Date: Fri, 23 Dec 2011 01:48:45 -0600
Reply-To: John Rodgers <inua@CHARTER.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John Rodgers <inua@CHARTER.NET>
Subject: Re: selecting a compression tester
In-Reply-To: <7EBD740A5787470AAB91839610E650A6@Mikelaptop1>
Content-Type: text/plain; charset=UTF-8; format=flowed
Mike that is a pretty good summation of the procedure. I still have my
old aircraft engine compression tester from my aviation days. Works.
Tells me what I want to know, exactly as you have described it. And you
are very correct to advise being very careful of kickover when the
engine is under that much pressure at TDC. It can break an arm, or
worse. Imagine a 6-8-10-12 foot propeller suddenly kicking over during a
compression test using the TDC method. Disaster - is how the newspaper
reported the incident the lady at the airport backed into a turning
propeller. Even a single blade kicking over from TDC can ruin your day -
and so can an auto engine.
John
John Rodgers
Clayartist and Moldmaker
88'GL VW Bus Driver
Chelsea, AL
Http://www.moldhaus.com
On 12/22/2011 10:01 PM, Mike wrote:
> 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
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 2012.0.1890 / Virus Database: 2109/4697 - Release Date: 12/22/11
>
>
| 
