Quote:
Originally Posted by burner31
Try this....
PURDY'S WAY:
The timing instructions that I've seen are very confusing to the unknowing. One of the highly regarded timing instruction states that the sweet spot that the tip of the rotor must point at is only good to get you home. Many that try to follow this one keep trying to get the points to be just ready to open and end up moving the points cam. Moving the points cam off the sweet spot gets the distributor out of time . The points can be adjusted at anytime without loosening and moving the points cam. Ford specs for points gap is anywhere from .018 to .022 . Increasing points gap causes the points to open quicker and advances timing. decreasing points gap causes the points to open later and retards timing . The other popular timing instruction says that the rotor tip should point opposite the number one contact in the distributor. This causes some to think that the rotor tip should point at the number 4 contact in the distributor cap and the timing ends up 180 degrees out of time . Neither timing instruction goes in to any real detail about rotational backlash in the distributor shaft and which direction that the backlash must be in when the points cam is tightened. Actually points gap isn't that great of a cause for the model A timing being that far off , as long as the gap is within Ford specs. The three most important things about model A timing is where the rotor tip points , direction of backlash after the points cam is tightened and that the upper plate has full swing within the window in the rear of the distributor cap. Full swing meaning that the lever on the breaker moves all the way to the right side of the window for retard and all the way to the left of the window in the cap for advance.
I don't set my timing by the points. When the timing pin drops in the dimple of the timing gear, I adjust the points cam so that the trailing tip of the rotor points at the number one contact in the distributor cap. When the cam screw is tightened , there must be no clockwise rotation in the distributor shaft. There is always some rotational backlash in the distributor shaft, sometimes as much as 1/2 inch . In other words, all rotational backlash must be in the counter clockwise direction , where it will have no effect on timing. The reason being is that when the engine runs, the distributor shaft turns in the counter clockwise direction . If clockwise backlash remains, the engine will have to turn to catch up the backlash before the distributor shaft can turn. When the engine must turn before the distributor shaft begins to turn , this causes the timing to be retarded to what ever amount of backlash that had to be caught up before the distributor shaft could turn. This is why direction of backlash is so important. If there is 1/2 inch of backlash in the clockwise direction after the cam screw is tightened, the timing will be so retarded that the engine probably will not even run. If it does run it will be very weak and the exhaust manifold will get red hot. As for points gap, I don't bother with retarding the spark lever. I turn the engine untill the rubbing block on the points is on the highest point on the cam lobe, I don't mess with the cam screw . I loosen the lock screw on the points block and turn the adjustable point untill the gap opens to .022 and tighten the lock screw on the points block. Twenty two thousants is maximum gap acording to Ford specs and advances the timing to the max before there is danger of starter kick back. For me this gives quickest throttle response and gives the most time before the rubbing block on the points wears to the point that the points will have to be readjusted. When the points gap closes to less than .018 it will be time to readjust the points or you will begin to lose power and the exhaust manifold will begin to over heat . Truth be known, the model A will run good as long as points gap is within Ford specs of .018 to .022. Some prefer a more conservative gap of .020. The highly respected method is when the timing is on the mark with the spark lever fully retarded that the points should be just ready to open. This can be correctly arrived at by points gap adjustment. I don't feel that it is worth the trouble and feel that it causes the confusion that ends up with the timing being off. There is only about .004 thousants leway in points adjustment within specs, that minor amount will change constantly as the engine runs and the points block wears . Cam lube will decrease wear and the length before points adjustments will be necessary. I don't believe that the small amount that the gap will fluctuate will be that noticable untill the gap closes to less than .018 .
Last edited by Purdy Swoft; 01-15-2015 at 12:52 PM.
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Let's back up the bus a bit and reflect on a couple of things. This statement first: "I don't set my timing by the points." Since a spark occurs when the points just start to open, it follows that the points' position and gap is what determines timing, NOT the rotor tip. The position of the rotor tip has absolutely no effect on timing. Initial (or base) timing is set with the pin in the timing gear depression, timing lever fully up (this is critical), points gap set correctly and points just starting to open. Tighten the center screw, crank the engine exactly two turns to verify, then leave it alone for the life of the engine! Just keep the point gap set correctly, and the timing will never change until the timing gears and distributor gears are worn out.
Second point: We have been talking only about initial timing so far. As soon as the engine starts, the timing lever is pulled down a little, and the faster we drive, the further we pull the timing lever down (thus advancing the timing) to our favorite position.
So in reality, while driving the timing is never where we worked so hard to set it!