How to do a compression check
T W
compression test on your car? I just acquired a used gauge with no
instructions and want to test my engine.
Also received a Vaccum guage and want to test that but no instructions!
Thanks!
TW
Mr. Floppy
news:%qI07.1530$oa1.1...@newsread1.prod.itd.earthlink.net...
1. Disconnect the wiring to the coil. (Consult a manual for your type of
distributor)
2. Mark and remove the spark wires at the plugs.
3. Remove each spark plug, noting it's location.
4. Block the throttle fully open.
5. Insert the compression tool into a spark plug hole.
6. While you watch the needle on the compression checking tool, have an
assistant crank the key until the needle reaches it's highest spot and stops
climbing. If it just bounces and falls back to zero you have a problem with
that cylinder. If it's a manal trans make sure you're in neutral!
7. Repeat steps 5 and 6 on each cylinder, noting the reading of each
cylinder on paper.
8. Re-insert spark plugs.
9. Re-install spark plug wires.
If the numbers are uniform within 10% of each other, you most likely don't
have any badly worn parts.
If the numbers are uniformly low on two cylinders next to each other you
have a blown head gasket.
If the numbers are low on one or more cylinders that are not next to each
other you have worn/bent valves or worn/broken rings, often warranting a
teardown.
--
Mr. Floppy
http://my73camaro.50megs.com/
Kevin Mouton
Preferably on a warm but not hot engine, remove all the spark plugs.
Disable the ignition system by whatever means is applicable to your
model.
Disable the fuel injection system if you have one.
Block the throttle plate in wide open position
Attach a battery charger to the vehicle battery.
Install the compression tester in a spark plug hole.
Crank the engine so that this cylinder comes up on compression 4 or 5
times.
Record the reading on the compression gage and repeat for every other
cylinder.
Any cylinders that are not within 25% of the others are suspect, and a
cylinder leak down test should be used to determine the cause of the
problem.
--
WARNING:
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* * * * * * * * * * * * * * * * * * * * * * * * * * * *
Kevin Mouton ..... Automotive Technology Instructor
"If women don't find you handsome, they should at least find you handy"
Red Green
T W
"Kevin Mouton" <kev...@bellsouthgarbage.net> wrote in message
news:3B43CC2F...@bellsouth.net...
Kevin Mouton
>
> How is a leakdown test done..can i use the same compression gauge?
>
You should use a special leak down test gage set. It has a regulator and
two gages, one for regulated pressure and one for indicating percent of
leakage. You use the gages and a compressor to put 100 psi pressure in a
cylinder while the piston is at TDC, then read the amount of leakage.
You can compare the percent of leakage to the manufacturer
specifications to determine if it is excessive. While the pressure is
applied you then listen for the hissing sound of the air escaping the
combustion chamber. If the hiss is heard from the throttle opening then
you know you have a bad intake valve. If you hear it in the tail pipe
then the exhaust valve is bad. You will hear the hiss through the dip
stick tube if the rings are bad and you will see bubbles in the radiator
filler opening if the head gasket is blown or the head is cracked.
You can just pressure up the cylinder without any gage if you have an
air compressor and an adapter that fits the spark plug hole. This will
not indicate the percentage of leakage, but you can still listen for the
escaping air to determine where the leak is coming from. This
information can help you determine weather or not you need to just pull
a cylinder head, or the whole engine for repairs.
CBHVAC
rings, apply compressed air to it, and you will without fail, hear some air
escaping. Ask anyone that has replaced valve stem seals on several motors
using that method..you use the compressed air adaptor to keep the valves in
place as you remove the keepers so you dont have to remove the head.
"Kevin Mouton" <kev...@bellsouthgarbage.net> wrote in message
news:3B4440DD...@bellsouth.net...
Kevin Mouton
I am confused by your statement that seems to implicate that a leak down
test will lead to unnecessary replacement of valve stem seals on stock
engines. First off, you need to explain how any leak down test can
identify or even suggest bad valve stem seals. A leak down test only
checks for leakage in the combustion chamber, not the valve stem seals.
