Ignition timing

rugblaster

Active Member
#1
I'm working on my latest bike, a Sears Drover, with the original engine, a H35. While taking apart the motor for the overhaul, I marked the stator bracket that holds the coil. Later, when setting the ignition timing I found the original position was way more retarded than it should have been. At least it was using the .065 thou measurement. I have a problem using the dial indicator to find TDC. Using a piston stop to find TDC is a better way to do it, I think. I'm given to understand the later model H35's used a .030 thou or so figure. Was that some emission measure or what??? I don't understand why one would be different than the other. Does anyone know what the degree figure BTDC actually is? I think I would just as soon use a timing light and a remote battery. My motor is running great with the procedure I followed, so I think everything is cool. Just wondering.
 
Last edited:
#2
There are some nuances to determining degrees, since there is that bit of nothingness at the top and the bottom of the stroke. Funny, I just deleted a spread sheet I had to compute that, but it is minimal. An HS40 with .035 inches BTDC was 12 degrees advance. I have computed that, and I have used a calc on a spread sheet, and I have slapped on a degree wheel. Your H35 is going to be slightly more.

I have also had "discussions" here with those who say a solid state version is 30 degrees using a light and a wheel. I wouldn't know, I have never had a solid state Tecumseh. I do know that using a dial indicator is a very accurate way of determining TDC, but I've been doing it with the head off and a fixture I made, instead of through the plug hole.

You would not be able to time a points engine with a timing light, though you can verify. You cant get past the flywheel very easily to move the stator plate.
 

rugblaster

Active Member
#3
Thanks Dave. I was going to find actual TDC, mark the flywheel, make a pointer and check to see how much BTDC .065 is. I'm guessing it may be somewhere in the 15 to 19 degree range. Somewhere mid-range between, say 8 degrees and 32 or so...... Like you say, taking the flywheel and fan housing on and off is a bitch and it is probably good to leave well enough alone.
 
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