Follow on models

[Tim754]

Noticed this flogged subject has raised its head elsewhere again and again and again.  My take on it...
 If you believe your or anybody else's Suziyamhonnaquacka or whatever bloody factory designated "1975" "1978" 1985" etc model is a direct unchanged item from the proceeding legal model, except maybe for  covers paint / graphics, Get off your soft ring cheeks and put in a submission detailing with proof! To the rules and eligibility controlling committee.
It is really no use bunging on here unless you are seeking" relevant physical proof and information " . Naturally 99.99% of all will not! as some other turd stirrer can do that for me!!!
 This rates along side "my favoured brand of old shitbox is better than your piece of prehistoric rancid pus"  posts........Cheers Tim

[Nathan S]

Taken from the thread that prompted Tim to start this one (my bold):

The factory designated 1975 model stanza was included to cut these disputes off at the pass. Remember that it's not just the MX B engine that's not allowed, it's the whole bike. The whole engineering concept of the MX B belongs in the next generation of motocross history, purely for its suspension package*. December 31 1974 was deliberately chosen as a cutoff date as it marked the end of the 7" and4" suspension travel era. Even though the MX B engine may be considered an update of the A model, the bike as an entire package is a whole new deal that launched Yamaha into its next phase of development. You can't seperate the engine from the whole unit and call it a flow on while still disallowing the monoshock frame. It's all or nothing.

This might be the crux of a lot of things.

I'm not sure that I agree that its so simple (although I'd like it to be), but I need more time to think before posting.

[Doc]

My last cent worth, I still say the best and easiest fix is have the rules changed so as not to accept flow on Tim. I agree, its a shit topic and I'm guilty of pushing it in the past but it opens a huge can of legality worms and since the bikes in question did in fact not exist before the cut-off date then they simply are not eligable. Whether or not they remained changed or unchanged after the date doesn't matter a zac. The only change I'd make is to scrap the flow on idea and enforce the cut-off

[firko]

The system's worked fine for over 20 years. Leave it alone.

[Doc]

okay 

[211kawasaki]

Sooooo thats your last word on the subject Doc?


211

[Tim754]

Doc if you reply to 211, that above would not be your final word...   I agree with Firko system has worked all along with only a few wrinkles that ironed out . Stop pushing this barrow   Cheers buggers.

[caps 999]

i can keep the 125e compeditive in evo so it dont bother me which way it goes

[Nathan S]

As much as I agree with Doc's suggestion (that the only way to make the problems/questions go away is to kill the follow on rule), in reality there needs to be such a beast. Without it, we'd lose a huge number of bikes to trivial ineligiblity.

Some bikes are obviously legal as follow-ons, others require further justification (75 CR125 for example), or some mods (76 DT250) to be legal as follow-on bikes.
But that side of things is generally pretty clear and uncontested.

Where it gets tricky is when you're looking at mixing and matching stuff, and when you're modifying bits.

The MX250B engine for example, is only a non-radial-finned head and a clutch cover away from looking just like a MX250A engine. It has the same number of gears as the MX-A engine, and nobody ever cares about the rest of the internals.
So (assuming it has the correct clutch cover and cylinder head) then surely it must be legal in a pre-75 bike?
At worst, you could reasonably argue that you're not using a MX-B engine, you're using an MX-A engine with some mechanically and cosmetically identical MX-B parts - even if one of those parts happens to be the engine case with the number stamped in.

Barrel porting is another vague area. ..that I'll come back to when I've got some time.

[Doc]

 

[felix7]

Well put, Doc. Leave it all alone. The very last thing VMX needs is excessive rules and bureacracy. The hardest thing I want to think about before a race is how many times I'm gunna fall off!

[firko]

Some bikes are obviously legal as follow-ons, others require further justification (75 CR125 for example),

I'll bite . What further justification is needed for the '75 Honda CR125 to be allowed in pre '75? To my understanding it's one of the more deserving flow on bikes.

[BETRIC]

Nathan you can pick the difference between a MXA engine from MXB engine straight away because the engine numbers are on opposite crank cases, (MXA left side) (MXB right side), gearboxs won't interchange either, you could always fit a MXA motor into a YZB or MXB frame with the a correct YZB frame number as they are basically the same frame, shock and forks , (some frame brackets are different) but that would be cheating using the MXB frame  

[shorelinemc]

what about  a 78/79 tt/xt 500 basiclly the same as a 77?

[firko]

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Nathan you can pick the difference between a MXA engine from MXB engine straight away because the engine numbers are on opposite crank cases, (MXA left side) (MXB right side), gearboxs won't interchange either, you could always fit a MXA motor into a YZB or MXB frame with the a correct YZB frame number as they are basically the same frame, shock and forks , (some frame brackets are different) but that would be cheating using the MXB frame 

Hallelujah ...I knew there were major differences but wasn't sure what they were. That  backs up the fact that with an MXB engine in his slider, Cliff Patton won an Aussie title on an illegal bike. Thanks Dave.