Crab Distributor Advance Curve?
- Thread starter glennpm
- Start date
I’d like to see one too. I swear I recall seeing something during my time spent researching info on these distributors. It still won’t be much of a curve though, as in the vids I’ve watched, the helmet style reaches a “max” advance of 10.5 - 11.5 degrees at only 600 rpm (without vacuum brake installed), and that is with the advance already moved to the 2 degree mark. My tests of the crab confirm this. With “0” advance, and no vacuum brake installed I got the following numbers:
500 cam rpm - 3.5 degrees
750 cam rpm - 8 degrees
1000 cam rpm - 10.5 - 11 degrees
1250 cam rpm - 11 degrees
1500 cam rpm - 11 degrees
500 cam rpm - 3.5 degrees
750 cam rpm - 8 degrees
1000 cam rpm - 10.5 - 11 degrees
1250 cam rpm - 11 degrees
1500 cam rpm - 11 degrees
Found some pics posted in this thread.
https://www.jalopyjournal.com/forum/threads/flathead-ford-ignition-advance-curve.118906/
https://www.jalopyjournal.com/forum/threads/flathead-ford-ignition-advance-curve.118906/
Attachments
petehoovie
Well-known member
rotorwrench
Well-known member
In 1941 Ford changed the flyweight set. The 11A set was used as the replacement set for all of the prior front mount V8 distributors and all late ones through 1948. I think there is a thread on here about that and Ford likely had a service bulletin as well. My SB set only goes through 1937 so I can't check that.
Last edited:
petehoovie
Well-known member
deuce_roadster
Well-known member
I just copied those numbers down and will put inside the door of my Sun machine. Always take the vacuum piston out when making these adjustments.
My method is to after complete dis assembly, cleaning,che cking and lube the bushings, install new points, condenser, customer's coil, Set at a very slow RPM that does not advance the timing, set the flash arrows at the zero degree mark, I set the initial advance at 2 degrees by loosening the screw that allows you to move the baseplate one way or another, run on the Sun machine 30 to 45 minutes at maybe 500 distributor RPM (1000 engine RPM) dry rubbing block to wear them into the cam. With a toothpick, I put a tiny bit of Sorenson point lubricant behind the rubbing block and on the rub surface. Put a piece of paper in the passenger side points to take them out of the circuit. Set the Driver's side points to 22 1/2 degrees dwell, Remove the paper from the passenger side and set the TOTAL dwell to 35-36. I then run the RPMs up and down watching the lighted arrows, they should be on the degree marks for each cylinder. If not the cam is worn or bushings are loose. I have had some really good distributors (helmet or crab type) that will stay solid up to 5000 engine RPM. (2500 distributor rpm) eventually cylinders will drop out as RPM goes up. Stock engines will float the valves long before ever getting to 5k RPM. Because the two sets of points are adjusted individually for a total dwell, that is why if you sent them both the same with a feeler gauge, it will run, but not as good as it could. That is my 2 cents.
My method is to after complete dis assembly, cleaning,che cking and lube the bushings, install new points, condenser, customer's coil, Set at a very slow RPM that does not advance the timing, set the flash arrows at the zero degree mark, I set the initial advance at 2 degrees by loosening the screw that allows you to move the baseplate one way or another, run on the Sun machine 30 to 45 minutes at maybe 500 distributor RPM (1000 engine RPM) dry rubbing block to wear them into the cam. With a toothpick, I put a tiny bit of Sorenson point lubricant behind the rubbing block and on the rub surface. Put a piece of paper in the passenger side points to take them out of the circuit. Set the Driver's side points to 22 1/2 degrees dwell, Remove the paper from the passenger side and set the TOTAL dwell to 35-36. I then run the RPMs up and down watching the lighted arrows, they should be on the degree marks for each cylinder. If not the cam is worn or bushings are loose. I have had some really good distributors (helmet or crab type) that will stay solid up to 5000 engine RPM. (2500 distributor rpm) eventually cylinders will drop out as RPM goes up. Stock engines will float the valves long before ever getting to 5k RPM. Because the two sets of points are adjusted individually for a total dwell, that is why if you sent them both the same with a feeler gauge, it will run, but not as good as it could. That is my 2 cents.
glennpm
Well-known member
Both the posts that Laurie and Duece_Roadster made taught me how quickly the advance starts. Before this, I didn't understand why test equipment started with only 200 RPM distributor RPM.
One anomaly that I've found is the difference in setting TDC manually versus results with a dial back timing light. I don't have a commercial test machine but made my own following an old post that Rumble Seat made.
I was very careful setting TDC for my crab with a test light. I then advanced the adjustment plate by an additional 4 degrees. Even before this additional push the adjustment plate indicated advance, that is, the adjustment plate was not in the middle position. I then put it back on my motor and found that with my dial back timing light, it was advanced by about 10-12 degrees which was much more than I wanted. I have it now set at 6.5 degrees advance.
The last couple of pages of my attachment give more detail of this.
One anomaly that I've found is the difference in setting TDC manually versus results with a dial back timing light. I don't have a commercial test machine but made my own following an old post that Rumble Seat made.
I was very careful setting TDC for my crab with a test light. I then advanced the adjustment plate by an additional 4 degrees. Even before this additional push the adjustment plate indicated advance, that is, the adjustment plate was not in the middle position. I then put it back on my motor and found that with my dial back timing light, it was advanced by about 10-12 degrees which was much more than I wanted. I have it now set at 6.5 degrees advance.
The last couple of pages of my attachment give more detail of this.
deuce_roadster
Well-known member
Glen, if you ever have the RH head off using a dial indicator get the #1 piston at TDC with both valves closed and take one of the lower timing gear bolts out and replace it with a stud that comes to a point near the pulley. Then mark the front pulley even with the point of the stud and you will have (TDC) and a way to use a timing light. Using math you can calculate timing marks on the pulley using the circumference/360 and make timing marks for 2, 4 or however many you need. If you have a non stock engine this can be helpful. Maybe you already have done this.
glennpm
Well-known member
I did that when I assembled the motor. I have my pulley marked every 90 degrees. This pic show TDC. In the middle of the white band on the flange, I have a notch. This is what I used when I used my dial back light.
Regarding my post above, this is where the plate and housing marker ended up when I set TDC manually
Regarding my post above, this is where the plate and housing marker ended up when I set TDC manually