The Stovebolt Site Forums The Shop Area Engine Shop Using a timing light

Hi All,

I am trying to adjust my ignition timing on my 1955 235in engine using a timing light. My timing light has an adjustable knob on it. I know that not all the timing lights come with the adjustable knob.
This is what I think I know, TDC on my fly wheel is the triangle mark but the bebee is the 5 degree advance at idle. The timing is done using the bebee.
So, here are some questions.
1. If my gun is set to zero, I should set the timing so that the bebee is aligned with the pointer. Correct.

2. If I adjust my timing light knob to be at 5 degree, should I adjust the distributor so that the triangle is aligned with the pointer?

I am a bit confused with how to use the adjustment knob. When I have the timing light set to zero and I have the bebee aligned with the pointer, turning the adjustment knob seems to retard the strobe so the bebee is being retarded. I think that it actually should be moving the bebee in the advance directions?
Can someone explain to me how I should time my engine using a timing light with the adjustment knob.

Thanks,
skipper

First, the triangle is not for setting ignition timing. It is used for checking valve timing.

There should be a UIC stamped near the BB. The line between the U and the C is TDC, or Upper Center. See picture.

With today's fuels 235's like about 5 degrees more advance than the BB.
I would set your dial on 10 degrees to start with and set the timing so the pointer is on the UC line and see how it runs.
You can also set timing with a vacuum gauge.

Hey Pre '68 Dave -

Thanks for your explanation and pic of the timing marks, plus the meaning of "U C".

Also - you have a neat blog. I bookmarked it in the "reference" section of my links.

- Lonnie

Nice picture of the mark Dave. The teeth on that flywheel make it obvious why it was removed.

Thanks Pre68Dave for the explanation, it make sense now. I did not know about the UIC mark I will have to look for it. For some reason I thought the triangle was TDC but now I know it is for valve timing.

Since so many of these old engine/clutch-assemblies have been moved around, it should be noted that TDC/UC (valve timing mark) is in the same location on the flywheels for all engines. (please correct me, if this is incorrect - did some/all 261s have different valve timing marks compared to some same-year 235s)

However, the timing marks differed between 1937 and 1963 on 216/235/261 engines (for different BTDC or ATDC timing settings). The timing marks on your flywheel might not match your engine (to say nothing about original timing marks not being useful due to different octane modern gasoline)?

Those are a few of the reasons why adjusting/setting timing using the maximum-vacuum technique or the "ping" technique are usually better than using a timing light.

tclederman:
I'm a little fuzzy on the whole "maximum-vacuum technique" for timing. would you mind explaining that?
thanks.

Here's a couple links to help grasp the vac thing. I found the first one useful.

Reading a Vacuum gauge
vacuum timing

A recent post on this topic.

Also, here is a brief discussion of the "ping" timing technique.

Thanks guys, that was really helpful!