leak down test

[ccm911]

The way I do it is to first make sure that the rotor is aimed at the cylinder I want to work with.  That tells me that we are at the ignition point for the cylinder.  Then I put a screwdriver in the plug hole and move the pulley until I find the highest point.  Most folks will tell you that you can only move in one direction, as reversing may foul the timing chains, but if you are only moving in small increments, it should not be a problem.  But then again, maybe I am just lucky.

Now you may wonder why the piston is not already at the top when you align the hash mark.  Have you ever seen the term BTDC?  Before Top Dead Center.  That is the degree measurement telling you when the ignition will fire. If it was Zero, then you would be at top dead center when the rotor points to the cylinder, and the hash mark(notch) on the pulley aligns.

Hope this helps.