Spark issues

[Marc]

...In a nutshell, point light at TDC mark on engine case...move distributor until timing light shows the 27.5 - 32 range For svda...

On the ACVW the reference point is the parting line between the case halves at 12:00. Few stock pulleys have a V-notch for TDC, but most of the later ones have a dimple on the rearmost rim. 27.5 to 32.5° is the normal range for the maximum timing lead on an SVDA with the vacuum-advance disabled.

A "standard" strobe light flashes at the moment that the sparkplug whose lead its pickup probe is attached to, so the pulley needs to have markings which cover the range of the area of interest. Fancier lights (the digital one you have coming is almost certainly one of those) have an internal electronic delay circuit which can be adjusted to alter when the flash occurs so that you can "dial in" the timing represented by the TDC mark on the pulley. With this type, you might set the light to "30" and then twist the distributor until the TDC mark is at 12:00 in order to set the timing to 30° BTDC.
Your pulley most likely has a 7.5° BTDC mark; you would therefore set the light to 22.5° in order to use that mark, in order to end up with 30° total. If the pulley had only a 5° ATDC mark, you'd have to adjust the light to 35 in order to use it when when setting the timing to 30°. Capiche?

[56rag1914cc]

Capiche!

[helowrench]

I have the old non adjusting strobe light, hence my instructions for the different markings.

Then again, I bought it before my oldest son was born, and he is outta college now.......

[Marc]

I have the old non adjusting strobe light.....

Could be you're better off - the "dial-back" type aren't always as accurate as one would hope for (I always double-check with the dial set to zero).

The timing mark(s) on various stock crank pulleys can signify different settings, so you can get messed up if someone's replaced the pulley with a different one at some time in the last 40+ years. Also, you may sometimes encounter one that someone's filed their own notches into which can confuse things.
The original pulley for a `72 went with the "DVDA" distributor which used initial timing of 5° AFTER TDC at idle - the one notch represents 5°ATDC. Look on the other rim of the pulley for a small "dent" about ½" clockwise from the notch - that's TDC. If the dent is ~⅝" CCW from the notch, the notch means 7.5°BTDC because the pulley was meant for use with an "SVDA" as used on most 1974s. If it's one of several possible earlier pulleys with no dent, the notch(es) can have other meanings - for example, if there are two notches very close together they are 7.5 & 10° BTDC.
Maximum advance is supposed to occur by 2500 RPM on the 0 231 178 009 distributor (going to ~3000 assures that the advance is "all in" before you make your adjustment).
The objective is to end up with 30-32° BTDC total timing at max advance - the engine can tolerate more at higher RPM, but that's the max that's considered "safe" under full load at ~2500 so you don't want to exceed it. What that will leave you with at idle can vary substantially from one distributor to the next, but ~12° should be about the max at idle; if you've got one that only has an 18° wide curve, you'll want it to span 12 to 30°...if you're lucky enough to have one with, say, a 23° curve you might set it to span 8 to 31°.
The accuracy of the dial-back timing lights should never be taken for granted - even high-priced ones can be off above 2000 RPM or so, and the cheapies aren't trustworthy at even lower speeds. They rely upon an electronic "delay line" which is sensitive to frequency (RPM). It's a nifty feature which makes it easier to check the action of the distributor's advance mechanism(s) but the accuracy at a given RPM needs to be verified before you can trust it. You're far better off making your own timing mark for 30°BTDC and leaving the knob on the strobe at "0". Once you've set the timing that way, you can recheck using the knob - but don't be surprised if the reading is a couple of degrees off of what you expect it to be. Some high-performance ignition systems (MSD, for one) don't play well with a dial-back strobe, either.

Measure the pulley circumference (distance around outer edge) with a tape measure. This is 360 degrees. Since 30 * 12 = 360, if you divide the circumference by 12 you will have the measurement for 30 degrees. Make a mark that distance to the right of TDC (0).
If you divide the circumference by 360 you have the distance per degree.
This method can be used on any engine....

When in doubt about a pulley's markings you can pull #1 or #3 sparkplug and probe the top of the piston while you "rock" the crank back & forth in the vicinity of TDC. A long soda straw is an effective, safe tool to use for the job. There's a more precise "positive stop" method which uses a sparkplug base with a threaded probe in it but IMO that's overkill when all you're trying to do is identify which stock pulley you have.

http://www.msdignition.com/forum/showthread.php?t=14309

Another way of verifying where the pulley's TDC mark is: remove the pulley nut/washer and rotate the crank until the woodruff key is exactly at 9:00. You can also "feel" where it is by slowly rocking the crank back and forth - the piston motion is so slight around TDC that the ring drag ceases for a couple of degrees of crankshaft motion on either side.

[56rag1914cc]

Motor timed perfectly....just in time for the 4th of July weekend.....thanks for the help everyone

[56rag1914cc]

...In a nutshell, point light at TDC mark on engine case...move distributor until timing light shows the 27.5 - 32 range For svda...

On the ACVW the reference point is the parting line between the case halves at 12:00. Few stock pulleys have a V-notch for TDC, but most of the later ones have a dimple on the rearmost rim. 27.5 to 32.5° is the normal range for the maximum timing lead on an SVDA with the vacuum-advance disabled.

