The Ultimate Chain Drive XJ Bike That does Exist!

For all the guys out there that thought a chain drive conversion was not possible, it's already been done, by Yamaha in 1984! The 1984 Yamaha XJ750R Endurance Race Bike (OU28). They modified the shaft into a chain drive to compete in the Suzuka 8 hour race. They finished 5th overall in the race. Who knew these engines were really put to the test?

 

It was done by people other than Yamaha even earlier on the XS1100

 

I heard that because of the way the case is designed on the xj series motor, it is much harder to modify?

 

my guess would be that they over bored a 600 engine to 750cc chain drive.

FU

 

This is not a modified fj bike. This is a converted xj driveshaft engine. The bike was based on the XJ750E production sports model.

reference: http://global.yamaha-motor.com/showroom/cp/collection/racing_xj750r_0u28/

 

Not unheard of, if you have ever taken out the middle gear, it is simply a pair of gears at a right angle to each other (not sure of the technical term for this). Like a normal chain drive engine, there is a countershaft spinning off the transmission turning a gear, this gear could be removed and an adapter machined to fit on the shaft with a sprocket attached to the adapter. Fab up a swingarm and rob a wheel from a chain drive bike and viola', chain drive XJ. Be the first kid on your block to have one!

 

but it's a 6 speed. all the shafties are 5 speeds.

FU

 

My understanding from a combination of memory and reading up:

Yamaha did chain drive conversions on several shaft driven models on a limited basis.

http://www.historicsuperbikes.info/info/topic.asp?TOPIC_ID=67

There is room inside of the case for a sixth gear (the 550, and the 400 (the original XJ) have 6 gears and the cases are not any larger). Yamaha also did those conversions for race bikes on a limited basis.

At one point there was a chain drive conversion for the XS11 that could be bought directly from Yamaha's racing development team. This was possible because the XS has the middle drive gear in a seperate housing that bolts to the rear of the engine cases.

Fun (and off topic) fact: The Later electric-start-only XS1100 actually has most of the kick start mechanisim installed, but is lacking the external bore for the kick start shaft and a few other peices that can be retrofitted.

Even funner (and on topic) fact. Manufacturers make all sorts of things that the consumer never, or only rarely, gets to see.

 

I'd love to get my hands on a 6-speed trans for my XJ. I'll keep digging on this bike. I wonder how Friendly Yamaha would be on sharing the modifications done? Not good odds I bet.

 

Some video from the factory museum (not mine):



Finished 5th overall:

http://www.motoracing-japan.com/result/spl/848h.html

A privateer team also ran an xj750 in the 1985 Suzuka 8 hour, finishing 33rd.

There were 3 XJs of varying displacements which finished the 1983 race.

http://www.motoracing-japan.com/result/spl/838h.html

 

I would count your odds at exactly zero. I would guess that the only 6 speed parts still in existence are in that museum bike. I read an article a year or two ago about recomissioning one of Kenny Robert's race bikes. They had to get nearly several internal components remade from scratch because of the engine not being stored correctly, and all of the factory spares having been used up when the bike was in the hands of various privateer teams.

 

There is an XS850 chain drive conversion being done locally for a guy racing one in pre82, look up the Rod Grey XS1100 that was built in South Africa which I reckon is the coolest chain driver converted bike I have ever seen

6 speed for a shaft drive bike? I'd get a 500/600 box and see if they fit but you'd need to check the ratios and see if there is any benefit, a 6 speed isn't automatically better than a 5 speed

 

Mmmm..... Thats a sexy bike.....

Thanks for sharing!

 

That rings a bell with me. I had a late XS750F model, the one that had the bugs all ironed out before they stretched it to an 850.
I read as much as I could find about it at the time, and something stuck with me - for the Australian market, there was an optional kickstart. I presume some buyers there liked the idea of being able to kick the beast into life with a flat battery, especially in the middle of the Outback. I don't recall if there was a blank piece on the casting where the kickstart would have gone, but in a similar vein I know for a fact the kickstart on the '79 GS can be fitted to the 80-on GS850 should I want to, either by boring the case or by simple case swapping - the kickstart parts will fit the later engine.
Maybe Suzuki did the same for Oz, but the lack of kickstart on the 80-on GS850 seems to be worldwide.