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Finding TDC on 4stroke 4inline engine

Finding TDC on 4stroke 4inline engine

Finding TDC on 4stroke 4inline engine

Hello all I have a specific problem:
How to find my correct TDC? The point is when I was removing the can chain all marks on the sprockets was ok and the can lobes was facing away from each other (so the piston was at TDC) but you can move the crankshaft another 360 degree and piston is still in TDC but the lobes facing each other. Now the problem is I removed the camshaft, and now I can have piston in two position TDC, so how can I figure it out to make camshaft lobes faces each other or away? It mean can I make engine timing 180off? Or its no matter? You can imagine this situation you have all set with the TDC but you only move camshaft to facing each other, what will happen?

RE: Finding TDC on 4stroke 4inline engine

If the spark plug is reasonably close to vertical, stick a long screwdriver down the spark plug hole and use that to feel where the piston is. You can even do it if the spark plug hole is inclined, but be careful about not jamming the screwdriver and damaging the threads. If the spark plug is vertical (typical 4-valve head) you can use it as a piston position indicator as you turn the crank with a socket.

Yes, there are two "versions" of TDC, one between exhaust and intake, and one between compression and power. But "which one is which" is determined by the orientation in which you install the camshafts (and, where applicable, the ignition distributor). As long as camshafts (and, where applicable, the ignition distributor) are in the correct positions relative to each other and to piston TDC, you do not need to concern yourself with "which" TDC.

RE: Finding TDC on 4stroke 4inline engine

Hmm. So bassicaly when I'm setting timing on my engine in manual Is say that the mark need to align with groove and the pickup rotor mark "T". Then you look at the camshafts and also setting marks to the cylinder head edge. And now it's the point what will happen If I turn pickup rotor 180 degree( it will point on T) without changing the camshaft position? It will work normally or it will not work because is another TDC?
Mayby this will explain a little more:
1 scenario = pickup rotor is algin with T mark > camshaft is set correct and the lobes point out each other (TDC)
2 scenarion =pickup rotor is algin with T mark > camshaft is set correct and the lobes point in each other (TDC)
so now what happen when you:
you have the pickup rotor as 1 scenarion but you install camshaft as second scenario. If engine know it's exaust or intake TDC?

RE: Finding TDC on 4stroke 4inline engine

Presumably the pickup rotor is for the crank position sensor. It's used for establishing when the spark plugs fire.

There are two possibilities for this engine.

Possibility #1: The ignition system knows the engine is nearing TDC, and there is another sensor detecting a feature on one of the camshafts which tells the engine controls which "version" of TDC is approaching (is it between exhaust and intake in which case no spark is needed, or is it between compression and power in which case it is time to fire the spark plug). Which "version" of TDC you have is thus fully determined by which orientation the camshafts are in. If you put the engine together the way the shop manual tells you to do it, the electronics sort themselves out.

Possibility #2: The ignition uses what is called a "waste spark" system. It fires the plug once per revolution, every single revolution, when the crank is approaching TDC whether it needs it or not. If that happens to be the version of TDC nearing the end of the compression stroke, ignition and subsequent power stroke follow. If that happens to be the version of TDC nearing the end of the exhaust stroke, nothing happens, because the spark is firing within spent exhaust. If you put the engine together the way the shop manual tells you to do it, it sorts itself out.

On an inline-four, if it has two ignition coils each with two spark plug wires coming out of it, and one of those ignition coils is dedicated to cylinders 1 and 4 (those spark plugs fire together whether the engine needs it or not) and the other one is dedicated to cylinders 2 and 3, then it is certainly a waste-spark system.

Notice the common words between the two scenarios ... "If you put the engine together the way the shop manual tells you to do it, it sorts itself out." You are over-thinking this.

RE: Finding TDC on 4stroke 4inline engine

Many thanks for your answers :)

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