80 Bobber

[ShootersHoliday]

Fix: How did you get the chrome look on the tank? Did you actually have it chromed? That is cool.

Oh, and here are the pics of the shaft. I didn't know where to stick the gauge, but there you have it.





Oh, and heres the start to the cover for the mid section (this is just a template obviously....)

[motoman]

Nicely done!............

[Fix]

I bobbed mine a bit, but maintained the shocks. I ride too many miles not to have 'em. I chopped the front fender as well, but left it there for structure. Even with that fender I can still twist the forks if I try. I need a tkat fork brace for my birthday.

[ShootersHoliday]

. Shooter could look at that himself and tell if driveline IS in fact running parralell with middle drive. If it is parralell in the 'hard-tailed' position that he has it located, then he is definitely gonna have a u-joint issue at some point in time. Running in a FIXED nuetral position WILL cause the needle bearings to pound out those yokes to look like they were machined that way.........in short order I might add.

Back to Shooter's scoot, with it being a bit costly, not impossible to put back as a correct model, got no issue with being set up as a nice bobber if done correctly, and his feet will easily set flat-footed when aboard. Safety-wise, ridability, and durability are ALL compromised at this point if hard-tailed and lowered like he has initially done. Hopefully checking out a few nicely bobbed 11's here will steer him in a more suitable direction.

I'll put the angle finder on the driveshaft tonight along with some pics. This week has been busy, so sorry I haven't gotten them up. I'll also measure for how low it actually is. If anyone who has a stock set up wouldn't mind measuring frame to ground at front and rear, I'd be much obliged. I'll measure as well.

I was aware of some of the problems with hardtailing this bike, but I suppose I may have misjudged the complexity of the single joint setup. I could talk automotive drivetrain all day, but did make the newbie mistake of assuming that knowledge was a direct translation.

Its gone under the knife again. It isn't going back to stock as I've allready cut off the back of the frame (aft of the shock mounts). But, I may set up a rear fender to look like a bobber, but allow me to kick the actual bike up higher (if necessary) and retain suspension movement. The factory shocks were pretty bad, so getting rid of them was necessary anyways.

As was mentioned earlier, I would just lower the seat and still retain the same standover height.

[bikerphil]

Don't forget though, used U joints for these bikes are dime a dozen. They rarely go bad under normal use. I thought someone found new replacement U joints somewhere for about $50. If the U-joint did fail it might put you down though.

Ah, here's the link...

http://www.theujointstore.com/yamaha-xs-and-xj-1100-u-jo1100.html

[motoman]

No apples and oranges here Steve, a needle bearing/cup U-joint DOES have a manufaturer suggested working angle, no matter the application. Those angles DO vary based on manufacturer suggestions. The reason I brought that all up, is the fact many years ago the DOT shop I worked in had a U-joint issue on a particular large snowplow(IHC). Even though there were several of same truck/motor combinations, this one in particular kept 'eating' those large Spicer u-joints. Had IHC reps. present and several other experts diagnosing the issue. After a couple days of measuring all the different angles, they found on that particular truck the rear bell housing motor mounts on the Cummins were indexed and drilled in frame just a tad lower causing the motor to angle down ever so little more than the other SAME trucks. Consequently, after that ordeal, several of us mechanics got to attend classes put on by Spicer and Borg-Warner pertaining to U-joints and there working angles, etc. So, yes, I DO have alot of experience pertaining to this deliema. Not actually 'seeing' the scoot involved here, and at this point just surmising whether or not that ONE u-joint involved is in fact running dead parralell with middle drive........be difficult to say one way or another. Shooter could look at that himself and tell if driveline IS in fact running parralell with middle drive. If it is parralell in the 'hard-tailed' position that he has it located, then he is definitely gonna have a u-joint issue at some point in time. Running in a FIXED nuetral position WILL cause the needle bearings to pound out those yokes to look like they were machined that way.........in short order I might add. Back to Shooter's scoot, with it being a bit costly, not impossible to put back as a correct model, got no issue with being set up as a nice bobber if done correctly, and his feet will easily set flat-footed when aboard. Safety-wise, ridability, and durability are ALL compromised at this point if hard-tailed and lowered like he has initially done. Hopefully checking out a few nicely bobbed 11's here will steer him in a more suitable direction.

[crazy steve]

Well, we're trying to compare apples and oranges here guys, so the automotive stuff doesn't really apply, and you need to understand where that recommendation came from....

