In very simple terms ignition timing is the thing that determines when the ignition spark is going to be triggered so that the air/fuel mixture is ignited - which in turn makes the car go.
Timing is controlled by the link between the position of the piston and when the spark occurs. If the ignition spark occurs too soon it can push against a piston traveling up the cylinder as it is compressing the fuel/air mixture. This causes detonation, lost power, higher combustion temperatures, backfires and potential for early internal engine failures. If the spark occurs too late, the ignition of the fuel mixture occurs after the piston is traveling back down the cylinder. This is wasted energy, unburned fuel, dirty emissions, and lost power.
There are two forms of timing - static and dynamic.
The Service manual for your car will tell you where the timing should be set but basically it will be a number something like 10 degrees BTDC (before top dead centre). For the purpose of this brief lesson I will talk about setting Static timings on an older pre EEC IV car although the basic principles remain the same. Please NOTE: It is not generally possible or desirable to set static timing on computer controlled ignition systems.
This involves no specialised equipment and a little bit of patience. What you are trying to do is make sure the distributor points (or electronic ignition trigger) are ready to fire when the engine is at the timing point.
1. On the timing pulley or harmonic balancer (which is mounted low at the front of the engine) there is usally a little white mark (you may need to clean this) and some similar marks next to the pully on a plate. One of the marks on the plate will be longer than the rest and this usually represents the static timing mark. It is a good idea to highlight the mark on the pulley with a bit of chalk as it makes it easier to see.
2. Remove the distributor cap so that you are able to see when the points/trigger are in the firing position.
3. Identify the distributor cap position that points to the N0. 1 cylinder plug lead (most distributors will have a mark on them indicatinfg this point.
4. Rotate the engine clockwise(in neutral) by hand until the rotor button is pointing towards the no. 1 cylinder mark. Check that the mark on the pulley is aligned with the bigger mark on the plate. If these are all aligned the points should be just about to open or the trigger unit set to fire.
5. If the points are not about to open it will be necessary to loosen the distributor hold down clamp bolt and slowly rotate the distributor in either direction until the points/trigger are ready to open/fire. When this has been achieved retighten the distributor and replace the distributor cap. Your static timing has been completed.
This is a far more accurate method and requires a timing light.
1. Disconnect vacuum hose(s) on distributor and plug them.
2. Remove the #1 plug wire either from plug or distributor and attach the correct lead of timing light in it's place.
3. Connect electrical leads of timing light to battery or power point.
4. Set engine to idle according to specifications with the engine at operating temperature.
5. Turn off the engine and loosen the distributor hold down clamp.
6. Restart the engine, aim the timing light at flywheel or harmonic balancer where the timing marks are. CAUTION: Care should be taken to keep leads away from moving parts. Rotate the distributor each way until the mark on your flywheel or balancer lines up with the correct mark on your timing pointer or plate.
7. Shut off the engine and re-tighten the distributor.
8. Recheck the timing in case you have moved the distributor when tightening it.
9. Remove the timing light and plug from vacuum hoses then reinstall vacuum hoses on distributor.
russelw should write technical manuals. That's better than Gregory's etc for clarity and explanation.
Just to add, on 3.9 and any subsequent Ford with same block and inlet manifold, the bolt to release the distributor to allow it to be turned to adjust timing is hard to get at. Easiest way I've found is to use extension bars on a socket with a universal joint wound with a spring between the socket and the extension bar. The spring around the outside of the uni joint stops it flopping around, so you can locate it on the bolt, but allows it to flex when you're rotating the bolt as it's on an angle. The socket is fed between the inlet tubes on ?No2 and No3 (or maybe 1 & 2 - been a while since I've done it) cyls. Near impossible to get at it with a spanner, certainly from above.
Also, advancing timing was a traditional way of getting a bit more go out of non-ECU cars, but I've experimented with my 3.9mpi up to about 6 degree advanced and, if anything, it goes worse. I lost about half a second or more on 0-100. Too much advance can also do damage as it's causing ignition when the piston is still pushing it's way up and peaks before it's completed the journey, whereas recommended ignition peaks so that it's at optimum point to push it down on downward leg. Leave it at manufacturer's recommended timing.
Make sure you use a timing light that's OK for electronic ignitions.
Inductive pick up timing lights (where a clip goes on the plug wire rather than having to remove it) are easier to use.
If the distributor doesn't have a vacuum advance i.e. it's controlled by computer, there's no need to disconnect vacuum lines. Vacuum or computer controlled advance advances the spark to fire earlier as rpm rises.
Cam timing is purely mechanical, and one of the many things that should not be buggerised around with unless you know what you're doing. Changing the cam timing will, in simple terms, determine whereabouts in the rev range maximum power will occur. Advance the timing, and the power comes on earlier, retard it for power coming on later. Move it too far and the valves clash with the pistons, which is quite undesirable.
Cam timing is beginning to be controlled/adjusted by on-board computers. This technology is used on the OHC Intech six and commonplace on many smaller engined cars, Honda, Toyota etc.
They go by various names (vvti) variable valve timing etc. What happens is the mechanical drive of the cam is advanced or retarded depending on revs and engine loads. The actual cam profile is untouched just the revs at which max. power/torque occur are varied slightly. Some multi valve engines also have the "additional" set of valves only come into operation at higher revs to aid breathing.
I read recently of developments where the cam is done away with altogether and valve operation is controlled by individually controlled solenoids under computer management. This will allow for maximum engine flexibility - think pulls like a truck down low yet screams like a top-fueler up top.
Oh BTW, good explanation russelw.
Gee you younger guys miss out on a lot. Adjusting timing and points gap was just about a weekly ritual on my hot Holden sixes. Not to mention valve lash, tuning the Holley or Triple Webers, etc. etc.
Then again I know shyte about fooling about with fuel or timing maps in an ECU and would much rather today's technology.
Originally posted by RAPTOR Gee you younger guys miss out on a lot. Adjusting timing and points gap was just about a weekly ritual on my hot Holden sixes. Not to mention valve lash, tuning the Holley or Triple Webers, etc. etc.
They're not missing anything.
God knows how many pointless hours I spent in my distant youth stuffing around with points gap and filing points and adjusting tappets with the donk running and buggering a feeler gauge in about 5 seconds and setting the timing, and then when you'd done all that it either made no real difference or you had to repeat the points gap setting etc.
It ranks with trying to improve your column shift by stuffing around with the trunnion rods, until you realise that pretty well any setting works and nothing makes the change any quicker.
Oh, and changing the oil in oil bath filters and repairing the diaphragm in mechanical fuel pumps, and short engine life because they didn't have oil filters, and dodgy distributors with centrifugal and vacuum advance, and vacuum windscreen wipers that related to engine speed, and valve radios that lost the signal passing a hedge, and skinny crossply tyres that threw you out of tram lines, and drum brakes that always seemed to have one leaky cylinder that got onto the linings so that you automatically corrected for it when braking and safety glass windsreens that broke pretty easily etc etc etc.
Anything made in the last 15 years is light years ahead of that stuff, and there's no reason to mourn its passing.
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