Timing Changed without twisting distributor

[1969911T]

1969 911T original engine with Bosch distributor. Had this car for 49 years.

Engine just stopped in the drive way. After checking all the usual actors(new distributor cap, rotor, new plug wires, have spark to plugs, relatively new NGK plugs), still wouldnÂ’t start, but acted like it was barely trying. 12.7 volts everywhere and 50 amp battery charger did not help. Checked static timing with a VOM and found it is about 20 degrees BTC. It is supposed to be 0. I never touched the distributor after it stopped running, so it did not twist by itself as it is tight. The distributor is centrifugal and is mechanical, not vacuum and advances like I think it should when you turn the rotor by hand.
I can twist the distributor to 0 degrees static and try to start it, but before it starts and maybe destroys something——has anyone had this happen? My guess is something twisted inside the distributor.

Suggestions?

I do have the old Marelli and it worked when I took it out, so that is another thing to try

[Arne]

Check the points. The rubbing block on them may have disintegrated. Or the points may have broken in some other manner.

[edmayo]

The distributor clamp on those engines are known to lose a little tension after 50 years. Even though the pinch bolt is tight I always grab the distributor and see if it will turn,,,if not then that won't be your problem.

[1969911T]

The distributor clamp on those engines are known to lose a little tension after 50 years. Even though the pinch bolt is tight I always grab the distributor and see if it will turn,,,if not then that won't be your problem.

Ed, The distributor will not rotate, so it is tight.
Arne, even though the points were only about 50 miles old, they are almost closed- certainly much narrower than the .014” spec. Will pull the distributor tomorrow and fix. Hard to believe that .010” less gap can move the timing 20 degrees. Sounds like a geometry problem.

[edmayo]

You said 20 deg. BTDC,,,just so you know,,,as points wear the timing retards, not advances. So that wasn't the reason for the overly advanced timing.

[1969911T]

Ed
I messed up. The static timing was about 32 degrees ATDC- not 20 BTDC. I used the distance from TDC to 35 degrees BTDC to use as my standard. Opening the points .010 moved the static timing to about 25 degrees ATDC, so about 0.7 degree change for each .001” gap change. No clue how the engine ever ran like this, but it did! I had the distributor one tooth off and fixing that got me back to static timing at TDC. Couple of things to fix before I try to start it.

[1969911T]

Ed
I messed up. The static timing was about 32 degrees ATDC- not 20 BTDC. I used the distance from TDC to 35 degrees BTDC to use as my standard. Opening the points .010 moved the static timing to about 25 degrees ATDC, so about 0.7 degree change for each .001” gap change. No clue how the engine ever ran like this, but it did! I had the distributor one tooth off and fixing that got me back to static timing at TDC. Couple of things to fix before I try to start it.

Started fine, set the timing, runs like a top! All I can figure is the width of the rotor tip was wide enough for the engine to run and when I originally pulled the distributor to change the points, I put it back, one tooth off and did not check the timing as it ran well. Probably one of those mysteries that make life interesting and confusing

[flat6guy]

Did you use any point lube on the distributor cam? It will prevent premature wear. Also make sure to pull the rotor and apply 1-2 drops of engine oil to the felt tab. This wicks down to lube the advance mechanisms. Lastly I was taught 0.016" of an inch when setting points. Then rotate the engine so they're closed. Push them open and let them close on a business card or a piece card stock. Pull the card out until it comes out clean. This will remove any residual oils.

As for the running well 1 tooth off, yah it's a Porsche they do that. I have an SC that I recently purchased. The engine was completely apart for repairs when I bought it. Going through the mess I found a ton of evidence pointing severe lack of maintenance. The largest indicator was the 8 broken head studs. The most I've ever seen in one engine. The previous owner just kept driving. These things will run well even completely worn and broken!