Hello!I'm setting the timing of my 67 289 engine, for the first time since I bought the car 10,000 miles ago.

I marked the 6 degrees BTC mark (factory spec) on the harmonic balancer. I connected the timing light to the #1 plug wire, removed and plugged the vacuum advance hose. To my amazement the light indicated the current setting as about 20 deg BTC at idle. (Yes, I am looking at the mark at the correct angle.)

I twisted the distributor CCW to get 6 deg BTC. It it sitting at a noticeable angle now.

I checked mechanical advance (works), reconnected the vacuum, checked vacuum advance (seems to work, mark seems to move farther than without, I don't have a tach so this is an estimate).

Here's what's bugging me: that the timing could have been so incredibly far off initially and the car still ran fine before. I road tested the car today, it is running fine now also.

This makes me wonder if something is wacky and the numbers I am seeing are not accurate.

By the way, the engine was definitely worked on in the past by one or more shade-tree mechanics (not like today!!!) so I can't rule out anything.

Here are my theories:
1. the distributor is off one tooth, making the timing marks inaccurate
2. the harmonic balancer is not aligned right, making the timing marks inaccurate
3. nothing is wrong and I should start working on my next project.

If "nothing is wrong", here is my explanation. The base timing is set/measured at idle, but the pinging problems that typically occur with timing that is too far advanced are at high RPM. Therefore, if the combination of my mechanical + vacuum advance is lower than it can/should be, the fact that my base timing was too advanced was compensated by the lack of sufficient added advance from the other 2 components. Result: high-RPM advance still within normal range, no ping.

Any comments onmy logic?Anyideas what to do before I go through all the hassle of checking TDC and checking the distributor positioning? Or perhaps find a way to check vacuum advance against spec? Thanks in advance!

 

Hiya,

1. the distributor is off one tooth, making the timing marks inaccurate
has not any affect. you can pull the thing put it another tooth off but you will still be able to time this properly, but the thing will be sitting more and more awkward (at angle as you say)

2. the harmonic balancer is not aligned right, making the timing marks inaccurate
that could well be possible. the balancers are known to slip over time. So I'd recommend as a first check to verify TDC matches what your balancer says.

the factory specs are somesimes 6, sometimes 8 degrees (is it a V8 nor an I6?). But most V8s run better when set at 10-12 degrees.
Full advance (at 2500-3000) should be 35degrees max (ignore and plug vac advance here). I know you have no revcounter, but you might want that information in the future

To test your vacuum advance simply plug a hose on it and suck at the other end. When you do that you should feel it working against a spring and if you block the hose (with your tongue) it should keep the vacuum.
In any case I don't think the vacuum advance can have such an effect as you dfescribe it so check on that last.

Further if your distributor has points check them first (adjust gap/dwell). As when they're misadusted the timing will off as well.
(maybe they had it set at 12degrees and the gap got bigger causing it to be 20 now)

As car runs nice before and after. you should feel a difference when you change the idle timing by as much as 14 degrees :-)

when the idle advance is too far advanced you feel that when starting the car as well. It causes stress on the starter so it seems like the battery is half dead. (whop - whop -whop instead of whopwhopwhop sound when starting)

To check if TDC matches with balancer an inaccurate way but for checking to see if it's off by 15 degrees is:
pull #1 spark plug
turn the engine to where you have TDC on balancer
stick a welding wire or any wire into the plughole so you touch the top of the piston and have someone slowly turning the engine back and forth MANUALLY (not using the starter or some idea like that). Make sure to have some kind of a bent at the end of the wire where you hold it so you can't accidentally drop it in there. I think you get the idea.

Ohh ... and what I've seen before is that the timing light has an advance dial as well. make sure that is set to 0 when you have your mark at 8 or 6. as well make sure your mark is 6 degrees Before TDC, not after!. just doublecheck)

 

is it points or electronic? if its electronic you may have the pickup wires crossed.

 

Thanks for the suggestions! I will be taking a look at all that this weekend or next.
(By the way I do have a Pertronix instead of points, but I was pretty careful installing it, I will double-check.)
(And the timing light is totally low-end, no dials to mess up!)
Cheers