Nu-Rex Centrifugal Advance

David in San Antonio

David in San Antonio

Well-known member
My ‘31 Fordor came to me with a Nu-Rex centrifugal spark advance mechanism, and the spark lever disconnected from the distributor. It has a “touring” engine (higher compression, counterbalanced crank, insert bearings), and a four speed transmission. I’m only familiar with the manual advance mechanism on my Roadster.
Should the spark lever be reconnected? It seems like the Nu-Rex by itself doesn’t have a way to adjust for the engine being under load, such as retarding when climbing a long steep hill or advancing when going down. Is this accurate? Does it matter?
What else should I be aware of? Any advice for this slow learner?
 
Reconnecting the spark rod won't hurt anything. Most likely it was disconnected by the previous owner to prevent an inexperienced driver from accidentally setting the advance too high. If you plan to manually adjust it on the reg, though, I personally would get a timing light and verify what it's currently doing. Or you can play it by ear if you feel confident enough.
 
NuRex works between the oil pump drive and the input shaft to the distributor. In setting up the system you start with the distributor at "Full Retard" - as if you're actually timing the engine.

I think you want to leave it that way since the NuRex device "advances" with that as a "starting point" - just like as if you were to advance the engine timing the "old fashioned way."

The video explains installation and gives pointers to use. Video about 12 minutes.

https://www.youtube.com/watch?v=_dnBoiVobO8

Note that advancing the distributor "manually" makes your engine start from cold (fully retarded) to be more "advanced" - as in you may put yourself into that range where the engine "backfires" and bends your starter shaft.

He claims the built in advance of the NuRex device is 33 degrees. That is a bit more than Vince Falter recommends for normal advance of about 20 degrees (slot) built into the distributor top housing. That may be intentional.

I guess I would leave manual advance "unattached" and prevent any mistake. Let the device do it's job - that is if you've set it up from the beginning correctly.

Joe K
 
I'd recommend looking up on how the centrifugal timing advances based on engine speed. Since it is a static advance you may find the desire to advance the timing under light load or reduce it under heavy load, as you would if you had a manual advance. A good idea would be to read on the timing curve of the Nu-Rex unit and then figure out how much you want to adjust the timing. You can do that by retiming your car by increasing/decreasing initial timing. Given your car is timed at TDC with the lever all the way up, if you want more you can leave your lever as it is and bring it down when you need it. If you need less then time your car at TDC with the lever two or three clicks (8 or 12 degrees) down, and bring it up when you need less timing (say when climbing a hill).
 
Joe K said:
The video explains installation and gives pointers to use. Video about 12 minutes.

https://www.youtube.com/watch?v=_dnBoiVobO8

...I guess I would leave manual advance "unattached" and prevent any mistake. Let the device do it's job - that is if you've set it up from the beginning correctly.

Joe K
Click to expand...

Worth noting that in the video you cited, he suggests reconnecting the control rod because it prevents the upper plate from being accidentally advanced, i.e., you might be working on the engine and unknowingly move the plate with your elbow, or you might be at a car show and some kid moves it. With the control rod in place, you always know the actual state of advance.
 
With the control rod in place, you always know the actual state of advance.
Click to expand...
And you write in your permanent memory list to retard before start. Just like a "real" Model A.

Connected, it would be fun to play with - just to see the results. It might even be a check on how well you installed the NuRex.

I kind of like the NuRex principle. Other "electronic" based systems aren't nearly so fool-proof, or perhaps as reliable? The physics of rotating angular bodies is possibly more predictable than electronic pulses.

Shields up...


Joe K
 
If I remember the nurex advances 30 degrees max and the manual A advance can go up to 40 degrees. Also when you lug the Model A engine it slows down and the nurex retards the timing as it slows down. It's pretty much an install it and forget it part.
 
Model A can advance up to 40 degrees, but it's not recommended to go that high. Vince Falter recommends about half way (20 deg?) for "ordinary" driving with perhaps a skosh (technical term) more for extended highway runs.

Some have said a full advance with the Model A timing adjustment CAN result in an overheated engine.

So perhaps the 33 degrees (did I see that somewhere in his advertising?) would be just about right-on.

I would like to see the "advance curve." It would be interesting to see a Sunnen plot.

Original operator manuals for vintage Sun Electric Corporation distributor testers (commonly called Syncrograph machines, such as Models 404, 504, 600, or 680) are out of print. You can find physical and reprint manuals for sale through specialty automotive literature vendors and auction sites like eBay Sun Distributor Manual Listings or vintage equipment restorers Benison Mediai
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NuRex has been around for a while. Doubtless someone has curved it. GMC Bubba was big 10 years ago. I think he's retired now. Online about "cleaning out his shop."


Joe K
 
Joe K said:
I would like to see the "advance curve." It would be interesting to see a Sunnen plot.
Click to expand...

Chart credit Chris Wickersham, 2019
 

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David, I had the same problem. The Victoria I recently bought had the Nurex centrifugal advance. High compression head, Mitchell overdrive and Mitchell transmission. I had pre ignition and engine knock. I could not get it timed where it would not knock. Nurex was very helpful to remedy the issues, but to no avail. I finally put the original distributor back in and no more problems. Maybe my skills were not there but I am happy with the original spark advance. Roger
 
I really like the stock manual advance system for all the above reasons. Maybe because I have been using the manual system for 60 years and this old dog cannot learn new tricks.

The best automatic advance is a combination of centrifugal and vacuum. The centrifugal adjusts for rpm and the vacuum adjusts for load.
 
meteorgray said:
The Victoria I recently bought had the Nurex centrifugal advance. High compression head, Mitchell overdrive and Mitchell transmission. I had pre ignition and engine knock. I could not get it timed where it would not knock.
Click to expand...

How high was the compression?
 
Vince Falter has an entire page devoted to NuRex - including yet another version of a "Sun Diagram" comparing the distributor performance to the Model B Distributor. Not precisely the diagram presented above. He also discusses the timing aspect of the Model A compared to both above, including the "starting timing" of the Model A at 0 degrees/crankshaft.

https://www.fordgarage.com/pages/nurexadvance.htm

Joe K
 
It's simple to set your timing so it’s safely retarded at top dead center for starting purposes. You pull your spark advance a lever down 2 or 3 notches and then set your timing at top dead center. Then when you're finished you push the lever all the way up when starting. Your Ignition will be retarded 3 or 4° or more depending on how far down you pulled your advanced lever When you initially set your timing.
 
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My engine is completely stock. I set my initial timing/point setting with the lever pulled down 3 notches so when I do start the engine with the lever all the way up my timing is definitely retarded. It’s plenty safe for hand cranking even though I don't hand crank it. This brings the timing at max travel my timing is running much less than 40° which is excessive even in a stock engine.
 
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