Failed XS750 Final Drive (Images and video link)

[DAVINCI]

Thanks for correctly assigning 'credit'....

But I have to admit that I agree with Scott. Yamaha went to the trouble and expense of redesigning the 750 drive for the 1100, putting in stronger bearings in the two places they would be needed to prevent this sort of issue and beefing up some other areas as well. This would make the rumor that Yamaha originally was going to use the 750 drive plausible, but the change IMO was made not so much in search of 1/4 miles times but due to durability issues found in pre-production testing. After all, this was their flagship performance model and you know they figured that many owners would beat the hell out of the bike. Get even a few reports of failed FDs, and the bike's reputation would have gone in the toilet...

Does that mean that every swap will fail? No, of course not. But I'd be willing to bet that the factory found that a certain percentage would fail, leading to the 'upgraded' unit that ended up in the production bikes.

Ah..key words there are "IMO" Unless one of us was actually there, it's all speculation. Out here in the REAL world, the 750FD works just fine.

[3Phase]

James:

The 750 drive just wasn't designed to handle an 1100 so, as Steve said, Yamaha had to make a few modifications to the 1100 final drive. Don't be afraid of the 750 final drive. It's tough enough, it's just not as tough as the stock 1100 final drive so try not to do too many launches or wheelies and NOS is right out!

When I first got it the oil and wear on the parts in the 750 drive looked more or less like the 1100 drive in the pictures, just not as beefy but it definitely was not burned, hammered, and worn out like it is now.

Look at the pictures that show the needle bearing contact patterns on the 750 and 1100 hub inner races. The 1100 has two wear marks where the roller cage for the needle bearing made light contact with the inner race. Similar marks were present on the 750 inner bearing race when I put the drive back together but they have been wiped out.

I don't know how many miles were on the 750 drive before I got it. Whatever it was it's "n + 40,000" now so it's done a few miles and it's not as though Yamaha skimped on the construction or materials for the 750 final drive.


Greg:

This ain't my first rodeo. When I set up the 750 drive the only thing I forgot to do was weigh it with a torque wrench but I'll definitely do that when I get the next 750/850 drive before I put it on the bike.

[crazy steve]

Ah..key words there are "IMO" Unless one of us was actually there, it's all speculation. Out here in the REAL world, the 750FD works just fine.

Randy, there's no point in anyone getting their panties in a twist over this. Neither Scott or myself are saying that a FD swap will inevitably lead to a failure. This is merely information that you may or may not use in deciding if this is for you, and may be a good reason to be vigilant about watching said swap for problems.

But the fact remains that the factory did fit a stronger FD to the 1100. I doubt that was simply because of the ratio change, as that could have been done without upgrading any of the rest of the 750 drive. It's my experience that the factories rarely fit heavier-duty parts unless they're needed; more often, they'll over-build the initial design, then start to 'cheapen' it as actual real-world use shows just how durable it really is.

[3Phase]

You're not making sense. What's the point of risking your life trying to destroy parts? It's either bull**** or sheer stupidity. Then you contradict yourself. If you WERE trying to destroy it you wouldn't have treated it so well.

Gosh, Randy, I guess I'll take, "Sheer Stupidity!" for $50, please, while you finish eating your lunch, chill out, and get your blood sugar back to normal.

There is a very distinct difference between intentionally overstressing a piece of machinery to test its limits while checking it at frequent intervals and just plain abuse.

When I got the 750 final drive and saw the differences between it and the stock 1100 final drive I didn't trust it at all. Not. One. Little. Bit.

Yes, I abused the 750 drive. Yes, I checked it at frequent intervals to see how it was holding up to the abuse.

When the 750 final drive finally began to fail I removed it from the bike and tore it down completely for inspection and photos.

Yes, I will be getting another 750/850 final drive but this time I'll have a better idea of what is and is not likely to fail and what to watch.

No hom^H^H^Hhyperbole.

[WMarshy]

You're not making sense. What's the point of risking your life trying to destroy parts? It's either bull**** or sheer stupidity. Then you contradict yourself. If you WERE trying to destroy it you wouldn't have treated it so well.

I dont think his intent was to kill the FD by neglecting it (i.e. not changing the oil) but rather trying to get it to fail from excessive loading. Hell, anyone could get any of the FD's to fail if they dont change the oil but then that doesnt prove anything does it?

[crazy steve]

I dont think his intent was to kill the FD by neglecting it (i.e. not changing the oil) but rather trying to get it to fail from excessive loading...

Ah, but what's 'excessive' for a 750/850 FD is 'normal' for a 1100 FD. Scott was doing a 'real world' durability test from what I see, trying to subject it to 'normal' worst-case riding conditions which isn't the same as 'abuse'. And not all of these are exactly equal; sure, some will have different wear from how they were maintained/used, but there's also minor variations in how they were set-up from the factory. Like I said, it's just something to think about if you have or are thinking about one of these swaps...

[psycoreefer]

What I'm taking away from this:
1. The 750 final drive is probably great if your doing what the swap was targeted to do - increase comfort and mileage when doing long miles on the highway at high speeds.

2. The 750 final drive does have differences and they make it not as tough for hard riding in the twisties and drag strip type launches, which is really counter to #1.

3. If you do both types of riding and really want the swap go for it, but keep an eye on your final drive so you don't miss the signs of impending doom.

[crazy steve]

What I'm taking away from this:
1. The 750 final drive is probably great if your doing what the swap was targeted to do - increase comfort and mileage when doing long miles on the highway at high speeds.

2. The 750 final drive does have differences and they make it not as tough for hard riding in the twisties and drag strip type launches, which is really counter to #1.

