engine timing?

[BerniniCaCO3]

Hi!

I don't have any problems, but I am curious.
To start from the ground up:
Engine timing is regulated by computer? Specifically the ignition module?
It's simply the order in which each of 8 pistons is ignited by the spark plug?

How precise should it be? At an average speed I'm just guessing of 2000rpm, or 33 revolutions each second, the timing should be perfect to 1/100 of a second, or more precise?

Now an error like swapping plug wires will create an instant and significant timing issue. If I ever do that, I hope I notice I've a problem immediately!

But can engine timing become more subtly off...? Is it worth using, from time to time, some electronic diagnostics tool to check the timing order? If it IS off, is there a way to tweak the programming in the ignition module, or, just replace the $40 part?

[1987cp]

I have a really dumb question .... what is it that you're meaning to ask?


Usually with ignition timing on a SEFI car, you make sure the firing order is correct (which if it runs OK it should be), then you unplug the "SpOUT" connector and set the base timing, usually to 10 or 14 degrees BTDC. The computilator will, in theory at least, take care of the actual advance curve for you, as there is no other mechanical adjustment other than base timing. Me, I never even set the initial timing myself when my wagon was SEFI, though of course I've done it quite a bit since messing with carb systems.

While I've never touched one myself I *think* that a fancy electronic tuning tool like a TwEECer (mrltd here and I think turbo2256 at Corral.net have used them) will allow you to alter the actual spark advance curve, somewhat like you would do on a normal distributor by swapping springs and advance limiters.

You can get timing lights as cheap as $15 or $25 if you have a Harbor Freight nearby or starting at $40 at AutoZone. Some people very much recommend getting a timing light with an advance dial, so that the TDC mark is the only spot on the balancer you ever have to worry about (I have a normal timing light and got myself a timing tape to apply to the balancer). And checking true TDC is pretty easy if you buy or make a piston stop, and then you can be certain that at least the mark is accurate.

While setting spark timing, keep in mind that different timing lights may have a slight delay in the circuitry, that different individual engines may like different amounts of advance for no good reason, and of course that your original timing marks may not be 100% accurate.



* I'm assuming you have a pushrod motor! (don't know that for sure)

** I'm all but positive the ECM controls all ignition advance functions, as I'm told that a TFI module is otherwise happy to be wired separately to a normal distributor like that from a Duraspark system, very much like I've done using a General Motors HEI module.

[gadget73]

On the EFI cars, the timing is partially computer controlled. You set the physical location of the distributor to get your initial timing, and the computer controls the advance. It can be a few degrees off and you may not notice. The only way to verify is to unplug the spout connector to disable the computer advance, and use a timing light. If the timing isn't right, you loosen the bolt on the distributor and rotate it until its right. The ignition module has nothing to do with it, it just makes a pulse to feed the coil.

[pantera77]

You can get timing lights as cheap as $15 or $25 if you have a Harbor Freight nearby or starting at $40 at AutoZone. Some people very much recommend getting a timing light with an advance dial, so that the TDC mark is the only spot on the balancer you ever have to worry about (I have a normal timing light and got myself a timing tape to apply to the balancer). And checking true TDC is pretty easy if you buy or make a piston stop, and then you can be certain that at least the mark is accurate.

My elcheapo Harbor Freight timing light has an advance dial. I personally don't use it, I just like making a few white lines on the balancer.

[BerniniCaCO3]

Yup, you've answered my question!

The only thing I was aware of was firing order,
and the word I was looking for was "timing light."

So if I have cash and find myself at harbor freight, I'll get one, and just see how tuned my engine is!

The timing chain is easy to adjust, should it need any...?
And, do I need any timing tensioner? Will it come with a kit, with fresh gears too?
(when I had a belted car, they would always talk about replacing the chain AND tensioner. I haven't actually seen into this part of teh engine).

[1987cp]

Chain?


