different cams

[mrbill204]

Is there any different in 1979xs11 and 1981xs11cam shafts? they have different part #

[jetmechmarty]

That's right. The cams are different between the '79 and the '81. The valves aren't the same, either.

[Prisoner6]

Is there any different in 1979xs11 and 1981xs11cam shafts? they have different part #

Hi, Bill -

Check out crazy steve's "Interchange Guide" on motors and transmissions:

http://www.xs11.com/forum/showthread.php?t=36652

[MPittma100]

Cams

If you look at the Yamaha OEM service manual, you will see 1978 and 1979 the same and 1980 and 1981 the same. The latter show different lift numbers than the earlier cams which makes sense when going to bigger valves.

So the question is: Is the book correct? To be certain, a valve lift measurement would be in order. The valve lash is also part of that measurement.

Mike

[crazy steve]

The intake cams, all years, all have the same lift; .347". The exhaust cam lift was increased .020" in 1980 to match the intake. The tighter intake clearance starting in '80 was to reduce valvetrain noise primarily.

The big difference between the '78-79 and '80-82 cams was duration; the early cams have about 20 degrees more. More top-end power, less low end, but you need the early matching ignition curve to get the full benefit.

[mrbill204]

i have cams for 79 and 81 I want the use the best ones

[crazy steve]

i have cams for 79 and 81 I want the use the best ones

Well, 'best' depends.....

Again, the early cams work best with the early ignition, same with the late cams; they really need to be 'matched' to each other. Yamaha changed the ignition curve every year, looking for the best compromise between performance and emissions (with the latter getting tighter every year). The late cams/ignition do offer better lower-speed performance, which is where most of us do the majority of our riding. The late ignition/early cams combo seems to be the worst of both worlds, with the ignition killing the high rpm capabilities of the early cams, and the cams hurting the low-speed performance because of the timing.

The '78 bikes made the most power, but also had the most aggressive timing curve. Modifying the late ignition to complement the early cams isn't easy, you'll probably need to do dyno runs to get it right, not a cheap deal.