It might help to understand what is going on if you can give more specific information. I have never seen an engine that had the same manifold vacuum reading if the RPM was constant but the ignition timing was changed. If I understand your other posts the manifold vacuum on your car is 20 inches and rock steady until just before it dies.

Confirm you are not using "timed vacuum" from above the throttle plates.

Can you put a manifold gage on AND a tach AND a timing light and take a series of reading starting from a cold engine and then advancing the timing in stages until you have the 27 degrees that you find works best?

With the vacuum advance disconnected and the dist timing at 10 BTDC the engine RPM is ----, the manifold vacuum is----, and the RPM is---? Do this every five degrees of dist advance AND POST THE NUMBERS. It should be very interesting. Pete

Pete, I'd be happy to do that. Just to clarify, am I taking those readings (vacuum and RPM) with the engine at curb idle (off the fast idle cam), and doing the full process once while the engine is still cold and once when it's hot?

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

So for about a month now my Fairlane has been in the care of a local shop. They are certain that the cause for the trouble is a loss of spark, but they (we) continue to struggle with an explanation for what's going wrong.

They say that the air gap between the rotor and dist cap is 0.150", and that consequently the coil is unable to reliably generate enough voltage to get a spark across the gap in the spark plug. I suppose that as the coil heats up its maximum voltage output decreases to the point that I have trouble symptoms, and that the rest of the time (before symptoms show up) the coil is working "wide open," causing it to run hotter than it should. They say that the coil makes a strong enough spark to jump 1/2" outside of the distributor, but they are not getting any juice out of the cap.

This theory makes sense, but since cap and rotor have already been replaced, the problem would have to be in manufacturing, and I have never heard anyone complaining about a similar issue. I am wondering whether there is perhaps some slight difference between the '57 distributor and the later, service-replacement unit you can buy at the parts store which makes the new parts the stores sell not quite right for the original dist. Anyone know anything about this?

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

Have them check the ground wire in the distributor. Also the hard wire going from the points to the condensor. I've seen them break internally where they can't be seen. Chuck

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

Did the problem arise after replacing the cap and rotor? If yes, then it could be the issue. If no, then it probably is not. It seems like the rotor could be shimmed to move it closer to the cap and test that theory.


Lawrenceville, GA

I had a similar problem with my 272 in my old truck. It drove me nuts. Tried different dist. carbs etc. advanced the timing a lot nothing helped. I would put the timing light on it and it wouldn't stop blinking but I did notice when it missed the timing mark moved. I didn't think much of it at first. Thought it was caused by the miss it self. The fuel pump started to leak and when I took it off I put my finger in the hole that the fuel pump goes into and felt the timing chain. And noticed the timing chain was very loose. Changed the timing chain and gears and the problem was gone.

That internal ground wire can be real tricky. It flexes as it follows the motion of the timing advance plate and over the years the wires can fatigue (break) while the insulation still looks good (if it has insulation). Checking its continuity may show it good while in reality it is bad when it is flexed in a particular position. Be sure and replace it with a wire designed to withstand many cycles of flexing.

57 Ford, I just replaced the chain and gears less than 3k miles ago. The timing marks are nice and steady even when it misses, but it's a good thought!

bn, you're right, the only way to be certain about that wire is to replace it. I think. heh.

I hope to go take the car back from the shop tomorrow or, at the lastest, Friday. Then I will replace that wire.

I am also contacting internal combustion engine experts in academia to try to get a handle on how the engine can stand such extremely advanced timing; clearly, the mixture burns very slowly, but why? It may be a critical clue.

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

I got the car back on Friday. It was missing so badly on the way home I had to pull over. I bypassed the resistor and it was smooth sailing the rest of the way, though I was expecting trouble at any moment.

I really thought the shop was on to something with the whole rotor-to-cap gap thing. I did my own measurements and agree that the gap was excessive. Amazingly, though there is no reference to this on any parts web site, there IS a different rotor available for this distributor, and Autozone sells it. All of the rotors the shop and I had tried were marked with an E on the firing bar. Something about that rang a bell to me. Some web snooping turned up the following info:

"In later GM vehicles with window style caps, there are two different gap specifications available, standard, and emissions.

Standard gaps are set to a spec of .100 and have a +/- tolerance of .030. These rotors have no marking on the end of the firing bar. These gaps have the least resistance of the two designs.

Emissions rotors have a shorter rotor firing bar length, to give a larger gap to bridge, to force the coil to make more spark energy, by having to overcome the larger terminal to tip gap. This was done to have the ignition coil work harder to make more volts from the coil, which ended up marginally increasing spark energy, but ended up just overloading the coil. Attempt was to make ignition output higher so it would help lighting off ever leaner mixtures, doesn't work well. Gaps for these rotors are usually set to .200/.250, and the rotor firing bar is identified with a letter "E". The large gap rotors are not the best for performance applications.

Not all small gap rotors are unmarked, example, NAPA RR167R is made by Echlin, is a short gap rotor, non-emissions, but the NAPA RR169R is a large gap rotor, has the E as well, so...best to measure the tip length and select the longer rotor tip when obtaining a new rotor. In the case of the RR167R, the E is for Echlin, the RR169R, emissions, somewhat confusing if you don't know what is what."

Of course, that was written about GM parts, but the E was there on the Ford rotor, so I thought, could be the same. Well, the non-E Autozone rotor was about 1/8" longer in reach than the others I had tried, so I thought for sure I had found the heart of all of this. Ultimately, even that has not resolved the trouble. I believe that most if not all of the intermittent missing has gone away with the new rotor. Also new is spitback through the carburetor, particularly if I snap the throttle open; I have never ever had that happen before. But, regardless, I can't idle the car in gear when hot, and I even had it shut off once or twice in today's tinkering.

Next, I will replace the primary wiring, one piece at a time, starting with the little ground wire inside the distributor.

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

i have nothing to offer but encouragement. this has gone on for a while now but think of the experience gained.

re the rotor gap, that stirs a distant memory from my motorcycle days when people used to introduce a coat button in the ignition lead. i never tried it but was told it made a better spark at the plug.

keep at it

wishing you a successful outcome

stuey