Compression difference 79 to 80

[markb80]

Does anyone know what was changed in 80 with the slight compression decrease 9.25 to 9.0? I found a set of new 2nd overbore pistons, and there did not appear to be any difference in part numbers. I would bet Yamaha just added a little height to the cylinder head.

[sixtysix]

I heard that the shape of the combustion camber was changed as well as the valve size. Never heard of any piston differences.

[markb80]

Thanks. That should mean having spare parts from a 78,79 should be ok on the 80. Or at least the engine top half.

On the head topic, I just got a spare parts engine. Unfortunately, the cam bearing areas were scored, and so was the cam. It looks like small particles came up through the oil hole and got in between the cam and the bearing surface. Since there really is no replaceable bearing, I assume the head is junk now. But the trans parts look great, as well as some other stuff, so it wasn't a total wash. I also have a nice valve shim collection now, a spare cam tensioner, starter, and a set of cylinders begging for a big bore kit.

I can probably add the kickstart back to my 80 also... well maybe, I'll look into that more. If I add the kick start, I will probably have to add a trampoline to the tool kit. At 145 pounds I may not be able to kick start one anyway