XS750FD. Safe? Unsafe?

[3Phase]

What I got out of Larry's rather long winded analysis of science and math is that if you ride your 30+ year old motorcycle like a 30+ year old motorcycle you'll be fine but if your riding style is little more befitting a later model sport bike then you may experience some accellerated wear, as recently highlighted.

Yes, Brian, you've said it, I've said it, Larry's said it and most of the people I've talked to about the XS11 have said it, too. I already do ride my XS11 like it's a thirty year old motorcycle with a frame that is infamous throughout the entire world for cracking even when it was new off the showroom floor because it's undersized for the power of the engine.

Getting 40,000 miles out of the wrong final drive for the bike is not anywhere close to riding a thirty year old motorcycle like a modern sport bike.

I was rougher on the first final drive than I will be on the second one because I was trying to make it fail but putting on another 750/850 final drive won't change the way I ride my XS. Sustained high speed riding through the desert with a passenger and a full set of bags with a fairing is harder on the entire motorcycle and the riders than a run through a canyon or the mountains and it has nothing to do with riding an XS11 like an R1. Even though it will beat the living daylights out of any final drive I put on the bike I don't plan on cutting back on carrying passengers or making fewer trips from the mountains to the prairies, to the oceans white with foam.

[cywelchjr]

Your poll forgot 'waist of time, energy, and performance.'

OH NO... some said something bad about the FD swap!!! Everyone, ralley the Okies!! Light the tourches!!! LOL.

Not at all. It's not for everyone, and depending on your riding style may be the worst possible thing you could do to your bike. Then again, depending on said riding style, it could be one of the best things you could do to it (IMHO) .

It's for sure not for everybody, and I for one don't advocate it for everyone. For my riding style it works well. I'm thinking though, what if a mod could be made for the middle drive, modded gears to change THAT ratio to give the desired final ratio while keeping the 11 FD? I'm thinking that since the optimum ratio is different from specials and standards, it would be two different gear cuts, ending up with the same effective final ratio in both cases. If done right, it would answer all the concerns I think, of course someone would have to be able to make the gears, which means we need a machinist with access to the correct equipment (aren't the MD gears straight cut gears anyways? Lot simpler that way too, still gotta harden them though). I know this would cost a bit more (ok a LOT more I'm thinking) but it would be a LOT more durable than the 750 FD, and you could keep the original setup from the u-joint back. I know it would be too much to have a quick switch to go back and forth between the two ratios, but at least the weak point could be gotten rid of.

[cywelchjr]

Getting 40,000 miles out of the wrong final drive for the bike is not anywhere close to riding a thirty year old motorcycle like a modern sport bike.

I figure that getting 40,000 miles out of these FD's is not a bad deal. If we can get that on a regular basis, or even beat it by a bit, I for one will be happy to enjoy the benefits. If needed, when the time comes I'll just go back stock if there are no more 750 or 850 drives at that point.

[crazy steve]

....The standards and the specials both have significantly more horsepower than the 750/850 and therefore have higher acceleration....

....Every device fails eventually. But when a final drive on a motorcycle catastrophically fails it isn't the same as if the rear differential on your automobile grenades. I have had that happen to me and the vehicle simply kept rolling down the road albeit without a connection between the engine and the tires. The internal parts of the differential sheared off but the axles continued to stay in place and just as importantly those axles continued to roll. (This was an example of an assembly failing in a "safe mode".) In my view, the design of the motorcycle final drive is one where catastrophic failure of the components is likely to result in a rear wheel "lock up" if one were rolling down the road at highway speeds. I would not consider such a failure as "safe" . Therefore I would put the 750/850 final drive as mounted on an XS/XJ as "unsafe"...

I see Larry and I are the only non-optimists on this...

It's not the horsepower difference, it's the torque difference that bothers me. Gearboxes are rated according to the torque they can withstand, horsepower has little to do with it. With the 11 putting out nearly 50% more torque over the 750, that explains why the factory fitted a heavier unit. They obviously felt that the 750 design couldn't handle the additional torque, so beefed the design.

As to the belief that an imminent failure will politely announce itself by fouling the lube and 'whining' about the abuse... well, maybe. All it would take would be for one bearing roller to disintegrate and jam the bearing, and you'll find yourself doing your attempt at a dirt-tracker full-lock slide. Like Larry, I've had differential failures in cars (I had one car in my youth that consumed an average of two a month, and by the way, they don't always fail in 'safe' mode ) and crushed bearings were the cause more than once.

Does that mean I think no one should do this swap? No, not at all. But I'll agree with Larry that you should carefully limit the stress you put on the FD, 'detuning' your riding style so to speak if you want 'safe'. But if you still want to be able to enjoy the rush of a XS11 in full cry even if only occasionally, be aware of the possible consequences...

