Ignition Timing

[Jandrews]

Boy I sure hate to surface this topic again.

This morning, I was adjusting the breaker points in my 73RS spec engine, as I think they closed up a bit during a recent track event. I got the dwell angle to approximately 38 degrees or 63.5%, and figured I would check the timing since the two functions are closely related.

The timing was off a few degrees, so I slightly loosened the hold-down nut and began making a few adjusting motions back and forth. Suddently, the timing marks for TDC and 5ATDC disappeared, as did the ones for 30 and 35BTDC, and my digital timing light was indicating 60 degrees of advance.

I stopped to sit down and think about this for a minute. As far as I could determine, this occurence should be physically impossible without removing the distributor. The only thing I could think of was that maybe the distributor "jumped" time. I didn't know how that could happen, but I figured that 60 degrees was one sixth of a full revolution and I believe there are six teeth on the distributor drive gear, so that was the only thing that made sense.

I went ahead and brought the crankshaft pulley to TDC for #1, making sure the rotor was pointing at the number one spark plug wire and notch on the distributor housing. I then pulled the distributor and reinstalled in slightly adjusted positions, one tooth in either direction. No help.

I think I have a good grasp on how the entire ignition process works, and have removed and disassembled various components throughout the system for cleaning on multiple occasions. I just cannot figure out how this could happen, and now, how to get back to TDC timing. I have seen recommendations on other posts that "maybe the distributor is 180 degrees out", but I know this was not the case prior to removal, and I cannot imagine how the engine could run with that configuration.

It is possible that I need a new distributor, but I would think that if I reinstall the distributor with all the marks aligned and the rotor pointing at number one, I should be close enough to see the timing marks. Not the case, and I am still seeing 60 degrees of advance on my timing light.

I drove the car down the street and it has fair power, so I am really confused as to what could be happening.

Any thoughts would be appreciated.

JA

------------------
John
70/73 RS Spec Coupe

[911pcars]

A couple of thoughts:
Is the inductive timing light connector on No. 1 spark plug wire? If so, your digital timing light could be wacko.

What makes this a "digital" timing light? Does this allow you to measure timing advance?

Sherwood Lee
http://members.rennlist.org/911pcars

[Jandrews]

Good questions, Sherwood.

Yes, I double checked that it was on number one. Obviously, that could certainly cause some erroneous results if it were on the wrong wire.

Second, yes, the light is fairly new, American made, and not a cheapo. It has LED readouts for advance, dwell angle, volts and rpms.

Thanks,

JA

------------------
John
70/73 RS Spec Coupe

[911pcars]

John,
I assume the engine runs fine other than the timing issue, yes? Here's how you can verify if it's the timing light or something else. It's called "dead timing". Please excuse me if all this sounds too basic.

Disconnect no. 1 spark plug cable from the spark plug and position close to a ground (spark will jump here shortly). With the ign. ON, rotate engine (manually with wrench on crank pulley or w/trans. in gear and push car forward) until the timing mark comes around toward TDC (firing on No.1). Spark should jump to ground from disconnected plug wire. The instant this happens, notice the relationship between crank pulley and mark on crankcase. This is the timing for your engine and should coincide with what the timing light indicates. Basically, this is what the timing light does, but we're doing this in very slow motion. If the timing light indicates 60 degrees off, return it and get one that works correctly. Make sure the advance control knob is rotated all the way OFF.

BTW, you can work backwards and set the desired timing this way too. Position the crank pully at the desired mark before or after TDC (BTDC/ATDC), swith ign. ON, rotate distributor housing in a direction opposite rotor rotation until the points open (or other signal device works) and spark jumps from no. 1 cable to ground. Tighten distributor clamp.

Sherwood

[pjv911]

sounds possible that your light has a advance adjustment if its a high end digital model. If this is the case you may have the base setting set above 0 deg.
Another idea is check the timing on the family mini van with the same light.
One other possible reason is the inductive end is not closed and your spark plug wires are leaking through there insolation and giving a mixed signal.With this in mind see if the rpm reading on your digital t-light is fluctuating erratically.

------------------
69`lightweight
RS carrerra clone

[Early_S_Man]

John, I doubt that you need a new distributor ... maybe an older timing light without the advance feature can be borrowed or rented to confirm a malady in the electronics of your new one!

As for your distributor ... 'basic' timing can be done with a simple 12 Volt test lamp connected to 12 Volts at the fuse block and the distributor points lead to CDI/tach, & speed switch. All of the pertinent data for ignition test data on your engine is in the following thread:

http://www.pelicanparts.com/ultimate/Forum3/HTML/009677.html


------------------
Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler