What's legal ?

[Iain Cameron]

Ok I know the 1975 MX250/400 Yamaha is not legal for pre 75 . but the frame ,wheels ,forks and s/arm are YZb so are they a carry over item if the rear is limited to 4" ?
If it is a carry over If I happen to have a SC 500 motor that will fit in can I race it ? this should stir up some ideas . Iain

[Nathan S]

I reckon yes, but you'd want to be prepared to weather the poop-storm that it will create.

[Iain Cameron]

Also I would like to fit MX360 five speed gears . 

[odd1]

As long as you don't start winning!

[firko]

Are you sure the YZ-B and MX-B frames are the same Iain? I thought that he engine cradle is a different shape to accept the newer engine on the MX. The engine mounts are different at least. I see what you're dreaming up but I doubt it'd be legal mate. As Nathan said, there'd be a shitstorm of opposition to it. Close enough isn't good enough either....the '75 Maico frame is the exact same geometry as the '74 and is pretty much identicall except for the steering head bracing and they aren't allowed in pre '75. I think the MZ-B frame would be knocked back for the same reasons the '75 Maico frame is.

[Iain Cameron]

Mark I think the engine mounts are the only difference . This bike is for club level only , and the only other riders Ive passed at the Nat's have either broken down or fallen off .

[Rossvickicampbell]

I think the MX shock is a bit longer also - meaning slight differences in frame there possibly?

[JohnnyO]

You're right Firko, the YZB has a lot smaller bottom end than the MXB so the frames are probably different. Lot of work to have it knocked back at scrutineering.

[brent j]

This could turn into 20 pages easily.

For club racing it comes down to who you beat and who protests, for major or National meetings I could see problems.
Whether it's club or national racing it's still pushing the idea and spirit of pre 75.
There seem to be few who want to push a bike down a class


The YZ360B is listed in MOMS as a pre 75 bike but not the YZ250B. Page 167, 18.5.4.9 Acceptable follow on models for pre 75.

Did the YZ360B get mistakenly put into pre 75 instead of pre 78?

MY OPINION is that this is that an oversight as as YZB's are a 75 model. Same with an MXB. I suppose you could push the point and use a YZ360B frame, as it is specifically mentioned as pre 75 legal, and build your bike from there.

I can't see any problem with MX360 gears or the SC500 motor.

[Nathan S]

Surely if you took a YZ-B or MX-B frame and modified it with an MX-A engine cradle, it would look just like a stock MX-B frame.

The shocks are slightly different between the 75 and 76 model monoshocks, mostly relating to total length. I am unaware of any/the differences between the 74 and 75 model shocks?

PS: Hi Brad.

[Davey Crocket]

Why not build it as a pre78 weapon?....my YZB is getting that treatment at the moment....instead of having 500cc's trying to kill you at every twist of the throtle, give it a bit more suspension and enjoy the ride.

[Davey Crocket]

Brett, YZB is classified as a 74 model.....they where all built in Feb 74 and likewise the A models where built in Feb73....Elsinores came out in 73.....MXB's came out as designated 75 models...YZB was a very close copy of the bike which won the world championship in 73 (250cc), Maico bought out there 74 1/2 model to combat it.... the race was on....im sure now someone will shoot me down.

[Iain Cameron]

Guys Im not a good rider my normal finishing place is last , Im only thinking about this hot rod as I have all the bits sitting in the spare parts pile . I allready own a Yz 400c and 400d for pre 78 in pre 75 Ive got Mx360 and Sc500 so this would be a fun bike Hence the Legality question . Iain

[JohnnyO]

Both the YZ250B and YZ360B are designated '74 models and were available mid '74, that's why they are pre '75 bikes.

[motomaniac]

Guys Im not a good rider my normal finishing place is last , Im only thinking about this hot rod as I have all the bits sitting in the spare parts pile . I allready own a Yz 400c and 400d for pre 78 in pre 75 Ive got Mx360 and Sc500 so this would be a fun bike Hence the Legality question . Iain

Go for it! As long as you are prepared to be disqualified from last place who givesashit?