Setting the Timing on My Thiokol Imp Ford V4

[Snowdancer]

After installing a Hot-Spark electronic ignition, I decided to set the timing properly instead of relying on the old “maximum RPM” method.

The factory setting I used was 6° BTDC at about 550 RPM, with the vacuum-advance hose disconnected and plugged so there was no vacuum advance. At that low RPM, the centrifugal advance should also be inactive.

Before this, I had timed the engine by setting the idle around 700 RPM, turning the distributor until I found maximum RPM, and then backing it off about 40 RPM. That actually got me fairly close—I checked with the timing light at 550 RPM and the timing was just shy of 10° BTDC.

My mistake using this method was I stopped backing off as soon as the engine started to sound a little rough. To get back to the factory 6° setting, you have to go a little farther. At 550 RPM with the vacuum disconnected and the timing set at 6° BTDC, the engine does not sound like a purring cat. It runs noticeably rough.

Once the vacuum hose is reconnected and the normal idle is restored, it smooths right out.

Finding the timing marks​

Finding the marks was probably the hardest part because I did not know where they were.

Facing the front of the engine, the timing index is located at about the 10 o’clock position next to the crank pulley . You can see and access it through the space between the bottom-front of the alternator and the heater unit on the right side of the machine.

Once you know where everything is, it really is not that bad.

There are two timing notches, one on each rim of the crank pulley. I cleaned both notches and painted them white. I also cleaned the timing index and painted the tops of the marks white.

After cleaning everything up, I noticed there is a noticeably larger bar at the 6° BTDC mark which confirmed for me that this is the correct timing target.

Using the timing light​

Getting the timing light onto the marks while also being able to see them and turn the distributor took a little creativity.

I used a mirror with a magnetic base, angled at about 45 degrees. I bounced the timing-light flash off the mirror and onto the pulley. From the same position, I could see the reflected timing marks while rotating the distributor.

Just make sure the mirror, timing-light wires, clothing, and hands are kept well away from the fan and belts.

What I observed​

With the vacuum hose disconnected and plugged, I set the timing to 6° BTDC at about 550 RPM.

As I then increased engine speed:

• At about 800 RPM, the timing began to advance toward the 10° mark.
• When I reconnected the vacuum hose, the idle jumped to about 930 RPM.
• The engine became very smooth.
• The timing appeared to move toward approximately 15° BTDC.

I then adjusted the normal idle to about 850–900 RPM.

My final procedure​

Set the timing to 6° BTDC at about 550 RPM with the vacuum advance disconnected and plugged. Reconnect the vacuum hose, set the normal idle to 850–900 RPM, and be happy.

The maximum-RPM method can get you pretty close, but do not stop retarding the distributor just because the engine starts to sound rough. At the correct low-RPM base setting, mine definitely was not purring.

I hope this saves someone else some time.

Pictures​

1. Cleaned timing index
2. Magnetic mirror for timing-light setup
3. Distributor-setting comparison: the green line on left shows the distributor set at 6° BTDC, and the two red lines show where it had been set using my original maximum-RPM method - not a big difference in the distributor rotation between 10 and 6.
4. Timing index and pulley marks, with the engine set at 6° BTDC

 

[BoyToys]

Good move to check it after installing electronic ignition in the dizzy. When I put my Pertronix in, it ended up too retarded and seriously impacted performance until I bothered to check it.

It is a royal pain doing this. Had to remove the right side of the dog house and bungie or duct tape the timing light beneath the alternator to point in the approximate direction of the timing marks and tape the light trigger closed. I'm able to see the marks from up top through the hatch and through maybe a half inch gap behind the radiator...as opposed to using a mirror down below.

I have my static timing set around 8 -10° BTDC, a bit more than spec, and she seems to like that. No engine pinging, ethanol blends offer a marginally higher octane rating, and I run a richer pilot jet (on my Solex, before swapping out for my current Weber) adding more fuel and managing latent heat a little better...entirely different subject.

Just the other day I was prepared to try the manifold vacuum method, much simplifying the process, but that requires a direct manifold tap as opposed to a ported vacuum source from the carb. There is no place on the manifold where I can grab a vacuum signal without drilling a hole and tapping in a nipple...not gonna happen, visions of metal drillings entering the intake. Now if there were an adaptor plate between the carb and manifold I could tap into that but noooo...the Weber is a direct mount.

Good informative post BTW.

 

[Snowdancer]

Interesting about the timing. If I find my Imp doesn't like 6° BTDC this winter, then I already have 9-10° BTDC marked with the red lines on the dizzy and I can easily make the adjustment in the field.

 

[redsqwrl]

BToy were you looking for a port for vacuumn?

Im drawing a blank at this instant. But i remember setting dwell and point gap with rpm. And timing with a vacuumn gauge.

The other useless info is that the marks on the front cover. That pulley is not the crank. Its either the cam or balance shaft. My saab racer guy told me to make smaller adjustments than normal.

This post might not be worth $.02

But that sdancer write up is great.

 

[BoyToys]

BToy were you looking for a port for vacuumn?

Im drawing a blank at this instant. But i remember setting dwell and point gap with rpm. And timing with a vacuumn gauge.

The other useless info is that the marks on the front cover. That pulley is not the crank. Its either the cam or balance shaft. My saab racer guy told me to make smaller adjustments than normal.

This post might not be worth $.02

But that sdancer write up is great.

Yeah, was looking for some nipple (old dreams of nipples) direct from manifold for a vacuum source. Can't use the ported vacuum nipple off the carb (that goes to the dizzy advance can) because...well...it's ported and won't see any vacuum until the throttle plate is opened well above idle. Thus can't use a vacuum guage to set timing to highest idle vacuum.