posted 09-22-2000 11:51 AM               

I have just rebuilt my 71 351c...KB hypereutetic 20 over pistons, double roller timing chain, Summit K5201 cam (218/228, 501 lift), rebuilt motorcraft distributer, ASF32 plugs, etc. we aligned the timing gear marks to 0/0 which is 4 degrees advanced relative to the way Ford originally did it (I heard they retarded it 4). I think this would change the relation of my damper timing marks, and thus when we put the distributer in with the the damper set to factory specs (6 btdc) the distributor is off. My problem is that I can only get my engine to run half decent with it now timed to 2 btdc and the vacuum advance plugged. Summit said my cam is 4 degrees advanced, is this in the machining or is it because they instruct you to put it in 0/0? I am concerned I may fail my yearly emissions test. any help greatly appreciated as you people know so much!!

posted 09-22-2000 01:04 PM               

Welcome to M&M! On your timing questions, I think you are confusing cam timing with ignition timing. If you didn't "degree the cam" you really don't know where the cam timing is set. But hopefully it's close enough. In any case it doesn't effect where tdc is on your damper as long as you used a straight (not offset) woodruff key between the crank and damper. The damper could be off, and the way to check that is with a t.d.c. indicator in cyl #1's spark plug hole. As long as your pointer is pointing to tdc when #1 is at tdc, you'll get accurate readings from the damper. Regardless of where the cam timing is set. Did this make sense? Let us know whether you're concern with ignition timing or cam timing. Thanks,

posted 09-22-2000 02:11 PM               

Just think of the crank as the boss. It controls the rods and pistons and their location during the engine's rotation. The cam is driven by the crank at 1/2 speed of the crank with your timing chain. The timing chain's sprocket controls the valve train's timing events. The distributor is driven by the cam and not the crank, but it's timing is infinately adjustable. If the cam timing is changed the distributor's rotor position will be slighly off, but you just turn the distributor to correct it, based on the crank's location (damper). The damper is two peices of steel connected with rubber. The outer part of the damper (with the timing marks) can slip out of the correct alignment with the center part of the damper (which is connected to the crank). This is why you should do a t.d.c. check. You can make a tdc stop, by breaking the ceramic out of an old spark plug and taping the center for a bolt. Inserted into the sparkplug hole you turn the engine by hand until the piston stops, mark the damper. The rotate the engine the other direction until it stops again, mark the damper again. Your t.d.c of #1 piston is the center point of the two marks. I'd do this first. As far as your timing curve you might try your old distributor, or compare the advance springs between the rebuilt distributor with the old one your curve is too fast. Good luck