Timing Light Came In!

[Webb]

My Equus advance timing light came in so I finally got to verify some numbers. Book says dwell should be 35 deg. plus or minus 3 deg. I got it fluctuating between 40 and 43 degrees. Now, it's either for every 2 degrees the dwell is off, the ignition timing gets off 1 degree, or vice-versa (for every 1 degree the dwell is off, the ignition timing gets off 2 degrees). Anyone know which way it goes? I read it, but cannot remember.

Also, found that the max advance I can get out of the distributor is 10 deg BTDC. Books calls for 12, but I think this could be remedied by getting the dwell set correctly.

Also, never use your tach to judge engine speed. This whole time I thought I'd been idling around 1000rpm. Nope....it reads 1000revs, but my timing light said 670 rpm!!

 

[Brosky]

Webb,

Don't get hung up on dwell numbers with the type of distributor that you have in a TR6. Just set the points to the proper gap and forget it. (Adjustable points were used by GM in the 60's & 70's before HEI took over. There was a window in the cap and an adjustment screw on the points).

When you do this be sure that the engine RPM's are at 850-900. Then adjust the timing with the vacuum retard or advance disconnected and the source plugged. If you have to advance the timing to get it to 10-12, the idle may go up. (or down if you are too far advanced already, but I doubt it from what you say.) Set it at 12 and lock down the distributor and reset the idle back to the proper speed. You may then have to reset the timing a degree or two to get it on the money, as well as the idle. That's why it's called tuning.

After that is done, you are ready to set the carbs, assuming that the plugs are cleaned and gapped properly already.

And on and on and on.......

 

[Webb]

Alright, thanks for the advice. Will do. I'm still curious about how the dwell affects ignition timing. If for nothing else but trivia, anyone know which way it goes?

Also, does centrifugal advance engage at all at 800-900rpms? i.e. Would this give me a little more advance that I can't get from the distributor?

 

[TR3driver]

I'm still curious about how the dwell affects ignition timing. If for nothing else but trivia, anyone know which way it goes?

More dwell = retarded timing.
The spark happens when the points open, so the longer they stay closed, the later the spark is.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Also, does centrifugal advance engage at all at 800-900rpms?[/QUOTE]I don't believe it should for a TR6, but it's quite possible there is something wrong with your distributor that lets it start early.

 

[Brosky]

I agree with Randall on both points (no pun intended!).

The advance should "be at rest" if you will, at idle. On the later 74 & up, TR6 with the retard unit, there will be a retardation of the timing when the unit is connected at idle. This was for emission and to insure smooth early throttle acceleration when the gas quality hit bottom in the early to mid 70's.

I run the best gas that I can find, with the highest octane possible. My base timing at 850RPM's is 16 BTDC. The retard unit pulls it down to 10BTDC when connected and my car goes like a bat outta you know what, so it works for me.

I've found that over the years, especially with the later models after 73 equipped with a retard that works properly, you can run the base up to 14-16 with no problems. I did verify that I had no ping or detonation during my dyno runs.

This will show what the distributor looks like all apart:

https://www.74tr6.com/distributor.htm

The two plates under the springs in the second picture are the advance weights and that area should work freely. That is where the centrifugal advance takes place.

 

[poolboy]

If you have breaker points in the distributor, dwell is the degrees the rotor rotates while the points are closed and the coil is developing high voltage. In other words, it indicates the duration of the spark as controlled by the point gap, not specifically the timing that the spark actually begins. That is still controlled by you, rotating the dizzy itself around the lobes of the shaft

 

[Brosky]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:] More dwell = retarded timing.
The spark happens when the points open, so the longer they stay closed, the later the spark is.[/QUOTE]

What Randall said above accounts for a very small portion of the actual timing of the ignition, but what you say is what I described as the actual timing procedure.

Everyone is correct, just slightly different ways of saying it.

 

[TR3driver]

No argument from me, I never meant to imply that the timing should be adjusted by changing the dwell ! Only that changes in dwell/point gap do have a (small but definite) effect on timing.

The most obvious example of this is when you forget to lube the point cam, and rubbing block wear retards the timing. BTDT

So the proper procedure is to set the point gap/dwell first, and then adjust the timing (if necessary).

 

[2wrench]

Another thread to save for future reference.
If I can learn to properly make these adjustments
to spec without having to understand why I'm doing
so, then well enough for me.

Hope my friends will be patient as I inquire about
some of the most simple of things.

 

[70herald]

Which timing light did you get? I bought the Equus 5568 earlier this year. Kind of nice having all the timing stuff on one tool.

At 670 rpm is your engine really smooth? sounds like a slightly low idle speed.

 

[Webb]

Yes, I bought the Equus 5568. It's a nice light. Do you know if you can "zero" the light for AFTER top dead center?

It is a bit low. I set it back up to about 850, at which the tach reads like 1200 rpms. Still, I was relatively surprised that it could idle that smoothly at 650-670 rpms. You could have easily done the wine glass trick at idle and it wouldn't have spilt a drop.

 

[poolboy]

I was wondering about that light. Do you have to set it for the number of cylinders that the engine has? Thanks.

 

[70herald]

You have to set the number of cylinders for dwell measurements. Probably doesn't matter but if you want you can set it for 2 cycle mode also, probably just doubles the RPM reading.
I don't think that the advance offset can go to after TDC.

 

[Webb]

Like the man said, you set it for dwell measurements, simply by pressing up or down on the arrows, but not for timing. It does have both 4-stroke and 2-stroke settings. I recommend the light, it's easy to use, comes in a nice case, and look pretty durable. Light is plenty bright to be used in the daylight, and it has an inductive pickup for timing so you don't have to even mess with the spark plug itself.

 

[Brosky]

These lights do have a nice readout. I forgot that I took this picture after I got mine in May. I think that it may be reading my dwell, as it's not my timing at that RPM.

EDIT:

OR, this could have been when I was getting the funky readings from the Magnecor wires. I now use a stock wire on the #1 plug to set engine up. I believe that may be the case here.