Leak Down Test?

[SethD]

Took my X to the Ford Dealership after enough agervation, and here is what I come out with. My number 6 cylinder is bad, at 75% compression, with all the rest at 125%. On the other hand, they told me that didnt do a leak down test due to the fact that the rocker arms have to be lossened. Is this the truth? Your help is greatly appreciated. Thanks guys. Seth

 

[mrboyle]

The only thing a leak down test will confirm is what failed in the #6 hole. It is clear that you have a problem, and if #5 was good, you most likely don't have a blown head gasket. You can determine what happened to #6 easily by removing the spark plug and (using a compression guage hose) forcing air into the cylinder (make sure it is a TDC first).
If air comes out: intake= bent intake valve
exhaust= burnt or bent exhaust valve
radiator= cracked head or bad gasket
oil fill hole= bad rings, busted piston or poss. bad head gasket.

 

[yob_yeknom]

How do you determine when the piston is at top dead center? Just curious.

 

[SethD]

Thankyou

Thanks for your quick response, I will definitly give that try, and let you guys know the outcome. It cost me a 120 dollars to find out number 6 was dead from the Ford place. GRRRRRRRR! Makes me sick. Thanks again. Seth D.

 

[mrboyle]

Originally posted by yob_yeknom
How do you determine when the piston is at top dead center? Just curious.

Pull the plug from the hole you are working on (it is easier if you remove all, but not necessary). Stick your finger in the hole, then, using a remote starter button, bump the engine over. When the cylinder nears the top of the compression stroke it will force your out of the hole. Now using a breaker bar and the correct size socket attached to the crank pulley, slowly turn the engine. It takes some practice, but you can feel when the piston reaches TDC and breaks over (the crank will suddenly become easier to turn).