swing arm widening woes, drive shaft q's

[Vishnuatepork]

So I am at the phase of my project where I have to widen the swing arm.

background, Suzuki vx 800, drive shaft 800cc Vtwin.  Engine almost done...first dyno pull was 23% over sock, no jetting or exhaust...it comin along

I need to fit some custom rim on it. Stock rims wont cut it, so the next obvious choice requires me to increase the space of the swing arm, easy cut and weld.

Where it gets difficult is the drive shaft.  Stock set up already has 1 ujoint at the engine out put, if I widen the swing arm I will require a second ujoint just before the drive hub.  My welder is saying I will require some sort of pillow block bearing somewhere along the length to help keep it in line/from flopping. I want alternatives because the drive shaft housing is the swing arm and putting a bearing in the housing is....not something I can picture.

I guess I want to know why would I require a pillow block bearing in the drive shaft?  Dont most drive shafts have 2 u joints in them anyways? As it would be welded onto the output end of the shaft.....Is it because the out put end has some play in it (the shaft has the ability to slide in and out of the drive hub about 3/4")?

Cheers 

[Jon]

Pretty much all car drive shafts have a slip joint on on end.
If there isn't much play in the slip joint you should be fine without a bearing in the middle.

Get the universal joints so that they are on the same plane along the shaft, when the front uni has the caps connected to the long shaft straight up and down the back uni needs to be the same to help cancel vibration.

Ideally the angle of the front and back unis should be the same when viewed from above and from the side.
From above should be easy as both will be parallel with the centerline of the bike.
From
The side the front one will change angle a fair bit as the suspension moves but the back one not much so it will be a compromise.
Set the suspension about mid travel and turn the rear hub so that the input shaft is parallel with the gearbox output shaft, this will be different than the original orientation unless the swingarm is horizontal midway through the suspension travel.

Ideally you want at Least 1/2degree angle on any uni to stop flatspotting the rollers.


jon

[Vishnuatepork]

Thanks for the 411, Jon

Another q.

Would it matter if the uni's are different.  The stock one at the front would be alot bigger then the one I want to add at the rear.
It wont be parallel to the center line of the bike....will that matter?
 

[sabat]

Have you considered a chain conversion? More efficient, less complex.

[Vishnuatepork]

@ sabat

not goin there...gotta maintain the shaft.

[wobblywalrus]

The guy might be right.  It is good to put the bike on a dyno, watch carefully, and see what happens.  Sometimes shining an ignition timing light on a rotating object will tell a person quite a bit about what is going on.

[Jon]

Differences in uni size won't make a significant difference.

Which bit won't be parallel with the centerline of the bike?



jon

[Peter Jack]

Be sure when you put the second universal joint in that you phase it correctly. Otherwise you'll definitely end up with trouble.

Pete

[Vishnuatepork]

Differences in uni size won't make a significant difference.

Which bit won't be parallel with the centerline of the bike?



jon

The drive shaft wont be parallel...it'll be canted to the left by about 7 degrees

[Jon]

7 degrees is more than you would want in something that was going to be doing high milage or pulling heavy loads.

If you drag it on a surface where you get good traction you could have some uni problems
Low milage on salt you should be ok, may get a bit of vibration at high shaft rpm.

Double check all the shafts are parallel at your normal ride height and that the uni orientation is right.


jon

[Grandpa Jones]

Here's a link to Dr. John's Moto Guzzi racer. There is a little blurb in the article about the
floating gearcase. Guzzi went to a similar design on their factory bikes a few years later.

https://picasaweb.google.com/kaistlouis/MotoGuzziDrJohn?authuser=0&authkey=Gv1sRgCPS5qYStw4OBGA&feat=directlink#

What is the reason for the wheel change?

Is the stock gearing going to limit performance?

Cheers,

Dave

[wobblywalrus]

See if you can find a Yamaha XS-1100 in a junkyard and look at the shaft joint.  They are constant velocity joints and they can transmit a lot of power with no problems. 

[46champ]

Wouldn't it simplify matters if you use struts instead of suspension?  You wouldn't have to worry about changes in drive shaft length.

[Vishnuatepork]

@ 46champ,  you mean a rigid rear end?  Id have to look at the rules for that... I dunno if thats allowed at the Mojave Mile

[Jon]

If the centre of the front uni lines up with the swingarm pivot fairly closely the change in length is miniscule.
Need to have some sort of slip joint in the system anyway.


jon