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I tested the "original" YZM500, created by the factory for Yamaha's biggest hope, Jacky Vimond -who was the '86 250 MX world champ- to attack the then-premier GP500 class as a factory Yamaha rider, for Moto Revue (French) magazine.
Jacky got heavily hurt in a freak accident at a party that Yamaha put together to celebrate his title in september of that year so he did not race the bike until his return in 1988.
I found the bike, although technically very interesting/exotic for those days, to be not as "good" as I expected but maybe (at least partly) that's because I was far from being of a GP-talented rider level (more like an intermediate)...
I tested many factory bikes by then though and the HRC Dave Thorpe '85 GP500 bike impressed me much, much more.
In comparision, the YZM chassis was (really, really) stiff, a little bit like the original '98 production Honda CR250 was going to be, a decade or so later.
I guess by then the importance of "some" flexibility in the frame had not been recognized by engineers/test riders the way it is nowadays.
The bike was going straight, no doubt about that, but was not very good in tight corners (while the Honda was terrific in every department of the game).
The motor was much better than an air-cooled 490YZ production motor, though : more/stronger power, more usable, pulled longer up the rpm's, etc.
I think it had a 4-speed gearbox.
Quite a lot of vibrations, although not as much as on the production Yamaha motor.
But the difference with the factory Honda motor was just ridiculous : HRC's motor was better on each and every department and was'nt vibrating at all.
On a scale from 1 to 10, the YZ490 production engine being a 5, the YZM would be a 6.5/7 and the HRC a 9.5 (assuming perfection is not from this world).
Don't get me wrong : the YZM was still a very cool works bike and Vimond liked it much better than the stock 490.
He even won the '88 GP of Sweden on it, giving that bike its only GP victory, which was a huge accomplishment, considering what he had been through, broken back, knee and all (Persson won the Le Touquet beach race on it, which was a pretty big deal by then as well); he had the speed to make that chassis show its good traits, which I did'nt.
But, again, the overall quality of the bike was pale when compared to an HRC bike.
The british bike seen at the Vintage MXDN is 100% legit, same bike as Jacky, just older and probably not as well maintained, as works parts were produced in limited quantity for these prototypes, I assume. .
Finland's Kurt Ljunqvist and Sweden's Leif Persson were the two other Yamaha factory riders to ever officially race YZM500 prototypes, I believe, in '87 (when Vimond was on the sidelines).
The sidecar engine showed in photos in this post has nothing to do with a YZM engine, except for the brand Yamaha, the more or less half-liter capacity and the fact that it is water-cooled.
JPX used to be a popular French big-bore kit company, specialized in producing such kits for the ultra-popular Yamaha trail bikes (the DTMX 125) and the trials Yamaha TY bikes.
They used Wiseco pistons, I think.
I assume it is the same company that produced the water-cooled half-liter showed on the photos above this.
Hostettler was the Yamaha distributor for Switzerland and sidecar MX was (is?) very popular in Switzerland, so I guess they got JPX in the project by pre-ordering a big enough quantity of kits to pay for the development/castings ?
I'm not sure if the Peterhansel Supermoto bike used that JPX kit (very possible, as Yamaha France had a connection with JPX) or of a Noleen 360 kit (Yamaha France race department had a couple of these as well but maybe was it a few years later?).
I heard through the grapevine that Vimond's former mechanic had enough YZM500 parts put aside to built a brand new bike but although he is a friend, I never asked him directly about it (he does not work as a pro mechanic any more).
It is to be noted that Yamaha produced a 500 water-cooled prototype for Carlqvist years before that YZM project (I believe it was in '80, water-cooled 500cc bikes were very exotic -never seen?- by those times!).
That bike was raced only once (that I know of) at a pre-GP season meeting in Holland, in Sint Anthonis.
It did not have an aluminium frame.
Carla (or maybe Mikkola, who was just retired but still involved with Yamaha's GP effort) did not like the bike, so I guess this is originally why Yamaha took such a step back and ended up never developing a production water-cooled 500 MX bike (ironically, Carla became famous, later on, for complaining -a lot- about his air-cooled Yamaha prototype, similar to the one Broc Glover was racing in the US, not being up to par with the water-cooled engines of his competitors)...
I never heard about that original Yamaha prototype being ever seen again after the Sint Anthonis meeting so if anyone has that piece somewhere, it is even more of a rarity (although not of comparable technical interest) than the YZM500 itself.
All the information you posted confirms how cool this motor is. I knew this was a sidecar motor and not much more when I purchased it. I had seen them a couple of times at races in Europe but never spoke the language of the owner and could not get much background. I had hoped it was related to the YZM as my plan is to put it in a YZF450 chassis and buid a YZM replica. I raced 465s and 490s both were fast and scary at the same time. I dreamed of owning a YZM since I fist saw the pics years ago. When I found this motor I had to have it. I was hoping by posting here I could find more info and others could would appreciate this cool find.
I now start my search for a chassis to put it in. I am looking for a 2007-9 YZ450F white like the YZM.
This wasn't supposed to be a sidecar/hack thread. I can start one of those. Can you say EML 1000cc two stroke twin sidecar motor.....
Thanks for the positive posts. Now I will STFU
The Shop
Wow, that EML 1000cc two stroke twin looks like it could pull both shoulders out of socket with one twist of the wrist!
As far as the original title, complete let down.
In all cases, that is still a cool engine, as said, 70/80 hp on a track is something you can holeshot with 95% of the time. Plus the sound is awesome.
I wonder if the chassis will be ok with it, you may need to reinforce all that and be careful with the bolt quality, then check it each time you ride if you do not want to break the frame.
The bike you build should either be a hill climber or a dune bike. It would be fantastic in those applications.
I have a kit similar to this for sale at the moment:
http://vintagebikeads.com/
I also have a JPX kit for sale for the Yamaha XT550.
Pit Row
Post a reply to: YZM 500 2 stroke-FOUND NO BS