Ignition Timing moving around

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jimbob
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Ignition Timing moving around

Post by jimbob » Tue May 22, 2018 9:17 am

Hi,
A couple of month’s ago, my original distributor failed, worn out, after 290,000km’s, timing was moving.
Replaced with a new Lucas distributor, from Paul & V8 Tuner, no issues at all for a few months.
But, its started again, fuel economy can sit around 14.9 to 16.5 ltrs/100km for 2 to 3 tanks, then when i pull up it struggles to hold idle, gives the feeling of stalling. Cleaned out the stepper valve clean no issues, no air leaks, vac advance is good, timing was set @ 8 BTDC, check the timing marks with a strobe, mark has moved.
Decided to cut a spark plug off and tap it out and insert a bolt in to find try TDC, marked the balancer, set the rotor arm to cylinder no 1, set the timing, and again it moved after a couple of thousand km’s. The bolt holding the clamp, i smear some silicone on the thread to stop it backing off, loctite would be overkill.
Cam has 70,000km on it, timing chain & sprockets were all new with Cloyes brand (pre-stretched) all sensors check out fine, 14 CUX is on the mark, using ECU fault mate.

My question is what am i missing?



GDCobra
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Re: Ignition Timing moving around

Post by GDCobra » Tue May 22, 2018 12:35 pm

If the timing is moving around then some part of the system must be changing it's relationship in relation to the others. Could be :
Timing chain - This would throw cam timing out too and then you'd have bigger problems.
Distributor drive gear on cam
Distributor drive gear on distributor
Upper distributor shaft moving on lower shaft - is the centrifugal advance working ok?
Trigger wheel moving on shaft. - This would probably also result in rotor arm to dizzy cap relationship changing and could lose path to plug lead
Trigger sensor moving - Same issues as above.
Distributor body moving in engine - Sounds like you already covered that.
Something else I missed!

Of course it could simply be the pointer moving but that wouldn't make the engine misbehave.

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Re: Ignition Timing moving around

Post by Darkspeed » Wed May 23, 2018 12:22 pm

Is this all from a fixed datum of a disconnected and blocked off Vac advance - and the same idle speed.
Sticking advance weights. Advance tube vac tube leaking / collapsing
4.5L V8 Ginetta G27

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jimbob
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Re: Ignition Timing moving around

Post by jimbob » Sun May 27, 2018 10:28 am

Thank you very much for the replies.

The Dizzy is brand new, i've rechecked the advance it all comes in as set-up, the split pin on the dizzy shaft is all set in place, so the two shafts cannot rotate.

Ordering some new 1/4 black rubber hose, from the throttle plate vac feed line to the dizzy. Removed the idle valve and cleaned, in all honesty not even sooted up. When its no playing up, the idle sits @ 750 with no A/C on, A/C comes on jumps up to around 850rpm ish,

Yes its a fixed datum, over the weekend, i again pulled spark plug, made sure TDC was where it was supposed to be, rotor arm aligned to HT lead ! etc, marked the balancer reset the timing.

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Re: Ignition Timing moving around

Post by GDCobra » Sun May 27, 2018 11:55 am

jimbob wrote:
Sun May 27, 2018 10:28 am
Thank you very much for the replies.

The Dizzy is brand new, i've rechecked the advance it all comes in as set-up, the split pin on the dizzy shaft is all set in place, so the two shafts cannot rotate.

Ordering some new 1/4 black rubber hose, from the throttle plate vac feed line to the dizzy. Removed the idle valve and cleaned, in all honesty not even sooted up. When its no playing up, the idle sits @ 750 with no A/C on, A/C comes on jumps up to around 850rpm ish,

Yes its a fixed datum, over the weekend, i again pulled spark plug, made sure TDC was where it was supposed to be, rotor arm aligned to HT lead ! etc, marked the balancer reset the timing.
IF the timing is actually moving (you don't seem 100% see of this as you are looking in other areas for the poor running issues) then something in the system is going walkabout. Just because your dizzy is nearly new does not mean it's not a problem. The mechanical advance could be sticking so giving different readings or the trigger wheel could be moving, or on the sdnsor side the plate holding the sensor may be sticking.
The vacuum pipe should not influence idle timing as it should be connected to a port which does not "see" vacuum when the throttle plate is closed and in any case you should check timing with this disconnected.

I don't understand why you had to re-mark the balancer, if your TDC mark aligned with the pointer when the engine was physically at TDC there should be no need to re-mark.

All this reminds me why I hate distributors with all their moving parts and springs, diaphragms and associated garbage. Nearly as bad as carburettors.

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