Rule re-write.

[Michael Moore]

I believe that there are some problems with people understanding the legality of aftermarket alloy swingarms and billet triple clamps in pre 75 (and possibly other classes). <snip>

I have yet to see any legitimate proof of billet alloy triple clamps being available prior to 1975. Profab cast aluminium and magnesium triple clamps should be allowed along with modern billet replicas of them.  I think that the swingarm and triple clamp situation should be clearly spelled out in the MoMs as both swingarms and triple clamps are deemed to be  'Major components'

I just pulled out my copy of Terry Pratt's "Grand Prix Motocross - the 1972 World Championship Season" and on page  102 there's a photo of a works CZ lower clamp with the caption:

Some of the CZ Grand Prix bikes are equipped with this special lower yoke.  It offers much greater gripping surface against the fork tube and has two pinch bolts on each side.  While the production single bolt yoke is made from an aluminum casting, these works parts appear to be machined from solid stock

If someone wanted a different clamp before the next race it is a lot easier to grab a slab of aluminum, bore 3 accurate holes and then the rest could be finished with a band saw, drill press and belt sander (or a dreadnought file) compared to making a pattern, having it cast, having the raw casting heat treated, and then doing the accurate boring and drilling/tapping operations.

Husqvarna and Rob North (among others) had fabricated steel clamps in the period so there's three different methods of making them -- fabrication/welding, machining and casting (which also requires machining).

Looking at some 1970s Maico single-bolt clamps I'm not seeing much to distinguish this cast part from a similar clamp machined from solid.  They are just a flat plate, no fancy contours or droops to them.  Casting makes sense when you are doing mass production. 

I've got early/mid 1970s Betor and Yamaha 35mm clamps that have two pinch bolts at each point so that is clearly a period feature.

Mark, it looks to me like the problem some people have with "billet" clamps is not that they are machined from solid but rather that some of them look like they are from a much later period than pre-1975.  That seems to be a no different problem from running a fat snail expansion chamber exhaust suitable for a 1995 bike on a pre-1975 bike.  The problem isn't that a welded steel chamber is out of period, it is that the design is out of period.

Rather than exclude a period manufacturing technique why not apply a "must look period" test?

cheers,
Michael

[FourstrokeForever]

Am sanding all day tomorrow. Wanna come

I thought you were going on a cruise with Simo Ted?
Can we get back on the subject? This thread's got nothing to do with suspension travel in pre 78. I'm sorry I mentioned it. 

There's always a few who want to argue about the most minute detail that has nothing to do with what was actually written Mark..... No wonder there is a need for a re-write of the MOMs when you can read the amount of reading between the lines that goes on here. Everything has to be spelt out in black and white, with no shades of grey.

For a start, Pre78 are allowed to run 38mm forks at the moment. It should stay that way.

Suspension travel is limited to 9" front and rear. It should stay that way.

Perhaps the shock mounting points rule could be removed altogether or altered to allow modification. Again, the rear wheel travel MUST remain at or less than 9".

As for Evolution, I think DT's brave decision to allow any drum brake front fork is a good one. Perhaps not for this year because of the confusion (by some) created by announcing it so close to this years Nats. But at the end of the day, the decision (and interpretation of the rules) is his to make and we have to accept what the chief eligibility scrutineer will and won't allow.

I think it's great to see so many on here making positive comments and giving ideas on how the proposed rule re-write should be.

I also agree that Firko's suggestion of getting a knowledgeable group of people together to nut out an updated list of follow on models is a good move.

[supersenior 50]

As these things always rear up just before a Nats, it appears that's when these issues become important to some.No surprise there.
With that in view it would be interesting to see how many on this thread, or the  other 20 pages, actually have ridden, sponsored riders, or in a business affected bythese issues, have in fact been directly involved in say the past three CMX National Championships.
It would also be interesting to see how many had been directly involved in organising or officiating at the last three Nats.

[09.0]

With regards to limiting rear suspension, specifically in relation to twin shock pre75 bikes, the rear should be restricted to 4 inches simply because it's easily done. How many race bikes still run the original shocks? Of the minimal amount that actually do run the originals, how many of them have not been rebuilt? It's easy to buy the correct length shocks or getting the originals modified whilst apart.

[firko]

In re dampers with external adjusters, Koni came out with them in steel (model 8211) during the 1960s.  The aluminum 8212 was introduced in 1967.  Those were for race cars but the technology was there for anyone to buy and copy.

I remember them Michael, not that any of the adjustments made much noticeable difference . I was actually referring to Arnaco shocks which have a modern style stacked shim method of operation, 10 click external dampening adjustment, multi adjustable preload and large dia shafts (I think 15mm). Whenever someone questions the validity of Ohlins, YSS or other modern style  shocks with shims and  external clicker adjustment for pre '75 I refer them to the Arnacos. I think Curnutts were of similar design but I'm open to greater knowledge on them. I've got a couple of pairs but have never pulled them apart.

