Join Date: Nov 2000
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Re: ?\'s about Setting Timing on the ole\' 4.2
In the end you are trying to acheive the best performance you can get, without getting any knock or ping. Consider the factory specs as a starting point. Take it for a drive, fully warmed up. In high gear, so it's under some load, explore all throttle positions and rpms. If there is no ping, advance the distributor a couple of degrees. Repeat road test. If it pings, back it off a couple. If it doesn't, add 2 more and road test again. Repeat till you find light pinging, and back it off 2 degrees until you don't get any more ping under any condition. As your engine wears ( and fuel quality varies), so will the timing change from factory spec. If you set your timing by road testing, you will know you have the optimum total advance and possibly better performance.
One caveat, make sure you know what ping or knock sounds like. It's usually a metalic ping, like marbles or steel shot dropped in a tin can. Light hail on a tin roof? Muffled by all the road noise, etc.
The rpm issue for setting initial timing is critical, as the mechanical advance will begin at some rpm. You want to set your timing at a low enough rpm that no mechanical advance has begun. Watch the timing marks with a timing light at low rpms and see where it starts to advance. Make sure you are no setting the initial timing without any mechanical advance having already begun, or else your total advance will be less than you think and performance will suffer.