[BA80]

Ok, here we have another case of over ANAL izinge. This mod hs been around since the latter part of 2006. Have there been ANY "catastrophic failures" reported?

I'll give you some time................................






























Nothing ? I guess everyone who has done it has been REALLY LUCKY huh?

[cywelchjr]

I think there is another point too. This has been done both on standards and specials, and there is quite a difference in the torque load on the FD for the same amount of input with the 16: special rear tire vs the standards 17" tire. One answer would be to put a 130/70-17 instead of the 130/90-17 that would normally be put on which would be putting the outer diameter close to the specials, AND decreasing the torque load on the FD in the process, that extra 1+" out from center (IIRC it was close to 2") is a significant increase in the load the gears get for a given amount of force applied to the road surface. It would also modify the final gear ratio. However, it does lower the bike and make it more likely to drag parts. I'm wondering if the specials forks keep the front of the frame at the same distance from the ground as the standard forks do, as that would change the whole aspect ratio of the steering with the smaller tire if it did.

[3Phase]

I see Larry and I are the only non-optimists on this...

[...]

With the 11 putting out nearly 50% more torque over the 750, that explains why the factory fitted a heavier unit.

[...]

As to the belief that an imminent failure will politely announce itself by fouling the lube and 'whining' about the abuse... well, maybe.

[...]

But if you still want to be able to enjoy the rush of a XS11 in full cry even if only occasionally, be aware of the possible consequences...

Bingo. You and Larry are absolutely correct but the overall problem is: the entire XS11 isn't 'safe' if you go by the numbers. Using the wrong final drive is almost a moot point in a whole chalkboard full of points. There is no solution except to try to stay on top of it the best you able or to stop riding the XS11.

I'm not able to watch my XS in slow motion while I ride it but from checking the entire bike afterward I'm reasonably certain that the engine and transmission move in their mounts and compress the rubber. The drive train itself, from the straight-cut transmission and output gears over to the hypoid gears in the middle drive and down through the drive shaft to the ring and pinion, don't flex as much. When they do flex you can feel it. It's not good for the rest of the bike because the motor and transmission mounts are hard over at their limits and the frame is flexing right along with the drive train so I try not to do that no matter which final drive I'm using.

I've broken, repaired, or replaced my share of differentials in cars, trucks and heavy equipment and they most definitely have not all politely announced themselves in advance. Tractors and heavy equipment usually just make a loud noise and quit moving unless the operator tries to use a lower gear to get rolling again and tears up the rest of the drive train or grenades the transmission. A lockup in a car or truck followed by a slide/jacknife or using the drive shaft as a pogo stick is guaranteed to be exciting no matter what else you thought you were going to be doing at the time. I try not to do that, either.

[Bonz]

I asked the "catastrophic" failure question in one of the other recent FD swap threads (maybe the poll thread I started?) and cannot recall hearing of one in normal use.

Just finished reading Scott's autopsy on his 750 FD, and all I can say is if a failure at 40,000 miles, with the intent to run it hard while doing proper maintenance is the worst that happens SO FREAKIN' WHAT?

I spent some time with 'ol Scotty at the Colorado rally, and he does put a ton of miles on Colombo, and he rides it hard in terms of at higher speeds, hot weather, loading it with gear, etc.

Hell, my bike has 18,500 original miles on it (5,400 of them under my ownership), 1,600 of which are with the 750 FD swap since April. HONESTLY, how many put even CLOSE to the mileage Scott puts on his, at the speeds he rides, the temperatures he runs at constantly for days on end literally? Not many I would suspect.

Who can seriously question at this point whether to do it or not based on reliability given what it took to make one fail. Put one on if you want, go for it!

The point is, the guru, the Scottster, made one fail and is STILL going to put one back on.

'Nuf said!

[James England]

Follow up

Well, as a little bagatelle, I changed my FD back to OEM about an hour ago. It took me 45 minutes. I checked the drive shaft and pinion and couldn't find anything untoward in the wear pattern or bits of metal floating about.

I'm going to take the bike out tomorrow, with the OEM drive on and see how I feel about the performance side of things. A previous posting mentioned detuning one's riding style and this is what slightly bothers me slightly. When my Triumph Spitfire diff locked up, it nearly threw the car off a cliff near Monte Carlo.

Much as I like the decreased revs at cruising speed and the easier feel of the motor, there is part of me that thinks driving an 1100cc bike in a 'detuned' way, as if it's a bike 350cc smaller is maybe a bit of a waste. I noticed today when I was overtaking several cars at once (on a straight road with good view, I hasten to add) that I wasn't exactly riding the bike in a 'detuned' way.... not abusing the bike though.

I don't do 1600 miles in one trip (Britain is only 800 miles long or so). Long, long hauls a la Zen and the Art just aren't possible here. Most of my riding is short haul.

So, what am I saying here? The FD swap feels great to me and perfect for the bike but the weedier FD side of things bothers me slightly. What's really needed is a 750FD built like the 1100 or a 6 geared box. They aren't available and the swap is definitely a compromise with, it seems to me a certain element of uncertainty thrown in. However, as someone has asked already 'how many have exploded? None'... I suppose we're unlikely to hear from anyone who has had a rear wheel lock up at great speed though, eh?

So... tomorrow, I'll try out the OEM FD and see what it feels like again. If too stressed,I'll have to change back to the 750FD and detune.... kind of hard though.....

[cywelchjr]

I don't think you really need to detune for the FD any more than for the rest of the frame and bike. Scott makes a good case for the fact that these frames are NOT in the shape they were 30 years ago, and won't take the abuse they would back then, and from hints I've heard they were indeed known for issues with frame strength and rigidity even back then. I think if your gonna get all worried about the FD you need to be magnafluxing the frame and suspension parts as well as strengthening critical areas.

Seeing how Scott had his bike loaded when he stopped by on his way home from Colorado, I'd guess that by the book he was probably over the factory load limit. I know with me on the bike, I can carry about 40lbs of cargo TOTAL before I'm overweight. Now this is with a full dresser and is figuring in the weight of the fairing, bags, trunk and related mounting hardware. So what I'm saying is all of that is going to go into the equation. I do NOT treat my bike like a modern bike, it's NOT. The frame is older than 2 of my 4 kids, and while I've gone over it for rust and the like, it's NOT been magnafluxed or otherwise tested for hidden cracks in the frame or other components.

Remember the other thing, SMOOTH. This was taught to me by my auto shop teacher. Components can take a LOT more stress if you don't snap the stress onto them, don't go from idle to full throttle in one go, the drive shaft might not even take it, but all the parts will be MUCH happier if you bring the power on quickly but smoothly, and things will last a LOT longer that way.

Watch a drag racer take off. They don't go from a fully pressed in clutch to fully released clutch at the green, they take up all the slack and actually have the vehicle bunched up with the tires almost ready to break loose and let the brake off and put full power to it just before the light, but all the drivetrain parts were already under stress, with NO slack in them, so no lost motion to break things.

I'll get off my soapbox now, but here's my point. I believe that one probably double at least Scott's mileage on the 750 FD, and still ride pretty spirited, just by being SMOOTH. Face it. You know the parts on most modern sport bikes (and even most modern sport touring bikes) are probably not as robust as these bikes drive train parts, but they weight a lot less, so you can be less smooth. But by being smooth you can STILL make the thing last a long time. I figure guys who get more mileage out of tires will get a lot more mileage out of the FD, and those who get less will get less, cause their flogging the bike harder, and maybe are less of a candidate for the swap.

[Bonz]

Hey James England,

I hear what you are saying, the thought of not being able to run the old girl as hard as she can be run crossed my mind, for about a second.

Don't know if you have had the chance to do any longer distance riding, in really hot temps, loaded down, etc. From you post I infer that short hops, etc are the norm for you on the whole.

I've never been a jack rabbit start kind of guy, I take care of my bike in terms of not jamming shifts, running the wee out of it at high rpm/speed for long periods, etc.

I know the exuberance you had when you did the FD swap, and I have the same feeling still, even after the great write up by 3Phase and his FD failure.

40,000 miles is a LOT of miles in a short time (the FD swap was "invented" in 2006 I believe, not sure when Scott did his) and Scott was real clear that the wear and tear came from ten of thousands of miles being ridden hard day in, day out, and most importantly to me, for long and extended periods of time where heat does become a factor, regardless of the lube quality or condition in the rear housing. I wasn't clear (or I missed it, very possible!) in his cycleopsy of the FD why only one of the bearing areas was the issue, and not other areas.

My take on all of it is for someone doing shorter hops, the potential for problems is vastly reduced to be a minimal-non factor IMO. Unless I'm gunning it at top HP and torque loads, I would very safely speculate the loads on the swapped FD in 95%+ of riding would still fall in the same range as what the 750/850 engine is doing. AND for those times when we do run it harder, it's not a regular thing, and the extra wear and tear we are subjecting it to is a non factor in my eyes.

I haven't researched the forum, but I venture a guess that there are stock FD housings that have been run hard and hung up wet, in what would be considered hard riding, and have failed.

Am I correct that other than Scott, the only other FD swap issue was oil draining out of someone's FD housing? I can't recall any other issues that can be attributed to sheer wear and tear like the test that Scott did. I have heard of some swapped FD's having issues with improper torque specs when being put back on thus resulting in pretty immediate failure.

I guess what I'm saying, is this test further enhanced in my mind that the FD swap is a good thing for my bike, and it will take a whole heap of use and hard use at that to potentially fail.

