Spark advance

[30 Closed Cab PU]

Personally with my A timed correctly have been unable to hear knocking/pinging, including full advance on hills, but still retard the lever on hills as a safe guard. Rebuilt motor with standard head, 87 octane ethanol free.


Have wondered if on the standard head it is not as much as a problem since the A was designed in the 20s when octane was lucky to be rated at 50. Now it is 87 or above.


What do you think?

[Dave in MN]

Observation: I have rebuilt 190 engines using insert bearings. About 15 are full pressure, another 15 have unfiltered oil direct to the center main and the rest are gravity fed. Of these engines I have had 6 engines come back to date with damage from running the engine with too much advance. In all 6 cases, the crankshaft was not damaged. The main bearings were the first to fail with the center main being the worst, the front journal following closely. The rear main had the least damage.

When the bearings failed, the bearing material was at the worst, pulverized, at the least shattered into course chunks.
The rod bearings in these failures all showed high pressure marking on the bearing surfaces. A couple of them had some early bearing material fractures.
The repairs to the main bearings were easy and not expensive to make. Change the inserts and thoroughly clean the engine. As a precaution, the rod bearings, also all inserted, were replaced even if they showed no distress.

All of the engines that returned for repair were fitted with High Compression heads. Most of the guys thought they were running their engines with the proper advance but when I checked their timing they were all over 30 degrees advance with one hard-of-hearing gent over 40 degrees. One gent ruined his bearings during a 6 hour run and less than 2 tanks of gas. Yes, It can happen that fast!

My point and advice: Too much advance will shorten bearing life. Back the timing advance down when using a head with higher compression than Ford's stock head. In most cases with heads of 6:1 compression, the advance should not be over 26 degrees before top dead center at full advance.

More concern: A new 7:1 head I dyno tested early this year, produced phenomenal power but started to noticeably knock at 22 degrees advance. No significant power was gained over 19-20 degrees advance. The owner brought the car back to me saying the engine "will just not run without knocking" and would I check it over. I immediately checked the timing and found he had the timing set at 28 degrees. I set his timing at full advance to 19 degrees and sent the car back with him. He reports: "It goes like stink but sure requires fiddlin with the timing to keep her from knockin". So don't assume by the book normal timing will work with anything but a standard head.
Good Day!
www.durableperformance.net

[eagle]

People love rules to follow. The trouble is "half way" or "5 clicks" or any other measure is simply a general guidance. Every car is different. Listen to your engine. Learn what ping sounds like. If you can't hear good enough then train a set of young ears what to listen for. Advance should be set for max until it pings when pulling, then back off timing just until it quits. Simple and straightforward, no guesstimate or magic involved.

[Purdy Swoft]

Again, I agree that retarded timing is the main cause of over heating . If momentum is kept up there will be much less problems when running at full advance . I feel that if the engine is in good condition , running at 50 MPH will greatly reduce the possibility of timing knocks and lugging . My model As easily cruise at 50 MPH and I have ran most of them that way for years .

[DNLs1930]

SOOOOO many learning points here!! Guess I shouldn't even ask about the automatic spark advance... ;-)

[Patrick L.]

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Originally Posted by DNLs1930

SOOOOO many learning points here!! Guess I shouldn't even ask about the automatic spark advance... ;-)

Nooooope ! Moving that lever is just one part of the wonderfulness of owning one of these monsters.

[GerryAllen]

Guys, I am finally getting to under stand the spark advance from this thread. I met Chuck one day by chance in Blaine Wa; and discovered we have engines rebuilt by the same fellow.
Long story short, being a newer Model A type at the time and still am, Chuck and I had a quick conversation about spark advance which helped my understanding. However this thread has really brought together my understanding and cleared up some miss-conceptions.
My question is; with being hard of hearing, I have being advancing the spark to the point of engine hesitation then back off a notch or two until no more hesitation.
Is that point of hesitation where the the engine begins to ping, I can't hear it but I feel it. In other words, I am advancing the spark until I get a nice surge of power from the engine and it runs smoother. I notice now that my car is running cooler, thanks to Chucks explanation. I know this because I shoot the Rad and brake drums temperatures after most outings. By virtue of the area I live in (not a big city) the car is my daily driver so am getting used to the vibrations and what little I can hear.
Once again thanks to all who have contributed to the thread a big thank you. The pictures were worth a thousand words.
Gerry Birch Bay WA