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.
Are you trying to disprove years of engineering? The fuel needs time to combust to give maximum piston downforce.
February, 10, 2011 AT 6:31 PM
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.
February, 10, 2011 AT 6:34 PM
If you're having trouble cranking at 6deg BTC then you need a new battery. That engine has a high compression ratio.
February, 10, 2011 AT 6:52 PM
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.
February, 10, 2011 AT 6:58 PM
0 deg will make it crank easier, not necessarily start faster, but the power loss will be considerable once it's running.
February, 10, 2011 AT 7:19 PM
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).
February, 10, 2011 AT 7:21 PM
No, it's not going to harm it. You just won't get optimum performance out of the engine at that setting.
February, 10, 2011 AT 7:37 PM
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!
February, 10, 2011 AT 7:42 PM
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.
February, 10, 2011 AT 7:59 PM
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.