Spark advance lock out

M

meteorgray

Member
What is the best way to lock out the spark advance?
I have a more modern distributor which uses weights
to advance the timing.
Roger
 
I assume you mean you don't just want to disconnect the linkage? You want to immobilize the lever so that drivers don't think the lever is doing something?
 
Hello , just disconnect the rod from control to distributor , goes from lower column,across head then to arm on distributor.
 
Just leave it disconnected so whenever you have a model A expert riding with you you can fully advance for starting and fully retard for high speed and see what comments you get. Gotta have some fun! ��
 
Not sure exactly what you're asking. Do you want to lock up the distributor so it doesn't advance on it's own? Or, as others have said, you want to disable the manual control.
 
meteorgray said:
Yes Alexiskai that is correct.
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One way to do this, and I’m not saying it’s the best way, is: take a small coupling nut, cut a notch 75% through it with a hacksaw, slide the notch in the nut over the quadrant, and then fix it in place with a set screw. This allows you to limit the lever’s travel up and down the quadrant. So then you just put the lever at the top or bottom of the quadrant, as you prefer, and lock it in place with the coupling nut.

Not pretty, but nondestructive.
 
I’d be inclined to just disconnect the shaft connecting the distributor and the knob at the end of the advance lever. Fixing the lever in place is inviting someone to force it, possibly causing damage. Everyone that I know who has installed a distributor with automatic advance has done it this way.
 
alexiskai said:
One way to do this, and I’m not saying it’s the best way, is: take a small coupling nut, cut a notch 75% through it with a hacksaw, slide the notch in the nut over the quadrant, and then fix it in place with a set screw. This allows you to limit the lever’s travel up and down the quadrant. So then you just put the lever at the top or bottom of the quadrant, as you prefer, and lock it in place with the coupling nut.

Not pretty, but nondestructive.
Click to expand...

So, lets just say that a guy has a Brumfield 6.1 on his A. How many degrees of advance would be the max spark advance? The original A span of 36 degrees seems like too much.

Is there an engineering way to calculate this?
 
Every engine is slightly different so there is no exact way to calculate the advance. My advice is to search for the knee in the advance curve using the standard distributor and then measure what advance that is. Then set up the automatic advance distributor to give you that advance when it is fully advanced.

The knee is where further advance will not give more power or rpm but a retard from the knee will lower the power or rpm.

If you automatic advance distributor has points then be aware that the timing will change as the points wear. You will need to check the points gap on a regular basis. If the block that rubs on the cam wears the points will have a smaller gap which will retard the ignition.
 
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Gene F said:
So, lets just say that a guy has a Brumfield 6.1 on his A. How many degrees of advance would be the max spark advance? The original A span of 36 degrees seems like too much.

Is there an engineering way to calculate this?
Click to expand...


Even with modern engines and computers, there is no way to calculate an engine’s maximum permitted spark advance mathematically. You have to put the engine on a dyno, try a bunch of different conditions, and see how it reacts. From that data you create the timing map and save that to the onboard computer.
 
Gene F said:
So, lets just say that a guy has a Brumfield 6.1 on his A. How many degrees of advance would be the max spark advance? The original A span of 36 degrees seems like too much.

Is there an engineering way to calculate this?
Click to expand...

The ideal max advance is an elusive figure. It varies with the fuel you are using, humidity etc etc. As a rough guess, for 6:1, I'd say 20° advance would be about your max but that is only a guess and about where I'd start with my refining drives (unless you have access to fancy equipment. Set it to that, go for a drive. If you can make it ping, retard it a bit, if it doesn't like to rev out, advance it a tad (love these technical terms!).
 
I have a Brumfield 5.9 head that I have been running for years. Larry suggested maximum advance of 18 degrees . After a bit of testing while driving , I found a sweet spot that worked well at elevated speed and less speed . I made a stop to locate the full advance that worked for me , and haven’t changed the location since . Driving in the city I use less advance. Not sure of the exact degrees of advance are ,but the lever is at roughly 9 o’clock. Fully retarded gives me a nice idle sound. Your results may differ, but Larry’s suggestion gave me a starting point.
Don S
 
A related question about timing advance. So if I time my spark with the advance handle down just one notch, once I am done about what will my timing be? I mean this as in day-after-day, when I get in my car, and I push the spark advance handle all the way up (to start my car), will the spark be a couple degrees BTDC? I think I saw a Paul Shinn video and he suggested this.
 
Gene F said:
A related question about timing advance. So if I time my spark with the advance handle down just one notch, once I am done about what will my timing be? I mean this as in day-after-day, when I get in my car, and I push the spark advance handle all the way up (to start my car), will the spark be a couple degrees BTDC? I think I saw a Paul Shinn video and he suggested this.
Click to expand...

If you time the distributor while the advance lever is down one notch, then when you move the lever all the way up, the spark will occur at roughly 4° ATDC. This timing is good for hand-crank starting (I think early Model Ts are timed at about this point) but has no other advantages. The reason this practice is often recommended has nothing to do with the initial timing; rather, it helps prevent drivers from over-advancing the timing while cruising.
 
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