A "standard" strobe light flashes at the moment that the sparkplug whose lead its pickup probe is attached to, so the pulley needs to have markings which cover the range of the area of interest. Fancier lights (the digital one you have coming is almost certainly one of those) have an internal electronic delay circuit which can be adjusted to alter when the flash occurs so that you can "dial in" the timing represented by the TDC mark on the pulley. With this type, you might set the light to "30" and then twist the distributor until the TDC mark is at 12:00 in order to set the timing to 30° BTDC.
Your pulley most likely has a 7.5° BTDC mark; you would therefore set the light to 22.5° in order to use that mark, in order to end up with 30° total. If the pulley had only a 5° ATDC mark, you'd have to adjust the light to 35 in order to use it when when setting the timing to 30°. Capiche?

Ok, got my fancy timing gun...I was getting a lot of backfire so I decided to mess with it. I set to 22.5 and on my degree pully it went straight to 7.5 BTDC as I went higher in the numbers...up to 30 on the timing gun the numbers on the degree pulley were changing as well without me moving the distributor. Im confused, did the timing even change? Please forgive the noobiness to timing.

[56rag1914cc]

Ok, I re read your post Marc. I set digital timing gun to 22.5 after setting it to 22.5 i saw about 7.5 btdc at the 12 oclock position on pulley. I turned distributor until it was at TDC mark. Tightened up distributor.

[Marc]

Ok, I re read your post Marc. I set digital timing gun to 22.5 after setting it to 22.5 i saw about 7.5 btdc at the 12 oclock position on pulley. I turned distributor until it was at TDC mark. Tightened up distributor.

You didn't say at what RPM this was done - but assuming you were holding the revs up above the point of maximum centrifugal advance (>3800 RPM w/SVDA) and had the vacuum-advance hose disconnected, you've now succeeded in setting the centrifugal component of the timing to 22.5° total (wrong!)

What I said was to use the 7.5°BTDC mark with the light set to 22.5 in order to end up at 30°BTDC total. You simply add the setting on the light to the degrees represented by the timing mark you are using.

Your pulley most likely has a 7.5° BTDC mark; you would therefore set the light to 22.5° in order to use that mark, in order to end up with 30° total.... Capiche?

[56rag1914cc]

What I said was to use the 7.5°BTDC mark with the light set to 22.5 in order to end up at 30°BTDC total. You simply add the setting on the light to the degrees represented by the timing mark you are using.

Your pulley most likely has a 7.5° BTDC mark; you would therefore set the light to 22.5° in order to use that mark, in order to end up with 30° total.... Capiche?

Just when I think I understand this timing thing...jesus.

I was at idle when I set to 7.5. With this digital timing gun when enter 22.5 i instantly see 7.5 on the degree pulley at the case halves, I then turned distributor until I saw TDC.

So now I must rev engine 3800 and turn distributor until I see 30-32 BTDC ?

I dont know why this is confusing me so much.

[Marc]

I've known professional mechanics who experienced "brain fade" when using a dial-back timing light, don't feel bad. Simplest approach here, since you've got a 7.5°BTDC mark (and an SVDA, correct?) is to just leave the dial on zero and use that mark at ~875 RPM with the hose off; rotate the distributor until the 7.5 mark is at 12:00 and lock 'er down.

Ideally, you should not see the timing change when you reconnect the hose at idle.

If you want to see what your total advance is, rev the engine up past 3800 RPM and turn the dial until the TDC dimple is at 12:00...the dial setting will then indicate the total timing (expect around 42° for a typical SVDA).

[56rag1914cc]

I've known professional mechanics who experienced "brain fade" when using a dial-back timing light, don't feel bad. Simplest approach here, since you've got a 7.5°BTDC mark (and an SVDA, correct?) is to just leave the dial on zero and use that mark at ~875 RPM with the hose off; rotate the distributor until the 7.5 mark is at 12:00 and lock 'er down.

Ideally, you should not see the timing change when you reconnect the hose at idle.

If you want to see what your total advance is, rev the engine up past 3800 RPM and turn the dial until the TDC dimple is at 12:00...the dial setting will then indicate the total timing (expect around 42° for a typical SVDA).

I do have an svda, thanks for breaking it down for me. When i see 42 degrees would that be 42 btdc or atdc?

[Marc]

...I do have an svda, thanks for breaking it down for me. When i see 42 degrees would that be 42 btdc or atdc?

If you're illuminating the TDC mark with the strobe set to 42, that's 42° BEFORE TDC.

Alternatively, you could use the 7.5°BTDC mark with the dial set at 34.5 for the same result - they're just additive.

The strobe dial can only "do" advance degrees...say that the only mark you had on your pulley was 5°ATDC, you could use that if you simply added 5 to the dial setting. Set the dial to 47 and when the 5°ATDC mark is at 12:00, the timing's at 42° BTDC. Catching on yet? It's not as hard as subnet masks, just don't overthink it

[56rag1914cc]

...I do have an svda, thanks for breaking it down for me. When i see 42 degrees would that be 42 btdc or atdc?

If you're illuminating the TDC mark with the strobe set to 42, that's 42° BEFORE TDC.

Alternatively, you could use the 7.5°BTDC mark with the dial set at 34.5 for the same result - they're just additive.

The strobe dial can only "do" advance degrees...say that the only mark you had on your pulley was 5°ATDC, you could use that if you simply added 5 to the dial setting. Set the dial to 47 and when the 5°ATDC mark is at 12:00, the timing's at 42° BTDC. Catching on yet? It's not as hard as subnet masks, just don't overthink it

I can subnet all day! Just a little different with timing, the wrong timing will jack my motor up. Ill tackle again tomorrow and report results!

[56rag1914cc]

Engine timed with electronic gun! Thanks Marc