A while back replaced timing gears and chain. On old setup, truck was set to 12 BTDC. I believe someone said the old set was retarded 4 degrees, and to install new set "straight up" for better low end. My question, should I be at 8 BTDC now? I haven't fooled with truck really at all lately, am replacing gas tank and working on body problems before winter arrives, just want to be sure of timing too. Thanks for any thoughts, Blair

 

when you talk about 12 degrees BTDC, you're talking about ignition timing, or spark lead. When you talk about a timing chain being retarded, that is describing the relationship of the cam to the crank, aka cam timing. ignition timing and cam timing are related only by the fact that the distributor drives off the cam, so if you simply advance the cam by pysically rotating it, you will move the distributor timing. The way to set your cam timing where it should be (strait up, or 4 deg. advanced to favor low RPM Torque) is to get a non-OEM timing set. You probably won't be able to get this at most parts stores, but if it claims to be OEM on the box, then it will have a machined in 8 degree retard. Cloyes, Edelbrock, Comp, and Crane all make top-quality timing sets that have multiple keyways, in other words, you can choose where to set your timing based on notches on the cam sprocket. Most will have 3 keyways: 4 deg. advance, 0, and 4 retarded. You set your ignition timing based on the marks on the balancer, if your marks are accurate. I have found it mostly convenient to set the ignition timing by trial and error. Unbolt the dist. clamp (1/2" bolt), and rotate it clockwise until it pings, then back it CCW until it stops. Take it for a drive, and run it hard to make sure it won't ping. If it does, bring it back CCW until you have no pinging.

My recommended baselines: set the cam at 4 degrees advanced, and start out with 12 degress BTDC on the ignition timing, and then advance as much as you can without pinging. TK

'77 F100, 302 (the aftermarket Prodigy), C4
Cadet Second Lieutenant John F. Daly III
South Carolina Corps of Cadets, The Citadel
The TorqueKing

 

 

TK, I failed to mention I already installed the new set. Its a comp cams Magnum Double Roller set. I did notice the three notches, 4 advanced, 0, 4 retarded. I installed mine at zero, and then set the ignition timing at 12 BTDC. I had a pretty good ping, haven't worked on it yet. Should I pull the set and reinstall at 4 advanced? The ignition timing was set to 12 BTDC before. Someone mentioned cam timing in another post when I complained of having problems ironing out finalities. Needless to say, the truck runs strong, I have some ping, and a little hesitation. She also runs hot, but I figure if I reset ignition timing lower it should be better. What would you do? I really don't want to take her apart again, but I do have a long weekend, and I want it to be correct. Any thoughts would be welcome. Thanks Blair

 

I think that if you're set at 12 degrees initial, then your timing marks are probably off. rotate the distributor body CCW until the pinging stops. Detonation will cause extra stress in the motor, thus the overheating, and prolonged occurances are can be very damaging to your engine. You can try to line it up, but I just like to move the distributor until it works the best, tune it by ear. This never fails, even if the marks are off!

'77 F100, 302 (the aftermarket Prodigy), C4
Cadet Second Lieutenant John F. Daly III
South Carolina Corps of Cadets, The Citadel
The TorqueKing