Building a race bike

julian

julian

Hero member
Location
Belgium
Hi folkes,

Thinking again now about finishing my SF project but having a little rethink.

Now the BSA is all done, I don't really love it like I do the others, It's too much of a "doesn't fit anywhere bike"  too much of a modern take on an old bike I think.

I don't want the same feeling with the Laverda so was thinking of doing something more fun, like racing it in pre 74 classic 750s.
Idea would be to build a very light weight frame but similar to an SFC frame but in 16g 4130 etc,  Make it look like an SFC but lighter, that way I can't help but love it.
De-stroke the engine to 67.5mm with my 84mm bore gives just under 750cc,  Fancy rods etc and I would have one hell of a max rev potential. Light weight crank as the size would be tiny.  Light weight all the rest as I can junk the starter and dynamo and everything else that even winkes at me. 
What do you all think?

Fun idea or not?

Regards,
Julian
 
First off, pics and video of the BSA now it's finished.
What about vibration?
Would your engine mods mean it will vibrate less?
I would be concerned of failures if it was lightweighted too much.
But hell yes, a fun project!
 
Do it. The more racers the better, but let the powers that be know in the ILOC as they are about to do away with the racers fund altogether. The more racers there are, the less likely they are to do it.

Why not race in F2 BEARs ? Liberal rules, and the class was won by a 750 Moto Guzzi that I beat regularly last year. Prove the bike, get a trophy, then move on to another series. I very nearly did it with my 750, but have new plans underway at the moment.

RACING IS LIFE. ANYTHING ELSE IS JUST WAITING.

Robin  :D :o :LOL:
 
Thanks for the encouragement guys,

Vibrate less yes due to lower out of balance forces,  I will also run it 90 degrees so that should also help.  Light frame etc will make the rider feel the vibes more though but I guess when you are racing you care a little less?

Will read rules very very well and my middle name is "interpretation"  my understanding of words stretches the rule makers to write EXACTLY what they mean and then some!
We raced one of our old GP cars some years ago, we had a 2 part race and we had to park in park ferme over night, the rules said we could only check and topp up "Fluids"  We did oils, water, and tyre pressures. The scrutes went mad,  ONLY FLUIDS they screamed.  Air is s Fluid, they meant "Liquids" but they wrote Fluids.  Tough shit..  Rules are Rules  ;o)    didn't help us to win and we didn't win but it was real fun.

Have some good ideas for the engine but not sure if i can print it all on a public forum  ;o)  most of it though.

Don't want the racers fund though,  I believe if you want o go out and play then you sort your own funds to do it with.

What is BEARs F2?    I'm probably going to leave the drums on though, just to throw a spanner in the works  :LOL: :LOL: :LOL: :LOL: :LOL: :LOL:

Juian
 
Ah, Julian, you are in Belgium.

BEARs is British European American Race series and runs in a few countries around the world. Nearest to you is the UK. It's run by the Vintage Motor Cycle Club British Historic Racing ( VMCC BHR) and the F2 class is up to 750.

Regards
Robin  :D
 
That sounds fun,

So no Japs?  not that I have a problem with them of course.  :LOL: :LOL:

I like classic looks though so certainly don't wan to do modern lookin mods.
Besides, then I would go stupid and I can't afford my own stupidness.  :o

Regards,
Julian
 
Great idea Julian - as long as the series you would be entering allows a stroke change - don't see why they wouldn't. Or go in the unlimited class with a larger motor - won't  rev as much - but still competitive in classic racing. - Regards - Phil
 
B.E.A.R.S. (British European and American Race Series) (AGM 11/13)

GENERAL:  Machines MUST be derived from a Production Road Going motorcycle freely available to the public prior to 31st December 1985. No motorcycle derived from any form of original competition motorcycle will be eligible. All components must be British, European or American unless otherwise stated. There will be three class championships

(1) Up to 500cc,  (2) 501cc to 750cc  (3) 751cc to unlimited.

FRAMES:  Free choice of frame, specials welcome as long as they are constructed to a type/design typically used before the cut-off date. Frames must be constructed from steel tube. Anyone building a new frame should submit the design to the eligibility team PRIOR to starting to build/modify same. Typical frames used in Formula 1, 2 and 3 series, Battle of Twins and Sound of Singles racing pre 1986 are eligible. Sears, Tanks, Fairings and other bodywork must be of a type or style as used prior to 1986. Japanese style fairings and seats NOT eligible.

FORKS:  No ?upside down? forks will be allowed. Hub centre steering type forks as used prior to 1986 will be eligible.

BRAKES:  No four-pot callipers and no Floating Disc?s unless fitted to the original road machine that the bike was derived from.

BRAKE MASTER CYLINDERS:  In addition to British, European and American master cylinders of the period, Japanese master cylinders of a type available prior to 1986 are eligible.