Yes, a 3-7 degree angle is what's generally recommended, but this is usually figured with the vehicle 'at rest', not in actual use. This angle gives you leeway in suspension movement and varying loads in the vehicle, plus with the 'down' angle, that causes the slip joint to go into it's coupler when the suspension is compressed. But it's not an absolute requirement; they'll happily run at smaller angles with no issues; it's angles over 7 degrees where you start having problems. Look under any vehicle with an independant rear suspension, and you'll see driveshaft angles down to zero degrees. My Jaguars are a prime example; these cars have a fairly short (4') driveshaft, with the trans output and third member input shafts almost perfectly lined up. The only reason for the u-joints in the shaft is ease of installing and to allow the small amounts of misalignment that occurs when the motor/trans and rear suspension 'cage' move around on their rubber mounts. U-joint failures on these cars are rare, which is a good thing as driveshaft removal requires dropping the entire rear suspension out of the car as it runs in a 'tunnel' in the floorpan...

If you look at the rear suspension/swingarm/etc on the XS, you'll see that if the shock/spring preload is set 'correctly' (with the recommended amount of sag when loaded), the swingarm/shaft ends up running at a near-zero angle in relationship to the middle drive. This is how it should be. This will give you your best u-joint life, and much more importantly, will allow the shaft/FD splines to run in their 'neutral' position. The XS driveshaft does move in an arc when the suspension is working due to the fact that the swingarm pivots and u-joint pivots aren't on the same plane, and while the u-joint will take it in stride, the spline arrangement at the FD isn't designed to be run continuously at an angle. If you look closely at the rear splines on the driveshaft, you'll see they're rounded, not straight. This allows the slight misalignment that happens while the suspension goes up and down, but it'll spend most of it's time in it's 'neutral zone' if everything is 'right'. So lowering the bike will cause more wear at this point. How much wear? Well, that's hard to say; it may still outlast the rest of the bike, but the lower you go, for sure there'll be more wear....

[fredintoon]

- - - Ideally, a U-joint NEEDS to be at a 'working angle so bearing needles and adjoining cups are under load at all times. That angle has been determined by experts better than me to be 3-7degrees. - - -

Hi Moto,
um, if the UJ ain't driving it's on over-run so it's "working" all the time anyway.
I can see that if the UJ is perfectly aligned the cups and rollers ain't moving on each other so they will be working in the static mode; that might well do them in quicker than if they were moving on each other.

[motoman]

But running it straight is bad? I don't see how.
__________________
That it is Fred! Been there several times in the automotinve world.......large deisel trucks and autos both. Ideally, a U-joint NEEDS to be at a 'working angle so bearing needles and ajoining cups are under load at all times. That angle has been determined by experts better than me to be 3-7degrees. I'm sure Steve and some other folks here upon doing implant conversions in the automotive world know exactly what that is all about. A U-joint spinning in a no load nuetral position will NOT last very long, suspension travel constantly changing that angle helps with that factor too. So, Shooter, I think you see the error of hard-tailing a 'shaftie', besides the fact of rear wheel not having constant GOOD road contact and adhesion. Myself, nothing against bobbing one of these scoots if its done correctly. A particular red Special and a black one comes to mind that are members bikes. I'm sure someone here knows the ones I'm talkin' about and can post a pic or two of them as I struggle a bit without help posting references like that.

[fredintoon]

Having the u joint horizontal is just about as bad as having too steep an angle. It needs to work at a slight angle.

Hi Nate,
running at an angle is bad because the U-joint is a Hooke's Joint and that ain't a constant velocity (CV joint like on your FWD car) joint.
If the drive in is at constant velocity, the drive out speeds up and slows down twice every turn.
Stick your head under a pickup truck and you see it's drive shaft has two joints so they cancel out.
Not on a bike, though. There's only one joint so the greater the angle, the more non-linear the drive.
But running it straight is bad? I don't see how.

[CaptonZap]

Educational material

http://www.4xshaft.com/driveline101.html

[natemoen]

Having the u joint horizontal is just about as bad as having too steep an angle. It needs to work at a slight angle.

[ShootersHoliday]

I'll take better pictures today. It seems fairly horizontal to the ground. I measured the "drop" more accurate today. 2.75-3" lower. I can always raise the hardtail and get a lower seat like you said. But honestly, it looks "ok". But, you guys are the experts, and if its wrong, I'll fix it.

[cywelchjr]

The angle doesn't look too bad to me though. Do the pics make it look like its out of safe operating range?

If your talking about the universal joint the 4" drop will have put it outside of the range it was designed to operate in, and will cause abnormal wear, and these universal joints are no longer available. This means if it goes out your looking for another used one, or something that might be sort of close, because there is nothing that is an exact match made anymore, so unless you happen to find an NOS one hiding somewhere you got troubles, so you don't want to put any stress on that joint you can avoid. Much better to do everything to lower the seat rather than the suspension, cause you really want to keep that joint in it's sweet spot.

[ShootersHoliday]

The angle doesn't look too bad to me though. Do the pics make it look like its out of safe operating range?