|
|
Posted by David Sherman on Wednesday, June 11, 2008 at 11:43:26 :
Have you noticed the TM is confusing on setting the timing? In paragraph 2-20.a, it says "Under ideal conditions, the spark should occur at two degrees after top dead center... However, in extremely high or extremely low altitudes ignition timing may be change to occur as early as two degrees before top dead center or as late as six degrees after...", which tells me the normal setting at idle should be 2 degrees ATDC, which is the only engine I know of where the normal timing is retarded from TDC. The PIF agrees with the that. But then in 2-20.c, it says "make a narrow chalk mark 2 degrees before the DC mark on the fan drive pulley... Aim the timing light... The light should flash the instant the chalk mark is directly under the timing pointer", which tells me the timing should actually be 2 degrees BTDC. Also, due the centrifugal advance, at any sort of speed at all, it's firing about 5 degrees earlier.
So, two questions. What's really the best idle timing setting (no vacuum advance here), and at what RPM should the centrifugal advance work? The latter question is because my advance mechanism has two different size springs, and they seem a little sloppy. I guess it just doesn't seem right to me to set the timing retarded, especially since a flathead requires the combustion to go further to get from the plug to the cylinder. Would there be anything wrong with how I've done it on other vehicles -- advance it until it just starts to knock when lugged down, and then back off a little bit?
Follow Ups: