Date:         Sun, 23 Mar 2014 15:04:44 -0400
Reply-To:     Michael <mbucchino@CHARTER.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Michael <mbucchino@CHARTER.NET>
Subject:      Re: Leak-down Test - How to??
Comments: To: JRodgers <jrodgers113@GMAIL.COM>
In-Reply-To:  <532F26D3.2020605@gmail.com>
Content-Type: text/plain; charset=us-ascii

Same procedure.  You don't have to lock the crank in anyway; if it's at true TDC it won't move and kill you like a prop can.  You use 80 psi, not 120.  You don't shut a valve and watch for a leak down; you set the first gauge at 80 psi and watch what the second gauge is reading due to leakages.  You listen in the intake for an intake valve leaking, in the tailpipe for a leaking exhaust valve, and in the breather for a leak past the piston rings.  You can add a squirt of oil in the spark plug hole and move the piston back and forth to improve the leaky cylinder reading.  You can stake the valves if a little is leaking out of one due to debris between the valve and seat.  If there's in excess of 10% difference between the highest and lowest cylinders, that's acceptable, but more isn't.

Mike B.  (Lic'd A&P since 1981)

Sent from my iPhone

> On Mar 23, 2014, at 14:24, JRodgers <jrodgers113@GMAIL.COM> wrote:
> 
> I have a differential compression tester and know how to do a leakdown
> test on an airplane engine - but not on a an automotive engine. Similar
> in principle I'm sure - but not familiar with the details.
> 
> On an airplane, you turn the propeller until the piston in the cylinder
> in question is at top dead center on the compression stroke, then lock
> the propeller in place (holding it tightly, then attach the differential
> compression tester, hook up the compressed air to to it, admit 120 psi
> pressure from the compressor - and watch the two gauges. When both are
> equal - turn OFF the gauge valve on the cylinder side and watch for any
> pressure drop. Below 90psi is unacceptable - time for top overhaul. Or -
> if all cylinders are being checked.....If pressure differential between
> any two cylinders is greater than 10 PSI - time to consider a top overhaul.
> 
> My Question is - on an automobile, how would you set up the engine for
> the leak-down test? Never done one myself on a car.
> 
> Thanks,
> 
> John