85 Cad 4100: When Doing A Engine Cylinder Pressure Test By Airing Up The Cylinders With A Compressor.


Do You Need To Have The Cylinder At Top Dead Center ?

Or Do You Leave Room In The Cylinder On The Compression Stroke ?

I Realize I Will Get A Minimal Amount Of Air Leaking Past The Rings And Will Probably Escape Out The Oil Cap Hole

But I Wanted To Know When The Test Is Ran, Do I Force Air Against The Piston At Top Dead Center Or Do I Leave Room In The Cylinder?

Forcing Air In The Cylinder With The Piston Not At Top Dead Center Will Obviously Force The Piston To The Bottom Of The Cylinder So What Is The Proper Way Of Doing This.
I Just Want To Make Sure I Am Doing This Correctly

My #3 Spark Plug Is Getting Wet With Coolant But When I Brought The Cylinder To Top Dead Center And Filled With 125 Psi Air And Let Sit For Approx 12 Minutes I Never Got Air Bubbles Or Level Change In Coolant. Another Person Tells Me (providing I Did The Test Correctly) That If I Am Not Getting Air Bubbles Or Coolant Level Change That My Head Gasket Is Not Bad And He Thinks It Could Be My Intake Gasket.

Hhhhhhhhhhhheeeeeeeeeeeeeelllllllllllllppppppppppp ppp????????????

As far as I know, you do not have to have the #1 piston at TDC. When doing the compression test, all that is needed is an observation of how quick and far the readings on the gauge go. Normally, the quicker the gauge comes within proper reading, the better the compression is. Normally, you want to have a fast compression build in less that 4 strokes of the crank.

If the reading exceeds specs, then you may have a high carbon buildup, and don't forget that each cylinder should be within ~10% in readings throughout the engine, i.e., 145 psi on #1 cylider, 135 psi on #2 cylinder, and so on.

I Am Not Doing A Compression Test, I Am Filling The Cylinder With Air To Check For A Head Gasket Leak.
I Was Wanting To Know If The Particular Cylinder I Am Testing Has To Be At Top Dead Center?
Thanks

I Am Not Doing A Compression Test, I Am Filling The Cylinder With Air To Check For A Head Gasket Leak.
I Was Wanting To Know If The Particular Cylinder I Am Testing Has To Be At Top Dead Center?
Thanks

Yes, TDC on the compression stroke for whichever cylider that you're testing. The valves will be fully closed and the only way for air to escape would be through other, not so good means. Sorry for the mis-read on your post :o

You are right that the compressed air will try to push the piston down. If you have the piston directly at TDC it will not move, though. That is why you want it as close to TDC as you can get it when you do each cylinder.