QuestionHello Bill.
I have 2 z50 engines (one early 70s, other late 70s). The oldest one worked fine, some leaks, no biggie. The second one, which I had never started was in need of a minor rebuild. I decided to proceed rebuilding both. I cleaned everything, did a proper gasket job and changed piston and rings on both bikes. I did not touch the valve heads at all. Now NONE will start. I do get gas and spark. I am wondering if it has to do with the CAM timing. "O" punch is horizontal aligned with mark, and flywheel "T" is at 90 degrees and aligned with its mark. Is this correct? What about the "F" mark? can this be the problem? Please advise, thanks.
AnswerBill, do you have compression on the rebuilt engine?
If yes, then you are missing the other ingredients.... spark or fuel/air.
If no, then the cam timing is incorrect and/or you bent a valve because it was incorrect.
F mark is FIRING mark.. the time when the points OPEN. Usually it is about 5 to 10 degrees before TDC, if you have a spark advancer. If the ignition doesn't have a spark advancer then that is when the spark will occur all the time! Usually that is more like 27 degrees BTDC or something like that.
Timing the camshaft is easy without the marks. Piston at T mark, roll the camshaft until you have both lobes down (away from the top of the head, if the engine was rotated vertically). When you turn the motor over one more turn, both valves will be slightly open equally (overlap stroke). Be sure that you have at least .002" valve clearance on both valves on the top of the compression stroke.
O cam
/ \ lobes at TDC compression stroke.
( T ) piston at TDC
--------------------------------------------
\ /
O cam lobes at TDC overlap stroke.
( T ) piston at TDC
Bill Silver
