YZ 250N

[monte34]

I have a 1985 YZ250N which came standard with a front disc brake. If I leave the rest of the bike as is but use the front forks and brake from a 1984 L model will I be allowed to run the bike in pre 85 club events or at a national level. I don't know if any other part of the N model is different to an L model that would preclude it from competition.
Please don't think that I am starting another eligibility problem, I just want to know if I am doing the wrong thing (excuse my naivety).
Cheers

[DJRacing]

Monte34, the 84 model has it's own set of identifying serial numbers on the frame and engine as does the 85 model so it wouldn't matter what you did to the 85 model bike the serial number will always says it's a 1985 bike and not a Pre85 bike, or at least that's how I understand Pre85 works.

[head]

different rear shock with Yamaha Bass (Brake Actuated Suspension System)  and different cylinder.

[monte34]

Thanks, sounds like there's no place in VMX for this model. BTW the rear shock looks identical to the previous model but I wasn't aware of the cylinder difference.

[Ted]

There are Pre 90 clubs in NSW, Vic and Qld that will welcome that bike with open arms. Bring it to Cessnock NSW this weekend and ride it in the Heaven / NDMCC inter club round. You'll be very welcome.

[monte34]

Thanks Ted, looks like I might have to leave the disc brake front on it. It won't be going anywhere for a while, its still in the reconstruction stage due to frame straightening and painting.
BTW how good were those Sea Eagles the other night, champion team at the business end of the year.
May have a set of forks and drum front wheel for sale soon.

[Ted]

Champion team all the time

GO MANLY

[Nathan S]

The shock isn't a problem - as long as you don't change the mounts and you respect any travel limits for your class, you can basically do whatever you want with rear shocks. This is how people can run new aftermarket shocks.

The cylinder is a problem, but likely to be overlooked at club level.
If it is just tweaks to the port dimensions (rather than a significantly different port layout), then you may be able to argue that it is a legit carry-over part, even at National level - but its probably less effort to just get the correct 84 barrel.

Frame number doesn't matter in itself, but you would need to prove that the two frames are the same apart from the number.
Ditto the engine (particularly the external parts, including cases).

Seeing as you have the easy option of riding it in Pre-90, I'd just go with that.

[monte34]

Thanks Nathan, that was the sort of information I was after, not being very familiar with the differences. I'm quite happy to leave the bike as is and run it as a pre 90 when I get it reassembled.

[POM]

FYI

The frame IS different (beefed up around down tube,bigger muffler bracket,strengthened r,brake pedal stop,thinner stronger tubing all over.
Barrel is almost externally identical but has minor port differences.
Power valve is different,but interchangeable.
Head is slightly different (externally identical apart from prefix no.s)
L/hand crankcase is different internally (at lower end of clutch actuator)
Magneto is an external rotor instead of internal.
Cdi is visually completely different....and has different wiring plugs.

There maybe more.

Even with all this it would take a very keen scrutiniser to spot any of it.....

[monte34]

Did all these minor differences add up to a better product or was it change for the sake of change?

[Spanish Armada]

please boofhead dont start another complicated topic there is enough on here know 

[POM]

Apart from the front disc (which to be fair wasnt that much better from the excellent drum) and a slightly lighter clutch action i realy can't see a whole heap of progress.......

I don't see why it couldn't be a "carry over model" with a drum front end fitted.

I think somehow i may regret saying that.

[DJRacing]

The YZ250N was a very very good bike in its own right being that it was a very sorted out bike coming from the factory. It was the last time they use that style of rear suspension and the motor was basically the granddaddy of the modern 250 2stroker motor of today(I could be wrong, and I'm sure someone will correct me if I am)
You wouldn't have a problem being out classed running that bike in Pre90 if you dial it in for yourself and as linkage bikes go IMHO the best looking of them all.
It maybe the oldest bike in Pre90 but it certainly wouldn't be the worst. And remember if you bet your fallow races you'll have even more bragging rights 

[Nathan S]

If my memory serves me, you can follow the progressive development of the YZ250 motors from the G model through to the mid-late 1990s - there were some big changes in there, but they were still developments of the same basic architecture (grandfather's axe, rather than a whole new axe at any point).

The K to T model motors are definitely very closely related to each other.