I've read through all the above and still have a couple of questions, can anyone answer the following for me?
A/ I have three shafts from my various engines with different large numbers cast into them, R9, R10 & R11. I don't have the slightest idea how to measure the various lobes
B/ Is there enough meat on the factory 650 pistons to allow them to be machined to fit under a 550 head? The reason being I have a very nice ported head from Mr Reick, and would like to use it on top of a 650 crank/barrel combination
Since I've just siezed a rod onto the crank in my 550's original motor, I now have all the time in the world (around work commitments obviously) to play about with it and the 650 I acquired at the end of last year
The bike gets to stay on the road in the meantime because I managed to get hold of a complete stock motor at a good price to throw in her for the interim
chris-
several people have PM'ed me about this, so i'll pipe in... i'd have to go back and do some measurements to be absolutely sure, but off the cuff i'd say that you could not make a 650 piston work with a 550 head. the dome of the 650 combustion chamber is dramatically larger, and the pistons reflect this. as is, the 650 piston will not even come close to fitting into the 550 head. maybe you could cut some serious amount of material from the edges of the piston, but you'll still have really high compression ratios, have to open the valve pockets, and likely have to work the combustion chamber portion of the 550 head a lot as well. that said, i'd be willing to bet there's a lot of room to work with the latter.
but, long story short: no, you're not going to make the 650 piston work in the 550 head. also, remember: the 650 pistons aren't much larger in diameter, the stroke is just longer on the 650 crank creating most of the extra displacement. if you really want more compression, deck the 550 cylinder surface or use a thinner head gasket.
i'll definitely second what kayaker43 said. the 650 ports are much better than those on the other SOHC4 bikes.