Distributor & Ignition Timing Woes

[Zed Head]

Are you using the factory 1976 distributor or ZX or aftermarket? Could be a factor.

Does your tang look like Picture #3 in Post #4 when the timing mark is at TDC on the compression stroke?

[kensval]

It's the factory 1976 distributor as far as I know. It's the one that came with the car, anyhow. I have a ZX unit on a spare engine. As for the tang, I'll have to get back to you on that one. I work away from home and won't be back there for a week. I'll post a photo when I get back home and can get under the hood again.

Edited June 27, 2013 by kensval
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[Kennymonster]

I don't recall seeing another adjustment bolt behind the dizzy. Doesn't mean it's not there, I just don't recall seeing it. What does it adjust?

It adjusts the ignition timing, just like the 10mm adjustment bolt you've been using, it's just another/secondary adjustment slot to play with. Unless that itself is maxed at one end, you should be easily able to get 4 degrees out of that one. You won't see it from the driver's side fender, but if you lean over the passenger side you'll see a smaller 8mm adjustment slot behind the dizzy. Loosen, rotate, just like the other one. *If you have a RHD then flip the driver/passenger reference.

I guess I'm confused because you stated that in the past you removed the oil pump shaft to align the dizzy the correct way (which implies the tang being set to 11:25 position), yet you're not sure if the tang is currently at the 11:25 position?

Right now with the timing light on the damper, and revving the engine up but without a tach to look at, and no offset timing mark, I'm guessing my total advance to be about 30 deg.

Hmm.. this isn't something you want to estimate. I measured with a piece of IKEA paper measuring tape to make an offset mark on the pulley, without having to remove anything, and even the slightest adjustment on the dizzy could bump the timing 5+ degrees each way, at least it seemed to be that way on mine.

Do you not have a tach in the car altogether, or do you mean you couldn't see the tach as you were performing the adjustment by yourself? I stuck a piece of vacuum hose in my linkage to hold the throttle open, confirmed the 3k on the dash, went around the car and checked the full advance.

Like I said, the car is not running badly, but I just want it to be right. It dynoed at about 20 hp over stock recently, and gets excellent gas mileage on the highway. As for coming down to sea level, and not being able to find high octane gas when I get there, I'm hoping that if I just take it easy on the acceleration and RPM I won't cause myself any trouble with detonation.

If it runs ok then you're probably close, but I agree on making it 'right' as either end of the spectrum besides the optimal setting means less power, risk detonation, less efficiency, etc. It doesn't cost anything except maybe an hour of your time

The JCCS has been my favorite event for the last couple years, hope to see you and others there!

[kensval]

I was fairly certain that I had the tang at the 11:25 position. How far out would it look if it were off by one gear tooth? It seems apparent that not being able to advance past 4 deg BTDC that something is out of position. If the centerline of the adjustment slot is theoretically 0 deg BTDC, how many degrees retard or advance should I be able to achieve going each way?

The reason I couldn't see the tach is that I was indeed doing the work by myself. Come to think of it, I've got an old aftermarket tach from another car kicking around. Maybe I'll put a magnet base on it and some alligator clips and then I'll have a tach wherever I need it to be to look at it. I think I'm going to swap out the 10mm bolt for one with phillips' head screwdriver slots as well. Easier to loosen and tighten that way.

I'll have a look for that 8mm bolt when I get home. It's a pain in the arse putting everything on hold for a week at a time.

Regarding the show... I've got a friend who lives in BC (I live in Saskatchewan, Alberta is in between us) who has a really nice 76 Celica. He wants us to do the road trip together. That way we can carry twice as many tools and spare parts :-)

My car is far from show worthy. It's a work in progress and will be that way for many years to come, but a long trip with an old buddy sounds like a lot of fun.

[kensval]

I googled photos of 280Z distributors and I'm fairly certain I know now what you're referring to as the "other" adjustment on the bottom of the dizzy. Will definitely have a good look at that when I get home, as I can see how it could be used to change the slot position of the main adjustment slot.

[madkaw]

You need to get as exact as possible to the 11.25 oclock. You will know it's off-ONLY if your sure where TDC is. You seem to be doing a lot of guessing about where things should be, and as been stated, a small adjustment means 5 degrees. I wouldn't get to hung up on getting exactly 3k rpms, just make sure your timing is not advancing anymore on the pulley and that you are maxed out. This is where a advanced timing light is handy.

Do you know when you are detonating? I mean you have heard your engine pinging? If so, let your ears help you here. Since your bumped up on the CR with a stock FI, I would stay conservative on the timing. Do you run premium fuel? I have had some old head tuners use the trick of running regular gas to pinpoint detonation and then run timing slightly backed off from there. Then use premium fuel for insurance.

Edited June 27, 2013 by madkaw

[kensval]

Well, I know how to determine TDC. It was fairly simple before the rebuilt engine was initially run because the piston top was still clean and easy to see. I just moved the crank back and forth from the damper until I was sure the #1 piston was exactly at the top of the bore. Since I'm going to have all the plugs out shortly to change to a colder set, I'm sure it'll be a similar deal this time. What I didn't know was how many degrees being one gear tooth out would put me. I could've counted gear teeth and figured it out, but I didn't. Then I set the timing by ear, a method I have used with success for a long time, but with domestic V8 engines where I wasn't as concerned about detonation due to higher compression. I've since purchased a timing light, but it's a basic unit, no fancy auxiliary functions.

I do know what detonation sounds like, and I am running 94 octane fuel, which is available up here in Canada at some Husky and Mohawk gas stations. It is an ethanol blend, but then almost all our fuels up here are these days. I hadn't thought of using regular fuel (that's 87 octane around here, what is it where you are?) to determine at what timing detonation will occur, then backing it off a couple of degrees, but it sounds like a reasonable plan to me. Once I determine for certain that I actually have the dist driveshaft in the correct orientation and the hold-down plate properly adjusted if that ends up being necessary, I'll try that.

The colder plugs shoud offer me a measure of reduction in the potential for detonation. Then, the closer I get to sea level, the less inclined I'll be to accelerate hard up to speed. I'm not worried about detonation at part-throttle. The combination of an aluminum head, cooler thermostat, the cooling effect of fuel spray from the injectors, colder plugs, and less spirited acceleration should all work together to keep me fairly safe from a catastrophic engine failure.

It's likely that the best I'll be able to find for octane during the trip to California will be 91, maybe even 89 in some places, so I'll carry some octane booster with me.