The other advantages to potentially reduced wear and tear on most of the other more expensive and harder to replace/repair systems far outweighs the thought of a swapped FD wearing out in 40,000 miles.

This has been really good to be part of the discussion and the hard work by Scott. We all are more informed because of it, and can now use that info.

Anyone have a 750/850 FD laying around they want to sell me, so I have another to go on in 38,400 miles (40,000-1,600 already on my FD)? Maybe that helps put it in perspective... 40,000 miles is a long time!

[BA80]

I'm sorry James. This whole thing has been blown completely out of proportion.

There is no doubt that the 750 FD is a bit less beefy than the OEM drive on the 11. However, as everyone here knows, Yamaha over engineered EVERYTHING on their bikes. Why do you think there are so many 35 year old 1100s,850s, and 750s still out there running?

I truly believe that there is NO danger in running the taller geared 750 FD.

I do however believe that it will more quickly be damaged if abused than the OEM FD, but a long and healthy life can be protracted for those who are looking for that type of performance.

If the bike is going to be abused, keep the OEM in there. It'll perform the way you want to run it.

The 750/850 FD has no problem handling the occasional "stupid hard run" but won't hold up to being constantly being abused any more than anything.

This whole freakin' thing has been a witch hunt in my opinion.

[cywelchjr]

+1 on what Greg says. Scott says that he got stupid with the FD because he wanted to be sure how it would handle being stupid, and it went 40,000 with that. I suspect most normal riders who appreciate the 750 FD will get more miles, why? Because modifying is not always about not getting to speed fast, it's about not jackrabbiting, about not doing wheelies (which are NOT good for the frame anyways, or the forks, I've seen modern forks and frames on lighter bikes than these break from wheelies) and such. I like to think I'm a smooth rider, and that I can put some push to the bike without stressing it in the process, and I think that is the whole point, don't POP the clutch, don't take it to the drags with the 750 FD (why would you do that anyways?) don't take it hill climbing with it, and don't see how long you can hold the front wheel in the air on torque. I'd be interested to see what the difference in weight and HP and torque is between the 850 and 1100, since the 850 used the same FD, that's a more valid comparison cause if it was overstressed on that bike they would have changed it on that bike would they not?

[Bonz]

CRAP! So what's this mean on the next group ride at the Colorado Rally, or Cali Rally, or whatever? That we're gonna have to put a yellow "rookie" stripe on our bikes if we've done the FD swap so anyone following us can white-knuckle it for miles on end, wondering if the dude in front is gonna frag his rear end? Or separate us into the "Likely to blow" and "Stock, but safe" groups?

Scott, it's all your fault... You've changed group riding in the brotherhood forever, you bastard! In any case, bro, just like in "Top Gun"... "You can be my wing man anytime" and with your FD swapped bike running right in front of mine! Which, by the way... Tom Cruise has a place in Telluride, we rode not far from it... I sold him some fitness equipment via his agent a few years ago for his place up there.

I'd be a whole lot more concerned following JWHughes and his fossil-fuel mind-altering rig that I could well go home with early on-set dementia from aspirating the unburned gas coming out his pipes! Or at least have a good "Rocky Mountain High" goin' on if it's a Colorado ride! No offense Big John, just lightening it up a bit around here...

Guys, in all sincerity, it's getting goofy around here... With this poll, how much of the rationale for either answer choice is grounded in anything but opinion, albeit forming opinions based on what Scott said and our individual interpretations of it? It's not a matter of whether the 750 FD is safe or unsafe, it's a matter of what potential reliability exists, end of story. Let's don't get caught up in the gloom and doom of this, We have a better chance of blowing a tire on our bike than losing it because of a swapped FD issue, I guarantee it.

So let's rewind this whole thing, use a bit of good old common sense and resist the temptation of making mountains out of mole hills, or in this case making something out of essentially nothing.

James, I hope you go back to your swapped FD with a renewed level of confident awareness, as I now have. I really believe you have not a thing to worry about. If I'm wrong, you can publicly chastise me via the forum at a later date!

Dudes, Scott went 40,000 miles trying to kill the 750 FD! If that doesn't say it all, I don't know what does!

Good night and Good luck. Sleep tight boys!

[3Phase]

Axle Tube Support Collar

I've been shopping for XS750 and XS850 final drives on eBay and I noticed a difference between some of them.

All of the XS850 final drives listed that have pictures showing the output hub have an axle tube support collar like the one on my XS1100 and XJ1100 final drives.

Some of the XS750 final drives listed that have pictures showing the output hub have the support collar but some of them do not.


My XS750 on the left without a collar; My XS1100 on the right with a collar.




I do not know if any Type I drives have the support collar.

The 750 drive that I have is a Type II but I don't know the year it was assembled. It doesn't have the support collar so that may be something that was added to later Type II drives to keep the ring gear from wallowing around under load and wearing out the carrier bearing and the gear teeth.