Cylinders

Interesting how the first models of all triples have high power spec cylinders! The numbers here are not accurate but, H1's approx the first 6,000 had the bridged port cyls, The S2 had high power for around 6,200 motors, the S1 250 had high power for the first 5,000 units and the H2 had high power for around the first 6,500 units - A sales ploy ? The only Triple that didn't start out with more power is the S3. - Rick Brett

Cylinder Base Dimensions (pdf)

Early H1 exhaust mount studs were stepped in size (8mm at cyl to 6mm at mount). Late H1 studs were 8mm.
The center to center spacing of studs is wider on the late cylinders by about 2mm.

The cylinder with the square cut out is a 1971 cylinder ONLY, it is totally unique and no other cylinder can be cut to match the porting as the liner and casting sit in a totally different position to all others. The 1972 and 1973 also had 2 more porting specs, the 1974 and 1975 are also a different spec, so there are FOUR cylinder port specs.
The pistons for the 1971 & 1972 models have a higher cut out in the skirt. - Rick Brett

Note: TP1, 2, etc are casting mold identifiers and have nothing to do with port or cylinder design.

The H2B/C cylinders are not fitted with oil "jets", nor are the cases drilled. To fit late cylinders on early cases you can tap the oil hole to 5 X.08, cut the end off of a #30 pilot jet, and install only the threaded portion of the jet in the hole. Don't drill all the way through when getting the hole ready to tap, so there is no way the jet can end up stuck to your piston. And use high strength loctite. The #30 pilot jet is about the same size hole as the pressed in jet in the early cylinders.
- Bryan H.

As we know, there is not enough room for the transfers on H2, so, on the KR the intake and exhaust ports are not fixed at 90 ° compared to the crankshaft inside the crankcases but are nearly perpendicular to the crankshaft inside the crankcases. This helps a lot to have more room for the transfer ports.
Notice also that the intake ports are very close to the bottom of the barrels this means the pistons at the bottom dead center are really on the bottom of the barrel sleeve. This explains why there is bridgeport on the intakes.
Suzuki did the same on the GT 750 2 stroke.
Notice also there are six studs on the exhaust side where the engine is hotter and the barrel could be deformed with only four studs on the intake side.