engine timing

[SiKiD_01]

could some one please explain to me about engine timing (in a carby)

what happens if it advanced to far, (wont start) and what does it do to your engine?

what happens if its retarded to far? (wont start) and what happens to your engine?

i'd just like to get my head around this, as i know how to do the timing with a light gun, but not exactly sure about what's going on.

thanks.
steve

[dumbdunce]

could some one please explain to me about engine timing (in a carby)

what happens if it advanced to far, (wont start) and what does it do to your engine?

what happens if its retarded to far? (wont start) and what happens to your engine?

i'd just like to get my head around this, as i know how to do the timing with a light gun, but not exactly sure about what's going on.

thanks.
steve

there are two different type of timing you will hear about with relation to 4 stroke spark ignition engines. The type you are talking about is ignition timing or spark timing. This is a measure of the crankshaft angle before (or after) top dead centre of the compression stroke where the spark is discharged, igniting the compressed fuel/air mixture. If it is too advanced, that is, the spark happens too early, before the piston is close enough to top dead centre, the mixture will ignite too early and detonate against the piston crown and cylinder walls. this can cause fairly catastrophic damage. This condition is accompanied by 'pinging', a rattly sort of sound as if someone has put a handful of marbles in your engine. If the ignition timing is too far retarded, that is, the spark happens too late, you will get poor power, very poor fuel economy, and a lot of heat will build up in the exhaust side - valves, head and manifold - to the point where the manifold will glow red hot as the fuel misture continues to burn after the exhaust valve opens. leads to cracked valves, dropped valve seats, cracked and broken manifolds. all bad.

as engine revolutions and load change, the timing is altered (either mechanically, by centrifugal cams in the distributor body, and vacuum advance/retard diaphragms, or electronically, by the ECU for full EFI vehciels) to suit the load and revs.

the manufacturer's base timing setting is usually a safe starting point but it pays to experiment a little - by a couple of degrees extra advance you may gain some power/economy, or you might find that at the manufacturer's recommended base setting you get pinging and poor power, so back it off a couple of degrees and record your results.

Other things that influence your optimum ignition timing will be fuel quality/RON, altitude/air pressure, humidity, ambient temperature, your driving style and the condition of your engine.


now for the other kind of timing - Cam Timing or Valve Timing, well, we'll save that for another day eh?

cheers

Brian

[SiKiD_01]

cool thanks dumbdunce,

now i know...... so more experimenting.

also, with cam timing etc, as you say, i have seen a couple of 1.3 sierra motors with an adjustable cam gear.

i see this one as way more risky to experiment with, as you should only adjust things a degree at a time.

i'll try to look this one up before i make myself look incompetant.

anyway, thanks again.

[J Top]

Manufacturer's timing marks can be incorrect,especially with a harmonic balancer type of front pulley.These are known to "Walk" the outer pulley arround the inner hub,making the timing marks incorrect.
There is also a condition known as parallax,which is where you can line up two marks from different angles and have different results.
As a control try connecting a vaccum guage up and advancing the spark to the highest stable reading and then retarding it by 2 inchs of mercury,2 divisions.
J Top

[mud4b]

sierras and vitaras use the same cam wheel....

it has 2 marks on it one is 60a the other is 80c..vitara is 60a,sierra is 80c..

forget what the book tells you about setting up the timing....

you need to remove your rocker cover and timing cover.....

you need to get no 1 valve rocking(you should be able to move the valves above cyl no 1)...when done no 4 will be on compression stroke(you will not be able to move the valves above cyl no 4)....

put your cam pully on and your belt(make sure no 1 cyl is at tdc,your crank dot has to line up with the arrow ) and rotate it 180degrees....put your distributor in making the rotor button facing no 1 spark lead....


will start first time.......

timing is set at 8degrees btdc...