The Stovebolt Site Forums The Shop Area Engine Shop Ignition / timing questions

Good Morning,
I have a 55.2 3200 pickup with approximately 76,500 original miles. The only engine mod was to a Pertronix ignition system - with coil - about 5 years ago. No Problems at all since the install.
As spring is just around the corner, I thought I'd do a tune-up and installed new AC 44-5 plugs gapped to .040" and torqued to 25 ft-lbs. Changed the oil and air filter and started to check the ignition timing.
That's when I discoverd something that I can't remember the answer(s) to....
I disconnected the vacuum line at the carb base and blocked the connection at the carb. Hooked up my timing light and could see that the BB is just to the left of the pointer. About 1/2" to the left, The timing light does not have an "advance knob" and idle was at 475 RPM.
Is my timing advanced or retarded when the BB is to the left of the pointer? The Octane Selector was not at 0. It has always been around the middle of the scale.
To advance the timing do I turn the distributor clockwise as viewed from above or CCW?
The truck runs fine - always has. Maybe I should have just left it alone and plan to finish my tune-up when I get my memory back!
All help and or suggestions will be greatly appreciated.

I do not know what the Pertronix wants. I do not know if your timing light setup is accurate. I do not know if your vacuum advance is operating correctly. There are reasons your motor will run good at the settings you described due to wear and tear of components, Germany gas, altitude, etc.

For stock 1955.2 6 cyl motor and ignition, Shop manual says pointer on ball. Plugs at .035. Octane at zero.

If ball is left of pointer, you are at retarded position. Ball is at TDC. Timing should be set at TDC.

If you turn the distributor in the opposite direction of the rotor rotation, you will advance spark. A Chevy dizzy rotor rotates CW.

Don't take this the wrong way but, you are not on the ball and you are retarded.

Advance it up to TDC with a zero out on the octane selector, you may be impressed on how much better it runs. Are you running 10% Alcohol fuels over there?

To get you started on this endeavor, the timing should be set initially at tdc for no. 1. So one way to get this orchestrated is to first pull all the spark plugs. Then cover the no. 1 spark plug hole with your finger. Using a remote starter switch or have someone turn the motor over, just a quick click. When you feel the compression out of the number 1 plug hole, disconnect the battery, and carefully turn the motor clockwise using the fan belt (pulling the plugs makes this easier) or crawl under the car and remove the flywheel pan and use a flywheel turning tool. Move the motor clockwise until the bb that is embedded in the flywheel is right at the pointer in the bell housing window. The motor is now at tdc.

Now, install the plugs and plug wires. Trace the number one wire to the distributor and put a verticals chalk mark directly under the distributor cap tower for no. 1 cylinder. Next, wipe off the distributor pad on the block (firewall side of the distributor). Shine a light down and you should see a hash mark/groove on the pad. Loosen the bolt on the octane selector/hold down plate.

If you look at the photos, one of the plates is original equipment, had the A (advance) and the R (retard) 10 degrees at either end, and a 0 in the middle. The other is a delco Remy replacement and does not have the scale, just the 0 mark. Adjust your octane selector so the 0 mark on the plate lines up with the hash mark on the distributor pad. Tighten the bolt down.

Then remove the distributor cap and see where the rotor is pointing. It’s needs to be pointing to the chalk mark you made on the distributor body. If it’s not, loosen the screw on the clamp and rotate the distributor so the rotor is pointing at the chalk mark. Tighten the screw. You should be exactly on tdc. Now start the motor and double check with a timing light.

Most of these motors can take a few degrees of advance with today’s fuels. So if you want, and if you have a dial back timing light, you can add a little advance, 3-5 degrees. To advance, turn the distributor counter clock wise.

Just one way to approach it.

Have used the manual system for years, advance the timing until knocking is heard under low RPM load, back off slightly.

Ed

If the ball is left of the pointer the timing is advanced- - - - -not retarded. The spark plug is firing BEFORE the ball reaches the pointer- - - - -if that's retarded timing, somebody has repealed the laws of physics. With the vacuum line disconnected and the engine running at normal idle speed, set the timing with the ball and the pointer aligned by loosening the clamp screw and the "octane selector" set at the zero line. Then tighten the clamp, and if you absolutely must tinker with the timing out on the road, you can tweak things a little with the selector. It shouldn't be necessary to do that.

