you probably mean...the piston[not the cylinder]Why does the cylinder need to be at TDC when replacing the head gaskets? I am just curious.
I would imagine it has to do with the fact that the headbolts also secure the valve train.
@ TDC there will (should ) be equal and minimal tension on valve springs et c.
you probably mean...the piston[not the cylinder]
i cant think of a good reason why it has to be.the head gasket can go on with the piston in any position.
.........other than saving anything from falling into the cylinder[foreign matter]and causing damage
edit,now educated,i always did it,just didnt know why,its just automatic
isnt that just normal,4 main head bolts gradually decending evenly in a cross pattern until the required torque is achieved.Good call on the 'cylinder' vs. piston bandit; I really missed that altogether.
But actually you are right; it dosen't HAVE to be @ TDC.
But one would have to be extremely careful in cinching down the head so as to not distort anything.
isnt that just normal,4 main head bolts gradually decending evenly in a cross pattern until the required torque is achieved.
i only put it to tdc so i can see the cylinder is clean
As stated, it doesn't matter, if all you are doing is replacing the head gasket. It does matter if you are installing valve gear.
Also, if there is a lot of oil in the head bolt holes, (if they are blind holes) it pays to gently blow them out with compressed air. The oil can actually stop the bolt from reaching the required torque, giving a false indication of tension.
To avoid warping the head, I always do up my head bolts in 3 stages, criss/crossing as I go. Never do them up to final torque in one go.
My 2 cents, which in America would be about one and a half.