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Two-timing mechanic?

Yesterday I decided to finally set the timing on my '84 Chevy C20’s 350 engine. It had been idling rough ever since I brought her up to Houston as my substitute vehicle. An accident left me car-less but it being my second vehicle I took my time with making repairs. That’s not to say I’ve not done anything; I’ve replaced an exhaust manifold, had the carburetor rebuilt, had the exhaust piping and muffler upgraded, changed the spark plug wires and spark plug themselves, replaced the power steering pump and lines, had the gearbox replaced, replaced fuel pump, air filter, and a host of other things.

But I finally got around to the timing yesterday. I warned up the engine, turned it off, found the mark, traced it with a white marker, hooked up the timing light and started her back up. I figured with the backfiring and exhaust problems she’d been giving me that I would need to advance the timing. When I shined the light I found my timing mark was advanced so far off the mark I couldn’t believe it. Then I noticed another mark that was at about 4 degrees ATDC. Two marks? Just to make sure I retarded the timing slightly to try and bring the mark I highlighted closer to range and the engine began to stall. So naturally I began to advance instead and bring the 2nd mark to the factory specs of 4 degrees BTDC. The engine sounded much better but I couldn’t get past 2 degrees ATDC. The vacuum advance hits the intake manifold and I can’t advance it further. I turned off the engine and took a look at the mark. It looks like someone made that mark with a hack saw. It doesn’t run across the entire harmonic balancer, just near the edge. To me it looks like whoever took this engine apart and put it back together didn’t align the #1 piston with the original timing mark at TDC. So they just sawed in a new mark at the new TDC location on the balancer. Thats my guess. How much work is involved in fixing this?

I would first set it at TDC one #1 CYL… Then see were the marks line up and check the rotor alinement. Also did you disconnect the vacuum line from the vacuum advance? Start there and then let us know what you find.

Its possible that someone had to replace the harmonic balancer and didn’t get the right one. Most people will tell you to determine true TDC by removing the #1 spark plug and poke something in the hole to determine when the piston is at TDC. I recommend that you remove two sparkplugs. If your firing order is 1-8-4-3-6-5-7-2, then remove #8 and #2. One of those will be going up (#8) and one going down (#2), but they will be at mid stroke which is where the most piston movement occurs per degree of rotation of the crankshaft. When you measure the exact same depth to piston top on both pistons, you are at TDC.

If your firing order is different, you still want the cylinder that fires just before and the one that fires just after the #1 cylinder

My best guess is someone in this trucks past, removed the distributor… When they re-installed it they, installed it one or two teeth off. Instead of pulling the dist again, they clocked the cap and retimed from there. Does the number one spark plug wire go to the #1 post on the cap?>?

gsragtop could well be right about the distributor being installed a tooth or two off and then the mechanic set the timing by “ear” and then made the extra mark on the harmonic balancer, or it could be the wrong harmonic balancer. Either way, the mystery mark has to be solved first and that means finding the true TDC.

keith & gsragtop make good points. I’ve come across this scenario before & it was because someone in the past removed the distributor to put in a new cam, but put the distributor back indexed differently with the cap than original. Anyway, to set base timing:

Get the #1 piston to TDC & the dist rotor pointing to the #1 dist cap electrode. If the electrode is not marked “1” then make sure the rotor is pointing to the electrode that has the #1 plug wire attached to it. Continue with proper cylinder numbering/firing order unless these items are already in order. Assume that Keith is right & the wrong harmonic balancer is on the vehicle. This situation ain’t kosher but you can get by by making your own timing marks. Start by getting the #1 cyl @ TDC & the dist rotor @ the #1 electrode as explained above.

Some timing scales are a scale mounted next to the balancer & there’s a groove cut on the balancer. We’ll call this scenario “A”.

Some scales are stamped right on the balancer & there is just a stationary reference pointer next to the balancer. (Scenario “B”)

Scenario"A", with a fixed timing light: Make your 1st mark on the extreme LH end of the scale & a 2nd mark on the balancer lined up with the 1st mark. Now, moving CW along the scale, make another mark on scale 4 degrees from the 1st mark on scale. When this 4 degree mark lines up with the sole mark on balancer–as you turn the dist–you’re at proper base timing.

Scenario “B”, again with fixed timing light: Find the scale on the balancer & using a ruler, measure & record the distance 4 degrees takes up. After getting the #1 cyl @ TDC & the dist rotor @ the #1 electrode as explained above, just make 1 mark on balancer lined up with the stationary pointer. Now, moving CW from mark on balancer, make a 2nd balancer mark at the distance 4 degrees takes up, which you’ve already recorded. This 2nd balancer mark is your 4 degrees BTDC mark.

Scenario “A” with a timing light w/an advance dial: After getting the #1 cyl @ TDC & the dist rotor @ the #1 electrode as explained above, make 2 marks lined up w/each other, one on balancer & one on scale. Now all you have to do to achieve base timing is set the dial for 4 degrees adv & line the 2 marks up as you turn the dist.

Scenario “B” with a timing light w/an advance dial: after getting the #1 cyl @ TDC & the dist rotor @ the #1 electrode as explained above, make a mark on balancer lined up with the stationary pointer. With timing light advance knob set to 4 degrees BTDC, when the mark lines up with stationary pointer, you’ll be at proper base timing.

Please post back & tell us how you made out. Seems no one ever does!

I’ll keep you guys posted, I gotta get out of the Houston area this weekend to get this done since it’s gonna be raining all weekend here. Thanks Karl, Keith, gsragtop and oldbodyman for the insight and detailed knowledge. Much appreciated and again, I’ll let y’all know.

The second grove in the pulley was to be used with a magnetic pick-up that is dropped into the holder seen near the ATDC area. The mag pick-up grove is usually wider than the timing light grove but only cut half way across the pulley.

All right, it’s fixed. The distributor and timing marks were off. I did the finger then screw driver in the number 1 spark plug hole method with my dad bumping the engine then he held the screw driver while I turned the crankshaft. I marked the new zero spot on the balancer and saw it was somewhat close to the second timing mark.

The distributor was the problem after that. I took it out and set it back making sure the rotor pointed to the one plug. Went to start it and nothing. Started advancing and nothing, retarding and nothing. I thought oh crap, I done screwed the whole firing order somehow. I double checked all the wires and everything was in firing order: 1,8,4,3,6,5,7 and 2. We held off till the next morning when my uncle came over to check it out. We started again from step one for TDC. Then he took the cap off the distributor, loosened the its clamp and lifted it and set it back in, making sure the rotor was pointing to the #1 plug also. He put everything back together again and noticed the wrong wire had been connected to the distributor. When he took the cap off he hadn’t pulled the wires out. When he put it on he saw I had the wrong wire in the ignition coil. There were two red wired in the distributor area and I didn’t notice which one I had unplugged. When I had put everything back together again I connected the wrong red wire to the ignition coil.

My uncle saw this and corrected it. After that we started her up and advanced the distributor by ear at first. When I connected the timing light the point I had marked as TDC was at about 4 degrees BTDC. We left it there and hooked up the vacuum advance. The difference was instant. Better idling, no more backfiring since, no more glowing exhaust manifold, and my overdrive doesn’t miss anymore. I MPG tested her between has gas stations on my way back to Houston and she did 16.3 mpg on overdrive which is awesome for this old '84 3/4 ton. Especially since the only major upgrade is the exhaust from the manifolds back. I want to thank everyone for their input. It saved me a trip to the mechanic and who knows how much on my wallet. Doing this with Family instead gave me peace of mind.