cams

[biz78251]

I swapped the head on my 79 xs1100 special with an 80 sg. I can' remember which cams I used though. How can I tell the difference between the 79 and the 80 cams? Also should I use the valve clearances for the year of the cams used or the year of the cylinder head used.

[79XS11F]

Should be a different part number and the part number should be on the cams somewhere
Rob

[John]

The older cams will have a taller profile and the lobes will be more 'pointy' than the shorter, rounder lobes of the newer ones. The word here on clearances is use what ever the specs were for the cams you are using.

[trbig]

Like Rob said, the part number will be on the cams. The '79's will say 2H7, and the 80's will say 3H5.

With the way you've set the bike up, you have lowered your compression quite a bit. The early model bikes had a lower domed piston, but a smaller area in the head where the valves sit, and the highest compressions of these XS's. The 80's and above had higher domed pistons, but a larger area in the head to accomodate the larger valves. So now you have a lower domed piston with a larger volume head space. You will gain some of the performance back using the early cams, but I think your best bet if you are still close to this point and haven't put in the cams, or you are going to remove them... would be to swap pistons from the 79's to the 80's, and I would personally swap the top two compression rings so that the rings are still running against the same cylinder walls they were... just sitting on different pistons.

It was stated that there should be at least .060" of valve to piston clearance for the intake, and .080 for the exhaust. Running with basically this same setup I was suggesting, there was a valve-piston clearance of .132". Double the intake needs and more than enough for the exhaust to shim it however you choose. The closer specs will = a quieter motor. I have heard that the specs go with the head, not the cams, but obviously others believe differently. You've got enough room to do whatever you choose.... even more so if you stay with the 79 pistons!

An even higher compression motor would be the late pistons on the early head and cams.... but I haven't heard anyone say if there's enough room for this setup. You'd be losing the bigger valves, but the added compression would make up for it. The best option would be later pistons and head with the early cams, but having the head shaved .015-.020.


Tod

[biz78251]

thanks all. I dont think I saw any numbers stamped on the cams but i will check again.

[mro]

With out checking...
Intake 78/79 cam 36.8 something mm tall
Exhaust 36.3 or 4 something tall


mro