Mark, it looks to me like the problem some people have with "billet" clamps is not that they are machined from solid but rather that some of them look like they are from a much later period than pre-1975.  That seems to be a no different problem from running a fat snail expansion chamber exhaust suitable for a 1995 bike on a pre-1975 bike.  The problem isn't that a welded steel chamber is out of period, it is that the design is out of period.

That's a part of the problem, some of these aftermarket clamps appear way too modern. The main bone of contention is the fact that triple clamps are considered a 'Major Component' along with the frame, swingarm, forks and engine and our MoMs (Manual of MotorSport) or rule book states ....."All major components must have been manufactured within the period, or be replicas of components manufactured within the period specified for the class in which the machine competes other than those listed in the Components Table" which, to my way of thinking puts anything not replicating something built during the period, in this case, pre '75, as not allowable. The paragraph is included to stop builders using later on non period parts to not only gain performance advantage but to spoil the period appearance of the bike. That's why the addition of alloy swingarms to a bike annoy me so much. I've researched this to the nth degree and can find only Boyd and Stellings*manufacturing aluminium swingarms on a commercial basis prior to 1975 (and OSSA on the first of the Phantoms). Thor, Kosman, DG, FMF, Profab and others didn't produce alloy swingarms for any dirt motorcycle prior to 1975 from what my research can uncover, and in fact there weren't very many producing Chro-Mo swingarms either. It wasn't until the 75-79 period when such stuff became 'must have' fasion items .

* There was a company producing solid cast aluminium swingarms prior to 1975 but they're very uncommon and as I write this I can't remember the company's name (A&A perhaps?).

[Michael Moore]

Yes, Mark, you are thinking of A&A Racing.  A friend had one of their cast swing arms on a C15/B25 he ran in AHRMA Premier Lightweight.  This looks to be one of them:

http://issuu.com/retromotoonline/docs/bsac15

and also

http://www.b50.org/photos/uploaded/_1e08feae8f0d78c6a9f6bc0995f217be_larryrbswingarm1.jpg

Ernie Earles built an entire chassis (including Earles fork) out of aluminum for a 500cc non-unit BSA twin back in the 50s (featured in the 06/87 Classic Bike and located in the S. Miller museum)



Don't forget your Swenco alloy LLF, the OSSA aluminum monocoque RR, the Alta Suzuki aluminum monocoque trials bike with magnesium fork yokes, the CRDC aluminum monocoques used on both RR and MX, Offenstadt RR monocoque, etc.  Aluminum is just another metal and different designers used different materials.  I suspect that many of the period alloy swing arms are probably less stiff than the steel s/arms.  The Ti BSA works bikes were certainly a step in the wrong direction.  IIRC the early Suzuki OEM alloy swing arms on the big GS street bikes were heavier than the steel parts they replaced.  Some of the modern "replica" alloy s/arms I've seen look pretty dodgy structurally to me.  Aluminum may be 1/3 the weight of steel but it is also 1/3 as stiff, so for a given size of tube you'd better have 3X the wall thickness in the aluminum part to have similar stiffness, but once you do that you've got the same weight and much worse fatigue characteristics.

I like steel. 

FWIW, when he responded to my request for "who knows the earliest instance of machined from solid alloy clamps" Tony Foale told me "I can offer early 1970s but I certainly would not claim to be the first.   When I started making frames as a business I then changed to getting basic castings done in magnesium which I machined on a lathe face plate.  Prior to that I made a couple sets from the solid."

So we've got at least Tony and the CZ factory making billet clamps in the early 70s.

There are some Curnutt articles here:

http://www.eurospares.com/graphics/suspension/

No shim stacks, they had a floating piston.  I've seen mention that Works Perf's Gil V started out by modifying Curnutts, but I don't have anything more than hearsay on that.

I'll admit that I'm biased away from stock motorcycles, having never had a new bike that stayed stock much longer than it took to get it home.  Rules that rewrite history by pretending some things didn't happen seem a bad idea.  Stock bikes are nice to see now and then and every museum should have some, but our sport is one filled with people like Les Archer racing cammy Nortons on the dirt, or Dennis Jones, Len Harfield and Bob Geeson who built entire race bikes including the engines in their sheds.

If it looks like someone could have built it in the period it is fine by me and I'm happy to see it, because I know there's a good chance that someone probably did build it or something even cooler.  But other people have different opinions.

cheers,
Michael

[Ted]

As these things always rear up just before a Nats, it appears that's when these issues become important to some.No surprise there.
With that in view it would be interesting to see how many on this thread, or the  other 20 pages, actually have ridden, sponsored riders, or in a business affected bythese issues, have in fact been directly involved in say the past three CMX National Championships.
It would also be interesting to see how many had been directly involved in organising or officiating at the last three Nats.

Because I have had a fair bit to say about some mooted changes some want, I will have a say.

A fu..cked wrist prevents me from racing MX. That's why I built a Vinduro bike. Go when you want , stop when you want etc.

However I will be entering two Evo bikes at Toowoomba. They will have two guys from the Heaven club on them.

I have only attended the last CMX in Qld. Am attending this coming PCMX in Qld and will attend the CMX in Port Augusta later in the year.

I sponsored a best effort award at the last CMX and always tip in for any charitable cause that is mentioned, as was the case at the last CMX.