Since we've had people choke on this before, let me clarify that "cam timing" or "valve timing" are NOT the same as "spark timing" or "ignition timing". The only relationship between cam timing and spark timing is that the distributor is driven off a gear on the front end of the camshaft.


Yep.


Now .... as far as messing with your timing chain, look at an exploded view and see where the timing chain is. Then decide whether you want to remove your alternator, a/c compressor, water pump, power steering pump, fuel pump (if mechanical), and front cover in order to mess with something that's not a normal service item. And even then, unless you perform a TDC check, obtain a dial indicator and the correct specs for your cam (and many people recommend buying or making a solid lifter to degree a cam, which means the intake manifold has to come off too), and buy or make a degree wheel, you won't be able to do anything more than verify that the two dots on the sprockets are lined up and/or decide whether the chain has stretched, as there isn't really any "adjustment" built into the stock system, and even if there were, it'd be useless unless you can verify what you're doing.


Other notes .....

Smallblock V8 engines do NOT have a chain tensioner. SFAIK, timing chain tensioners are only for OHC or DOHC engines. Smallblocks are pushrod motors, and the cam is located below the lifter valley, requiring only a very short timing chain (if you've looked at an exploded view, you already know this).

Yes, timing kits usually include the chain and both sprockets. The stock cam sprocket usually has nylon teeth, and yes, they do occasionally fail. So far as I know, actual failure is rather rare, so the main reason to replace your timing set would be if you suspect or verify that the chain has stretched significantly, or just feel like it's a good idea to do so. If you want to get anal, for something like $120-$150 (I think) you can get a fancy aftermarket timing set with little adjustment slots so you can phase your cam exactly where you need/want it. For less coin ($70ish IIRC), you can get a set that has multiple keyways on the crank sprocket so you can advance or retard the cam somewhat that way, I think in 2-degree increments. I once bought a cheap double-roller set for $25 that included three crank keyways, so one could use that to adjust the cam phasing in 4-degree increments. Stock sets, which can be had starting around $10 or $15 (again IIRC), do not have any adjustment provisions at all, so folks rebuilding a stock engine usually do like at the factory and throw the set on, eyeball it to make sure the dots on the sprockets are lined up as close as possible (I suppose you could use a straightedge if you wanted to), and button it up and call it good.

Also, engines equipped with a timing BELT do not use a timing CHAIN. It's one or the other, not both ..... people fitting aftermarket timing sets do sometimes choose to buy an expensive ($700ish? I think?) belt-drive system from a brand such as Jesel, and that involves a different machined-aluminum front cover that's thicker than the stock one and requires respacing all your accessory drive pulleys. People also sometimes opt for gear drives, which use one or two idler gears in between the cam and crank gears and do not use a chain or belt.

[gadget73]

The timing chain is not adjustable in a practical manner. You just rotate the distributor to adjust the timing. Loosen the bolt at the bottom, and it will rotate freely. When people talk timing, 90% of the time they mean ignition timing. There is cam timing as well, but its not something that can be readily changed. It will change somewhat due to timing chain stretch, but its usually not going to be enough to actually matter.

[BerniniCaCO3]

ahhh, no, I don't want to take that apart until I'm doing something else at the same time.
Was thinking about it when I did the water pump, but decided I wasn't ready to mess with the engine.

Ah, so the distributor rotates? I'll get a cheap timing light and see what it says!
I mostly just want to learn how this works, for the day when my timing really does drift off.

[1987cp]

Funny, I thought everyone knew that a distributor was a shaft inside a housing, and the housing rotates with respect to the engine block to phase the ignition events.

On the other hand, I was the one who was afraid to remove the distributor cap, because I didn't realize the cap was positively located with respect the housing!

[Glen]

We all had to learn how to do it and how it works. That's part of the fun.

[1987cp]

True, true!

[1990LTD]

This time last year I was afraid to touch the +/- terminals at the same time

[1987cp]

Well, I generally do avoid that.

[sly]

I touch both... just not with the same wire.

[1987cp]

:lol: