Buying my first rotary
01-18-2017, 06:06 AM
#1
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Buying my first rotary
Hey guys, i am fairly new to rotary engines and am looking to buy a rx-8. There is a very nice one for sale in the city I live in and it seems in really nice condition, have a family member who is a mechanic take a look at it and he said everything looks fine, apart from the psi on the compression test. The owner told me that her mechanic said the test was showing 85psi, I know there should be more than one reading, what would you guys advise ? I really want to buy this car but am afraid I may end up forking out more money just to do an engine rebuild, it has done 117,000 km and never had a previous rebuild, it's a 6 speed, manual, 2005 model.
01-18-2017, 08:15 AM
#2
There should be 6 numbers at a stated rpm, but none of those numbers should be 85. Pass or talk them down based on the need for a new engine. The best way to have it tested is a Mazda dealer with a rotary tester and it shouldn't be a big deal for them to have it done, if they believe the engine is healthy.
01-18-2017, 10:07 AM
#3
Yes, to be perfectly clear, no "rotary-specific compression test" = no deal.
And note that this test is not the same as an ordinary compression test performed on piston engines. It must be done by a Mazda mechanic at a Mazda dealer or by a mechanic who knows rotary engines.
I know... sounds like a pain in the neck to have to do this before purchase, but without it there's a very good chance you'll end up with an RX-8 that needs a new engine. It's that simple.
And note that this test is not the same as an ordinary compression test performed on piston engines. It must be done by a Mazda mechanic at a Mazda dealer or by a mechanic who knows rotary engines.
I know... sounds like a pain in the neck to have to do this before purchase, but without it there's a very good chance you'll end up with an RX-8 that needs a new engine. It's that simple.
01-19-2017, 11:54 AM
#5
40th anniversary Edition
Here is our chart to read your six rotary-speciifc compression numbers
RX8club's Rotary compression numbers chart
You should have gotten numbers in a format something like this:
Rotor 1: 7.5, 7.6, 7.5
Rotor 2: 7.2, 7.3, 7.3
250 RPM
- The 6 numbers, 3 for each rotor, are your compression scores, one for each face of each rotor in the engine.
- If you don't have all 6 rotor face scores and at least 1 RPM number, your compression scores are going to be vague and hard to interpret.
- You may also have your compression scores in a different scale, such as PSI.
- The RPM is the speed at which the test was done.
- The RPM is critical to interpreting the numbers, as rotary compression changes with engine speed, especially at low RPM.
- Since the engine is spun by your starter, this is ALSO a good indication of the health of your starter!
The general guideline for how good, or bad, the scores are, WHEN NORMALIZED TO 250 RPM AT SEA LEVEL!
You should have gotten numbers in a format something like this:
Rotor 1: 7.5, 7.6, 7.5
Rotor 2: 7.2, 7.3, 7.3
250 RPM
- The 6 numbers, 3 for each rotor, are your compression scores, one for each face of each rotor in the engine.
- If you don't have all 6 rotor face scores and at least 1 RPM number, your compression scores are going to be vague and hard to interpret.
- You may also have your compression scores in a different scale, such as PSI.
- The RPM is the speed at which the test was done.
- The RPM is critical to interpreting the numbers, as rotary compression changes with engine speed, especially at low RPM.
- Since the engine is spun by your starter, this is ALSO a good indication of the health of your starter!
The general guideline for how good, or bad, the scores are, WHEN NORMALIZED TO 250 RPM AT SEA LEVEL!
Last edited by gwilliams6; 01-19-2017 at 12:03 PM.