- Home
- About Us
- Join/Renew
- Member Benefits
- Member Pages
- Log In
- Help
- Museum Store
Tagged: Straight 8, Timing, Tune-up
Using the IGN marks on the flywheel, do you set the timing for both of the cylinder sets 4-5 and for 1-8?
Do you set the manual spark advance Spark Control button on the dashboard for Full Advance (pushed in) or for Full Retard (pulled out) when adjusting the distributor’s points based on the flywheel’s IGN marks? I have seen conflicting advice regarding this Spark Control setting. My inclination is to set the Spark Control at full retard so that when the button is pushed in the manual spark advance plus the distributor automatic advance at 1500 RPM will be 30-40 degrees.
To complicate the issue, I have installed electronic points in the distributor so I have to use a timing light flashing on the crank pully. I marked the crank pully to match the UDC marks on the flywheel. I intend to set the dynamic idle advance at about 7 degrees (advanced) to account for the static advance of 5 degrees plus the distributor’s automatic advance of about 2 degrees at 600 RPM. Does this sound about right?
Does this help you at all?:
https://archive.org/details/NationalServiceManual1927Through1941OCR2246Pages/page/n659/mode/1up
The National Service Manual you referenced is a very informative and useful document regarding the ignition timing procedure. However, I have not been able to understand why the engine is timed at 5 degrees (flywheel IGN mark) before top dead center (flywheel UDC mark) with the Spark Control at Full Advance. This precludes the driver adding any more spark advance while driving car. This also limits the total advance potential to 18 degrees, which is the static advance (5 degrees) plus the 662-J distributor’s max automatic advance (13 degrees @ 3100RPM). This is far short of the spec sheets that highlight a manual advance capability of 33 degrees. Since the spark can only be manually retarded by the Spark Control, how does the driver get a manual spark advance of 33 degrees?
I sent you an e-mail, Salvatore.
I always thought (maybe unqualified to do so…) that timing controls were intended to enable the driver to retard spark in case of detonation and not to add advance. Therefore the timing setting was max advance with control so positioned. I realize we may run more advance with modern fuels etc. but I don’t care much for max performance on a Pierce with rare parts, etc.
Yes, that’s the way I understand it. The spark control is used in case one gets a batch of low octane fuel and it starts to knock. In the case of a 1930’s car that probably means on the order of 65 octane or less. With 87 octane being the norm the idle timing can be advanced a bit, I use 10 degrees BTDC instead of 5. It will add a very slight amount of power, a very slight improvement in fuel economy, more advance than that not much. Heat added to the coolant will go down slightly and exhaust gas temperature will also, reducing valve recession tendencies, again very slightly. Back in the ’70’s California added devices to retard the spark to reduce pollutants and there were complaints about overheating and reduced power. My 49 state 1966 Chrysler had timing of 12.5 degrees BTDC and the California version was actually 5 degrees ATDC. If all is well it would be surprising to have any knock and any need to touch the spark retard on a ’30’s. My Packard with 6.5 compression instead of 5.5 does not have a manual spark retard at all.
Looking through the tune-up guide I see the confusion factor is the backwards way it talks about advance. It says “Manual advance: 33 degrees (engine – maximum). Consists of retard operated by pulling out button on dash. Used for hand cranking or heavy pulling“.
The ’35 owners manual states “the spark control button is provided to meet unusual conditions. In its innermost position, the spark timing is held “advanced” and, under normal driving conditions, it should remain in that position. There are conditions which may arise that require “retarding” the spark. This is accomplished pulling the the button out until the desired position is reached. Evidence that the spark is advanced too far is indicated by “pinging” in the engine. However, this is not harmful to the engine. A slight “ping'” indicates that maximum power is being obtained from the engine. There are many causes for “pinging”, the more common causes of which are, inferior grades of gasoline and heavy pulling on steep grades.
The confusion arises from calling the 33 degrees “maximum manual advance”, when it would be clearer to call it 33 degrees maximum manual retard. If set for maximum advance with the knob pushed all the way in and considered “normal driving conditions” 33+5 degrees 38 degrees BTDC would be a ridiculous amount of advance. It would likely try to kick backwards trying to crank it. The 33-5 = 28 degrees of retard ATDC with the spark control pulled all the way out is pretty extreme also. At that setting maybe kerosene wouldn’t knock if you could get it to fire at all.