Originally Posted by bardtrailrider
Drained primary case did a low running RPM timing check, and spark was ~10 degrees after TDC at idle to 10 degrees before TDC at the max RPM I would run it to, probably <2500 RPM. Bad valve timing I paid someone else to fix burned a hole through a piston.
I can't imagine a valve timing error causing a piston to melt.Is the valve timing right now?At TDC,you should have about 0.140" lift on the intake and exhaust valve.Obviously,the other cylinder will be on compression with both valves closed.
If either valve is open 0.055" less than that,the timing is out by one tooth on a camwheel.It would still run,but be down a little on power.If there's more valve lift at TDC,there's a risk of crashing a valve into a piston and bending the valve.
It probably ran alright when it had points,and most of this trouble has come from trying to time the electronic ignition.If the locating pin is still fitted in the exhaust camshaft,it can sometimes foul on the taper of the ignition rotor.Remove the pin or grind the rotor to get clearance for the pin.
The timing mark on the alternator rotor should be 38 degrees BTDC.The pistons will be 0.415" below TDC.You can check this at the timing plug,behind the barrel.The 38 degree flywheel notch lines up with the timing plug hole.You just want to know where 38 degrees is on the rotor.Rotor pole position and phasing is not an issue.
Static time it in this position (38 degrees),according to the EI instuctions.The timing will then be close enough for the engine to start.The timing will still need to be set with a timing light.At 5000 rpm,the timing should be 38 degrees BTDC.
35 would still be safe,but 39 may not be.One degree is approx 0.025" at the timing mark.
You float level is on the low side of tolerance,but still OK and within 0.17"-0.24" of the top of the bowl.The 0.080" setting does not apply to new "stay up" floats.