WHEELS/TYRES:  Treaded Tyres only, no wet type tyres allowed. The use of tyre warmers will not be allowed. All BEARS machines can utilise either 17? or 18? wheels due to availability problems regarding many popular wheels used ?in the period?. Many early magnesium (Dymag, Campagnolo etc), wheels are now in poor metallurgical condition and the Astralite wheels, a popular contemporary are no longer available. A wide choice of 17? wheels and tyres are readily available at much more attractive prices. The maximum tyre width at the rear is 160mm.

CARBURETTORS:  British, European and American carburettors of any type available prior to 1986 are eligible. Japanese Round-slide, Mikuni and Keihin carburettors will be eligible. IT IS ADVISED  that should you propose to use carburettors other the British, European and American types, you should check with the eligibility team as to being eligible.
 
Does sound interesting! Although ther "should be" a lot of stuff pre 84 that would piss all over a poor old SFC no matter how light I make it.

The Belgian race series I was thinking about has a 74 cutoff, may be more in keeping with my ideas and then I could play at BEARs if I wanted to have a LOL at my own expense.  :LOL:  which I do often anyway  :P

Julian
 
Great idea Julian. As said be very careful of the rules for the class you race in, and talk to some of the people who are racing in that class to find out what the realities of it all is. Here in Scandinavia it is pretty different to England so it is probably a similar situation for you.
Here the 750 classic class is up to and including ?73 but people get all sorts of things through however they are strict re e.g.fork size however one Ducati gets away with 38s (for some reason).The 750 class is also extremely competitive here with lap times to cry for and a normal Lav just does not have the power, so the short stroke route for high revs is the only alternative for more power, for any chance to get to the tip ot the pointy end. Keep us posted.
 
julian said:
Air is s Fluid, they meant "Liquids" but they wrote Fluids.  Tough shit..  Rules are Rules  ;o)   
Click to expand...

Ha! Being a pedant sometimes pays dividends  :D. That's where lawyers earn their money.

You probably could have charged the battery too. While the fluid theory of electricity is pass? these days, it still has some credence in certain applications.
 
Hi Julian,

the engine - no matter how light you make it - will be one of the biggest portions of the weight. Friend of mine does RAU-alike frames for the 750's that are handling great and are around 11-12 Kilos  if I remember right. Single best place to search for weight reduction on the bike... Next big points are the wheels. more modern ones with modern, lightweight brake rotors can reduce the overall weight by up to 8 Kilos; and that are important kilos, as they are rotating... Battery: if you go from a sealed gel battery to a LiFePo4, you safe another 7 kilos or so. Removing lights, mirrors, turnsignal etc. brings another couple of kilos, as does changing the tank and seat to light weight ones. Fairing or not is a question of personal preferences. No fairing is another 2-3 kilos, but not as comfortable and aerodynamic as with fairing potentially... small tank, only as much fuel as you need and you get competitive... Oh - and not forgetting the exhaust... saves also kilos to have a light weight one...

His own racer is down to around 160 Kilos (no fuel, with oil and battery) or so and the engine has something like 65 HP, maybe a bit more. With tons of work, you can bring this engine up to maybe 90 HP, which gives a good power/weight relation. He says he mainly wins on the brakes and while cornering, not so much under accelaration (while weights to much, which is an important factor, too...). Seeing what Drmsby does with Steve's 750 Ethanol-SFC, I think there is a fair chance to be competitive - the right rider assumed...

regarding the revs, I think the limiting factor is the valve-area, not so much the pistons or stroke. but maybe I am wrong. your setup with a desmo valve actuation would be giving you what you want.
 
Once you've achieved your lightest possible bike, the rider's weight is critical.

I remember the Williams F1 engineers reducing the car weight to the extreme then porky Mansell struggling to get into the cockpit.....  :D
 
Hi,
Yep, all suggestions good there, thanks everyone.

Methanol is allowed over here so that sounds good. (Iv'e worked a lot with that and like it)
Engine weight can come down quite some in my opinion if I go like a mad man on all sorts. Which I probably will knowing me.
Frame will be light but not silly material as it needs to be repairable in the field.
I like drums so that will seriously hamper my win potential but we will see.
I don't mind things being "lifed" so maybe will help in loosing weight.

I could make it radio controlled and fit a blowup dolly on top  :LOL: :LOL:
But I had better keep her in the pit with me  :D

Julian

 
In my experience a weight relationship between 2.5 and 3 :1 is easily achievable with a "conventional" frame.

That is to say the dry weight of the rolling bike will be between 2.5 and 3 times that of the bare engine.

A relevant example, 500 water cooled twin, porky motor, weighs 68Kg dry, all up weight of the racebike was 140Kg with big brakes, fairings etc. 72hp at the wheel on alky....
 
It will be very interesting to weigh all the sub assemblies to compare.  I'll try to make a little table to show the comparisons.
The crank will be the most interesting to me.
I recon almost half the weight of standard.
Fun times ahead.
J
 
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