3. If you do both types of riding and really want the swap go for it, but keep an eye on your final drive so you don't miss the signs of impending doom.

That's pretty much it....

[3Phase]

Interestingly enough the only part of the 750 drive that did not fail was the pinion assembly and pinion bearings with the new crush washer that I had to install and adjust.

Yes, this was pretty much a durability test of the 750 final drive. It mostly passed the test as far as I'm concerned by lasting 40,000 miles before it started to fail. It was still quiet and seemed to roll smoothly before I took it off and stripped it down for the autopsy but I don't believe it would have been much longer before it began to fall apart in a more, uh, spectacular manner.


If anyone is wondering, the stock final drive from my '80G was abused as a child too so it's not exactly like it's a completely undocumented and pristine example of a gently-ridden XS11 final drive. The stock driveshaft and pinion coupler had showed definite signs of abuse when I took off the final drive and I took and posted a few of the pictures here on XS11.com as I did the work. The original driveshaft was ovaled inside the pinion coupler and had to be replaced, the pinion coupler itself had rocked over to one side under load and rubbed against the pinion housing. The pictures I took yesterday show that the 1100 final drive took that abuse without failing.

Who Ya Gonna Call? Grease-Busters!


Better XS11 u-joint for 750 final drive

[crazy steve]

I ...The original driveshaft was ovaled inside the pinion coupler and had to be replaced...

Scott, that 'oval' shape at the FD/driveshaft is normal. The shaft swings in a small arc when the suspension moves because the centerline of the u-joint pivot isn't lined up with the swingarm pivot. If that was a 'straight' spline, it would bind...

[3Phase]

Steve, the damage to the driveshaft in that picture wouldn't happen if I removed all the grease from the splines, then took the bike off the center stand and just bounced up and down on the suspension for a few ten-thousand miles without letting the rear wheel turn.

I know the driveshaft teeth are crowned front to back but the driveshaft in the picture is not round at the end, it's oval like a giant hand squeezed the teeth together. I have several XS11 driveshafts including the XJ driveshaft I put into my bike a couple of days ago and none of them have been ovaled. The teeth on the bad driveshaft have high wear on opposing arcs around the circumference that almost wiped out the crown on the teeth. It gradually changes to low wear on the teeth and crowns on opposing arcs and back to high wear again. It's not round and crowned, it's bent.

It may have been a partial lube-related failure, not enough grease on those pesky splines, but I knew the original owner. He was a rather large but not fat individual if you know what I mean. He wasn't a drag-start kind of person but he used to ride to and from work via a nice, narrow canyon 'road'. Some of the corners on that 'road' will almost allow you to read your own license plate as you ride through them. I think he hit the throttle too hard in low gear in the middle of one of the uphill corners and bottomed out the suspension and that made the drive shaft bind up and bend as it rocked the pinion coupler off of its axis.

[BA80]

I'm finding it difficult to understand how 16HP could make that much of a difference here.



Yamaha XS 850SG Special

Make Model
Yamaha XS 850SG Special
Year
1979
Engine
Air cooled, four stroke, transverse three cylinder, DOHC, 2 valves per cylinder.
Capacity
826
Bore x Stroke 71.5 x 68.6 mm
Compression Ratio 9.2:1
Induction
3x 34mm Hitachi
Ignition / Starting
Battery powered triggered / electric
Max Power
79 hp 57.7 KW @ 8500 rpm
Transmission / Drive
5 Speed / shaft
------------------------------------------------------------------------

Model: Yamaha XS 1100
Year: 1979
Category: Sport touring
Rating: 73 out of 100. Show full rating and compare with other bikes
Engine and transmission
Displacement: 1101.00 ccm (67.18 cubic inches)
Engine type: In-line four, four-stroke
Power: 95.00 HP (69.3 kW)) @ 8500 RPM
Top speed: 215.0 km/h (133.6 mph)
Compression: 9.2:1
Bore x stroke: 71.5 x 68.6 mm (2.8 x 2.7 inches)
Valves per cylinder: 2
Fuel control: DOHC
Cooling system: Air
Gearbox: 5-speed
Transmission type,
final drive: Shaft drive (cardan)

[crazy steve]

I doubt if it does.... what you should be comparing is torque. The 750 (which is what this FD was designed for) only put out 45.6 ft-lbs. The 1100 on the other hand puts out 66.6 ft-lbs, a increase of 46%. Add in the 20% higher weight of the 1100 vs the 750, you're asking a lot of that FD....

[jwhughes3]

I think what he meant...

Don I think what I interpreted Scott to mean was he wasn't holding back from treating the FD just like he would the stock drive to see if it would fail - he didn't baby it with loads or drive the bike like his grandma... (no offense to your grandma Scott - maybe she rides like a bat out of Hell)

Personally I think it was the off-roading up the Colorado mining trails loaded up that did it in


Great write up and pics - I tend to agree with Greg that a failure of the lubrication somehow killed the bearing - the chattering seems more a symptom of the gears not being shimmed right in the automotive world - where preload and tooth contact are checked with the marking stuff and pattern adjusted with shims...

I guess I will stick with stock FD until all you smart people figure it out


John

[BA80]

We'll see. I've had mine in for between 20 and 30K now. I'm not sure because I didn't note my miles when I installed it and I also switched speedometers about 14K ago.

It's been to the Ozarks 2 or 3 times now and in about 10 days it will make it's second trip up north to the Lost Rally in Minnesota, not to mention several trips to Texas, and Kansas. And I NEVER do wheelies or speed shift.