No More Pinging!

[Oiluj]

Always had slight pre-ignition, even with premium, (91 octane), fuel. Had this problem since doing a stroker upgrade to my Z, which increased compression.

Did some research and determined I should look at my distributor advance. It was one of the few things I didn't look at when rebuilding the car.

I opened-up the distributor, and found the 40 year old centrifigal advance spring was completely stretched-out. (See Pics).

Lack of spring force was allowing the centrifugal advance to max-out at between 1400-1500 rpm's!

Pic 1: Stretched springs in Distributor. Pic 2: New vs. Old spring.

I cleaned everything up and replaced the springs with new parts having equivalent spring rates from a local auto store.

What a difference! No more ping at any load or speed! Now I may even try advancing the timing a few degrees...

[madkaw]

What dizzy are you running?

[Zedyone_kenobi]

Are you ever going to try a Unilite? That wan you can totally customize your ignition advance

[Oiluj]

I'm running the stock dizzy. The pre-ignition was very minimal, but it was just enough to bug me...

I'll check-out the unilite dizzys, but now that the stock dizzy is working well, it'll be a lower priority. Need to complete the cosmetic refresh of my neighbor lady's 240, and fabricate / install a coolant overflow bottles for both Z's.

I'm also saving my pennies to get the bumpers re-chromed this winter...

[Wade Nelson]

I'm thinking any Nissan distributor with over 150K miles usage needs overhaul, or at least inspection. Cars didn't used to last 150K miles, and most newer cars with fuel injection ALSO went to computerized ignition / crank / cam sensors. The 280Z/ZX is right on the cusp, with FI but still running a distributor, and since it's so collectible, a lot of cars see more than 150K miles.

My gas mileage, in town, has skyrocketed since I installed a re-man distributor @ 220K miles -- and got the vacuum advance line properly plumbed. I don't track it but I'd guesstimate a 4-5mpg improvement.

Complex, unlubricated mechanical devices wear out, it's that simple. And timing is very important to engine performance AND efficiency.

[Oiluj]

Wade, I couldn't agree more. Old, mechanical systems do wear out...

Even as an engineer, I was truly surprised to see how much that spring had stretched. It was literally doing nothing.

[Zed Head]

:bulb:You know, that much stretch looks more like a POs tuning trick, to get more advance sooner. Why would one stretch and the other not?

How did you determine spring rate, for the auto store replacement spring?

[Gary in NJ]

How did you determine spring rate, for the auto store replacement spring?

Yes what are the spring specs? Better yet, what did you use?

[Oiluj]

My search guided me to information about fatigued dizzy springs on an MG/Triumph site.

I just measured the old spring and did some quick spring rate calcs, using spring formulas on the "Engineer's Edge" website. So much easier than digging out my books...

http://www.engineersedge.com/spring_extension_calc.htm

You can do more detailed calcs, but I didn't think it was warranted, as the replacement springs are made for use in dizzys. I don't recall the actual spring rate, I was doing it on my phone in the autoparts store.

Springs do wear-out under cyclical loading, and heat accelerates the process. The centrifigal spring gets more of a work-out than the vacuum spring, which I think accounts for the difference. Even so, the vacuum spring was stretched-out as well, just not as much. Both springs showed evidence of micro-cracks on the surface when viewed with a 10X loop.

Makes me glad I have all new valve springs!

Edited July 24, 2012 by Oiluj