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Setting up basic ignition and valve timing on an internal combustion engine.
On a 4 stroke Otto engine as the name suggests there are 4 strokes, induction, compression, power and exhaust, now if you ever get a broken timing chain or belt etc, if the valves are damaged well you have to remove the head and do all the necessary repairs. Once they are done you have to re-time the engine, sometimes that can be a bit daunting.

With multi cylinder engines like a 4 cylinder, 1 and 4 go up and down at the same time, and 2 and 3 go up and down at the same time, the only difference is the valves are open and shut in different places, so although you think you are on number 1 TDC, you could be on number 4 TDC, and if you get them round the wrong way relative to the spark at the plug, the engine wont run, as it will be firing on exhaust stroke.

Now quite often there are kits you can buy to set up engines when you are replacing belts and chains, but very basically if you are trying to set the timing up basically on a 4 cylinder engine, you would have to do this, get number 1 piston on Top dead centre, you can do this by several methods, the easiest is to turn the engine my hand in the direction it runs, and put a probe, like a screwdriver down number one plug hole and hopefully as you turn the engine you can feel the piston coming up, when it gets to the top it will start going down again, you have to find the exact peak, that is TDC, now the valves at that point will either be closed or on the rock, if your trying to set it up on number 1 cylinder you want the valves all closed on number 1 cylinder and on the rock on number 4 cylinder, that is basic static valve timing.

If you turn the engine 1 complete turn from there the crankshaft will rotate once and the camshafts half a turn, so from that you can see that now its firing on number 4 and exhaust is on number 1, so the valve on 4 will be closed and the valves on 1 will be on the rock, the same is true for cylinders 2 and 3 when there turn comes, most firing orders are 1-3-4-2, they can be 1-2-4-3 depends on the design of the camshafts.

Ok now on a Vauxhall 1-0 litre, 3 cylinder the firing order is 1-2-3 believe it or not, there are some 3 cylinder engines made that are 1-3-2, but Vauxhalls are 1-2-3, and the ignition coils are in one piece and fit on the plugs, and the coil is triggered from the ECU, via the Crank sensor and to some degree the CAM sensor, but that is more for telling the firing order and location of TDC, to do the basic timing on a 3 cylinder Corsa, you would get number 1 piston at TDC, on compression stroke, at that point numbers 2 and 3 would be half way up and half way down respectively, and with number one piston at TDC the front camshaft lobes would all be pointing outwards, so all the valves are closed. if they are pointing more inwards, you are on number 4 cylinder compression, and they will be pointing outwards, doing the ignition timing is another thing, you could have a look in the crank sensor hole and see if the fins are in the right place, there should be a gap in the fins about 5 degrees before TDC, that's the only place there should be a gap, the rest is worked out by the ecu, if the flywheel was on wrong that gap wouldn't coincide with number one piston on TDC. and the cam sensor also has to be set right.

There is a kit of tools you can buy for the Corsa 3 cylinder, consisting of an arched tool for cam sensor alignment, and a big dowel tool for screwing in the crankcase to locate piston TDC on number one, also a flat metal plate that slides in the end of the camshafts to align them for number one cylinder, it fits in the Gearbox end of the camshafts, you could probably check the firing positions with an oscilloscope but an easy way to do it would be to lift the coil pack off, make 3 long plug extensions out of metal rod, turn the engine to TDC on number one cylinder and put a Tipex mark on the crankshaft pulley and casing that line up on TDC, then get an old type Timing light, clip it to number 1 cylinder extension, connect the light to the battery depending what type it is, try to start the car and see if you can see the two marks align as the engine fires, the firing point should occur roughly 5 degrees before TDC mark, if you dont see anything when the strobe light flashes its firing on the wrong cylinder, you could try it on 2 or 3 cylinders as well, it should be right if no one has changed the wires on the coil or ECU or haven't got the Flywheel on wrong. Above mainly directed towards Magnetic Crank sensors. It's possible the plugs may fire on exhaust stroke as well as compression stroke as the flywheel is in the same place, i'm not sure on that, or the CAM sensor may not let this happen, i dont really think it matters either way.

If you have an old fashoned engine, with number one piston on TDC or a few degrees before, both valves should be closed and contacts should be just breaking, and rotor arm pointing to number one plug lead on distributor cap.
Some engines have wasted spark ignition, where 1 and 4 fire together and 2 and 3 fire together, Ignition timing not normally adjustable.

Now Just one thing here about testing compression's, for the engine to run you need good compression, a 1-0 litre Corsa is probably about 200 lbs/psi or 13 to 14 Bar, the best way to test them is with a pressure gauge, you just screw it in the plug hole and crank it over for about 5 to 10 seconds, dont forget to open the throttle on let some air in the manifold some how, if it cant get in it wont get compressed, you could probably make some kind of gauge using an old spark plug, break the ceramic top off and some how connect a pipe and gauge to it, but it must be made properly you dont want it flying apart under pressure, another way you could check relative compressions is with an induction amp meter, or clamp meter as its somtimes called, the idea is you put the meter on one of the battery cables and crank the engine over, it should read about 150 to 250 amps, depending on the engine, on a diesel a lot more.

If it only reads about 50 to 100 amps you probably havent got any compression, of course this doesnt tell you any specific cylinder its just for all cylinders in general, point being if its really low you either have a mechanical problem, like bent valves or cam timing wrong, or pistons etc, or no valve clearence, i have heard somtimes after an engine rebuild the hydraulic tappets can hold the valves open, and you might have to take them out and squeeze them in a vice to let the oil out, to get any valve clearence. principal is as the starter turns the engine it will use little current until it comes up against compression stroke, then it has to work hard so the amperage goes right up, if it doesn't you have little compression.

Lastly a bit about 2 stroke timing, you have no valves to worry about on normal run of the mill 2 stroke engines, so to do the timing all you have to do is get the piston about 1/16 inch before TDC and the contacts just breaking and that's it job done...unless its electronic ign, in which case it prob wont be adjustable anyway.
From Fred in Essex.
 
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