moving the engine back and straightening it out

[jaybar6]

Using the magic of GIMP, I want to move the engine back about an inch and straighten the engine up like it was when it was first designed. The picture shows the engine moved back and how much metal needs to be removed. It is now hard up against the three tubes - one the swinging arm pivot, the other two footrest and brake lever respectively. This entails a swinging arm pivot hard up against the engine and closest to the engine sprocket (not shown, it's on the other-side obviously). This has the advantage of reducing chain ware. The tilting of the engine according to GIMP is about 11 degrees. This would add cooling of the engine as the air can now flow through the fins.

 

[Raymond]

Won't it need major frame surgery to move the engine back and level it? Not sure of the payback/effort equation here . . .

 

[650Skull]

Could one argue on 2 points. Centre of gravity is raised and moved back making the bike handle worse. The fins now being horizontal have less cooling effect due to the wind having less contact than angling into the wind.

 

[Charles13]

Could one argue on 2 points. Centre of gravity is raised and moved back making the bike handle worse. The fins now being horizontal have less cooling effect due to the wind having less contact than angling into the wind.

It would handle better as the it would move the center of gravity closer to the center of the bike

 

[jaybar6]

Won't it need major frame surgery to move the engine back and level it? Not sure of the payback/effort equation here . . .

Raymond, major surgery is required to improve the patient's health and increase longevity.

 

[jaybar6]

I will be also reducing the rake on the head stock from 27 degrees to 24 degrees. There fore reducing wheel base and reducing the turning circle.

 

[Charles13]

I will be also reducing the rake on the head stock from 27 degrees to 24 degrees. There fore reducing wheel base and reducing the turning circle.

24* is pretty steep but with a 19” front wheel you should still have sufficient trail ~4”, I’ve shortened the swingarm on 2 of my bikes.

 

[jaybar6]

One could move the engine back further (another 3/4 inch) but there is a strange protrusion on the right side back? If only the back of the engine was flat.

 

[jaybar6]

24* is pretty steep but with a 19” front wheel you should still have sufficient trail ~4”, I’ve shortened the swingarm on 2 of my bikes.

Cool charles13, what is the effect, can you feel the difference?

 

[Charles13]

Cool charles13, what is the effect, can you feel the difference?

More traction in slippery conditions, turns a lot faster and wheelies are a lot more controllable, there are a few people making swingarms for the XS mostly for flat track, that are a lot sturdier and also shorter.

 

[650Skull]

I will be also reducing the rake on the head stock from 27 degrees to 24 degrees. There fore reducing wheel base and reducing the turning circle.

Are you building a new frame or altering the factory frame.

 

[halfmile]

What year of frame are you using?. Sounds like it would be much easier to just buy a repro Champion Frame.

 

[jaybar6]

More traction in slippery conditions, turns a lot faster and wheelies are a lot more controllable, there are a few people making swingarms for the XS mostly for flat track, that are a lot sturdier and also shorter.

Charles13, these changes are all good things, an increase in performance. Not sure about the wheelies though! I have pretty high gearing on mine and have not pulled a wheelie, lol. I don't have a picture but from memory there is three inches from the tyre to the swing arm. That is with a 18 inch rear wheel. I think about welding a tube in that gap to strengthen the swing arm. I would consider shortening the swing arm in future. One thing at a time.

 

[jaybar6]

What year of frame are you using?. Sounds like it would be much easier to just buy a repro Champion Frame.

That is one way to go, and I like it, but i am just improving the standard xs650 without losing it's character as a roaster.

 

[jaybar6]

Are you building a new frame or altering the factory frame.

Altering the factory frame, but by the time I have finished the only thing left could be the steering head stock!

 

[jaybar6]

That gap between the swing arm and the tire leaves me to be believe that Yamaha originally was going to put a 19 inch wheel in there, like the Norton commando. i have considered that myself, but I don't think there is much tyre choice . So i have not done it.

 

[Charles13]

Charles13, these changes are all good things, an increase in performance. Not sure about the wheels though! I have pretty high gearing on mine and have not pulled a wheelie, lol. I don't have a picture but from memory there is three inches from the tyre to the swing arm. That is with a 18 inch rear wheel. I think about welding a tube in that gap to strengthen the swing arm. I would consider shortening the swing arm in future. One thing at a time.

There is a Company in Thailand Motollana that makes a very nice ally swingarm xt500/xs650 and it’s reasonable

 

[Its been a long time]

There is a Company in Thailand Motollana that makes a very nice ally swingarm xt500/xs650 and it’s reasonable
View attachment 343284

That's very nice indeed.

 

[jaybar6]

There is a Company in Thailand Motollana that makes a very nice ally swingarm xt500/xs650 and it’s reasonable
View attachment 343284

Looks nice, but I prefer steel on the swing arm.

 

[jaybar6]

Using the magic of GIMP, I want to move the engine back about an inch and straighten the engine up like it was when it was first designed. The picture shows the engine moved back and how much metal needs to be removed. It is now hard up against the three tubes - one the swinging arm pivot, the other two footrest and brake lever respectively. This entails a swinging arm pivot hard up against the engine and closest to the engine sprocket (not shown, it's on the other-side obviously). This has the advantage of reducing chain ware. The tilting of the engine according to GIMP is about 11 degrees. This would add cooling of the engine as the air can now flow through the fins.View attachment 343227

I have just realized I have not rotated the engine enough! The top red line is where the engine split is in the cases. This is where the center of the sprocket will be. It should be aligned with the center of the swing arm pivot. I will get back to you with another corrected picture.