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I was looking to get a compression test done, so I can start troubleshooting my hot start problems. My 8 has a rebuild with only about 15,000 on the new motor, so I was really hoping it wasn't low compression. So I called around everywhere and this shop swore up and down he had a rotary compression tester, and could do the test for me. I picked my car up and he told me that my compression was fine. He gave me a paper, and all it says is "Test compression. Front cylinder 100 lbs Rear cylinder 120 lbs" which I found odd because I don't see any results like that online. So, my question is. Are those numbers good?? Or did he not do the test correctly? Any guidance would be much appreciated!
I was looking to get a compression test done, so I can start troubleshooting my hot start problems. My 8 has a rebuild with only about 15,000 on the new motor, so I was really hoping it wasn't low compression. So I called around everywhere and this shop swore up and down he had a rotary compression tester, and could do the test for me. I picked my car up and he told me that my compression was fine. He gave me a paper, and all it says is "Test compression. Front cylinder 100 lbs Rear cylinder 120 lbs" which I found odd because I don't see any results like that online. So, my question is. Are those numbers good?? Or did he not do the test correctly? Any guidance would be much appreciated!
Yikes. Sorry to be the bearer of bad news, but the shop most likely did not have a rotary compression tester tool and simply just used an analog compression tester as one would with a piston engine.
Reasons why that doesn't work is simply because a rotary engine has three faces (and three seals) per rotor housing (cylinder, as shown by your test results). You need the compression scores for each face of the rotor, normalized to roughly 250RPM cranking speed.
As you can see you simply have two numbers there in your report, with no RPM information or individual rotor face data. Unfortunately that means that those numbers are essentially useless to you.
useless, I agree with TheClemsonFan, you should demand your money back. Then go get a rotary-specific proper compression test done by a Mazda dealer or rotary wrench with the proper rotary engine compression test equipment. You will get six numbers, one for each of three rotor faces, and for each of two rotors, plus your two starter rpm numbers, all then normalized to sea level altitude. Then follow our chart to interpret your resulting numbers:
Last edited by gwilliams6; 05-01-2017 at 07:50 AM.
Like others said, these results are NOT useful at all. In short, you can't use a piston engine analog compression tool to test the compression of a rotary engine.
Like others said, there will be 8 numbers in total: 3 numbers for rotor 1, 3 numbers for rotor 2, and the cranking RPM for both of them.
Once you get these numbers, use this to normalize your numbers, which will give you an idea of the condition of the engine.
My dealership is courteous enough to actually give me a photocopy of the results - most of the members from the States don't get one. It should run you US$150 or CAN$200 to get a test done at a Mazda dealership.
Last edited by UnknownJinX; 05-01-2017 at 01:10 AM.
It all depends in what region you're, the demographics and if you are one of their regular customers. It also depends on the experience of that dealership with Rotary's as I have seen some Mazda dealers have almost 0 knowledge of rotary engines and refer you to another dealer. I have even Heard of a dealer making it so hard on a customer for a warranty on an engine that they have you provide service Records and other kinds of problems they give you such as the car needs to show an obvious problem or a misfire code. Even up to the fact of having the upgraded starter so it could make compression without the correction which is ridiculous as this will only serve as a Band-Aid for the customer to continue driving the car as it is. They are supposed to refer it to North American Mazda And from there it's out of the dealerships hands as they will make the decision on whether to honor the warranty or further investigate. But we have no control over what Mazda decides because you either get a bad service writer or a technician to call you out to the service writer.
Last edited by 3RTR09eight; 05-04-2017 at 11:02 PM.
04-27-2017, 05:38 PM
