Weight of the XS650 frame

[jaybar6]

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).

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

 

[Its been a long time]

There are a few people around the UK who will build you a modern, lightweight frame for an XS650 motor. The one thing that would bother me about doing that is the solid bolted in motor. No vibration isolation. All the vibration is transmitted straight into the frame, probably accounts for why the Yamaha frame is so heavy? But it's very doable in principle.

 

[jaybar6]

Using the magic of photoshop, I shoehorned the xs650 engine in the Continental gt535.

 

[member43148]

Using the magic of photoshop

Do that again but flip those shocks right side up

 

[40north]

The fatigue life of light frame is poor, they require periodic inspection. I remember fixing the cracks in some old Trumpets from the late 50's...in the late 60's. That said, some light frames only see a few hundred hours. Or less for Bonneville stuff. The choice of steel (or other alloy) and the type of welding used, and heat treat matters very much. Once longtimeago I used an industrial oven at a foundry to anneal and stress relieve a light frame I built for a flat-head Harley. It never cracked, and I tried to get it to crack. A seriously light frame would look at the way racing bicycle frame are made, then learn and 'speriment. It is non trivial.

 

[gggGary]

I did some weighing of a stock and a light weight frame.
https://www.xs650.com/threads/garys-junkyard-tracker-build-up.8395/
"simple" way to a light XS?

butcher a late model steel dirt bike to fit the XS motor.
https://www.facebook.com/marketplace/item/1619310952203067/

 

[jaybar6]

I did some weighing of a stock and a light weight frame.
https://www.xs650.com/threads/garys-junkyard-tracker-build-up.8395/
"simple" way to a light XS?
View attachment 327577
butcher a late model steel dirt bike to fit the XS motor.
https://www.facebook.com/marketplace/item/1619310952203067/

Hi Gary:
Interesting article there. I particularly like the rear swinging arm arrangement, as it moves the swing arm pivot closer to the sprocket, giving the chain an easier life-time as it is not stretched as much. I had that image in my files and forgot where it came from. That article was 2011! Has there been any progress on that adventure? Jay

 

[jaybar6]

The fatigue life of light frame is poor, they require periodic inspection. I remember fixing the cracks in some old Trumpets from the late 50's...in the late 60's. That said, some light frames only see a few hundred hours. Or less for Bonneville stuff. The choice of steel (or other alloy) and the type of welding used, and heat treat matters very much. Once longtimeago I used an industrial oven at a foundry to anneal and stress relieve a light frame I built for a flat-head Harley. It never cracked, and I tried to get it to crack. A seriously light frame would look at the way racing bicycle frame are made, then learn and 'speriment. It is non trivial.

That reminds me of the mettise frame. it had nickel (?) plated exterior not to look good (although it does) but to show up cracks. Apparently they are easier to see.

Now this is what Yamaha could of done, in my opening statement for example. Jay

 

[gggGary]

Has there been any progress on that adventure?

nope

 

[jaybar6]

here is a comparison between the xs2 frame and the later standard frame. the xs2 frame is in pink and the later standard frame in blue. I put the head stocks of both images together to see the alignment differences:

 

[Grewth]

There's a hell of a difference between the weight of a XS1 frame and a TX650A.
Percy Tait added a whole lot of "doublers" to the basic design to try to stiffen it up.
Considering how different the '74 TX650A is from the '73 TX650, I think that Yamaha probably should have gone the whole hog and designed a brand new frame from scratch.
Apparently the senior management at Yamaha had ruled this out

 

[jaybar6]

There's a hell of a difference between the weight of a XS1 frame and a TX650A.
Percy Tait added a whole lot of "doublers" to the basic design to try to stiffen it up.
Considering how different the '74 TX650A is from the '73 TX650, I think that Yamaha probably should have gone the whole hog and designed a brand new frame from scratch.
Apparently the senior management at Yamaha had ruled this out

I cannot find anything on Percy Tait working for Yamaha? He was a test rider and racer for Triumph. I only did a brief search with his name. I think the Bonneville frame would of being good choice for the xs650 engine.

 

[jaybar6]

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. Jay

I wonder if somebody has done this engine swap? There cannot be much interest in the TX750, and thus low buying price.

