Potential Group Purchase - Wiseco GS650 741cc pistons

[Kenny]

I hope I caught you in time, do not buy that Cruizin Image kit. Although they make some great pistons for other applications, this was a huge blunder on their part. These are basically just GS750 stock bore pistons and have only the correct pin size and compression height to fit a 650 or 550. That's where it ends. The dome and valve reliefs are completely completely wrong, and are not compatible with the 650 head.
The 650 combustion chamber shape and intake runner shape is why the 650 is such a superior engine, it is the best two valve for cylinder design Suzuki had back then. It's possible that someone could machine out the 650 head to go back in time to an inferior hemi dome chamber to fit these, but you would lose about the same amount of power that you would have gained just by running stock 650 pistons and stock 650 head...
They make a note saying that these are not the same design as the factory 650 pistons. That basically means they just saw that they were the correct height and wrist fin size to make a 3 mm overbore 650... So the manufacturer made the same assumption / mistake that a lot of amateurs do, and thinking that they can stuff listons from a different application into their engine and everything will work perfectly...

Cruizin Image made a huge mistake by just assuming that all two valve per cylinder GS models would be similar, they probably never even looked at a 650 combustion chamber. Very surprising because all of their hemi pistons are same quality as OEM, impressing a lot of people for their price especially.

Yeah i noticed this error. So no 740 conversion for me. But i saw they had 650 +1mm overbore and that will be almost 700cc if i am correct. I can get 650 head and cylinder. So if i am correct i need to grind out a bit on the bottom end to make cylinders fit, and something about timingchain tensioner? Or was it to use the 550 camsprockets on 650 camshafts? And 650 exhaust and carbs… and need a thicker lower headgasket too? Please advice if i missed something or got it wrong. 🙂

[Chuck78]

Yes, cam sprockets from 550 or GS650E cams, NOT GS650G cams.
thicker custom head gasket ot base gasket.
I may have a big bore gasket to spare that didn't meet my specs, I cant remember if I sent them all back or not.
Cometic can make a custom thicker base gasket,but the oil pressure o-rings would then need to be thicker, & they are a proprietary shape, egg-shaped. I shoopose one vould possibly manipulate a specially selected thickness and diameter round viton o-ring through clamping and heat gun to take that shape if one got ambitious, then all that'd be needed would be a custom thickness Cometic GS550 base gasket to fit 650 sleeves, or a GS650 custom thickness base gasket to fit 550 oil/stud outer rear passage o-rings.