I also helped with scrutineering on the first morning at the last CMX

Just because I can't race anymore does not prevent me from being active in our sport.

Bring in one armed racing Col and I'll be the first entry

Cheers

[supersenior 50]

Why defensive Ted ? You sponsored a rider and an award, therefore obviously are directly involved as described in my post.

[Ted]

Sorry mate, didn't intend it to be 

Looking forward to it.

[Slakewell]

Without starting a thread Hi jack and Im happy to move if you chose to debate this Topic.
Does anyone disagree with the following statements?
Pre78 at the Nats race on mostly smooth terrain and more than 9” travel has no real advantage.
Major travel increases will decrease the bikes turning prowess
Because of counter shaft sprocket location large suspension mods lead to chain problems.
More models don’t fit with in the rules in standard trim than do.
Un engineering or backwards engineering goes against the spirit of our sport. 
Most people in 75/77 era were engineering suspension and frame mods.

[Ted]

Without starting a thread Hi jack and Im happy to move if you chose to debate this Topic.
Does anyone disagree with the following statements?
Pre78 at the Nats race on mostly smooth terrain and more than 9” travel has no real advantage.
Major travel increases will decrease the bikes turning prowess
Because of counter shaft sprocket location large suspension mods lead to chain problems.
More models don’t fit with in the rules in standard trim than do.
Un engineering or backwards engineering goes against the spirit of our sport. 
Most people in 75/77 era were engineering suspension and frame mods.

True
True
True
False
True
False

My main concern is raising the limit above nine inches will lead to backyarders pushing the limits on what the fork can handle. If they were 43mm forks, I wouldn't care.

[FourstrokeForever]

Without starting a thread Hi jack and Im happy to move if you chose to debate this Topic.
Does anyone disagree with the following statements?
Pre78 at the Nats race on mostly smooth terrain and more than 9” travel has no real advantage.
Major travel increases will decrease the bikes turning prowess
Because of counter shaft sprocket location large suspension mods lead to chain problems.
More models don’t fit with in the rules in standard trim than do.
Un engineering or backwards engineering goes against the spirit of our sport. 
Most people in 75/77 era were engineering suspension and frame mods.

True
True
True
False
True
False

My main concern is raising the limit above nine inches will lead to backyarders pushing the limits on what the fork can handle. If they were 43mm forks, I wouldn't care.

Come on Ted, the '75 to '78 era was when most of the frame modifications by the average punter happened. All sorts of shock positions and lengths were tried. Even the minibikes started to get modified "monoshock" frames. Yes Ted, if backyarders start extending more than 9" of wheel travel from a 38mm diameter tube, there will be problems that could result in serious injury from metal fatigue and stresses on the lowers. I would never like to see any diameter fork tube beyond 38mm in Pre78 machines.

[Ted]

Mick put up " most people in 75/77 era were engineering suspension and frame mods"

That's more than 51%.  Not a chance.  I agree plenty were, but more than half the grid in every class in every race. Pfffft

You only speak of 38 mm forks. What about all the 35 and 36 mm forks that are also in Pre 78
If you increase Pre 78 travel limits you increase them across the board in all classes

More 125's were sold in this period than all the other classes combined. What do you really think will happen when a bloke tries to get 11 inches out of his 36 mm forks

MA write the rules. MA are also the insurer.  Do you honestly believe they would condone these ridiculous travel limits. Negligence in the first degree.

[FourstrokeForever]

Mick put up " most people in 75/77 era were engineering suspension and frame mods"

That's more than 51%.  Not a chance.  I agree plenty were, but more than half the grid in every class in every race. Pfffft

You only speak of 38 mm forks. What about all the 35 and 36 mm forks that are also in Pre 78
If you increase Pre 78 travel limits you increase them across the board in all classes

More 125's were sold in this period than all the other classes combined. What do you really think will happen when a bloke tries to get 11 inches out of his 36 mm forks

MA write the rules. MA are also the insurer.  Do you honestly believe they would condone these ridiculous travel limits. Negligence in the first degree.

I agree with you on most points and yet you still want to argue. Why? Of course there are smaller diameter fork tubes in pre78. I just used 38mm as an example because 38mm is the maximum diameter of fork tubes allowed in Pre78. Does it make no sense to you that any fork tube under 38mm that is increased in travel limits will be even more dangerous than that of 38mm?

For the record, I wish you would spend more time reading what is written than reacting to what you think is written. I have never once written that I think the pre78 suspension limits should be increased. As a matter of fact, I suggested the travel limit of 9" front and back should remain unchanged.

As for the percentage of racers that modified their suspension during the '75 to '78 period, are you sure there weren't more than not? Can you back your figures up? Do you have proof other than saying you were there? Or are you looking at it from a clubman level where not many could afford to start drastically modifying their bike and were quite happy just to go for a roost with their mates on Sunday?

[Davey Crocket]

Going by bike sales in the pre78 era, more upgraded to the next years model than tried to modify bikes....next years model was always better unless you rode one of those red things......also, the best bikes in class sold in huge numbers and the others didn't.