Timing and spark knock

[Aerocraft]

It would help if you could post a picture of the distributor as installed on the engine. Gar Williams

[Benson]

Carl this not aimed at you ... just some facts that I learned over the years.

Originally Posted by CarlG

When you say "Modern Distributor" if it has automatic advance, then the spark adjustment on the column would have no effect one way or the other.

Very true.

A modern distrbutor also comes in different spark curves.

For instance 40 years ago Mallory had two automatic advance distributors. 2301105 and 2301106. As of 3-4 years ago they were still selling these.

The 1105 For Model A spark curve was about 0 to 35 as I remember.

The 1106 for the B model had less total advance. I have not looked at the numbers for years. But you must remember that the Stock Model B dist started at 18 degrees advanced (using the special B timing cover on front of engine that starts the timing at 18 degrees.

If you put a Model A 1105 on a car with a higher compression head, you are WAY over the recommended 28 max on spark advance! The 1105 is OK with a stock low compression head.

Personally I like the Model A distributor so I can control the advance.

FS Ignitions (FSI) and others sell auto distributors with 0 to 28 or 30 degrees Max advance that are more fitting for a HC head.

You have to check with the manufacturer if you buy new one to see how the dist is setup.

If you buy a dist on ebay or swap meet who knows what you have. The Mallory curve weight stops are manually adjustable (to change max advance), springs can be changed and etc so who knows what someone has done to the curve).

Note Mallory Inc is now owned by Prestolite or maybe Mr Gasket I forget which and First Street Ignitions (FSI) is owned by Mel Mallory (unrelated to the other company) so when someone calls a dist a Mallory you have to ask more questions to find out just what the dist really is.

The only way is to put it on a dist machine and see what the advance curve really is.

[Duffy1]

Gentlemen ;

My error . I said modern distributor when I should have said a new distributor with modern point set up .Apologize . I do appreciate all the good info on modern distributors . My "B" engine has the correct ( model A ) timing cover to run a model " A" distributor . Thanks for the help .

[rollingsculpture]

Originally Posted by Aerocraft

Duffy: The spark control has 40 degrees of advance. 3/4 of the way would be 30 degrees so 28 degrees is just short (above) of that position. When one uses the timing pin to find top dead center I doubt that the method is accurate and the accuracy will vary by individual. If you keep the lever above the 3/4 mark you will be very close.

James Rogers warnings about detonation should not be ignored. There is a meltdown in every higher compression head just waiting to happen. Gar Williams

the JS says that the spark advance range is 20 degrees in figure 950 on pg 480 which is the august bulletin for 1930 so how do you get 40?

[Greg Jones]

James-I like your description, marbles shaking in a tin can. I called it similar to bolts shaking in a can. Don't ask me how I know this sound, but I do have a Model A engine sitting in my shop that needs a new bore job. Let's just say you speaketh wise things.

[Jim Johnston]

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If anyone is interested in an excellent explanation of the detonation/pre-ignition phenomenon read Kevin Cameron's column titled "Knock, Again" in the June 2012 issue of Cycle World Magazine.

[Tom Wesenberg]

Originally Posted by rollingsculpture

the JS says that the spark advance range is 20 degrees in figure 950 on pg 480 which is the august bulletin for 1930 so how do you get 40?

20 distributor degrees equals 40 crankshaft degrees of rotation.