90* Timing

Got this one from a friend of mine.

When he times engines with a timing light he doesn't use #1 cylinder or even the cylinder 360* down the line in the firing order.
(Which would be #6 on a typical GM firing order of 1-8-4-3-6-5-7-2.)

He connects the light to the coil wire.

Right up front, sounds crazy, but it works.

Gave it a try a couple of days back when I did a modest tune-up on the Buick engine in the 32.

Besides the plug replacement, I advanced the initial timing, but kept the same all-in timing.
12* initial and 32 * all-in fwiw.


I did the timing as usual with the light connected to #1.

After I was done, I hooked the light up to the coil wire.

It is a tad different since you're getting a flash every 90* instead of every 720* like you would when connected to #1.

Generally, you can see the separate flashes if the engine idles slow enough.
Mine does, 550-600 rpm and most times at 600.

The flash from the strobe only lasts a few milliseconds and creates the illusion that the harmonic dampener - which is where the timing marks usually are - is standing still so you can determine where the ignition is firing on that particular cylinder.

When you have the timing light connected to the coil wire you're getting a flash every 90*.

The effect with this is that the strobe light looks to be a solid beam of light, but you can still the timing.

Weird it is, especially to a guy who's always used #1 for timing - except for the few times #6 was used because it was easier to connect to.


I didn't try it, but I wonder if you had a missing spark, bad plug etc. that the light would show it.
It wouldn't point out a problem on a particular cylinder, but maybe the missing cylinder would be visible in the short flashing imparted by the strobe . . . if idle speed was slow enough.


An interesting bit of information.

Makes you wonder where some of this stuff comes from.

My friend is a very bright guy and probably thought it through one day.
It could have been discovered by accident, but I don't think so.


And fwiw, the additional timing on the 32's engine is working out pretty good.

I don't think the rubber ring on the harmonic dampener has slipped, but maybe.
I need to find the two center punch marks and compare them to see if they've moved.
The dampener was marked when the engine was built.

I think I have a couple ways figured out to combat the slipping rubber ring bit.
Easy enough to say, "get a new one", but new or NOS isn't available for some engines and for street running it's not necessary to install a racing dampener.

 

..sounds good, but my daily has eight coils and my hot rod doesn't have any!?!

-well it does but, it's inside the magneto..

 

When connecting the timing light to the HV coil wire you can check for misfires and also check the timing chain.

The light flashes with every firing of every cylinder, but the timing mark only shows 1 and 6.
If all is well, you see a sharp defined timing mark, if the timing chain is stretched the timing mark will look blurred.