Hello guys. I'm stuck on assembling this magneto on a newly rebuilt block. I am wondering if based on these marks, you'd be able to read my grandfather's mind when he first built this car. I'm assuming that with a magneto, you get what you get. Meaning, one tooth off and the timing is off. I'd appreciate any thoughts...
Here is #1 cylinder at TDC on the compression stroke...
Here is the gear side of the magneto...
Here are "memory marks". This is where the mind reading takes place. When the front housing marks are aligned, the rotor points straight up, several degrees before number 1 cylinder fires at the rear housing mark.
Any thoughts on assembly would be greatly appreciated. If I have to buy a degree wheel, etc.
I think if you rotate the crankshaft 180 degrees the timing marks will align.
Oops! I meant about 360 degrees on the crankshaft.
Thanks Ted. Aligning the crank and cam marks leaves me on the exhaust stroke, right? Shouldn't I set the magneto up on actual TDC compression stroke?
I think Ted was right the first time. Rotate the crankshaft 180 degrees and see what it looks like.
The marks on the timing gears mean nothing for what you are doing. You had it right in the first photo. You want the #1 piston at (actually a few degrees before after starting) TDC on the power stroke when the magneto fires.
Time for me to go have a nap. Ted is correct. I, on the other hand, had a brain fart. Sorry.
You want to set it to fire at just past TDC. DO NOT PAY ATTENTION TO TIMING MARKS AFTER YOU SET THEM. THEY JUST SET THE CAM SHAFT GEAR TO PROPER ORIENTATION TO CRANK GEAR.
The timing marks on the cam and crank do not have anything to do with the timing of the spark for fire. On 99.9% of the T engines when the pin for the pulley/hand crank is horizontal you are at TDC ether on the compression or exhaust stroke. (9 and 3) Just past that is on the down stroke. This is where you set the timing after using your finger to see if you are on the compression stroke or look at the valves.
No apologies needed! Is there any guide to "degreeing in" the magneto? I can turn the magneto so that the rotor points to Number 1 plug wire right before it "snaps" or fires, but that wouldn't take into account how much advance I need?
Sorry you posted first, mark. How much past would I set the firing of number 1? Is it an exact degree?
The amount of degrees past I don't really worry too much as I run coils. I just set mine so the piston is over the hump and on the down stroke.
Perfect, thanks guys. I hope to put this together tomorrow. Between gaskets and oil lines, it won't be something that I'll want to keep experimenting with one tooth at a time.
That might make the marks in the last pic make more sense. If the home made marks on the front of the magneto are aligned, and the magneto installed on engine at true TDC of the engine, the engine will have to move a few degrees ATDC to get #1 to fire. That may have been where it was set. Thanks!
If you think of the crank pulley pin as a clock's hour hand, #1 should fire halfway between 3 and 4. That's at 15º past TDC.
Remember the mag will fire when the points break, so you want the points to open slightly before the piston is at TDC on the compression stroke.
Sorry but if the points open just before TDC there is a good chance of breaking your hand, arm or bendix if it kicks back. Even the Model A, you set the points to open after TDC not before.
What's the gear on the front of the camshaft?
I think I got it. The magneto's impulse thingy wouldn't'snap' while upside down, only right side up. So I turned the motor back over, set to TDC as pictured, attached the magneto and experimented by preloading it on different teeth setting until it fired/snapped right at 3:30/15° ATDC for #1 cylinder just like you guys described.
Ken, that's for the tachometer, I believe.