Electronic Ignition Module - Questions

[Unregistered]

Hi Don
We have a late A4 in a Tartan 34C. We are considering replacing the points with the Petronix kit. Should the distributor be rebuilt with different springs to allow for the mass difference between the Ignitor and the points? What should the total advance be? What should the advance curve be? Should I have the distributor spun and the advance curve verified? The engine will top out at about 2300 rpm (when not towing the dink) and cruises at 1500 - 1600 rpm. Timing has been set statically at TDC. Should the timing be set at full load while underway to maximum achievable RPM?

The advance mechanism has always been prone to rust and sticking. I have to clean the slide surfaces, masses, and pivot pins and lube the assy with lightweight white lithium grease every other year. The wick in the distributor rotor shaft is kept wet with engine oil. If this continues, it would negate the maintenance benefit of the Ignitor.

[Don Moyer]

You're asking good questions. I'll try to answer them all in turn.

1) Should the distributor be rebuilt with different springs to allow for the mass difference between the Ignitor and the points?

I never considered this difference before you asked the question. It must be the case that at normal cruising engine RPM, the drag of the "rub" plate on the points must be minimal because we never noted any difference in the advance mechanism between conventional and electronic ignition systems.

2) What should the total advance be?

Universal never published an official advance curve for the Atomic 4, but quite some years ago we measured the average advance on several engines at idle to be 8 degrees, and the max advance as 17 degrees. This advance equates to approximately 7/8" around the circumference of the flywheel at idle, and another 7/8" for 17 degrees which occurs (conveniently enough) at approximately 1700 RPM.

2 and 3) What should the advance curve be? Should I have the distributor spun and the advance curve verified? I'll take both these questions together.

The only place we ever published our "home-made" advance curve is in our Newsletter Compendium. It would be difficult for me to send the curve to you, and I don't really believe it would be worth the effort.

Universal's recommendation was to simply set the timing statically at TDC, and then "power time" the engine at your favorite cruising RPM with the engine fully warmed up. Power timing is accomplished by loosening the distributor hold-down bracket and slowly rotating the distributor in each direction to look for an increase in RPM. If you can increase the RPM in this way, lock the distributor back down in that new location.

If the RPM is already at a maximum, it means that the flyweights have advanced the timing perfectly. If you can improve the RPM, then the advance will be perfect at the RPM at which you spend almost all of your time. The point that Universal made is that our application is more industrial than an automotive environment where the proper advance is critical over a wide range of RPM.

4) Should the timing be set at full load while underway to maximum achievable RPM?

This was actually Universal's specific recommendation. We recommend setting the timing at your favorite cruising power setting since you will be at this setting much more frequently than at maximum power.

You didn't actually frame this issue as a question, but having to clean and oil the flyweights every other year is unusual and indicates to me that you have a moisture problem in your engine compartment. I'd recommend using Marvel Mystery Oil to lubricate the flyweights, rather than lithium grease, but I'm not sure that it will prevent moisture damage.

Lastly, I don't see the connection between the flyweights rusting and converting to the Ignitor. It seems to me that it's just as easy to remove the Ignitor plate to deal with the flyweights as removing the points and condenser. In any case, one of the benefits of the Ignitor is that it is less affected by moisture than points, which would seem to be a good thing given your apparent moisture problem.

Don

[ArtJ]

You're asking good questions. I'll try to answer them all in turn.

1) Should the distributor be rebuilt with different springs to allow for the mass difference between the Ignitor and the points?

I never considered this difference before you asked the question. It must be the case that at normal cruising engine RPM, the drag of the "rub" plate on the points must be minimal because we never noted any difference in the advance mechanism between conventional and electronic ignition systems.

2) What should the total advance be?

Universal never published an official advance curve for the Atomic 4, but quite some years ago we measured the average advance on several engines at idle to be 8 degrees, and the max advance as 17 degrees. This advance equates to approximately 7/8" around the circumference of the flywheel at idle, and another 7/8" for 17 degrees which occurs (conveniently enough) at approximately 1700 RPM.

2 and 3) What should the advance curve be? Should I have the distributor spun and the advance curve verified? I'll take both these questions together.

The only place we ever published our "home-made" advance curve is in our Newsletter Compendium. It would be difficult for me to send the curve to you, and I don't really believe it would be worth the effort.

Universal's recommendation was to simply set the timing statically at TDC, and then "power time" the engine at your favorite cruising RPM with the engine fully warmed up. Power timing is accomplished by loosening the distributor hold-down bracket and slowly rotating the distributor in each direction to look for an increase in RPM. If you can increase the RPM in this way, lock the distributor back down in that new location.

If the RPM is already at a maximum, it means that the flyweights have advanced the timing perfectly. If you can improve the RPM, then the advance will be perfect at the RPM at which you spend almost all of your time. The point that Universal made is that our application is more industrial than an automotive environment where the proper advance is critical over a wide range of RPM.

4) Should the timing be set at full load while underway to maximum achievable RPM?

This was actually Universal's specific recommendation. We recommend setting the timing at your favorite cruising power setting since you will be at this setting much more frequently than at maximum power.

You didn't actually frame this issue as a question, but having to clean and oil the flyweights every other year is unusual and indicates to me that you have a moisture problem in your engine compartment. I'd recommend using Marvel Mystery Oil to lubricate the flyweights, rather than lithium grease, but I'm not sure that it will prevent moisture damage.

Lastly, I don't see the connection between the flyweights rusting and converting to the Ignitor. It seems to me that it's just as easy to remove the Ignitor plate to deal with the flyweights as removing the points and condenser. In any case, one of the benefits of the Ignitor is that it is less affected by moisture than points, which would seem to be a good thing given your apparent moisture problem.

Don

are the flyweights visible to be oiled when the plate is replaced to convert
Delco distributor to Petronix?

Is there any additional steps necessary beyond standard points change out when changing from Indigo to
Petronix Electronic Ignition?

Regards

Art

[rigspelt]

Art, the flyweights are not visible unless one lifts the plate on which either the EIM or points sit.

[ArtJ]

Art, the flyweights are not visible unless one lifts the plate on which either the EIM or points sit.

Thanks, just wanted to know before jumping in and converting.

[Dave Neptune]

Don, do you know at what RPM the stock A-4 distributor should achieve full centrifugal advance? My guess is that it would be above our cruising rpm's in such a low compression engine. That would be the reason for power timing instead of setting the timimng.

Dave Neptune:cool:

[Don Moyer]

Dave,

In all our tests the stock distributor reaches its max advance around 1700 RPM and it's quite linear with half the advance being in at idle (around 850 RPM).

Don