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Just why do H2 flywheels have their distinctive shape over other smaller H series cranks, then???
BALANCE FACTOR. Pistons for an H2 are heavier than ones for smaller H series, and, the counter weights need to be altered to have correct balance.
If anyone doubt that, you need to see the factory cut crank I have sitting outside in its box, H1R Very Special, has flywheels with cut-away's like an H2. That crank was worth 6 MPH in Yvon's Ontario bike for 1971. That special "pork chop" cut crank vibrated far more than a regular H1R crank, like all get out, but, H1R engines were rubber mounted, different than a street bike, but, rubber mounted anyway.
The holes in H1 street cranks are "pickled", filled with plugs, so, why are they there? To balance the crankshaft to a rudimentary specification, close, like in mass production factors. Yamaha's have these as well, this way, the cranks can stay full circle, so crank case "stuffing" is enhanced.
If balance wasn't important in a full circle crankshaft, then, why did Honda use a set of wheels in their RC450 dirt bikes that had 3 holes in them, with close offs, so individual weights inserts of 96, 100 and 104 grams could be added to set the balance? Because the balance factor needed to be changed for that engine, because it had a hollow crankshaft wheel set. The weights were changed from behind the magneto, through an access door in the cases, and, a second door on the primary side of the right case. that engine was not the same as a production CR450, it was a mirror image engine, clutch on the left, chain on the right.
When Campbell Cycle, a Suzuki dealer in Whittier, Ca., (my old home town) built a TM400 single road racer, they had a hard time finding anyone that wanted to ride it more than once, because it vibrated so bad, it put riders hands and feet to sleep from lack of blood circulation. It also had a pork chop crank. I did the second and further engines, re-balancing the crank, and the vibration was reduced considerably, down to a reasonable level, and, it won a bunch of AFM and ACA road races.
So, the myth that a full circle, multi-cylinder crankshaft has inherent "prefect balance", and that reverses in both rotating and reciprocating balance is just that, A FULL ON MYTH. Stress reversals in our triples as they run, don't have any adverse effects, never have, never will.
Saab Month Carlo and 99 series three cylinder two stroke engines have pork chop flywheels, and are factory balanced, they run smooth, and they are well over 750cc size.
Anyone ever been inside a rotary type aircraft piston engine? Remember how the counterweight is attached to the crank? The counterweight is held in place with pins through it, tightly, and through the crankshaft, in loose fitting round holes. This allows the weight to "find its own center" as the engine is running, to compensate for slight off balance of the whole rotating/reciprocating mass (mess). the clearance between the crankshaft holes and weight pins os the reason we hear one fo those engines make the mechanical "clanking" sound, like they have something loose inside them, as they almost reach full stop when shutting down. In essence, they do have something "loose" inside them, the weight itself.
Anyone that says balancing a triples crank is just a waste of time, or, is not needed, is simply not knowledgeable about how a crankshaft really works, and there are many persons in the business that have NO CLUE.
I also weld every pin, not with TIG, but MIG weld. Big end pin holes in our cranks are hardened, TIG welding anneals (softens) that heat treat, allowing reduced ton press fits, and problems. MIG welding doesn't to that nearly as bad. I use my 110 volt body and fender MIG welder, has worked better than any other method so far in my doing pressed together crankshaft rebuild and modification, that's been over 40 years.
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FAQ
Matching reciprocating weight to crank counterweight is a different thing entirely, but cylinder to cylinder.....no point.
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