Quote:
Originally Posted by Clarke
First of all, this is not my area of expertise, so I appreciate your feedback. Given the subject of this thread, I'd like to explain how I arrived at 16 degrees (in lieu of the factory spec of 7.5 degrees).
Many old timers I've spoken to over the years say they never use a timing light; they adjust the distributor (advancing the timing) until the motor starts to run rough (detonation), then back it off a little. (What's a little? I don't know? LOL!) I tried that with my 305 and it started running rough at 20 degrees, so I backed if off 4 degrees.
Correct me if I'm wrong, the engine achieves the greatest amount of power when the combustion process happens when the piston is at it's highest position (least amount of open area), just as the piston is starting on it's "down stroke". This is why when you advance the timing from factory spec, the engine idle increases. As you are reducing the amount of open area during the combustion process, the increased energy pushes the piston down, resulting in more power.
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First, the "old" method of adjusting until it runs good is, in my opinion, only valid for engines of our era. Once computers got involved with the engines, you lost control of the timing. What this method does do is take wear into consideration. As the timing chain stretches the timing does change.
Second, While you are correct, the most power should be gathered at top dead center, you have adjusted the firing to be 16 degrees before top dead center, meaning it is firing well before TDC. According to the information on Jolly's site, 450 RPM idle and 5 degrees BTC.
Is your engine old or rebuilt with all new innards? If all new then with that much advance (triple stock) I would suggest something is terribly wrong. If it is an old, worn, engine then it is possible that the wear is the reason for the advanced timing. Which suggests, to me, a rebuild will be in your future.
One thing people do need to do when working on an older engine is to not rely on the tools (timing light) but rather on what the engine is telling you. You can time it all day with the light, and it will run rough if it is really worn. I have seen "kids" get frustrated trying to work on non-computer all manual older systems. They can't even figure out how to set the points (which could also affect the timing).
Having said all that...
If it works for you at 16BTC, then that is good for you. You could be compensating for wear, or have something else going on. If you are confident that everything else is as it should be, then enjoy your truck.