’25 Series 80 distributor adjustment/TIMING question.

Hi Tom, the owners/operator’s manual for your car has a discussion in it for setting the timing. It can be a bit difficult to follow, so I’ll post some instructions here:

To find TDC [Top Dead Center], you have to access the top of the flywheel. Behind the cylinder block, on the top of the aluminum crankcase covering the flywheel, is a steel 3″ diameter cover that when removed, shows the top of the flywheel.

The flywheel has three brass plates riveted to the outer diameter just behind the ring-gear. You need to hand crank the engine until the brass plate for Cylinders 1+6 is visible. There is a scribed line, or sometimes a hard to see pointer on the edge of the opening in the aluminum crankcase.

The brass plate has line labeled ‘DC’ for ‘Dead Center’. Next to that are two markings labeled ‘exhaust valve closes/intake valve opens’. Then at the other end of the 2″ long brass plate is another mark labeled ‘IGN’. This is the ‘Ignition’ mark.

With the older, low compression engines, with a hand crank, and a driver-adjustable spark advance in the cabin, the timing is set quite retarded for safe ‘hand cranking/starting’. Personally, I don’t think I’d ever consider trying to crank start any of my Series 80 cars!. Because there is so much driver-settible spark timing, there is not a great concern about ‘exact’ timing of the spark. This is quite different from more modern, higher compression engines that can get very pronounced spark knock or ‘ping’ if the timing is just a few degrees too-advanced. I’ve NEVER been able to get a Series 80 engine to spark knock or ‘ping’.

The big problem now arises: getting your head up against the inside of the firewall so you can look down through the ‘D’-shaped hole in the top of the crankcase. I suppose if a person way young, [limber], 5’6″ or less tall, and weighed less than 110 pounds, this would not be a big problem. I’ve resorted to the use of a mirror and light, and someone else to hand crank the engine while I peered into the mirror waiting for the brass plate to appear.

You can find the ‘rough’ TDC for #1 cylinder by removing all 6 spark plugs [for ease of hand cranking] then holding a finger or thumb over #1 spark plug hole, and have someone hand crank the engine. You will feel the compression trying to push your thumb off the spark plug hole when the cylinder is on the compression stroke. About 1/4 of a turn of the hand crank from when you first feel the compression pressure is close to TDC. Now go look through the ‘D’ shaped timing hole in the rear of the crankcase. Continue to turn the engine until the left side of the ‘D’ lines up with the ‘IGN’ mark. This is where your engine should have the points ‘just open’ with the timing lever on the steering wheel at full retard, which is with the lever pointing at about 7-O’Clock.

Now, remove the distributor cap if it isn’t already removed, the rotor should be pointing right at the water-jacket on the side of the engine, and the distributor cap retainer clip. The #1 spark plug wire is right above the inner ‘ear’ on the distributor cap. If all these parameters are met, then look at the points: Are they open? Closed? or just about to open?

What does ‘just about to open’ look like? The rubbing block on the point-arm should be on the ‘front’ side of the ramp or lobe on the 6-lobe cam on the distributor shaft. If the distributor shaft rotates clockwise [normal direction of rotation], the ramp of the cam-lobe will push the points open.

When a set of points is closed, the coil is being ‘charged’ with potential current. When the points open, this ‘charge’ collapses, and exits the coil through the ignition wire, going to the Distributor cap, to be routed or distributed to the appropriate spark plug. The ‘Dwell’ measured in # of degrees of distributor cam rotation, is the period of time [in degrees] that the points are closed. If the point gap is too narrow, the points just barely open, the dwell-time is too great. If the point gap is too wide, they will open too soon. Pierce did not publish a ‘dwell’ setting, I’m not sure if ‘dwell’ was used in the ’20’s. But Pierce did publish a point-gap setting, a rather wide range of from .018″-.027″. The fixed point is on a threaded shaft, with a lock-nut holding it from turning and changing the gap setting. As the rubbing block on the point arm wears, the point gap will close up. Make sure there is a small amount of cam grease on the point arm rubbing block to reduce wear rate.

So: the timing is correct when the CYL.1+6 ‘IGN’ mark on the flywheel brass plate is straight up, aligned with the left-side of the ‘D’ shaped opening in the crankcase. And the timing lever on the steering wheel is in full-retard, and the points JUST OPENED. When the points open, the coil generates a spark. The rotor must be pointing at the #1 spark plug wire in the Distributor cap.

What if the rotor is not pointing at the right wire? or the points are already wide open, or closed and won’t open for a significant amount of distributor cam rotation??

Well, here is where the Series 80 Delco distributor is a bit different than most other distributors: The 6-lobe cam on the distributor shaft is NOT part of the shaft. It can be loosened, and rotated so that the rotor is pointing at #1 plug wire in the cap, and the points are just breaking open.

Remove the rotor from the top of the cam. Down inside of the cam is a slotted-head screw. Use a good-fitting screwdriver, loosen the screw [turn counter-clockwise]. The screw will get loose, then after about one full turn, the screw will push the cam up off the end of the distributor shaft, The end of the shaft has a slight taper, matching the taper in the inside of the cam. The screw has a ‘C’ clip between the end of the shaft and the bottom of the cam. So the ‘C’ clip pushes the cam up and off the taper as the screw is turned out.

With the cam loosened, you can reinstall the rotor and use it to turn the cam, or you can use a 1/2″ open-end wrench over the flat on the cam, to turn the cam. Use the rotor to confirm that the points are just opening, and the rotor is pointing to the correct wire in the distributor cap. Then gently tighten the screw in the cam, it does not need to be extremely tight, DO NOT STRIP THE THREADS !!

This completes the timing setting. If you want to double-check the setting, Take a test light, this is a ice-pick like tool with a light in the handle and a wire with an alligator clip. Fasten the alligator clip to the screw and wire on the outside of the distributor, or the other end of the wire where it is connected to the coil. Then ground the probe or ice-pick end somewhere on engine.. With the ignition on, the test light will light up whenever the points are open. Hand crank the engine with the distributor cap off the distributor until you see the rotor approaching the position for #1 plug wire, when the test light comes on, go check through the top of the crankcase timing port, to see if the brass plate for #1-#6 cylinders is under the left side of the ‘D’ shaped opening. If the left side of the opening is over the brass plate, you are in ‘the ball-park’. I like to see the left side of the ‘D’ opening to be near the middle of the brass plate. I prefer to have more advance available than Pierce had, because our higher-octane fuels today can handle more spark advance without knock or ping.

If anyone needs to see photos, I’ll try to post some images over the next few days.

Greg Long