
I'm not too clued up about the Ascot TBH, because it's never really appealed to me.
I remember that with the Commando, the swing arm pivot was connected rigidly to the engine/transmission, so that the isolastic mounts would not affect the chain tension.
A brilliant idea.
Did the Ascot have the same system ?

 

[jaybar6]

here is another idea I have. Brace up the swinging arm pivot with a pyramid structure (power to the pyramid!), which directly ties the head stock to the swinging arm. The magic of photo-shop. I know it adds weight but the trade off is better handling. Jay

 

[jaybar6]

I wonder how the TX750 handled, compared to the TX650? And frame weifgts? That 750 frame seems to have a lot in common with the RD350 frame, and the RD was known for decent roadholding. Also, that frame style makes it possible to play with longer intakes, even with linked carburettors. If I had access to a 750 frame like that, with papers, I surely would look into a swap.

me too. i would like to know how the tx750 handled in comparison and if better, put the xs650 in it. One could have the big bore conversion too. Jay

 

[Its been a long time]

John Hand Racing will put together a very nice frame for an XS650 if you have a couple of grand laying around doing nothing. John Hand was the main frames fabricator at Wasp before he set up on his own. The bronze welded and nickel plated frames are a joy to behold. Artwork really.

 

[jaybar6]

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I wonder if one only fitted the rubber thingy from the ascot to the front bracket and left the rest, and that would be enough to quell the vibes to the handle bars. So one could cruise at 70mph on the motorway (highway) comfortably without removing the character that we all love.

 

[Wacajawaka]

On perusing the book “Motorcycle Handling and Chassis Design” by Tony Foale. I read chapter 17 “a case study” on the improvements to a Kawasaki 750 frame. Where the motorcycle was to be used in racing. In that article the weight of the frame, to my surprise, was given as 12.7Kg (28lb)!

In the article https://www.xs650.com/threads/large-spine-frame-xs650-egli-rau-cafe-racer.51029/ on xs650.com forum, Rauel had measured the weight of the xs650 frame to be 60.8lb (27.6Kg).
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I find it incredible that a late 1980’s motorcycle has a frame that is half times lighter than the xs650. I just think that the xs650 would still be around into the 90’s if a well designed frame was designed for it. Like the Royal Enfield frame, designed by the Harris group. As the engine is/was an engineering masterpiece (the best of the air-cooled), it could still have the same style, tank, shape, seat, etc.

It leads me to believe one could just swap out the Kawasaki engine and slot in the xs650 engine. Giving one a “modern” xs650 – bigger diameter forks, lighter chassis, better handling, etc. A missed opportunity by Yamaha. Maybe I should buy the xsr700 and stop moaning! Jay

Interesting, did you see the fella (he might be on here?) who put the xs650; lump into an early fz600? It looks quite happy in there.

 

[arcticXS]

I wonder if one only fitted the rubber thingy from the ascot to the front bracket and left the rest, and that would be enough to quell the vibes to the handle bars. So one could cruise at 70mph on the motorway (highway) comfortably without removing the character that we all love.

I believe that a single "pivot point" at the rear of the crankcase is required, for a front rubber mount to be effective.
The most commonly known anti- vibration engine mounting is of course Norton Commando Isolastic, but Buell also had an interesting setup. And MZ 250 2- stroke singles, which may well be the best, or at least simplest system for a hobbyist builder.

 

[arcticXS]

The rubber damper is the piece at the rear of the cylinder head. On an XS, the rubber should be at the front engine mounts.

 

[gggGary]

The trick is to allow the 360 twin to oscillate up and down yet have the mount help keep the frame neck stiff and not flex side to side under riding stresses.
The word is Norton bowed to space and expense concerns and eliminated the original design of an isolastic from cylinder head to frame back bone. There are now aftermarket "solutions" for this area on the Nortons. But yes one pivot point at the rear, the rest have to have some give or it will commence tearing the frame apart.