80 XS11 Midnight Special chop/rebuild log

[cywelchjr]

i think the u-joint angle can be plus or minus 5 degrees from zero, because i was researching that same thing when i started my hardtail. i kept mine at zero for safty reasons, and i didnt need it to be that low for my tastes.

As motoman has covered in the past, 0 deg is bad for u-joints and will cause them to wear out quickly due to them not getting any movement of the bearings (this is a very bad thing or u-joints, they were designed to move). They need to be a little bit off 0 so that the joint is getting some movement of the bearings, else the joint will beat itself to death, and these are NLA which means your stuck looking for a donor machine or something.

[jimbyjimb]

These bikes look pretty when they're lowered. The roads I drive on I think I'd bottom out a lot. Still, that will make a neat round town cruiser. It's always good to see people reusing old stuff rather than buying everything new.

[crazy steve]

It's not so much the u-joint as the final drive splines that will suffer from too much angle. The splines on the driveshaft aren't straight/rigid; they're 'rounded' to allow about 3-4 degrees of movement (which happens when the swingarm goes up and down), but the suspension was designed so that at 'normal' ride height the swingarm is running level and there's very little angle at the final drive. Lower the bike, and it's now running in permanent misalignment which would have to shorten the shaft's life...

[cywelchjr]

It's not so much the u-joint as the final drive splines that will suffer from too much angle. The splines on the driveshaft aren't straight/rigid; they're 'rounded' to allow about 3-4 degrees of movement (which happens when the swingarm goes up and down), but the suspension was designed so that at 'normal' ride height the swingarm is running level and there's very little angle at the final drive. Lower the bike, and it's now running in permanent misalignment which would have to shorten the shaft's life...

That part is correct, but as motoman covered in a post last fall, u-joints were designed to move as they rotate and need some movement as they rotate to not destroy themselves. I don't remember the exact amount but he mentioned problems with a snowplow that didn't have enough of an angle on it's u-joints and was eating u-joints because of this.

[crazy steve]

I've never looked to see what angle the u-joint is at when the swingarm is level (and you have zero angle at the FD) so I can't say if that 5 degree number is right or not; I suspect not in some cases, as my Jags all run the driveshaft u-joints at or near zero degrees and they're not known as failure points, typically running well over 100K. The only reason those have u-joints is because of the rubber mounts on the trans/rear suspension.

But running that spline out of alignment increases the wear a lot; if the angle is zero, the only wear will be at the contact points on the splines in one axis (90 degrees to the spline face), and nearly all will be caused by loading/unloading the coupling. But put some angle in there, and now you've got back-and-forth wear too, the more angle the more wear. I suspect the shaft failure that Scott had was caused by this, as from what he says he likes to 'load 'er up' and may have run enough miles with the suspension compressed more than normal to do that.

[motoman]

I've never looked to see what angle the u-joint is at when the swingarm is level (and you have zero angle at the FD) so I can't say if that 5 degree number is right or not

As Cy stated, that u-joint issue came about some 30+yrs.ago, so having u-joint factory engineers involved in that situation it kinda turned into a cluster, but I do remember them stating that a u-joints ideal operating angle is 3-5degrees. So your close with the 5degree Steve. If you've ever seen the torture angles u-joints run(70degrees+) in a gravel pit shaker/crusher operation, would make you wanna duck. Very doubtful of any effect at the shaft/pinion splines other than torque load as the PIVOT point is at the swing-arm/u-joint for suspension vertical travel. From there back to axle would operate as one piece in effect, least I would hope so(rollin' on the slab @75+), or things could get ugly.

[Nightengale]

i will check mine tomorow

As motoman has covered in the past, 0 deg is bad for u-joints and will cause them to wear out quickly due to them not getting any movement of the bearings (this is a very bad thing or u-joints, they were designed to move). They need to be a little bit off 0 so that the joint is getting some movement of the bearings, else the joint will beat itself to death, and these are NLA which means your stuck looking for a donor machine or something.

i need to double check mine tomorow before i make all my final welds, this is why i love this site. you guys have so much information, i learn something new everyday, that is why my build is going slow, i am checking and double checking things like this so that when i am done with my bike i know it will be something that i will enjoy for a long time. thanks for the info guys.

[motoman]

and these are NLA which means your stuck looking for a donor machine or something.

Not true, IIRC there was a post quite some time back where someone came across a replacement from a different application. Aside from that, can be almost sure I could godown to my local Drivetrain Industries and get one from measured dimensions. Have done alot stranger applications with off-set cup sizes and such, so this would be an easy find, IMO.

[BA80]

yeah, i think it was a u-joint for a forklift or something.

[crazy steve]

... Very doubtful of any effect at the shaft/pinion splines other than torque load as the PIVOT point is at the swing-arm/u-joint for suspension vertical travel. From there back to axle would operate as one piece in effect, least I would hope so(rollin' on the slab @75+), or things could get ugly.

No, there is, because I've seen it. The u-joint and the swingarm pivots aren't in line, the u-joint is closer to the motor. Here's a pic of my big-tire modified swingarm before I covered the hole I cut for the shaft...

[IMG][/IMG]

In this pic the swingarm is level, and you can see the driveshaft is evenly centered in the slot with a gap top and bottom. Move the arm up or down, and the gap will almost disappear (which is why the slot is as wide as it is; I originally had the slot narrower, but had to make it wider to account for this). That changes the angle at the final drive, which is why the driveshaft has those curved splines.... and I agree, running the shaft at a continuous angle (rather than the intermittent angles it's designed for) is a bad thing...

[fredintoon]

Hi Guys,
just to throw another cupful of gas on this fire:-
The XS11 Ujoint is a classic Hooke's joint and they are non-linear.
If the input turns at a constant speed the output goes fast then slow twice each turn.
On car driveshafts there's two of them so it cancels out.
On the XS11 there's only one so as the drive angle gets bigger the fast/slow effect gets bigger.
If this noticeably affects the drive, I dunno.
Just one more thing to consider.

[Nightengale]

tire size

No, there is, because I've seen it. The u-joint and the swingarm pivots aren't in line, the u-joint is closer to the motor. Here's a pic of my big-tire modified swingarm before I covered the hole I cut for the shaft...

[IMG][/IMG]

In this pic the swingarm is level, and you can see the driveshaft is evenly centered in the slot with a gap top and bottom. Move the arm up or down, and the gap will almost disappear (which is why the slot is as wide as it is; I originally had the slot narrower, but had to make it wider to account for this). That changes the angle at the final drive, which is why the driveshaft has those curved splines.... and I agree, running the shaft at a continuous angle (rather than the intermittent angles it's designed for) is a bad thing...

so how big of a tire can you put on the bike with that swing arm mod?

[natemoen]

so how big of a tire can you put on the bike with that swing arm mod?

was it 150-160ish?

[crazy steve]

so how big of a tire can you put on the bike with that swing arm mod?

160/80-16.... that's the upper limit for the Special rim width, and leaves about .050" clearance to the swingarm if everything is fitted just right...

I'll be posting this mod once I get further along assembling this bike.

[Nightengale]

checked

i need to double check mine tomorow before i make all my final welds, this is why i love this site. you guys have so much information, i learn something new everyday, that is why my build is going slow, i am checking and double checking things like this so that when i am done with my bike i know it will be something that i will enjoy for a long time. thanks for the info guys.

i check the angle of the shaft and i am at -1 degrees, a little bit lower than normal.