leak down test

[Mike Thomas #828]

when performing a leak down test....when is the cylinder exactly at TDC?...when the crank pulley notch lines up with the case line? or when the distributor rotor lines up with the notch in the distributor housing?....the reason i ask is because they dont line up simultaneously....when i have the distributor rotor lined up with the distributor notch, the crank pulley notch is about 1 centimeter passed the case line.....i seem to remember reading something about a 4 degrees timing advance...is this accurate?....

having said that...what is best to use fot a LDT?....if it is the rotor/distributor notch...then i would assume that for the rest of the cylinders after #1, you have to advance the crank pulley notch the same distance past the case line every time to get TDC...is this correct?

also, is it the center part of the rotor that should line up with the distributor notch or the leading edge (right edge when viewed from top) of the rotor that should be lined up??

 

thank you for your answers!

 

[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.