Timing with Distributor vs. Mag

Mon Sep 23, 2013 4:35 pm

Hello Folks,
I am looking for a little help on re-installing the Distributor after a complete engine rebuild on my 1972 Cub, here are my questions:

1) Are the steps for timing a distributor the same as with a magneto?
2) I had to install a new Belt Drive Pulley and the new one doesn't have the timing notch (notches). I have the oil pan off and the valve cover off so I can see TDC, but how important is it that I get it perfectly in TDC and what's the very best way to find TDC without the notch on the Drive Pulley?
3) I have seen a couple of post on how to time a mag. system, but am still a bit confused on how the drive shaft for the distributor is timed properly with the governor. What is the best source ( for dummies) of information on how to properly re-install the distributor and time it properly?
4) any and all additional information on this topic is greatly appreciated.


The Riot

Re: Timing with Distributor vs. Mag

Mon Sep 23, 2013 7:48 pm

Hey I can answer this!

1) They require entirely different steps.
2) Pop off the plug for cylinder #1 and crank the engine with the hand crank while holding your finger over the hole. When you begin to feel air pressing against your finger you're approaching TDC. The best thing you can do here is put the end of of foot long (so you don't drop it in) thin rigid wire into the spark plug hole while trying to find the edge of the cylinder. It will only fit in the cylinder at 12:00 when standing facing the engine from the left side as if you're standing at 6:00. Slowly hand crank the engine and watch the wire rise. When it stops rising you're at TDC. You'll be more familiar with the height if you do this twice so you're comfortable.
3) read the manual here http://www.cleancomputes.com/Cub/Cub%20 ... 1-5-55.htm and start at page 34. I believe the timing is identical so the years don't matter. I'm just familiar with this manual. The next steps are laid out clearly. It's a five minute job!

Re: Timing with Distributor vs. Mag

Mon Sep 23, 2013 8:47 pm

Piston top remains at it's highest elevation for several degrees of crankshaft rotation. TDC is a term used to indicate the crankshaft's position as opposed to the location of the piston in the bore.

I haven't needed to try this. Dial indicator a spark plug hole. Rotate engine until dial indicator moves - then adjust crankshaft until the indicator reads zero. Mark the pulley directly under the pointer. Rotate engine backward (opposite previous rotation direction) until indicator moves, adjust crankshaft rotation until indicator reads zero. Mark pulley. TDC will be exactly half way between the two marks.

You can use an implement similar to Calvin's suggestion, as long as it is immobile.

When finished, your TDC mark on the pulley needs to be very accurate.

OK. Another TDC check is the location of the key holding the pulley to the crankshaft. The key is centered at 12 O'clock with the engine/crankshaft at TDC.

Re: Timing with Distributor vs. Mag

Fri Sep 27, 2013 7:38 am

Thank you, Gents. I think I got it now and will be trying to put the governor and distributor back in this weekend. It appears to be a matter of meshing the proper gears in the complete lineup and making up the difference with adjustments on the Distributor itself.

Thanks again,

The Riot