Secondly, I agree that you will hear hissing even on a brand new engine.
That is why you have to go by the manufacturers specs for percentage of
leakage allowed and then only identify the source of the hiss in those
cylinders that are leaking more than is allowed. This is a long time
tried and proven method for diagnosing low compression problems on any
engines, including those with stock rings.
Or maybe I just don't understand your reply ...! Please explain what a
leak down test has to do with valve stem seals?
Thomas A. Anderson
keeping the valves in place to allow removal of the valve springs
without removing the heads. I believe he doesn't understand the
similarity and/or differance between the two methods of applied
compressed air to the cylinder.
On Thu, 05 Jul 2001 19:52:50 -0500, Kevin Mouton
<kev...@bellsouthgarbage.net> spewed his liquistic talents:
CBHVAC
One more time so those that cant understand, go into teaching can
understand....
the statement that was made NOT BY ME about putting compressed air to a
cylinder and listening to the air leaking by to indicate worn rings, is
wrong, and something that a 1st year automotive student knows.
I COMPARED it to when you replace the valve stem steals using compressed air
to hold the valve in place....you get air leaking past the rings as well, on
a new motor, a worn motor..etc.
If this is the kind of teachers we have today, its no wonder we have idiots
for children.
--
www.carolinabreezehvac.com
"Thomas A. Anderson" <andersonthomas_a@NO_SPAMhotmail.com> wrote in message
news:h38akt43vkjlk8lp0...@4ax.com...
Kevin Mouton
You obviously do not understand the process of a proper leak down test.
It is bad manners to accuse others of ignorance when you do not know
what you are talking about. Furthermore, I do not participate in flame
wars so you will get no more replies from me on this thread'
BTW, top posting of replies causes difficulty in following threads.
Thomas A. Anderson
and comprehend what is stated. Basiclt that is exactly what I said
you were talking about. Obviously you do not realize the differance
between the two tests. You remind me of the Mechanic with over 15
years of experience who tried to tell a customer that they had a bad
cam shaft in an engine because "the computer told him so". The
complaint was about an intermitent miss in the engine. In reality the
engine had a spark plug wire that was grounding out. But, NO he was
too smart, "Because the Computer told him SO" UNFORTUNATELY, HE
COULDN'T THINK FOR HIMSELF EITHER.
END OF THREAD
On Fri, 6 Jul 2001 01:54:18 -0400, "CBHVAC"
<in...@carolinabreezehvac.com> spewed his liquistic talents:
Brad
to pay attention to what you read. CBHVAC said putting air into a
cylinder to check for leaks doesn't work because you will always get
some leaking -- such as if you've ever put compressed air into a
cylinder to hold the valve stem up, you should have heard some leaking
even though you weren't checking for leaks. Kevin agreed with him on
that point, actually, but then he wondered how CBHVAC could say
compressed air causes bad valve seals, and I'm still scratching my head
trying to figure out how Kevin got that from the post.
Alex Rodriguez
says...
>Preferably on a warm but not hot engine, remove all the spark plugs.
>Disable the ignition system by whatever means is applicable to your
>model.
>Disable the fuel injection system if you have one.
>Block the throttle plate in wide open position
>Attach a battery charger to the vehicle battery.
>Install the compression tester in a spark plug hole.
>Crank the engine so that this cylinder comes up on compression 4 or 5
>times.
>Record the reading on the compression gage and repeat for every other
>cylinder.
>Any cylinders that are not within 25% of the others are suspect, and a
>cylinder leak down test should be used to determine the cause of the
>problem.
Can you just disconnect the battery and then turn the engine over by
hand? that way you avoid fiddling with the ignition and fuel system.
-----------------
Alex __O
_-\<,_
(_)/ (_)
B.P. - iSpelunker.com
> T W wrote:
> >
> > Can someone who has done this post a short checklist on how to do a
> > compression test on your car? I just acquired a used gauge with no
> > instructions and want to test my engine.
> >
> > Also received a Vaccum guage and want to test that but no instructions!
> >
> > Thanks!
