100cc classic production build

[roflhat]

Aiming for BMST 2021, been doing bits and pieces on the bike. New fuel line, fuel tap, got a steering damper and kill switch to fit. Still trying to get hold of the tires I want, think I've found a source though. Need to tape the headlight too, it'll look the part then. Almost ready to try get it running, then it'll be doing a couple things to the engine. Got another carb to use for the CG class record. Got some polishing done on the mudguards, came up pretty well. Looking at some Alpinestars leather, going for used ones. Then gloves and boots.

[Doc B.]

Looking good! I crunched some numbers and at the rated 12hp it looks to be competitive in production. As I pull stuff off my bike from last year and lament the amount of corrosion in spite of a very through cleaning after the event I'll suggest you think about waxes, anti-corrosion sprays, etc. while you have the bike going together. Worst places for salt buildup are front and underside of the motor, under the front end of the swingarm and everything around the rear wheel. Looks like you might want to get fresh paint or powdercoat on the swingarm to protect it.

[roflhat]

It was up there with the fastest bikes of its capacity back in the day so should work alright.

[roflhat]

Been trying to start the bike, has fuel, spark and compression but isn't going yet. Going to go over the timing next. Looks good though!

[Koncretekid]

I find 2-strokes very sensitive to gas fouling of the spark plug.  Make sure you have some extra plugs on hand.  I've also actually used a propane torch to make sure there's no gas down in the plug on my chain saws and weed whackers - - Dodge hard things to start and keep tuned up!  My Ossa (piston port timing) requires absolute flooding of the carb (IRZ carb, like Amal) including tilting the bike back and forth to get some fuel into the motor to get it to light up.  Bridgestone (rotary valve)  is just the opposite, as flooding will prevent it from starting easily.

Good luck, it looks great!

Tom

[firemanjim]

Have not looked at the classic rules but production bikes just need to appear stock from outside. Internal moids allowed, better piston, thinner gaskets, coatings , porting etc

[rgdavid]

When was the moter last taken apart ?    Old dry crankshaft oilseals could be a problem and can suck/blow air on the ignition side and the same for gearbox oil on the transmission side, and will lack primary compression  its imperitive that these are in good condition or youll never be able to tune the moter properly.  Go little gp.  A shame you cant use a expansion chamber...these moters are very tuneable.

[edinlr]

In theory you can use an expansion chamber if you can get the dimensions within the stock exhaust.  The muffler is pretty big, so it should be possible to split the pipe, add a chamber and seal it up again and either polish the heck out of it, or get it re chromed.  You might even be able to get away with just leaving it very dirty.  The rule is "no visible" modifications, so as long as dimensions, outlets etc. match, then you should be good to go.

[Seldom Seen Slim]

"no visible modifications" can be liberally interpreted if you ask nicely.  The canisters on Nancy's bike got opened up, emptied and re-welded to original appearance.

Well, not very original.  The inspector saw the ugly buggered-up welds and questioned them and I replied that "It must have been the Kawasaki factory's new guy's first day on the exhaust welding line and he used coat hangers instead of rod" - and got away with it!

[roflhat]

Cheers everyone, going to get the timing to stock and go from there.

The motor will be getting a full rebuild, and a bit of a tune at the same time. I'd actually thought of that very idea with the exhaust, thought it was a bit cheeky but I might look further into it now! Want to get the maximum out of it. Also thinking of going for the P-AG class, from what I can gather thats similar to P-PC and P-CG anyway but I'd be allowed a proper expansion chamber and a bigger carb?

Does anyone know if I can go for the P-P record even though it's a classic bike? potentially 5 record classes I could enter
Thinking
P-PC - standard(ish)
P-P   - as above?
P-CG - as above but bigger carb
P-AG - as above but also expansion chamber (not 100% sure if this class exists for 100cc)
P-AF - as above but any fuel

[Chris V]

Modifing the exhaust visably ( chambers) puts you in "M" modified class

[roflhat]

Modifing the exhaust visably ( chambers) puts you in "M" modified class

I thought the M designation was for the frame being modified? does the exhaust come under frame?

[Doc B.]

I thought the M designation was for the frame being modified? does the exhaust come under frame?

Yes. AMA Bonneville supplementals, page 29 - Production (P) Class frames

  Production class motorcycles
shall not be modified from original equipment at time of
manufacture. e.g., frame, forks, gas and oil tanks, seat, front and rear
lighting, fenders, wheels, brakes, air intake box and (unmodified)
exhaust system.

Section 5.D., page 32  - Modified frames

EXHAUST AND MUFFLERS
Length of exhaust/muffler assembly shall not extend past the rear
edge of the rear tire. It must be sufficiently anchored.

[wobblywalrus]

About 45 years ago my friends cut apart Susuki 500 Titan mufflers and put expansions chamber inside.  Then they took apart the engine and did major work to decrease the crankcase volume and increase the lower end compression ratio.  They put a six speed gear cluster in it from another suzi, as I recall.  It was for an AFM production racer.  The work that went into it to keep it looking OEM was amazing.  It would have been a lot easier to make a modified bike.

[roflhat]

Ah ok, thanks for the clarification!

Liking this exhaust idea, managed to find this online - https://vanguardcycles.wordpress.com/2010/12/03/mini-cafe-sleeper-pipe-project/
I've done a bit of "hiding" modifications before, got a world water speed record in 2018 at Coniston