1975 c3 won’t start
Melting Slicks
Joined: Mar 2005
Posts: 2,095
Likes: 299
From: Midlothian VA
If true you need to remedy that first.
But if you have Air, Fuel, and Spark and still have a no start condition the your next step is to verify ignition timing.
In your initial post the failure condition you described could also be due to a jumped, stretched, broken timing chain.
The OEM timing chain cam gear had nylon covered teeth. As they age the teeth become brittle and are prone to dropping off which eventually impacts timing.
When enough teeth fail the chain can "jump" or skip one or more of the sprocket teeth throwing off timing to the point that the motor will not run.
You can check for this condition easily enough before you throw more unnecessary money at parts:
Rotate the motor until you find TDC on the #1 cylinder (pull the plug and verify that the piston is at TDC on the compression stroke)
With the #1 piston at TDC pull the distributor cap and verify that the rotor is pointing to the #1 piston tower on the cap (on or very near)
Finally, look at the timing mark on the damper and verify that it indicates TDC (on or very near).
Simply spinning the motor and watching the rotor turns only tells you that the cam is turning with the crank. It tells you nothing about timing.
Last edited by Hammerhead Fred; Jul 12, 2024 at 10:59 AM.
Thread Starter
Heel & Toe
Joined: Jul 2023
Posts: 19
Likes: 1
From: Missouri
tested the rotor it turns when cranked. was going to post a video of it, but keeps saying format not accepted. ok will check what hammerhead said, but it will be sunday before I have time to work on it again. Thanks so much for everyone's suggestions.
Air, Fuel, Spark - at this point it sounds like you cannot confirm that you have any spark at the plugs.
If true you need to remedy that first.
But if you have Air, Fuel, and Spark and still have a no start condition the your next step is to verify ignition timing.
In your initial post the failure condition you described could also be due to a jumped, stretched, broken timing chain.
The OEM timing chain cam gear had nylon covered teeth. As they age the teeth become brittle and are prone to dropping off which eventually impacts timing.
When enough teeth fail the chain can "jump" or skip one or more of the sprocket teeth throwing off timing to the point that the motor will not run.
You can check for this condition easily enough before you throw more unnecessary money at parts:
Rotate the motor until you find TDC on the #1 cylinder (pull the plug and verify that the piston is at TDC on the compression stroke)
With the #1 piston at TDC pull the distributor cap and verify that the rotor is pointing to the #1 piston tower on the cap (on or very near)
Finally, look at the timing mark on the damper and verify that it indicates TDC (on or very near).
Simply spinning the motor and watching the rotor turns only tells you that the cam is turning with the crank. It tells you nothing about timing.
Air, Fuel, Spark - at this point it sounds like you cannot confirm that you have any spark at the plugs.
If true you need to remedy that first.
But if you have Air, Fuel, and Spark and still have a no start condition the your next step is to verify ignition timing.
In your initial post the failure condition you described could also be due to a jumped, stretched, broken timing chain.
The OEM timing chain cam gear had nylon covered teeth. As they age the teeth become brittle and are prone to dropping off which eventually impacts timing.
When enough teeth fail the chain can "jump" or skip one or more of the sprocket teeth throwing off timing to the point that the motor will not run.
You can check for this condition easily enough before you throw more unnecessary money at parts:
Rotate the motor until you find TDC on the #1 cylinder (pull the plug and verify that the piston is at TDC on the compression stroke)
With the #1 piston at TDC pull the distributor cap and verify that the rotor is pointing to the #1 piston tower on the cap (on or very near)
Finally, look at the timing mark on the damper and verify that it indicates TDC (on or very near).
Simply spinning the motor and watching the rotor turns only tells you that the cam is turning with the crank. It tells you nothing about timing.
Race Director
Joined: Mar 2017
Posts: 11,953
Likes: 4,510
From: Virginia
I don't try to post videos here. I post them on YouTube instead, and provide a link.
So the rotor turns. That's good news! I once found a broken timing belt doing that test.
How did you confirm that you have no spark? Do you have a timing light, and did you test on both a working vehicle, and on your C3, to see if the light's behavior is different? Did you pull a plug wire, and look for spark in a dark garage, while a spare plug was grounded to the engine?
Videos of any of this could be a great help!
So the rotor turns. That's good news! I once found a broken timing belt doing that test.
How did you confirm that you have no spark? Do you have a timing light, and did you test on both a working vehicle, and on your C3, to see if the light's behavior is different? Did you pull a plug wire, and look for spark in a dark garage, while a spare plug was grounded to the engine?
Videos of any of this could be a great help!
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Verdad Gallardo
Team Owner
Joined: Aug 2000
Posts: 21,460
Likes: 463
From: Massillon,Ohio USA
2020 C3 of the Year Finalist - Unmodified
Cruise-In VI Veteran
St. Jude Donor '08-'09-'10-'11-'12
...and with a lot of people unknowingly owning these cars and not using a high zinc motor oil I'd expect this to happen more often, but there was a time some years ago where it did seem like there was monthly postings of someone loosing a cam possibly by not using high zinc motor oil in their C3. Not needed as much if the car has been changed over to a roller lifter cam.