O Degree Timing Mark

[Zed Head]

The cam sprocket position won't affect the timing mark on the damper.  The damper mark is tied to the crankshaft.  But aligning the notch and groove should give a fair idea if the timing mark is even close to TDC.

 

You could also build a piston stop and determine where TDC really is, then make a new zero mark.  That would work for you since you have the dial-back light.

[siteunseen]

Ok. I never have been able to wrap my head around that whole mechanical/electrical timing thing. I can't make sense of it for some reason?

That sounds like a much better plan/idea.

Thank you ZedHead.

[240260280z]

Electrical timing has to do with when to ignite the fuel and air mixture relative to where the piston is in its rotation. You want to ignite at the right time so that the pressure wave from the explosion reaches the piston at the optimal time/location to give it a good and proper push (like pushing someone on a swing). If the ignition is too advanced, the explosion will reach and push the piston too early when it is rising. This would be like pushing some one on a swing as they come towards you.... very painful!   If the ignition is too retarded, the explosion will reach and push the piston too late when it has fallen too much. This would be like trying to push someone on a swing after they started to move away from you.  It is not efficient.

 

 

Mechanical timing has to do with the valves opening and closing  relative to where the piston is in its rotation.  It is the inhaling and exhaling but not the exploding. The cam and timing chain mechanically connect the pistons (via crank) to the valves.  If the valves open too early or too late, not enough air will be captured on the intake stroke, or the captured air will leak out on the compression stroke, or the exhaust will go back into the intake on the exhaust stroke, etc.

 

 

The two E & M do interact but are independent. For example,if the car was really out of tune and the electrical timing is too retarded, the explosion burn will continue out into the exhaust manifold as soon as the exhaust valve starts to open. If you ever see a car with glowing headers the ignition is very retarded, or the exhaust valves are opening  too early, or the valves are burned and not sealing.

[rossiz]

blue's example is spot-on. the thing that used to confuse me was how timing is measured.

 

electrical timing is when your spark happens in relation to the pistons - measured with a timing light.

your timing light fires off the ignition system (the pickup on the #1 plug wire), so it measures electrical timing relative to the crank position (the 0 mark on the pulley). the distributor (which fires the plugs) is run by a gear directly off of the crankshaft - no connection to the valve train. electrical timing is altered by the following actions:

• manual adjustment: loosen the mounting nut and twist the dizzy back and forth to advance/retard the entire timing curve
• mechanical advance: the plate inside the dizzy twists back and forth based on the speed of the engine (controlled by springs, which set the timing curve). the timing curve is the rate at which the mechanical advance is applied - at what rpm it starts, and at what rpm it maxes out.
• vacuum advance: the plate inside the dizzy twists back and forth based on throttle position and resultant vacuum (controlled by a diaphragm)

 

mechanical timing is the relationship of the valve train to the crank position and isn't measurable by your timing light. on our L6 engines, mechanical timing is altered by the relationship of the cam sprocket to the cam (the 3 positions on the sprocket and the V-notch). mechanical timing is measured with a degree wheel and a dial indicator which measures valve lift in relation to the crank position. much more complicated...

[Zed Head]

Dang.  I can see how it can be confusing.  Rossiz is using "mechanical" to describe cam shaft timing.  But many people use mechanical to mean centrifugal, or RPM-based, distributor timing.  I tend to interchange the words, even though, technically, the vacuum advance mechanism is also mechanical.  The three most descriptive common words would be cam-, vacuum-, and centrifugal-, timing (please nobody bring up the centripetal v. centrifugal thing).

 

Regardless, all of the "timing" events are described in relation to the piston's position in the cylinder, which is described by degrees of crankshaft rotation before or after the very top (TDC) of the piston's travel in the bore.

 

I would do what you planned and see where the cam timing is.  It should be close to zero (within ~8 degrees, I think) with the sprocket and groove marks aligned.  If it's not, then your damper has slipped or some other weird thing is happening.

[siteunseen]

I've got the help of some good teachers.   

 

I just woke up and will reread when I'm home from work.

Thanks again,

Cliff. 

[SteveJ]

Cliff, come out my way and bring your new toy. I'll help you figure out how to use it.

[FastWoman]

I don't know what this means but I went for a few test drives this morning and after finding the sweet spot on the dizzy came home and hooked the light. Up button up up up until the pointer matched the zero notch on the pulley. 34 was where it matched up at 700 rpms with the vacuum plugged off and taped over.

 

Maybe your breaker plate is sticking?  It's a known issue/weakness with S30 distributors.  Pull off your distributor cap and rotor, and rotate the breaker plate assembly with your fingers.  It should turn smoothly, under spring tension.

[madkaw]

Don't think it would run if it was really 34 degrees. If it did- it would run ON

something's not right with the marks. Correct pulley? Slipped pulley?

[Zed Head]

Seems like it would knock severely with 34 degrees at low RPM.  Any gas at all while driving and it should be a knockarama.

[siteunseen]

I did a quick "non-alcoholic" test. Same results, 34 degrees at 900 rpm 50 at 2500 rpm. Golf tee in the vacuum line and tape over the vacuum advance dashpot nipple. Shifted from 2nd to 3rd at 6500 rpm. Runs like deer, quick!

I'll do more testing when it runs bad but I'm going to drive the tires off like it is.

And the light was on 6 cylinders, not 2 or 4 or 8 or 12.

I think the mechanical timing is off from chain stretch or the pulley has slipped.

Also checked breaker plates. It's a reman so could've been that but no.

It pulls good. Thats all I care about right now. Rebuilding soon and it'll be right then. Enjoying for now.

Thanks for the help,

Cliff

[siteunseen]

OK, problem has been found, SEVERELY RETARDED.  I knew the moment I saw this car we were meant to be together.  We have a lot in common.  The vin number starts with my birth year and it's just like a model car I've had since I was a kid.  Oh and it's retarded too. 

 

I'll put it back together tomorrow and do a commpression check to decide if moving the sprocket ahead to #3 will be good enough.  I'd just as soon pull the motor and rebuild it, reinstall with a new clutch and a fifth gear.  The clutch is shot anyway and I don't want to drive to Memphis in 4th gear.  What do you all think?

Number 1 plug looks good,