timing marks

[cutlassguy]

i should have posted here in the first place lol i have a 87 cutlass with a 305 and i recently bought a timing light so im wondering if anyone knows what each point on the tab is (degrees) and which degree i should be timing it at? theres a small tube on the bottom of the tab...is that what the factory timed it with? why is it even there?

 

[cutlassguy]

heres a pic of the tab. whats the tube for???

 

[jmt455]

If you clean the timing tab, you will find that it has the retard/advance readings stamped next to the timing marks.
IIRC, it goes from about 12 degrees advanced to 4 degrees retarded.
I find that filling the indentations with white or silver paint makes it much easier to see what you're doing.

The tube is a provision for a magnetic timing probe.

 

[cutlassguy]

hmm itsa b*tch to get in there but im sure i could use a screw-driver and some sand paper or something. so based on what you see in the pic where is 0 degrees and what would you recommend i set mine at? is each point 2 degrees? also is the retarded part of the tab closer to the tube or the end? thanx man! (if your bored you can explain base timing in a lil more detail) im assuming its when the vehicle is idling but...

 

[jmt455]

This photo (from an old article in Rod & Custom magazine) shows the stock timing tab.

In the photo, the timing mark on the balancer is close to 0 degrees; you can see the "0" stamped into the timing tab at the bottom of the widest V notch. The outlined white arrow is pointing at the 6 degree BTDC mark.
Ignore the solid white arrow in the photo; it was just pointing at the timing tab in this magazine article.

You must follow the proper procedure to set the base timing.
The procedure is printed on the emissions control decal that is affixed to the top of the upper radiator cover/shroud.

To set the base timing, the engine must be at operating temperature (thermostat open, stable operating temp), the engine must be operating in closed loop mode and the air cleaner must be installed. The A/C should be turned off.

Block the drive wheels and set the E-brake.

To set the timing, disconnect the 4-wire EST (Electronic Spark Timing) connector from the distributor. Connect the timing light pick-up to #1 spark plug and set the timing as specified (I believe the recommended setting for your engine is 6 degrees BTDC @ 500RPM IN DRIVE...verify this on your Emissions decal)

You adjust the timing by slightly loosening the clamp at the base of the distributor and rotating the distributor to the correct position while the engine is running and you are watching your timing light flash at the timing tab.

ANY movement/rotation of the distributor affects the timing; make your adjustments in very small increments and check the timing light continuously. Shine your timing light directly on to the timing tab and watch the position of the timing mark on the balance relative to the timing marks on the timing tab.After adjusting the distributor to the proper timing, tighten the distributor hold-down clamp, then double-check to verify that the timing is exactly where you want it. Shut off the engine and re-connect the EST connector.

 

[cutlassguy]

THANK YOU that pic told me what i need to know, where zero is lol im not sure if it was you but someone told me they think this motor is timed at 0degrees am i correct to assume every inner outer point of the tab is 3 degrees more? if so i timed mine to 9 or the 3rd outer tab and it seems ok but not 100%. should i try going all the way back to 0 and see how it runs? its a far ways from where it now tho lol

 

[cutlassguy]

one more thing, whats a closed loop mode?

 

[jmt455]

Each leg of the notch is 2 degrees, so the outer points are 4, 8 and 12 degrees BTDC and 4 degrees ATDC.

Does your car still have the computer-controlled carb, EST and ECU? If you still have those engine control circuits and you didn't follow the proper service procedure, you didn't really set the base timing.

The specified base timing for my '83 is what I mentioned in my previous post. I am not certain what your timing is supposed to be. It is printed on the emission control label. What does that label say?

 

[jmt455]

one more thing, whats a closed loop mode?

I'm no expert, but here's how I understand it:
When the engine is at normal operating temperature and no fault codes/conditions are present that would prevent normal ECU operation, the engine control module has control of engine operating parameters (primarily air/fuel mixture and timing). The ECU uses the inputs from the various sensors (O2, engine coolant temp, knock, etc) and varies the operating parameters to optimize power/fuel economy/emissions. When the engine/ECU are running under these conditions, that it "closed loop mode".

 

[cutlassguy]

sounds like expert munbo jumbo to me lol the previous owner either romoved or painted EVERY stick that was on the car so as far as what the factory settings were...who knows. 8 degrees runs ok but im going to bring it back to 6. its almost there, just not quite. i still dont get why it would be set all the way back to zero. when i first put the light on it (running ok) the pulley mark was about a 1/4 inch completely about the tab...theres something to ponder