ENGINE IGNITION TIMING

  • Tiny
  • dnivens
  • 1967 Ford Mustang
  • V8
  • 2WD
  • manual

Will an engine start OK if the base timing is set at TDC (0 degrees)?

I am modeling a standard, classical, distibutor ignition system, like one in a Ford 289, circa-1967, and I can't figure out why everyone I talk to tells me that when I start cranking the engine on startup I want a small amount of static advance. It seems to me that if the engine is not turning and the spark happens at, say, 6 degrees BTDC, the piston will try to push the crank backwards. Maybe the starter-motor is strong enough to force a burning cylinder-load of fuel past TDC?

Thank you very much for any insight you can offer.

Thursday, February 10th, 2011 AT 5:02 PM

12 Answers

  • Tiny
  • Wrenchtech
  • Expert
  • 19,583 posts

Are you trying to disprove years of engineering? The fuel needs time to combust to give maximum piston downforce.

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Thursday, February 10th, 2011 AT 5:35 PM
  • Tiny
  • dnivens
  • Member

Well, thank you, and I am very happy to hear from you. Note, from the question, that the engine isn't running, it is stopped. I am speaking about a very-specific point in time when the engine is just starting to be turned-over (i.E, during the first few sparks). I noticed that I can even rotate the distributor around, quite a bit actually, when the engine is at idle, vacuum hose disconnected, and it still runs (not very good at the extremes) when the strobe goes through from more than -10 to +10 TDC. If I crank it too far above -10 it starts to ping, and then too far over +10 (or so estimated) it runs unsteadily. Then I turn it to the factory static advance setting of 6 degrees BTDC and lock-down the distributor and it all works great. It seems easier to start this engine with the timing at TDC (0 degrees) when the battery can only produce a very low cranking speed, say under 60 RPM.

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Thursday, February 10th, 2011 AT 6:31 PM
  • Tiny
  • Wrenchtech
  • Expert
  • 19,583 posts

If you're having trouble cranking at 6deg BTC then you need a new battery. That engine has a high compression ratio.

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Thursday, February 10th, 2011 AT 6:34 PM
  • Tiny
  • dnivens
  • Member

Correct, the car has no battery in it, and I am running the engine off of a power supply on by workbench so it turns-over rather slowly. Thanks for your help, I just need to setup the engine so I can lock-down the distributor and put the car back together. I was curious about why it was so easy to start at 0 degrees TDC? Plus, when I rotate the ditributor and the engine is idling at low RPMS, it is not too particular about the timing (+/-10 doesn't seem to matter much). Any other comments? I appreciated your knowledge and replies.

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Thursday, February 10th, 2011 AT 6:52 PM
  • Tiny
  • Wrenchtech
  • Expert
  • 19,583 posts

0 deg will make it crank easier, not necessarily start faster, but the power loss will be considerable once it's running.

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Thursday, February 10th, 2011 AT 6:58 PM
  • Tiny
  • dnivens
  • Member

Well, I understand about the power loss, but as soon as it starts to run, I strobe it in at 6 degrees BTDC and tighten-down the distributor. What I am really hoping for here is for you to confirm that this "0-degrees TDC startup procedure" (which only lasts for a minute or so, until I adjust it to -6 degrees) is perfectly OK (since my power supply won't crank it over very fast).

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Thursday, February 10th, 2011 AT 7:19 PM
  • Tiny
  • Wrenchtech
  • Expert
  • 19,583 posts

No, it's not going to harm it. You just won't get optimum performance out of the engine at that setting.

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Thursday, February 10th, 2011 AT 7:21 PM
  • Tiny
  • dnivens
  • Member

That is a great answer, excatly what I was asking, I want to thank you very much for your time. Since you seem to be very knowledgeble and able to discuss this issue can you comment about your experience? Why do you know so much? I have asked many mechanics this very question and none were able to give as good an answer as you just did!

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Thursday, February 10th, 2011 AT 7:37 PM
  • Tiny
  • Wrenchtech
  • Expert
  • 19,583 posts

LOL, I've been doing this for over 40 years and have been certified as a Mastertech for over 20 so I have a lot of experience in that era and had my share of muscle cars too.

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Thursday, February 10th, 2011 AT 7:42 PM
  • Tiny
  • dnivens
  • Member

Well I wish I could meet you, I have really enjoyed your perspective and value your advise. Thanks again for everything, and have a very day, or night, depending on your location. I'm in San Diego, CA, so it's 12-noon just now. Cheers.

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Thursday, February 10th, 2011 AT 7:59 PM

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