Starting problems / ignition / distributor

[GMCTom]

Hi everybody,

hope someone can help me with my problem.

In October 2025, I took the last ride of the season. Suddenly, the car died at walking speed. No sputtering or stuttering, no warning. It just shut off, as if the ignition key had been pulled out. There was no way to restart it. The starter motor turned, there were no unusual mechanical issues or noises. I then towed the car home.

The following points were checked:

- Fuel: present, also in den carburetor
- Spark: present but weak
- Carburetor: no issues
- Other mechanical issues: none to see, nothing to hear
- Distributor: still in the marked position (not rotated)

The following work was carried out:

- Distributor: points replaced
- Ignition coil: replaced
- Spark: now present and strong
- Starter: replaced (turns like a dream). The old one was a bit weak.

Result: Won't start

Here's what we found (many thanks to David/Prowbar here from the GMC forum :thumbsup:):

- Engine set to 1 TDC, valve cover removed, both valve springs on cylinder 1 are relaxed. Valves closed.

- Distributor cap removed. Distributor rotor points to cylinder 6 and not cylinder 1 (see photo). Engine turned 10° by hand. Spark on cylinder 6.

- Distributor pulled out: no abnormalities except that the vacuum mechanism isn't working. It's extremely stiff.

My question: I'm able to install the distributor so that it points to cylinder 1 and try to start it. Is that a good idea?

I'd like to know why the distributor position is incorrect.

At first, I thought the crankshaft and camshaft were misaligned, but both valves close at 1 TDC.

The timing chain was replaced during the restoration (200 km ago). Could the woodruff keys have sheared off? I think you'd hear that, and the valve position would be off.

Maybe you have a suggestion for me. I'm at my wit's end.

Many greetings

Tom

https://up.picr.de/50665948xr.jpeg

[FetchMeAPepsi]

I sure would like to help, but you're in over my head. Maybe Prowbar will pop in later and offer some insight.

[James]

Did you check the centrifugal advance in the distributor? If the springs had broken it would go full advance while running. Turning the rotor by hand the distributor should rotate clockwise against the springs. There should always be some spring pressure on the rotor and no looseness (no spring pressure/feel sloppy). Another possibility if you had just operated the engine to over 3500 rpm, it is possible that the centrifugal advance had stuck in the full advance position from dried up lubrication.

You can see if the engine will run by resetting the distributor to fire on the crankshaft timing mark. If it run OK, then you rule out other issues. You will need to repair or replace the distributor.

[AZKen]

Do not remove distributor.

Cap off, all plugs out. Thumb over cylinder 1 hole. Turn motor with starter. Watch rotor. See where rotor is when pressure hits thumb. Watch several rotations to see if rotor repeats. report.

Also, where is harmonic balancer mark when rotor is in position shown in your photo?

[beerman]

Did you move the distributor? Looks to me like the vacuum advance has been turned counter clockwise maybe you timing is too far retarded. Like AZken said check that balancer mark

[James]

Also, where is harmonic balancer mark when rotor is in position shown in your photo?

I don't believe the 305 series have a Harmonic Balancer, just a flange with the timing disc riveted to the flange and a pulley bolted to it.

[AZKen]

You are right James, no balancer. Thank you. Thinking Chevy. May have markings on disc. Sorry, Tom. Continue with thumb test. It's a good way to confirm you are on compression stroke of no. 1.

If you are sure you have gas going down carb throat and sure you have spark....must be spark is at wrong time. If no noise, or trying to start with some firing, the timing is off. If you have backfire from carb or exhaust, it is WAY off.

Your valve position test is one of the ways to set timing. You can make mistakes in any method. You can be 180 deg out of time. It's a little more tricky without a timing mark.

"- Distributor cap removed. Distributor rotor points to cylinder 6 and not cylinder 1 (see photo). Engine turned 10° by hand. Spark on cylinder 6."



Please explain in detail.
If I understand what you did.....
1. You removed the cap?
2. You rotated crankshaft CW by hand until both no. 1 valves are closed and rockers are loose?
3. Then you observed rotor location was at no. 6?
4. Then you rotated crankshaft again? CW or CCW?
All this is Correct???

Keep in mind that there is supposed to be 5-10 deg advance spark. So after initial position of rotor, you would rotate crankshaft back CCW and at the same time observe if points are open or closed. Points should fire just before TDC not at TDC or after TDC.

Reference from member bigblockV6: Probably the same for 305, not sure.

"The one thing that can help is depending on what year your 351 is there were two different locations for the number one on the distributor, 1960-63 number one was in the 6 o'clock position. On 1964-74 number one was in the 5 o'clock position, the vacuum pot for the advance should be roughly in the 6 o'clock position leaning towards 7 o'clock."

He is just speaking about how the distributor will look visually using rotor position and vacuum advance can position as reference.

[beerman]

I snapped some pics of the pointer and hub markings I was talking about. In this case since the heads off you can see that #1 is at TDC. hope this helps

[GMCTom]

Thank you for your feedback. My fault I have a 305E engine. 1965 GMC 1500

@AZKen
Please explain in detail.

If I understand what you did...

1. You removed the cap?
Yes

2. You rotated the crankshaft (CW) by hand until both cylinder 1 valves were closed and the rockers were loose?
The rockers are loose; I can move them by hand. Crankshaft position: 1TDC

3. Then you observed the rotor position was at cylinder 6?
Yes, 6 in the photo.

4. Then you rotated the crankshaft again? CW or CCW?
When I stand in front of the engine CCW from 1TDC to the 10° mark, and when I reach this point, I get a spark on cylinder 6 (with the cap on the distri) because the rotor is in position 6.

@James
I tried to turn the rotor on the distributor (while it was installed), but it won't move. It's stuck. There's no movement against a spring or springing back. I assume it should look like this:

https://up.picr.de/50668146mu.gif

I'll check the mechanism of the distri. Perhaps as you said the finger is actually locked in its maximum position.

@beerman and FetchMeAPepsi
Many thanks for your help and photos. Yes, I have this 1TDS marking on my engine/pulley. The piston on the 1 cylinder is also in its top position (up) and the valves are closed.

[James]

@James
I tried to turn the rotor on the distributor (while it was installed), but it won't move. It's stuck. There's no movement against a spring or springing back. I assume it should look like this:

https://up.picr.de/50668146mu.gif

I'll check the mechanism of the distri. Perhaps as you said the finger is actually locked in its maximum position.

That is what it should do.

Also with a good distributor vacuum diaphragm, the plate that the points is mounted on, should move counter-clockwise with vacuum applied. Did you check the diaphragm for leaks. If the no leak under vacuum the plate might also be stuck. If it does leak the the diaphragm will need to be replace. This part is use to provide better gas mileage while cruising down the highway.

[beerman]

Exactly, here are some pics for reference on the amount of movement

[Prowbar]

I think you guys are onto something.
Tom and I made sure to set the distributor to initial advance but as you mentioned the vacuum advance is stuck. At least the canister wasn't moving, and on the initial videos you could hear it kick back on the starter significantly, indicating too much initial timing.

From what I could see the spark was definitely good and strong now.

The video he sent me this morning sounded much better, it was trying to run. Told him to move add a little more initial timing but haven't heard since.

@GMCTom could you chime in and update us on the situation?