compression check
06-03-2005, 01:35 PM
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compression check
i know i can have it done by the dealer. i'm not a mechanic but is there an easy way to do this at home? I would wanna check the compression once in a while. please advise. thanks.
06-03-2005, 04:16 PM
#2
it takes a special equipment to tell you the individual compression of each rotor side and the rpm, I saw a new one on Mazdatrix for mid-$1600 range, apparently it has to synch with the timing/position sensors and uses a pressure transducer
here's a general kluge, it will only detect a bad situation
here's a general kluge, it will only detect a bad situation
Compression Tests on Mazda Rotary Engines
by Jim Newkirk
Mazda rotary engines have been around for a number of years now and yet are some of the most misunderstood power plants in the industry today. One of the most common misconceptions is that a special Mazda test tool is required for compression testing a rotary engine. It is true that if the Mazda electronic or thermal graph compression testers are available they will produce quick, accurate and easy-to-interpret results. Terrific if you work in a Mazda dealership, but not so good for the rest of us. The good news is that a manual compression test is possible on the rotary engine using a standard compression gauge set.
The rotary engine used in the RX-7 consists of two rotor chambers each containing a three-sided rotor. Each corner of the rotor has an "apex seal" dividing it into three compression producing regions. As a rotary engine turns, three distinct compression pulses are produced for each revolution of the rotor. These compression pulses can be monitored with a compression gauge placed in the trailing spark plug hole. Remove the Schrader valve from the compression tester. This enables the compression tester to register each pulse as the rotor turns. A compression pulse will cause the needle of the compression gauge to jump up momentarily. The compression pulses must be in a regular pattern and even in intensity. This tests the integrity of each apex seal. A failed apex seal will cause the pulses to become uneven in intensity. If the pulses are in a regular pattern and even in intensity, the engine should be able to produce about 85 psi of compression. To test for available compression, replace the Schrader valve in the compression tester and place it once again in the trailing side spark plug hole. Crank the engine - compression should be about 85 psi.
The Mazda compression testers test engine compression and apex seal integrity in essentially the same manner as the manual test. In other words, the Mazda testers monitor compression pulses and total compression and provide the technician with an easy-to-read result. While not as accurate as the electronic testers, the manual test will give the technician a good idea of the internal condition of the rotary engine.
Jim Newkirk is ASE master and L1 certified. He is an IDENTIFIX Asian and European carline specialist with 22 years of experience.
by Jim Newkirk
Mazda rotary engines have been around for a number of years now and yet are some of the most misunderstood power plants in the industry today. One of the most common misconceptions is that a special Mazda test tool is required for compression testing a rotary engine. It is true that if the Mazda electronic or thermal graph compression testers are available they will produce quick, accurate and easy-to-interpret results. Terrific if you work in a Mazda dealership, but not so good for the rest of us. The good news is that a manual compression test is possible on the rotary engine using a standard compression gauge set.
The rotary engine used in the RX-7 consists of two rotor chambers each containing a three-sided rotor. Each corner of the rotor has an "apex seal" dividing it into three compression producing regions. As a rotary engine turns, three distinct compression pulses are produced for each revolution of the rotor. These compression pulses can be monitored with a compression gauge placed in the trailing spark plug hole. Remove the Schrader valve from the compression tester. This enables the compression tester to register each pulse as the rotor turns. A compression pulse will cause the needle of the compression gauge to jump up momentarily. The compression pulses must be in a regular pattern and even in intensity. This tests the integrity of each apex seal. A failed apex seal will cause the pulses to become uneven in intensity. If the pulses are in a regular pattern and even in intensity, the engine should be able to produce about 85 psi of compression. To test for available compression, replace the Schrader valve in the compression tester and place it once again in the trailing side spark plug hole. Crank the engine - compression should be about 85 psi.
The Mazda compression testers test engine compression and apex seal integrity in essentially the same manner as the manual test. In other words, the Mazda testers monitor compression pulses and total compression and provide the technician with an easy-to-read result. While not as accurate as the electronic testers, the manual test will give the technician a good idea of the internal condition of the rotary engine.
Jim Newkirk is ASE master and L1 certified. He is an IDENTIFIX Asian and European carline specialist with 22 years of experience.
06-03-2005, 05:20 PM
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tester is expensive, manual test sounds difficult to undertake expecially for a non-mechanic like me, i guess i would rather get it from the dealer. much needed before the warranty runs out.
06-05-2005, 05:00 PM
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I tested mine at 1200 miles to have some reference. I use the digital factory tester
which records cranking RPM and 3 compression readings per rotor (as explained above) Readings were in the 7kg/cm3 range which would be ok to fair normally but the cranking rpm was very low as you may have noticed with your own 8's.
I normally see about 250-265 rpm cranking speed from most 1rst-3rd gens and my 8 cranked at 200rpm. I have not tested with the new battery/starter combo but it's noticeably faster turning over.
Dealers can use the WDS for compression test or the old unit like I've got.
which records cranking RPM and 3 compression readings per rotor (as explained above) Readings were in the 7kg/cm3 range which would be ok to fair normally but the cranking rpm was very low as you may have noticed with your own 8's.
I normally see about 250-265 rpm cranking speed from most 1rst-3rd gens and my 8 cranked at 200rpm. I have not tested with the new battery/starter combo but it's noticeably faster turning over.
Dealers can use the WDS for compression test or the old unit like I've got.
06-05-2005, 05:33 PM
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I'm not a mechanic either, but those directions do not sound difficult at all.
All you need to do is removove the trainling plug, attatch the manual compression tester without the valve and look for erratic pulses, then attatch the tester with the valve to get the psi. Most likely, you do it once on each rotor. The plugs are easy to get to if you pull the left front tire. You may be able to get to the trainling plugs from under the car without pulling the tire.
So, does anyone know if the manual method is a good indicator of compression goodness?
All you need to do is removove the trainling plug, attatch the manual compression tester without the valve and look for erratic pulses, then attatch the tester with the valve to get the psi. Most likely, you do it once on each rotor. The plugs are easy to get to if you pull the left front tire. You may be able to get to the trainling plugs from under the car without pulling the tire.
So, does anyone know if the manual method is a good indicator of compression goodness?
Originally Posted by tRiX8
tester is expensive, manual test sounds difficult to undertake expecially for a non-mechanic like me, i guess i would rather get it from the dealer. much needed before the warranty runs out.
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