Engine timing

FORDSMB454

MEMBER
2005 CHEVROLET TRAILBLAZER
4.2L
6 CYL
2WD
AUTOMATIC
130,000 MILES

Hey, I was just wondering how I find top dead center on this motor 4.2 6L. I put a rag in the first cylinder cranked motor by hand no pop or do I just keep cranking it? I'm so confused, I haven't touched or pulled the timing gears off or chain. I see they had there is a punch and l mark but just confused wanted to pull chain out and gears. How do I know if I'm at top dead center without knowing I'm on compression stroke?

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

Unfortunately, the rag in the engine works sometimes but as you are seeing, it does not work all the time.

The best way to do this is to use a whistle on a compression gauge and then turn the engine over by hand.

When you reach the compression stroke the whistle will blow and then when it stops you have reached TDC. Clearly the best way for this is to give the crank pulley quick hard pulses so that you force the air out to blow the whistle.

There are other ways to do this. You can put your thumb over the hole and when the air blows your thumb off, then put a thin piece of wood like a chop stick down the spark plug hole. Then when the stick comes up and pauses and before it starts to go back down, you have reached TDC.

Short of all this, you will need to access the crank pulley to line up the dot which is not the easiest.

Please see the attached picture of the whistle that I am talking about.

Let us know if you have questions on this and we can go from there.

Images (Click to make bigger)