Hey guys, I'm about to change the Head Gasket by myself but I just dont understand how I'm supposed to leave the engine in the Top Dead Centre position after disassembling the cylinder head. Any tips to this home mechanic?

Why do you need it at TDC?
If the head is off, TDC is easy, when pistons 1 & 4 are at the top of the bores.

Normally when the cambelt timing marks are aligned, the pistons are all half-way, so all level together. At that point, no matter the position of the camshaft when the head is put on, valves and pistons cannot meet. Then the camshaft can be rotated to align its mark without worry before the cambelt is fitted.

Thanks! So to be clear only the cylinder block is needed to be at TDC position?

ddrexj said:

Thanks! So to be clear only the cylinder block is needed to be at TDC position?

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That is not what I said.

Align the timing marks. Then dismantle.

The timing marks place the pistons half-way up the bore, so a safe position.
If you wish to clean the piston tops, once the head is off, you can move them as you wish.
Before replacing the head, put them back at the half-way point.
Fit the head. Then align the camshaft timing mark.
Fit the cambelt.

portland_bill said:

That is not what I said.

Align the timing marks. Then dismantle.

The timing marks place the pistons half-way up the bore, so a safe position.
If you wish to clean the piston tops, once the head is off, you can move them as you wish.
Before replacing the head, put them back at the half-way point.
Fit the head. Then align the camshaft timing mark.
Fit the cambelt.

Click to expand...

Okay, there must have been an error in translation, sorry.

So the steps should be:

-Align to the TDC the using the marks on the camshaft and crankshaft pulley
-Take out the timing belt and dismantle
-If I happen to move the camshaft by accident there's no problem, just re-align it using the marks
-Re-assemble

Right?

ddrexj said:

Okay, there must have been an error in translation

Click to expand...

I think so.


TDC is only referring to the position of the crankshaft.


TDC does not have any meaning for the camshaft which has to be separately positioned.


When you say:

"Align to the TDC the using the marks on the camshaft and crankshaft pulley"


You cannot really do that because you do not think about the relative position of the camshaft and crankshaft 'with respect to TDC'. Instead when the engine is correctly timed, the crankshaft is at TDC, and the timing mark on the camshaft is correctly set/positioned.


When you dismantle the engine you cannot use TDC to know what the camshaft position is. Both positions have to be separately identified.

When you dismantle an engine it is not unusual that the working engine is in fact incorrectly timed with the camshaft being wrongly positioned compared to the crankshafts TDC.

My experience is that the timing marks on the FIRE engine are not TDC. The pistons will be set half-way up the bore, so in a safe position.

Forget TDC. Just align the marks.

Understood.
When reading the Haynes Manual they say: "For this reason it is important that the correct phasing between the camshaft and crankshaft is preserved whilst the timing belt is off the engine. This is achieved by setting the engine in a reference position (TDC) before the timing belt is removed and then preventing the camshaft and crankshaft from rotating until the belt is refitted".
And that's what made me confused on how I'm supposed to do that.

If the only thing that's necessary to time the engine is align the marks (which comes in the Manual as well) then there's no need to prevent it from moving. When reassembing it and refitting the timing belt, I only need to line up the marks and that them timing of the engine done. Right?

ddrexj said:

Understood.
When reading the Haynes Manual they say: "For this reason it is important that the correct phasing between the camshaft and crankshaft is preserved whilst the timing belt is off the engine. This is achieved by setting the engine in a reference position (TDC) before the timing belt is removed and then preventing the camshaft and crankshaft from rotating until the belt is refitted".
And that's what made me confused on how I'm supposed to do that.

If the only thing that's necessary to time the engine is align the marks (which comes in the Manual as well) then there's no need to prevent it from moving. When reassembing it and refitting the timing belt, I only need to line up the marks and that them timing of the engine done. Right?

Click to expand...

The first paragraph is a standard statement, not necessary applicable to all engines. Haynes is like this at times.

Correct way to time the engine is to align the marks.

Put the pistons half-way before refitting the head. Then valves will not hit pistons.

portland_bill said:

The first paragraph is a standard statement, not necessary applicable to all engines. Haynes is like this at times.

Correct way to time the engine is to align the marks.

Put the pistons half-way before refitting the head. Then valves will not hit pistons.

Click to expand...

Thanks a lot! And sorry for any inconvenience

portland_bill said:

My experience is that the timing marks on the FIRE engine are not TDC. The pistons will be set half-way up the bore, so in a safe position.

Forget TDC. Just align the marks.

Click to expand...

Sorry. I was totally forgetting about that.