Intense read, loads of information here which is a weath of infomation for newbies like ME.

I think what was confsuing to most newbies is the fact that you have to look at the sweeps and each sweep is a rotor face. But which rotor face is it are we looking at in terms of compression.

But for all intese and purpose for the question is my motor blown or dying a regular piston tester will answer that question

hybrid

 

If you're using a piston compression tester, you can remove the bypass valve or just hold the pin in. We will need to see three pulses for all three rotor faces for each rotor, so the check valve needs to be bypassed.

Mazda has set minimum compression pressure to be at 70psi, but with the FD3S, the number has been lowered to 60psi. Good compression are readings anything above 100psi. Compression testing under 80psi is a sign of an engine requiring a rebuild soon. Compression should be even across all three rotor faces on both the front and rear rotors. It is more important to have all even compression numbers across the rotor faces versus one really high number on one face.

Unless you're using an official Mazda compression tester, you might need to "calibrate" your (piston) compression tester. Some compression testers read a little low, so it's nice to know what is good for your tester. If you're getting lower readings than expected, test a known good engine for it's compression to make sure the readings are valid. I had a compression tester that tested my motor at around 80psi, but this was what a normally good engine would read on this particular tester.

 

Well, *that* clarifies everything.:uh

 

I'm curious, why would you need to identify a specific rotor face with a specific compression reading? What does that buy you? Not being a smartass, just that I believe that would be irrelevant to determining the health of an engine and I'm trying to get your input.

Ah yes, that is true if you have a failed apex seal and/or possibly a damaged housing. But if it isn't "blown", will you have enough compression information from such a test to determine if the engine is something less than blown, still in acceptible condition perhaps, or soon in need of a rebuild or replacement?

 

I have always tested by holding the side valve down (I thought that was the only way) and I get sweeps of at least 80. I don't know where that 30 comes from. Now I'm gonna have to remove the bottom valve and compare.....

 

I'm a little late responding to your post, but I appreciate your comment and I couldn't agree more on everyone buying one.

Spoke with the SpeedSource guys at the recent Rolex 24 and they were very pleased with the multi-rotor tester they had purchased last fall. Got a nice "pat on the back" from both Sylvain Tremblay and David Haskell.

 

i used a compression tester and got horribly low compression results. considering 50 is the lowest PSI i guess the front rotor around 30-35PSI while the rear has 25-30PSI.

Mind you this is cold compression test, and i have had it running eight diffrent times since ive owned it. i have to inject some ATF everytime i want to start.

After it starts up it runs great, and even idles fine, just smokes horribly (im not running any catalitic converters though either).

do you think that possibly im gettin such low results because it hasnt been ran in a while (hence no oil being injected while running, low compression)?

by the way, all bounces were even for each rotor, only the front had higher numbers.

 

If those numbers are anyway near accurate, your engine is badly in need of a rebuild or replacement. Are you using a conventional tester? Make sure you are using it correctly. Better yet, have a good test done by a tech using a proper rotary-engine compression tester.

Otherwise, you should run the engine until it is fully warmed up before doing another compression test. That likely will NOT result in much of a difference in the numbers if the compression test was otherwise conducted correctly. Also, the gas pedal should be held to the floor during the test. That CAN make quite a difference in the readings. So it's probably worth running another test before springing for a rebuild or reman engine.

 

Quote from Rotary Resurrection

Compression test using a piston engine tester :

"1) note battery strength. A weak battery will yield low compression results.

2) Remove both lower plugs and wires.

3) remove EGI fuse from engine fusebox.

4) have a friend floor the accelerator pedal, opening the throttle for more airflow

5) insert your tester into the leading hole

6) hold the valve on the side of the tester open

7) have your friend crank the car over for 5+ seconds.

8) observe the needle bounces. You should see 3 in succession without skips, even bounces, in roughly the 30-35psi range.

9) let out on the valve now, and let the tester reach an overall compression value for all 3 faces(highest of 3 will be displayed). 115+ is like new, 100-115 is healthy, 90-100 is getting weak(1 year or less in most cases) below 90 could blow at any moment.

10) repeat for opposite rotor. Note difference in overall compression between rotors, which should be no more than 20psi max. "


you are supposed to see 30~ psi for each face...I still don't understand why there is not an authoritative standard for compression testing. misinformation is the reason so many people are confused.

 

Is there an echo in here?

 

There is an standard methodology and tool that will yield accurate, repeatable conclusive results-

http://rotarydiagnostics.com/

Every other method and tool degrades into a discussion of opinion, jousting, name calling-then silence...

 

http://www.mazdatrix.com/pictures/tools/t1-5.jpg

That tool is the "standard". Its Mazda's own.

As far as method descrepency, if you're not pleased with the differing methods formulated by some popular shops, the FSM has a clearly laid out method which is what Mazda uses in conjunciton with their own tester.

The incosistencies are only there because people ask for others opinions/their own methods instead of reading the stinkin' manual.

 

Absolutely I stand corrected here. Too bad it costs more than many '7 owners spend on their cars! The linked electronic tester from Larry may be more useful, because it is more accessible.

Mazdatrix Price Check
Part Name Description Part Number Price
TOOL COMPRESSION TST DIGITAL COMP TESTER 49-F018-9A0B $2,037.50

Sure, but then again, $2037.50 USD.

*$2037.50 USD* (repeated for effect)


You're preachin' to the choir, Brother.

The reason people ask for other opinions is that the piston compression testing methods, using differing pressures for guidelines from various sources send most rotary enthusiasts into confusion.

Personally, I am comfortable with my own methodology testing my own engines in my own cars for my own purposes. This thread has cleared up some things in my own mind. I feel I am quite solid on testing rotary engines with a piston compression tester. But the moment I want to sell a car (or honestly to buy a car) the gloves are off and the controversy begins again...