Date: Thu, 22 Dec 2011 23:01:04 -0500
Reply-To: Mike <mbucchino@CHARTER.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mike <mbucchino@CHARTER.NET>
Subject: Re: selecting a compression tester
In-Reply-To: <1324609683.3865.19.camel@landallc>
Content-Type: text/plain; format=flowed; charset="utf-8"; reply-type=original
Not sure which ones are better than others, but I'm not sure if you
understand the use of these diagnostic tools.
A compression tester and a cylinder leak-down tester check different
things in different ways, so you should use both.
You could get a compression tester on loan from Autozone or Advanced Auto
Parts, and test for general overall compression readings. This is done by
turning it over with the starter, with all the sparkplugs removed. You want
to see no more than a 10 percent total difference from the highest cylinder
reading to the lowest one. For example, if the highest cylinder read 130
psi, then 10 percent (13 psi) subtracted from that would be the lowest
acceptable reading from any other cylinder, which equals 117 psi minimum.
All four cylinders should be in that range from highest to lowest, or
there's too much imbalance between cylinders compression. This would
indicate that something needs attention.
Here's where a leak-down tester is the next step in engine diagnosis. You
turn each cylinder to TDC and hold it there with a socket and breaker bar,
then add 80 psi of compressed air on the first gauge of the leak-down
regulator. (be careful, that cylinder can turn fast and hard enough to
break your wrist!) The second gauge will read the pressure that that
cylinder is leaking-down. If it's a little, it's okay. If it's leaking a
lot, something is wrong. You can hear the air pressure that's leaking
coming from somewhere in that cylinder. If you hear it at the intake, then
it's leaking from the intake valve; if you hear it at the tailpipe, it's
leaking from the exhaust valve; if you hear it leaking from the oil filler,
it's leaking past the rings. This test is really only needed if the
compression test is very low, or extremely uneven across the 4 cylinders.
If the engine runs well, smooth and powerful, your compression will probably
check high and even. 100 to 160 psi is fine, and is dictated by the
compression ratio of the engine, so it obviously differs from one engine to
another.
Hope this helps,
Mike B.
-----Original Message-----
From: John Lauterbach
Sent: Thursday, December 22, 2011 10:08 PM
To: vanagon@GERRY.VANAGON.COM
Subject: selecting a compression tester
One of the few advantages of the recent problems with my '84 Vanagon is
that my Son, age 13, has taken a sudden interest in the Vanagon and
wants to get his hands dirty testing it and fixing it.
Several list members have mentioned need for a compression test and a
leak-down test. Local shops are already on Christmas schedule
(remember, this is the Deep South), so any testing will be DIY and a
chance to further my Son's practical education.
Are any of the compression testers at the stores still open any better
than others? Local AutoZone has a tester for $40 that included the
screw in adapters for doing the leak-down test (already have air
compressor). I have the usual array of stores available to me.
Thank you in advance.
John
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