Xs650 sprint bike

[jay760]

Managed to get my hands on an old 80s dragbike frame, it's been sitting at the back of the shed for a while while I kept looking at it wondering how to get the very tall xs engine in it,
Finally decided to take the plunge and drill the frame as with the bottom mount above I couldn't get the engine in end below the casings hit yhe frame, worked out the front and bottom two mounts just got to try and work out the top rear engine mount and the head

 

[Signal]

That's a great project.
You may not need a top engine mount. A lot of XS sidecars don't run them and considering you are only going straight it could be redundant.
Are you going to use an XS rear wheel ? I ask because it could be difficult to fit the small rear sprocket to the mag wheel in the picture.
(Edit)
Just been looking at Halfmiles LSR build, it looks like he used the rear down tube from a stock frame. If you can get one that could save a ton of work making brackets as you can use the stock ones.

 

[jay760]

I'm going to use a cb400 wheel as I have it, laced up with a wide 18 inch rim which so can start off with a 130/90 race conti road attack tyre, eventually ending up with a vintage drag tyre

 

[jay760]

Bottom engine mounts are finished and welded up, need to get the engine built then decide if I'm putting a top engine mount on and how low i can get the tank

 

[jay760]

Engine is starting to go together now, Shell rods with 80.5mm JE pistons, head will have 2mm over valves and Shell #3 cam, this is a lot different to the #1 cam

 

[halfmile]

I just now noticed this thread. I really like the frame. I almost used the double upper main tube design on my LSR build. What is the wheel base of your build? I went with a 72" wheel base but probably should have made it 80". (After Thought as usual). Your motor choices are spot on.

 

[jay760]

Ù

I just now noticed this thread. I really like the frame. I almost used the double upper main tube design on my LSR build. What is the wheel base of your build? I went with a 72" wheel base but probably should have made it 80". (After Thought as usual). Your motor choices are spot on.

Thanks,
The wheel base is around 72" it's a period frame so will work with what I've got, it's just too long to stay in classic class which is 68" but that's no hardship ad they changed the classes this year and includes all bikes up to 94 and 1500cc so virtually no difference to racing class,

 

[jay760]

Engine mounts have been welded, engine is in very tight fit but its in

 

[halfmile]

Your bike is coming along nicely. What are your plans for the fork tubes?

 

[jay760]

Your bike is coming along nicely. What are your plans for the fork tubes?

I've stiffened them right up with spacers in the top of the tubes, the only other thing to do would be to get a lowering kit for them just to bring them down a bit, but as the legs will be the same length there will be no weight loss.

 

[Mailman]

I really hope you can get a video of this bike at the track someday for us to see. It’s looking like a really cool build!

 

[jay760]

Haven't done much to it lately, I've been having problems with the bike I'm riding at the moment, finally last weekend I'm hoping I've found the problem, basically running out of fuel, I had done a calculation of if the bikes doing 120mph which it would be probably doing more if it had the length of track, at 10 mpg I needed a ltr of fuel per minute, I'm obviously doing less than 10mpg, I've changed the pipes and drilled some big holes in the cap now up to 1.5ltrs a minute will find out at the next meeting if this has worked.
Other than that the bike was running extremely well, 1.75 at 60 ft, 7.55 at the 1/8th and coasting over the quarter at 12.13 at only 100mph where it was dropping out due to fuel.

 

[halfmile]

7.55 at the quarter?? Did you mean the 1/8th?? If it went 12.13 at the quarter short of fuel It`ll surely go mid 11`s. What gear ratio are you running?

 

[jay760]

Yes was supposed to be the 1/8th changed now to avoid confusion,
Was figuring it should be in the 11's been a long time since I've been there would be pretty good as I'm not the lightest person at 215lbs.
Running 16/33 first time I've tried this gearing as have been running 17 on the front but looking on gearing commander site it only worked out at just over 7000rpm across the line

 

[jay760]

Slow progress lowered the forks by 4 inches and finally found a fuel tank that's now fitted, with this in place I can lie along the top tubes.

 

[jay760]

Gear and brake linkages have now been done, for ease the brake is virtually a standard setup using xs650 brake rod, just had a tube welded to the frame for the original linkage to fit through, luckily with the gear linkage I found a bent up lever already made up in the garage which was lucky as I was wondering how to make it miss the frame,
Also have a guard to stop the majority of debris ending up in the engine, though will probably still use Ramair velocity filters that fit over the velocity stacks

 

[jay760]

 

[jay760]

Just about finished now, unfortunately due to a fatality where I race there are still investigations ongoing as to what happened so won't get to run it until next year

 

[jaybar6]

Just about finished now, unfortunately due to a fatality where I race there are still investigations ongoing as to what happened so won't get to run it until next yearView attachment 335403View attachment 335404

Hi jay760, what is the length of your inlet manifold tract, from the head to the bell mouth?

 

[jay760]

Manifolds are about 4 1/2 inches, length to end of velocity stack around 9 1/4 "