HOW TO: Find #1 TDC on the compression stroke.

[Don S]

First thing you need to do is remove all the spark plugs. This makes the engine easier to turn, and if using a remote start button keeps the engine from kicking back when you are trying to make very small movements.

The Merc OEM service manual suggests you put your finger over #1 spark plug hole and turn the engine until you feel compression building in the cylinder. In real life, that can become almost impossible to do and turn the engine at the same time. What I have found that works very well is to use the hose from your compression tester. Just put your thumb over the end of the hose to feel the compression. It’s a lot easier to reach.

Now, bump the starter over with a remote start button or turn the engine by hand until you feel compression building on the #1 cylinder. Once you feel compression building, you no longer have to feel for the compression. Now you need to watch the timing mark on the vibration damper and the timing tab. Continue turning the engine in the same direction until the timing marks line up on 0 TDC.
You now have #1 piston at TDC on the compression stroke.

At this point, if your distributor is in the engine, remove the cap and look at where the rotor is pointing. That is where #1 spark plug wire should be located.