Listening for detonation on an uphill pull is a fool's mission- - - -by the time you hear the knock, you're WAY into engine-damaging over-advance. I had 20-something years of dyno run documentation to prove that until an idiot assistant principal decided to clean out some filing cabinets in the high school auto shop I ran for decades.
Jerry

You know I have tried to run my 235' at 0 TDC. and she just doesn't want to run very well there. I'm not sure if it is the Mellings hydraulic cam CCS-6 . 5 to 7 degreese advanced is where mine runs the best and no pinging under loads or going up hills.

There are a lot of things that affect your timing. The cam, compression, carb, and the fuel you use etc.
With today's fuel, that seems to light off slower, most engines run better with some additional advance over stock setting.
I have been setting ignition timing by advancing the timing until a slight ping is heard, and then back off slightly for 40 years without a problem.
You certainly do not want to run an engine for very long with it pinging or some damage can occur.
It is interesting to me though that my 1997 Blazer with 385,000 untouched miles on the engine has pinged on hard acceleration it's hole life, and that is computer controlled.

I believe most pointer/ball relationships are around 5 degrees advanced before TDC, but there are several possible bellhousing/flywheel combinations that might not make that an absolute fact. It's fairly simple to establish a true TDC reference by using a probe that screws into the #1 spark plug hole and stops the piston travel slightly before the piston reaches the top of the stroke, marking that position on the flywheel, and turning the engine backwards until the stop point is reached again. Mark that position, then measure halfway in between the two marks. That's an accurate top dead center position. Once true TDC is known, a delay-flash timing light can be used to evaluate initial timing, centrifugal, and vacuum advance. Any other timing method is either a WAG, a SWAG, or maybe a T-LAR!

Dave, your Blazer has a "detonation sensor"- - -basically a piezoelectric crystal that generates a voltage when it hears a ping, and sends a signal to the computer to retard the timing 3 degrees and listen for a ping again. It keeps doing that until the detonation goes away. It's doing that dance 10 times a second- - -much faster than a human ear can accomplish, and it's hard to reach the distributor housing to tinker with the timing from the driver's seat! The way to test the det sensor operation is to run the engine at a steady 2500 RPM and tap on the exhaust manifold with a hammer, and watch with a strobe light as the timing retards. I've seen a noisy valve lifter drop the timing back to 5 degrees AFTER TDC!
Jerry

Many Thanks to all who offered sugestions and help with ny timing questions! I think I've got everything sorted out for now.
My truck runs better than ever with the BB lined up with the pointer.
Left the plugs adjusted to +.040" because that is the recommendation of my Pertronix rep. I have Pertronix in all my older
vehicles and run them all with the extra .040" plug gap.
There is just one last thing that I can*t figure out. With my old ignition timing - which was incorrect - I had an engine noise above
2500 RPM that drove me crazy. It was a loud rattle and everything was OK as long as I kept the RPM's below 2000.
With the new (correct settings) the "rattle" noise is just about completely gone. When it's cold and the oil pressure hasn't gottten up to
where it should be there is a slight rumble that goes away as soon as the pressure is up. Drove a short stretch today at 3200 RPM - NO MORE RATTLE NOISE!
Was I hearing detonation with old retarded timing settings? BB left of the pointer in the window was definately retarded! Adjusted
the distributor to the correct BB/pointer setting by turning it CCW.
Checked my plugs after a short test drive earlier today - no problem and no sign of detonation. No residue on the plugs.
Compression is excellent and all cylinders are equal at approximately 145#'s. That's warm and WOT.
There's no smoke warm or cold.
Starts fine and idles just right at 475 RPM.
We have great gasoline over here and I run 95 octane with 10% Ethanol. There isn't any "regular" anymore and there is a no ethanol 95 octane high test and 105
octane super high test.
Any ideas?
Thanks again to all.

The .040 on the plugs is too much. The petronix is not a high performance ignition. Its just a different way of triggering the ignition. Instead of the opening and closing of the points to allow the coil to do its job, the petronix does the triggering. So there is no spark enhancement. These 235 motors can sometimes be sensitive to gap size given the position of the plug tip high up in the funky exhaust pocket. The wider gap just makes it harder to get the best spark. Try going back to .035.

.040 gap will work fine until you put significant miles on them. After 1-2 thousand miles you can expect some degradation of spark due to buildup of normal deposits on the plugs.
I agree with the .035 recommendation.
Carl

The secondary firing voltage difference a .005" change in plug gap might- - - -if the alignment of the planets is just right, and you use the proper voodoo spells from Marie LeBeau on a moonless night down on the bayou- - - -maybe could be measured on the firing line of an accurate oscilloscope. Of course, a tiny bit of difference in the mixture swirl pattern around the spark plug tip would probably make the same amount of voltage difference with identical plug gaps!
Jerry