Question about stabbing a distributor

[Ohio Ken]

Hello
I would like your input on this subject
1st let's say you had a totally stock 351w (mine is not but for sake of a baseline)
It would call for base idle timing of 10 degrees btdc.
I have read many threads that if you are installing a distributor you would stab it at 0 degree tdc, where as others say you would want to stab it at 10 degrees btdc. It makes sense that stabbing at 10 degrees btdc would make it easier to start the car before fine tuning with a timing light.
However, the part that confuses me is as follows:

If you stab at 0 degrees tdc and rotor is to point to #1 terminal, it would make sense that you would then advance to the 10 degree mark under a timing light.

However, if you stab it at 10 degrees btdc and also point the rotor to the #1 terminal, would this not show as 20 degrees btdc using the light?

The reason I ask, is I did stab mine at 10 degrees btdc, but under the light it shows 20 degrees. If I turn the dizzy to 10 degrees under the light, the engine runs way retarded, and runs very hot, and hard to turn over when hot, and when cold turns over fine but doesn't want to fire.

The way I figure it, if you stab it at any degree advance of 0 degrees, the timing light would not read accurate against the timing slashes on the balancer..

Edited: I was wrong in my assumption, it turns out that the extra 10* was coming from my mechanical advance, thus giving me 20* initial and 34*!at 3000rmp, thanks to all for sharing your knowledge!
Thanks Ken

[olddog]

The timing light flashes when the plug wire it is connected to fires. Your eyes see the crank shaft mark, when it flashes. Where the engine was, when the distributor was inserted, has absolutely nothing to do with the accuracy of the timing light.

If forger the number of teeth on the distributor gear, but you're just trying to get the right tooth lined up. All you can do is move the distributor one tooth +/- at a time. You cannot align it any finer than one tooth. That is why you rotate the distributor with a light. Frankly rotating the engine 10 deg doesn't amount to a hill a beans.

What is most important is that number 1 is on the compression stroke when you put the distributor in, because if it is not you will be 180 degrees out of time.

If this is a fuel injected engine, which position in the distributor cap you choose to put #1 cylinder in matters! On a fuel injected engine, you have to set the distributor up correctly because it also controls when the injectors fire.

[bingo2]

The distributor turns at one half the speed of the crankshaft; 10 degrees at the distributor would equal 20 degrees on the balancer.

[Ohio Ken]

Originally Posted by olddog

The timing light flashes when the plug wire it is connected to fires. Your eyes see the crank shaft mark, when it flashes. Where the engine was, when the distributor was inserted, has absolutely nothing to do with the accuracy of the timing light.

If forger the number of teeth on the distributor gear, but you're just trying to get the right tooth lined up. All you can do is move the distributor one tooth +/- at a time. You cannot align it any finer than one tooth. That is why you rotate the distributor with a light. Frankly rotating the engine 10 deg doesn't amount to a hill a beans.

What is most important is that number 1 is on the compression stroke when you put the distributor in, because if it is not you will be 180 degrees out of time.

If this is a fuel injected engine, which position in the distributor cap you choose to put #1 cylinder in matters! On a fuel injected engine, you have to set the distributor up correctly because it also controls when the injectors fire.

To clarify, I inserted the distributor with the harmonic balancer set at 10 degrees btdc, while distributor rotor was lined up with #1 plug wire. Then under timing light it shows 20 degrees btdc on the timing mark. It is a carbureted car with a mechanical advance (no computer). If I leave the light set to 20 degrees, then throttle the rpm's to 3000, the timing advances to about 34 to 36 and seems to run strong at high and low rpm.
But, if it use the light and turn distributor to light at 10 degrees at idle, it runs hot and doesn't want to restart.
This seems to indicate that wherever your stab the dizzy, under the light would be twice that amount.
Example
Stabbed at 0 , 0 x2=0
Stabbed at 6, 6x2= 12
Stabbed at 10, 10x2=20
Does that make sense?

[Ohio Ken]

Originally Posted by bingo2

The distributor turns at one half the speed of the crankshaft; 10 degrees at the distributor would equal 20 degrees on the balancer.

So that would amount to stabbing the distributor with the harmonic balancer lined up with 10, would amount to 20 degrees using the light? If so that makes reasonable sense to me.
I know that it is important to stay around 34 to 38 at over 2500rmp. Which in my case, under the light at idle 20 and under revs is close to 36.

[Gaz64]

If the distributor is static timed at 10BTDC on the balancer, it should show up as 10BTDC on a timing light.

Ignition timing is always quoted in crankshaft degrees. Distributor degrees is half, but irrelevant.

