Timing specs and ignition advance curve

dave11

I have a 1931 Plymouth model PA which was the correct 4 cyl flat head. The engine is stock, rebuilt a number of years ago and is in good running condition. My issue is with the ignition timing specs. On this particular engine there are no timing marks on the flywheel. The manual states that the procedure to set the ignition timing is to set the piston position of number one  cylinder to .046" before TDC, then set the ignition point gap to .020", next rotate the distributor base until the points break using a indicator light. Following these instructions the engine runs but it is labouring at road speed, as if it would like more advance.

Advancing the timing a bit at the distributor really makes an improvement while driving, however when starting the engine it kicks back against the starter.

So , digging into things a bit deeper I have rebuilt the distributor, it seems the bushings were sloppy, so I made replacement ones which has removed the excess play in the shaft.

The specs in the Plymouth manual say that initial timing when starting the engine is 10 deg BTDC, they also list the mechanical advance specs, which I have verified with the use of a friends distributor testing machine. Everything tested as it is supposed to, with 16 degs maximum advance at 2600 RPM.

My math says this engine has a total ignition advance from TDC of 26 deg. Wondering if this is in the ballpark for this type of engine?

There are alternate mays of setting ignition timing, using a vacuum gauge is one, the other which I like is to set the timing  (advancing) until the engine pings at road speed. The problem here is the Plymouth has a compression ratio of about 5 to 1 so it will not ping, at least you cannot hear it. I know it is not a good idea to run with excessive ignition advance.

My math tells me this engine has a total ignition advance of 26 deg from TDC. I am wondering if this is in line with similar engine types of this type??

Dave

dave11

dave11 said:

I have a 1931 Plymouth model PA which was the correct 4 cyl flat head. The engine is stock, rebuilt a number of years ago and is in good running condition. My issue is with the ignition timing specs. On this particular engine there are no timing marks on the flywheel. The manual states that the procedure to set the ignition timing is to set the piston position of number one  cylinder to .046" before TDC, then set the ignition point gap to .020", next rotate the distributor base until the points break using a indicator light. Following these instructions the engine runs but it is labouring at road speed, as if it would like more advance.

Advancing the timing a bit at the distributor really makes an improvement while driving, however when starting the engine it kicks back against the starter.

So , digging into things a bit deeper I have rebuilt the distributor, it seems the bushings were sloppy, so I made replacement ones which has removed the excess play in the shaft.

The specs in the Plymouth manual say that initial timing when starting the engine is 10 deg BTDC, they also list the mechanical advance specs, which I have verified with the use of a friends distributor testing machine. Everything tested as it is supposed to, with 16 degs maximum advance at 2600 RPM.

There are alternate mays of setting ignition timing, using a vacuum gauge is one, the other which I like is to set the timing  (advancing) until the engine pings at road speed. The problem here is the Plymouth has a compression ratio of about 5 to 1 so it will not ping, at least you cannot hear it. I know it is not a good idea to run with excessive ignition advance.

My math tells me this engine has a total ignition advance of 26 deg from TDC. I am wondering if this is in line with similar engine types of this type??

Dave

dave11

dave11 said:

I have a 1931 Plymouth model PA which was the correct 4 cyl flat head. The engine is stock, rebuilt a number of years ago and is in good running condition. My issue is with the ignition timing specs. On this particular engine there are no timing marks on the flywheel. The manual states that the procedure to set the ignition timing is to set the piston position of number one  cylinder to .046" before TDC, then set the ignition point gap to .020", next rotate the distributor base until the points break using a indicator light. Following these instructions the engine runs but it is labouring at road speed, as if it would like more advance.

Advancing the timing a bit at the distributor really makes an improvement while driving, however when starting the engine it kicks back against the starter.

So , digging into things a bit deeper I have rebuilt the distributor, it seems the bushings were sloppy, so I made replacement ones which has removed the excess play in the shaft.

The specs in the Plymouth manual say that initial timing when starting the engine is 10 deg BTDC, they also list the mechanical advance specs, which I have verified with the use of a friends distributor testing machine. Everything tested as it is supposed to, with 16 degs maximum advance at 2600 RPM.

My math says this engine has a total ignition advance from TDC of 26 deg. Wondering if this is in the ballpark for this type of engine?

There are alternate mays of setting ignition timing, using a vacuum gauge is one, the other which I like is to set the timing  (advancing) until the engine pings at road speed. The problem here is the Plymouth has a compression ratio of about 5 to 1 so it will not ping, at least you cannot hear it. I know it is not a good idea to run with excessive ignition advance.

My math tells me this engine has a total ignition advance of 26 deg from TDC. I am wondering if this is in line with similar engine types of this type??

Dave

dave11

Can someone (administrator?) delete #2 and #3 posting. tried to edit my original, obviously without success

Dave

cchancel

I am not sure if this helps, but the following is an excellent discussion about timing the Hudson "Big 6":

https://openforum.hetclub.org/discussion/168682/timing-question-262#latest