 

[Grewth]

I cannot find anything on Percy Tait working for Yamaha? He was a test rider and racer for Triumph. I only did a brief search with his name. I think the Bonneville frame would of being good choice for the xs650 engine.View attachment 327714

I think that the information about Percy Tait going to Japan to sort out the TX650's handling issues has come from the late Mr Tait himself.
Apparently it was arranged through Yamaha's European HQ in the Netherlands.
I don't think that Yamaha themselves were actually too keen on publicising the fact that they'd had to employ Triumphs (ex) chief test rider to sort out their handling issues.
As for fitting the XS engine in a T140, or any other Meriden Triumph frame, it's a non-starter.
The XS engine is just too tall.
Allegedly it will fit in a RE Bullet frame, I've actually seen one in a Featherbed Norton, and also a BSA A10, so probably the B33 frame too.
But even the frame from an Ariel Huntmaster (BSA A10 powered) won't take a XS engine, not properly anyway.
It's only when you get a XS650 engine out and put it on the bench next to a unit BSA or Triumph twin engine, that you realise just how bulky the XS engine actually is.
All the extra strength and robustness that Yamaha built in had it's cost in size and weight.
Yamaha did an excellent job of designing the XS1 rolling chassis to make the engine appear smaller than it actually is.

 

[jetmechmarty]

I think that the information about Percy Tait going to Japan to sort out the TX650's handling issues has come from the late Mr Tait himself.
Apparently it was arranged through Yamaha's European HQ in the Netherlands.
I don't think that Yamaha themselves were actually too keen on publicising the fact that they'd had to employ Triumphs (ex) chief test rider to sort out their handling issues.
As for fitting the XS engine in a T140, or any other Meriden Triumph frame, it's a non-starter.
The XS engine is just too tall.
Allegedly it will fit in a RE Bullet frame, I've actually seen one in a Featherbed Norton, and also a BSA A10, so probably the B33 frame too.
But even the frame from an Ariel Huntmaster (BSA A10 powered) won't take a XS engine, not properly anyway.
It's only when you get a XS650 engine out and put it on the bench next to a unit BSA or Triumph twin engine, that you realise just how bulky the XS engine actually is.
All the extra strength and robustness that Yamaha built in had it's cost in size and weight.
Yamaha did an excellent job of designing the XS1 rolling chassis to make the engine appear smaller than it actually is.

I remember getting off of a vintage Triumph (1970?) and onto an XS650. Looking down toward my feet, the XS bottom end is huge. I don’t think the XS was better than the Triumph in every way. Off the shelf the Triumph was probably the better performer. The Yamaha was probably easier to live with.

 

[40north]

I cannot find anything on Percy Tait working for Yamaha? He was a test rider and racer for Triumph. I only did a brief search with his name. I think the Bonneville frame would of being good choice for the xs650 engine.View attachment 327714

The previous Triumph with the bolted together frame may have been much lighter. And they cracked around the rear brake lever pivot, and where else I can't say. For myself, I'd just position the XS engine on the jig and start cutting tube...never mind frame swap..except that one ought to keep a headstock with clean numbers and title for the cops.

 

[Grewth]

The previous Triumph with the bolted together frame may have been much lighter. And they cracked around the rear brake lever pivot, and where else I can't say. For myself, I'd just position the XS engine on the jig and start cutting tube...never mind frame swap..except that one ought to keep a headstock with clean numbers and title for the cops.

I've honestly thought about building a "Triumph" type frame around a XS650 engine - I mean just like the two piece bolt together Unit Triumph type.
I don't suppose that this would have any real advantage over any other design, but I just like the look of it.
I'm a fabricator/welder, but I build modular buildings, so building a motorcycle frame would be something of a challenge, but still.

 

[jaybar6]

The previous Triumph with the bolted together frame may have been much lighter. And they cracked around the rear brake lever pivot, and where else I can't say. For myself, I'd just position the XS engine on the jig and start cutting tube...never mind frame swap..except that one ought to keep a headstock with clean numbers and title for the cops.

How about taking out all this metal above the swinging arm pivot? Jay

 

[jaybar6]

I've honestly thought about building a "Triumph" type frame around a XS650 engine - I mean just like the two piece bolt together Unit Triumph type.
I don't suppose that this would have any real advantage over any other design, but I just like the look of it.
I'm a fabricator/welder, but I build modular buildings, so building a motorcycle frame would be something of a challenge, but still.

I don't know how much weight advantage the triumph has over the xs, but it look stronger with its larger diameter top and down tube. Probably astronomical prices now though, so can not justify the build. Jay

 

[jaybar6]

Of course removal of the sidecar brackets, must be 2lb, right there: