5.7 Thunderbolt IV Timing

Brentathon · Jul 18, 2012

I want to check timing.
Was there a revision to the timing advance curve in the Service Manual #15?
That curve shows the advance starting as slow as the 400-600 rpm range (see attached)....

If the "base timing" is 8 deg BTDC, the curve shows I should add 5 degrees to that (i.e. 13 total) if checking at 700 rpm.

Don S · Jul 18, 2012

Re: 5.7 Thunderbolt IV Timing

I think you are trying to use the curve as a way to set your timing, and that is not how you do it.
What you do, is set your timing per specs, write down what you have and at what rpm you set the timing at.(usually around 650 to 700 rpm) then bring the rpm up to 2400 rpm and see what the advance is.
Then compare your numbers with the chart. You can also plot other points at different rpms, but you have to know your rpm exactly and your timing exactly.

Eric 3.7LX Alpha 1 · Jul 18, 2012

Re: 5.7 Thunderbolt IV Timing

you need a timing light that reads advance. Newer ones are digital today. I have an older Craftsman with a knob on it.

Basically, with the advance light, You keep the light flashing at the zero mark (TDC) and rotate the knob until at zero?. The knob will display the total timing at the given RPM you are at.

Can use the advance light for timing at idle as well, same way or keep the dial at 0? and see where the light aligns with what mark on the tab.

Brentathon · Jul 18, 2012

Re: 5.7 Thunderbolt IV Timing

Thanks for replies.
But, I'm still confused, maybe even moreso. First, I only have a normal/basic light, with NO advance reading/dial/gauge, etc.

So, you're saying I should confirm/set the timing at 700 rpm to 8 degrees BTDC?
I don't see how I can check timing at 2400rpm, the advance would be 8 + 22 = 30, no? The timing tab doesn't have marks that go that high?
Also, why do they show advance down in the low rpm range, if you're not supposed to account for that?

Don S · Jul 18, 2012

Re: 5.7 Thunderbolt IV Timing

I don't see how I can check timing at 2400rpm, the advance would be 8 + 22 = 30, no? The timing tab doesn't have marks that go that high?

That is exactly right, and the advance does go that high. Advance timing lights make it easy. You could also do the math with diameter and circumference into degrees and mark an 8? and 30? mark on your dampner. Then run your engine and see if your marks line up on the 0? mark on the timing tab.

Or just eyeball where the dampner mark goes and estimate how many degrees by looking at the tab. If you are WAY off, you need a new module or something.

Eric 3.7LX Alpha 1 · Jul 18, 2012

Re: 5.7 Thunderbolt IV Timing

If you want to check total timing/advance timing, you either need a damper with all degree marks like below or an advance timing light.

When you have a damper like below you only use 0?on the timing tab.

Brentathon · Jul 19, 2012

Re: 5.7 Thunderbolt IV Timing

Ok, back to the original question.
I'm mainly interested in checking/adjusting the timing, as it's set via distributor. I don't think I have any suspicion that the electronic advance is not functioning. Should I?
Therefore, when checking/adjusting the timing: Do I have to add the advance from the curve (corresponding to the rpm that I'm running at) to the 8 degree "initial timing"?
To rephrase/clarify: If I'm checking at 700rpm (idle), should the timing be 8 + 5 = 13 deg BTDC?

Scott Danforth · Jul 19, 2012

Re: 5.7 Thunderbolt IV Timing

always double check the total advance and a few points in between to be sure.

if you dont have a timing light with an advance knob, and you know your harmonic damper diameter, you can buy timing tape that will have marks all the way to 40 or 50 degrees advanced. this is similar to Don's mentioning about doing the math based on the diameter of the damper

http://www.summitracing.com/parts/MSD-8985/

they are available at most auto stores.

Brentathon · Jul 19, 2012

Re: 5.7 Thunderbolt IV Timing

Ok, but first I need the basic timing questions answered, to at least check what the distributor is set at.
If checking at 700 rpm, what should the timing be?

I just found page 12 of Service Bulletin 95-11 (attached); Does that new chart tell me that I don't have to worry about any advance if checking/setting at 700 rpm? It should just be 8 deg at 700 rpm???

Eric 3.7LX Alpha 1 · Jul 19, 2012

Re: 5.7 Thunderbolt IV Timing

Timing at idle is set without worry about advance timing. Don't even look at that chart to set basic timing at idle.

The chart is a reference to what you should have for total timing at various RPM's WITH your idle timing set per spec.

If your advance timing doesn't match the chart then something isn't right, but you don't fix it by changing the idle timing.
If that makes sense.

With older dizzys, advance is set with weights and springs under the plate which the points are mounted to. The springs can get worn or corroded and can throw off the total timing, so that would be a reason to check total to see if everything is right.

I don't know how the thunderbolt IV total timing is done.

81 Checkmate · Jul 19, 2012

Re: 5.7 Thunderbolt IV Timing

Should be 8 deg at 700 RPM with a normal timing light. Reading the tab on the balancer, should read 8 BTDC

With the advance light set at 8 on the knob and it should read 0 on the mark on the tab on the balancer.

Then with the advance light.... say you rev and hold the motor at 2500 rpm...... shine the light and adjust the knob untill you read 0 on the balancer... then look at the knob on the light.....say it reads 18, then that is your advance timing at 2500 RPM. Thus 18 deg ATDC total advance at 2500 RMP. Check your chart and compare notes for that given RMP.

I might be wrong, but this is the way i understand it. Please chime in if this needs to be corrected.

Good Luck!

Don S · Jul 19, 2012

Re: 5.7 Thunderbolt IV Timing

All the timing will be BTDC never ATDC. When you set your base timing with an advance timing light, you set the light at 8? BTDC and the timing mark on the engine will be a 0? TDC on the timing tab. Then you set the rpm to 2400 and adjust the timing light to again be 0?TDC on the engine. Then you check where the timing light is adjusted. The timing light should be around the 30? BTDC mark.

Brentathon · Jul 19, 2012

Re: 5.7 Thunderbolt IV Timing

Ok, so it sounds like the chart in Service Manual #15 is WRONG, and it was in-effect replaced by the Service Bulletin 95-11, which I posted.
Therefore, at a 700 rpm idle, I NEED NOT worry about any advance, and the timing should simply be the "spec timing" of 8 degrees BTDC.
Unless someone knows this statement in bold to be wrong, I will go with this.
Thanks!

Don S · Jul 19, 2012

Re: 5.7 Thunderbolt IV Timing

Brentathon said:
Therefore, at a 700 rpm idle, I NEED NOT worry about any advance, and the timing should simply be the "spec timing" of 8 degrees BTDC.

That's it, just like the book says.

81 Checkmate · Jul 19, 2012

Re: 5.7 Thunderbolt IV Timing

So i was close.... No ATDC...All BTDC

Thanks Don for clearing that up....

5.7 Thunderbolt IV Timing

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