It runs! Gs550/650 Top end swap w/pics

[Nerobro]

Suzuki_Don had a pretty involved writeup after his initial 673 build. The title of the write-up was more of a troubleshooting thing trying to figure out a noise after the swap, which led him to discover the deck heights were different and a 650 top end on a 550 required thicker head gasket or thicker base gasket, otherwise the Piston will be tapping the head slightly, especially at higher RPMs when the engine is warmed up.

I'm... Not sure that's right. Using GS750 pistons you do need to do some work. But I had no head clearance issues with my GS650 top end on my GS550 bottom end.

[Chuck78]

Different engines are machined at slightly different tolerances, you might find some that have barely enough clearance to not have noticeable interference, but Don and I have measured several engines, and it's quite uniform that all 650 top ends on 550 engines need a slightly thicker head gasket than the stock offerings in order to have proper piston to head clearance.

750 pistons require massive work to run in a bored out 650 cylinder with a 1980+ GS550 2-valve per cylinder head. Not compatible at all with a 650 head unless you ruin the advanced design of the 650 head transforming it into an old school hemi had like a 1980 550 head. But the valve pockets on a GS750 piston aren't spaced properly for 550 or 650 head, you need to set them up on a milling machine to use a fly cutter to adjust the valve relief locations.

A 673cc conversion with a tight piston to head clearance, K&N filter(s), aftermarket high flowing exhaust, & precise jetting will be more efficient and make more power than a stock bore 748cc GS750 or 740cc GS550 with 750 8v pistons. It's not worth it to lose the swirl chamber combustion chamber shape and advanced design

[Nessism]

Planning on mounting above the rear tire with a fan to pull air from the area where the air box used to be. Not sure how much pressure will be lost pushing it through a larger volume cooler. Looking to avoid running lines around the cylinder to the front. I have enough to build 2 bikes plus so getting Home done first, been collecting parts for years.

The air up front will be much cooler than that coming off the back of the engine.