Compression Check
02-07-2004 | 09:45 AM
#2
Senior Member
Joined: May 2003
Posts: 989
From: Dover DE
Ok since I am in a typing mood this morning I will list some of the basics for a compression test.
1) tools needed: Spark plug socket and ratchet, Compression testor (more on this later) flathead screwdriver, and the most important, a fully charged battery! Starter button (optional for one person operations)
2) the prep work, remove the EGI fuse, located in the engine compartment in the main black fuse block. remove the air filter and air flow sensor ( if you have a N/A remove the inlet duct to the throttle body, if you have a turbo remove the top mount intercooler this will take these items out for restriction elimination) Remove the leading plugs on both rotors, and place them aside. If doing a one person setup connect the starter button cables as follows, one to the small terminal on the starter and the other to the battery cable on the starter. also wedge the throttle open to full. If using the two person method the starter and the throttle can be controlled by the other individual.
3) compression tester, most of us do not have the money to purchase a Mazda digital compression testor so the average $29.95 auto store piston engine type is used. most of these units have a peak hold feature which comes from a schrader valve in the line (if you have a push button release on the unit, just hold the release, if you do not, you need to purchase a tire valves stem removal tool and remove it from the line)
4 The test... Ok we have our unit ready, install it in the laeding plug of the front rotor and crank the engine over, having the unit in your hand look at the max numbers the needle hits 3 times. This may take several tries to get them right and see what I am talking about, but you need 3 not 4, not 6 not 10 just 3, I suggest once you get the reading of the gauge down you do it one last time to get the best readings, then repeat on the rear rotor.
Now there will be posts below me saying I have added too many steps, I have told you to take off things you do not need, etc etc. Use my information as you see fit, but I will explain my reasons here quickly before the flames begin
Removal of the intake ducting or intercooler is to make sure there are no restrictions into the throttle body, and wedging the throttle open gives you a more accurate reading as far as compression. Trying to get an accurate reading through closed throttle blades, an air filter and a turbo will not give as accurate readings as the steps I have listed.
When finished just put everything back together in the reverse order it was removed.
Hope this helps, and feel free to ask questions if you do not understand anything I have posted.
1) tools needed: Spark plug socket and ratchet, Compression testor (more on this later) flathead screwdriver, and the most important, a fully charged battery! Starter button (optional for one person operations)
2) the prep work, remove the EGI fuse, located in the engine compartment in the main black fuse block. remove the air filter and air flow sensor ( if you have a N/A remove the inlet duct to the throttle body, if you have a turbo remove the top mount intercooler this will take these items out for restriction elimination) Remove the leading plugs on both rotors, and place them aside. If doing a one person setup connect the starter button cables as follows, one to the small terminal on the starter and the other to the battery cable on the starter. also wedge the throttle open to full. If using the two person method the starter and the throttle can be controlled by the other individual.
3) compression tester, most of us do not have the money to purchase a Mazda digital compression testor so the average $29.95 auto store piston engine type is used. most of these units have a peak hold feature which comes from a schrader valve in the line (if you have a push button release on the unit, just hold the release, if you do not, you need to purchase a tire valves stem removal tool and remove it from the line)
4 The test... Ok we have our unit ready, install it in the laeding plug of the front rotor and crank the engine over, having the unit in your hand look at the max numbers the needle hits 3 times. This may take several tries to get them right and see what I am talking about, but you need 3 not 4, not 6 not 10 just 3, I suggest once you get the reading of the gauge down you do it one last time to get the best readings, then repeat on the rear rotor.
Now there will be posts below me saying I have added too many steps, I have told you to take off things you do not need, etc etc. Use my information as you see fit, but I will explain my reasons here quickly before the flames begin
Removal of the intake ducting or intercooler is to make sure there are no restrictions into the throttle body, and wedging the throttle open gives you a more accurate reading as far as compression. Trying to get an accurate reading through closed throttle blades, an air filter and a turbo will not give as accurate readings as the steps I have listed.
When finished just put everything back together in the reverse order it was removed.
Hope this helps, and feel free to ask questions if you do not understand anything I have posted.
02-07-2004 | 01:00 PM
#3
Thread Starter
Senior Member
Joined: Jun 2003
Posts: 224
From: Panama City, Florida
I know how to do the test. I was just wondering what the reading difference would be if it had a bad seal. I had 93 on front and 74 on rear. I just did the MMO trick and have not tested it yet though.
02-07-2004 | 01:29 PM
#4
Senior Member
Joined: May 2003
Posts: 989
From: Dover DE
you have one reading or that is the average of three?
if you have 90/20/20 that would be the sign of a blown apex seal
or 90/70/70 would be a sign of a burnt corner on an apex seal.
these are just exapmples of how the numbers may look, not true known examples of bad motors
if you have 90/20/20 that would be the sign of a blown apex seal
or 90/70/70 would be a sign of a burnt corner on an apex seal.
these are just exapmples of how the numbers may look, not true known examples of bad motors
02-07-2004 | 03:50 PM
#7
Senior Member
Joined: Apr 2002
Posts: 2,930
From: IL
don't forget you need to know the approximate rpm the test is done at.
you can time the test to 15 seconds and count the # of spikes you get (assuming you get 3 spikes for 3 sides of the rotor, not blown to hell).
after 15 seconds take the count and multiply it by 4 and thats your test rpm.
this only matters if you are trying to get useful #'s out of it, not simply trying to see if it's blown vs not blown, that is obvious without any knowledge of the cranking rpm.
you can time the test to 15 seconds and count the # of spikes you get (assuming you get 3 spikes for 3 sides of the rotor, not blown to hell).
after 15 seconds take the count and multiply it by 4 and thats your test rpm.
this only matters if you are trying to get useful #'s out of it, not simply trying to see if it's blown vs not blown, that is obvious without any knowledge of the cranking rpm.
02-07-2004 | 04:14 PM
#8
Thread Starter
Senior Member
Joined: Jun 2003
Posts: 224
From: Panama City, Florida
I have no idea what that rpm thing means. All I know is that when I did that compression test, I saw it bounce three times and ended up at that number for the rotor. Am I doing it wrong?
02-07-2004 | 05:23 PM
#9
Senior Member
Joined: Jul 2002
Posts: 2,315
well it sounds like you are halfway there.. when the engine spins/cranks faster (at more rpm) the compression numbers will be affected and increase. are you trying to see the exact numbers for the compression? if so you have to consider that you said you put mmo in the engine, that will definately throw off your numbers because the oil won't be in your engine all the time lubricating correct? so first off clean out all the oil you have in there and let it dry. then follow pengaru's method to test. otherwise if you are just trying to see if it needs a refresh rebuild just look to see if all sides have compression and are uniform in psi.
02-09-2004 | 09:55 PM
#10
Thread Starter
Senior Member
Joined: Jun 2003
Posts: 224
From: Panama City, Florida
Well I don't know if the coolant seals are good because I can see a little water or moisture in the oil. But I don't know if it is the seals or not, because there is moisture right at the filler tube too.