What timing light are you using?

What camshaft is in the engine?

By the sound of it, you have 16 degrees of mechanical advance, what distributor is this?

[Ohio Ken]

Originally Posted by Gaz64

If the distributor is static timed at 10BTDC on the balancer, it should show up as 10BTDC on a timing light.

Ignition timing is always quoted in crankshaft degrees. Distributor degrees is half, but irrelevant.

What timing light are you using?

What camshaft is in the engine?

By the sound of it, you have 16 degrees of mechanical advance, what distributor is this?

Well I guess that blows my theory for being at 20 degrees

Using an older Sun timing light dial less
Bought car used so I do not know cam, but it does not sound real Lopey
Dist is Mallory Unlite for 351w. (Note, inset says it has 24 degree advance) however like I said at base of 20, fully advanced I am reading 34-36.
Windsor has alum SVO heads with rollers.
Only other notable issue, is my manifold vacuum is low at idle at approx 10". If I set timing at 10 degrees, vac drops to about 7"

[kiwi408]

Check and make sure TDC on no. 1 is 0 degrees on balancer.Just a thought.

[Dwight]

I always find top dead center on number one cylinder and move the timing marker to "O" on the damper.

If someone installed the timing marker, do you know that it is correct???? I think this is the one thing most guys miss on setting their timing.

Next I install the distributor with the number one plug in a convenient location. I make sure I can turn the distributor clockwise and counterclockwise, to adjust the timing. I install the dist. and line up the rotor with the number one plug.

Now with the timing light hooked up I start the motor and adjust the distributor till I have my base timing (10 degrees) lined up on the timing mark / damper.

If you have vacuum advance, you need to disconnect it and plug the hose. Vacuum will give you 20 degrees on top of the base timing.

If you have mechanical advance, (it should give you 20 degrees on top of the base) just adjust the distributor for total timing at what every rpm you want all your timing to come it. Say 34 degrees at 3,000 rpms.

Then there are springs and bushing in the distributor to fine tune your timing.

Dwight

[ame]https://www.youtube.com/watch?v=UYGU7mTwsZc[/ame]

Set your timing - for more performance!

I would buy a new timing light

[Ohio Ken]

Originally Posted by kiwi408

Check and make sure TDC on no. 1 is 0 degrees on balancer.Just a thought.

That is my point! TDC it does not point to #1 because it was installed at 10 degrees btdc pointing at number one.

That's what led me to believe that 20 degrees on the light is 10 degrees with the static drop in timing.

[Ohio Ken]

The only other possibility would be that the weights on the mechanical advance, are advancing it to 20 degrees when engine is running with timing light. I am doing this at 850 rpm. On a vacuum advance you plug off the vacuum line to test. But mine is mechanical.

[Ohio Ken]

[quote=Dwight;1342518]I always find top dead center on number one cylinder and move the timing marker to "O" on the damper.

If someone installed the timing marker, do you know that it is correct???? I think this is the one thing most guys miss on setting their timing.

Next I install the distributor with the number one plug in a convenient location. I make sure I can turn the distributor clockwise and counterclockwise, to adjust the timing. I install the dist. and line up the rotor with the number one plug.

Now with the timing light hooked up I start the motor and adjust the distributor till I have my base timing (10 degrees) lined up on the timing mark / damper.

If you have vacuum advance, you need to disconnect it and plug the hose. Vacuum will give you 20 degrees on top of the base timing.

If you have mechanical advance, (it should give you 20 degrees on top of the base) just adjust the distributor for total timing at what every rpm you want all your timing to come it. Say 34 degrees at 3,000 rpms.

Then there are springs and bushing in the distributor to fine tune your timing.

Dwight

thanks Dwight
Being that it is a mechanical advance, it must be affecting my idle timing . As I said in first post. I did verify that at full advance at 3000RPM is around 34. And she starts great and revs great. So I should be good to go. I just didn't understand why I am pointing at 20 (makes sense that the mechanical advance may be why.
Thanks to all for your input
Ken

[olddog]

No vacuum advance will make your engine do exactly what you describe if you set it at 10 BTDC. It needs the vacuum advance to run properly at anything other than WOT. There will be people who disagree. Racers don't want vacuum because it is one less variable, and they only intend to run the engine flat out. People think it's better cause racers do it. They are wrong!

Bottom line:
Watch the timing as you rev the engine and find out where maximum mechanical is at. Then set the timing to 35 give or take when the mechanical is fully advanced. Then see what you have at idle. My guess is that it will be somewhere approaching 20. That is a typical trick to try to get some reasonable drive-ability on the street without vacuum advance. It is critical that the timing be right at full throttle, because that is when the engine can be destroyed if you get it wrong. The best way to find out what your engine needs is to run it on a dyno.

If you want it to run the best it can on the street, put a vacuum advance distributor in it.

[olddog]

Originally Posted by Ohio Ken

Being that it is a mechanical advance, it must be affecting my idle timing . As I said in first post. I did verify that at full advance at 3000RPM is around 34. And she starts great and revs great. So I should be good to go. I just didn't understand why I am pointing at 20 (makes sense that the mechanical advance may be why.
Thanks to all for your input
Ken

On a typical vacuum advance set up you set the initial at 10, with vacuum disconnected. The vacuum pulls in ~15-20 deg. The mechanical pulls in ~20-25 deg. At WOT the vacuum does nothing and the mechanical controls the WOT timing. At light loads, the vacuum pulls in the extra timing needed. With the vacuum connected (before the ported vacuum abomination to meet emissions) 25-30 deg at idle was typically what the engine needed.

A street engine will run like crap, if you set initial timing at 10, with no vacuum advance. So what they did was set the initial at 20. Then they set the mechanical to advance 14. 20+14=34. This is robbing Peter to pay Paul, but it half ass works. The problem is if you open the throttle below ~2000 rpm you will have too much timing, and the engine may well go into detonation, destroying it. So do not go WOT at low rpm with this distributor! Additionally you do not have enough timing at light loads. Your engine runs hotter, makes less power, and wastes fuel. The emissions suck, too. So you have an engine that only runs well at WOT and higher rpms. Everyplace else is a half ass compromise, but it's cool cause racers do it!

[Gaz64]

All very good info lads.

As others have pointed out the OP needs to check the balancer ring has not shifted by verifying TRUE TDC.

[Ohio Ken]

Old dog
Your explanation makes sense. I will look into a vacuum advance dist for my next set of upgrades. Meanwhile, it looks like I am dialed in pretty good. I bought this used and only had the distributor out to replace the intake gaskets.
Spring is coming so she will be road tested soon. Thanks
Ken

[Gaz64]

Originally Posted by Gaz64

All very good info lads.

As others have pointed out the OP needs to check the balancer ring has not shifted by verifying TRUE TDC.

Ken, have you verified TRUE TDC using the positive stop method?

[Ohio Ken]

Originally Posted by Gaz64

Ken, have you verified TRUE TDC using the positive stop method?

Yes pointer and balancer show 0 when I put a rod in spark plug #1 with piston at highest point.
Everything looks right as I have now verified the following.

Dropped dist right on 10*btdc
Mallory mech advance dist has 24* max advance
At 850 rpm times at 20* and at 3000rpm times at 34* so that is 24* plus 10*
I don't think I can get better than that, except for adjusting the advance curve. But I am not racing, just touring the country side with an occasional hard rip through the gears.

In the end, I didn't take into account that the mechanical advance, was giving me 10* extra advance at idle. I bought the car last spring and it ran fine all summer. I never checked the timing until I had to pull the dist to replace intake gaskets
So in my opinion mystery is solved thanks to every one here!
Thanks to all!
Ken

[Gaz64]

Ken,

Seems a little odd that your distributor is supplying 10 degrees under 850 rpm, and yet doesn't reach max until 3000 rpm.

I'd say either a spring is missing/not fitted, or one is broken.
It may have given the result the previous owner wanted, and if you are happy with how it is, that's all that matters.

So in the end, you have 10 BTDC cranking, 20BTDC at idle and 34BTDC at 3000 rpm. If the timing is steady, you have the best of all worlds, low timing to allow easy hot starts, and enough for a quality idle.

http://i155.photobucket.com/albums/s...llory-2010.jpg

[Ohio Ken]

Originally Posted by Gaz64

Ken,

Seems a little odd that your distributor is supplying 10 degrees under 850 rpm, and yet doesn't reach max until 3000 rpm.

I'd say either a spring is missing/not fitted, or one is broken.
It may have given the result the previous owner wanted, and if you are happy with how it is, that's all that matters.

So in the end, you have 10 BTDC cranking, 20BTDC at idle and 34BTDC at 3000 rpm. If the timing is steady, you have the best of all worlds, low timing to allow easy hot starts, and enough for a quality idle.

http://i155.photobucket.com/albums/s...llory-2010.jpg

To clarify it it does not Take until 3000 rpm to reach 34*. It simply does not exceed 34*. As you rev it up it gradually advances . I did not pay particular attention to when it reaches 34*, but I noticed it advancing along with the revs.