Valve hitting piston?

[ZombiePotatoSalad]

I fixed the plastic popping sound, but another problem has persisted: when I'm rotating the engine manually, it reaches a certain point, then stops. The line on the advancer is pointing at the 2, and the camshaft is pushing the valve in the 2 slot down, so I'm guessing there's the rub. How do I resolve this?

EDIT: The pistons go, from left to right (rider's perspective), 1-3-2-4, right?

[chuck hahn]

Sounds like a cam jumped a tooth. Follow the service manual on cam installation and reset cam timing. Then pray you didnt bend a valve. After resetting cam timing do a compression check on all cylinders. If a valve did bend youll have no compression on that cylinder

http://members.dslextreme.com/users/bikecliff/

[1978GS750E]

EDIT: The pistons go, from left to right (rider's perspective), 1-3-2-4, right?

NO! Cylinders are numbered 1-2-3-4 from left to right as you sit on the bike I believe.

[Rich82GS750TZ]

EDIT: The pistons go, Cylinders are numbered 1-2-3-4 from left to right as you sit on the bike I believe.

this is correct.

[ZombiePotatoSalad]

I fixed it. I had my notes from the last time I did the valve shims. A few of the shims were mixed up, as they fell out when I got the cylinder head serviced, to get that misdrilled hole fixed.