> >
> > TW
>
> Preferably on a warm but not hot engine, remove all the spark plugs.
> Disable the ignition system by whatever means is applicable to your
> model.
> Disable the fuel injection system if you have one.
> Block the throttle plate in wide open position
> Attach a battery charger to the vehicle battery.
> Install the compression tester in a spark plug hole.
> Crank the engine so that this cylinder comes up on compression 4 or 5
> times.
> Record the reading on the compression gage and repeat for every other
> cylinder.
> Any cylinders that are not within 25% of the others are suspect, and a
> cylinder leak down test should be used to determine the cause of the
> problem.
What if all the cylinders are within 25% of each other but read very low on
compression?
B.P.
Kevin Mouton
No, a compression test needs to be done with the engine turning over at
cranking speed. You can not do that by hand. The accuracy of the test
also requires that each cylinder tested is cranked at the same speed.
That is why you should attach a battery charger during the test, so that
the cranking speed does not diminish during the test as the battery gets
weaker from all the cranking. You can however leave the ignition in the
off position and attach a remote starter switch to the starter solenoid.
Then you will be able to crank the engine using the remote switch
without the fuel or ignition system operating.
Thomas A. Anderson
I took apart a 4.3 ci 6 cyl. engine that ran great but was low on
horse power and compression. It turned out that all of the rings have
rotated and lined up the ring end gaps. ALL rings on ALL cylinders
were lined up perfectly. Mains, Rod bearings and cylinder walls all
looked like new after 125,ooo miles. Aparently the Slick 50 additive
made the walls so slick that the compression blow by caused the rings
to rotate and line up causing low compression.
Wierd.
On Fri, 06 Jul 2001 22:06:14 GMT, "B.P. - iSpelunker.com"
<no_spa...@ispelunker.com> spewed his liquistic talents:
Kevin Mouton
Well, assuming that the compression test was done properly and the gage
accuracy can be trusted, then the engine is most likely worn out, but
keep in mind that there are many variables that can affect the
compression test results. Something as simple as a worn starter which
does not develop full cranking speed could result in low compression
readings on a good engine. There again, a cylinder leak down test would
be a more accurate test for determining the condition of the engine.
One common mistake is assuming an engine is in good condition just
because fairly high compression readings are observed. This is often the
result of excessive carbon deposits which cause higher compression
ratios in an otherwise worn engine. Compression testing is primarily use
to find one or more cylinders that have a great deal of difference in
compression than the others.
Thomas A. Anderson
<kev...@bellsouthgarbage.net> spewed his liquistic talents:
>"B.P. - iSpelunker.com" wrote:
I agree a good teakage test is probable a better indicator of overall
engine condition. BOTH test if performed properly are still only tools
for a GOOD mechanic to use in diagnosing an engine. Neither should be
considered the gospel. Things likes a worn cam shaft or bad cam timing
will not necessarily show up with either test. Neither will bearing
conditions.
Robert Hancock
:-) There's probably enough leakage past the rings in any engine that by the
time you got it up to TDC by hand, much of the compression would have leaked
out.
--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from hanc...@nospamhome.com
Home Page: http://www.roberthancock.com/
"Alex Rodriguez" <ad...@columbia.edu> wrote in message
news:9i54s4$k5p$1...@newsmaster.cc.columbia.edu...
Neil Nelson
andersonthomas_a@NO_SPAMhotmail.com wrote:
>I agree a good leakage test is probably a better indicator of overall
>engine condition. BOTH test if performed properly are still only tools
>for a GOOD mechanic to use in diagnosing an engine. Neither should be
>considered the gospel. Things likes a worn cam shaft or bad cam timing
>will not necessarily show up with either test. Neither will bearing
>conditions.
I'll respectfully disagree with part of this...
A running compression test can be very useful for diagnosing a worn cam lobe,
and can be useful at optimizing cam timing.
Of course, modern engine analyzer technology allows us faster, easier
methods to spot a worn cam or timing set.
hit the reply to sender@button.com mr_spock
stock
rings, apply compressed air to it, and you will without fail, hear some air
escaping. <<
Unquestionably true.