rotary compression tester
 

Hey I have been searching this forum as well as others to see what people do for a compression test.

I see a lot of people use regular piston comp. testers but I know that it’s no the most accurate.

I have been searching and found this website

http://rotarydiagnostics.com/

This seems to be pretty dam close to a OEM tester except its does not have an immediate digital read out.

Has anyone bought this or used this before?


Hybrid

Nice! I didn't know anyone but Mazda even made 2 rotor rotary compression testers.

That tester has the potential to be very accurate. With advances in circuitry and measuring tools over 20+ years ago I'd bet these work quite well.

That's not a bad price at all honestly speaking. Granted it's not as cheap as good ol' normal comptester, but it's nice to see tools designed specifically for the 13b

I think Mazdatrix has a rotary compression tester (it may be whatever Mazda uses)...

Yes, but its super expensive, way to much for anyone to ever buy one for themselves.

350 bills for the basic model???? 400 for the multi rotor tester w/out accessories.... that's way to expensive for a no money having college student like myself. I could get my car tuned for that amount...plus pay to have a shop do the compression test for me and still have money for a new cd. Or I could take that 400 add three more testers and have a new engine..

I won't be buying one anytime soon either, but this could be a great purchase for the picky diy mechanic or guys who run a rotary shop.

I wouldn't pay more than $100 for a rotary engine specific tester. That's my limit, and I think it's reasonable.

Why wouldn't it be?
Have a problem with something non digital?
Your eyes have a hard time trying to follow the sweeps of an analog gauge?
Your typical piston compressor tester allows you to check the condition of your rotary engine just as good as fancy schmancy "rotary" compression tester for a fraction of the cost.

BTW, I've seen "custom" testers built with just a MAP sensor and a datalogger for about $200...

And...why is this stuck in the FC section?


-Ted

just used a old analog tester on my car today...and it worked perfectly. I paid 32 + - dollars for it at the auto parts store....

swoosh...swooosh...swoosh...90 psi

so what is a good compression for the 13b is there a range or limit or something

1-2 psi is good. Front Rotors only!

90-100 = Good
100-110 = Very Good
>110 = Excellent

Eh.. I could see me buying that for that much... I like spending way too much for a cool tool.. Even though my analog one works fine, it would be nice to have something cool like that.

hey those ranges are for after the engine has been warmed and shut off right?
what are ranges for cold compression test??
the problem is a no-start unless deflooded and ATF is thrown in there
im trying to figure out if i have low compression or a falulty injector :uhh:

i should really have included more information about the problem =\

purchased my 88 convertable for $1500 (wish i had pics to show) with the belief of a blown motor.

after tinkering around, (deflooded and squirted in some ATF) the beast fired up and it smoked like a forest fire (due to many things--no catalitic converters being one of them)

after warming up it idled out and seemed to be running great... still smoking (hopefully due in most part by having no cats).

it does not start at all without doing this process.

im thinking that i have either low compression (not enough to start car, but enough to run on) and im temporarily solving the problem every startup by injecting ATF

or

i have a faulty injector that is flooding it out before it has a chance to start (i dont touch accelorator at all... just sit ready to catch it if it tries to start)

any suggestions would be wonderful. thanks.

That is correct.


Numbers are not consistent for "cold".
This is why Mazda does these test when the engine is fully warm.
An engine sitting in -30F temps is going to push a *little* differently than an engine sitting at 70F.
Get my point?


SLIGHTLY low compression is not going to cause the engine to not run.
You don't even need a gauge or a tester to see if compression is preventing the car from running...
Just remove both trailing spark plugs and listen for CONSISTENT "whooshes" from the spark plug holes.
It'll sound obvious if compression is uneven.


-Ted

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You SEEM to be saying that it won't start when cold. Most RX will low compression seem to start good Cold but hard to start Hot. Your case is the opposite.

What can cause a hard/difficult start when cold, is a bad water thermo sensor. With the key to ON, engine OFF, go check the voltage on pin 2I at the middle ECU plug. It's a green/white wire. With a fully HOT engine it'll read a half volt dc approx. Can't tell you what it reads cold. Depends on the temperature.

There is a way of checking the sensor per the FSM. Emissions and Fuel section.

If your engine is hard to start both hot and cold........probably isn't the signal from the water thermo sensor. A open signal from the water themo sensor on the whole can't cause a Hot start problem since it defaults to 180* F when the ECU sees a open b/t the ECU and sensor.

You might just go look and see if the plug is on the sensor, and if it is, then take the plug off and see if one of the sockets is *pushed back* in the plug not making contact.

A person could go to Sears and buy a Fluke PV350 pressure transducer. It reads up to 500 psi. You connect it to a common digital voltmeter and put the voltmeter on DCMV. One MV equals one psi.

You need to remove the check valve in a piston compression checker for it to work right. The reason is b/c you need 3 seperate numbers per rotor, and with that check valve the compression tester will only give you 1 (the highest one).

$350 for the linked tester is cheap compared to $3k for the mazda tester.

Well, if you leave the valve in you can test for maximum compression reached by any face, then hold it in to check for even compression on each face. If you remove it, you lose half of the gauge's function.

When using a standard compression gauge-
 

Has anyone ever noticed the variance in testing methodology amongst even the 'experts' on this forum? I find it confusing. The differences lend confusion to diagnosing a motor. The very same test results can be interpreted to either bash or to pump an engine or car that is for sale.

What about a 90 psi test result on rear and 92 on front? This is one man's great result and another claims the engine is 'about to pop'. Now, frequently, this becomes part of the negotiation regarding the sale of a vehicle.

I think this tester is valuable in documenting the state of an engine prior to sale. If I were in the business of selling/rebuilding rotaries, I would have one.

Failing that, why doesn't the community at least standardize the methodology and interpretation of the test using the piston compression tester?

Back to the tpic at hand, the reason i was looking for a real rotary tster was with my piston tester i am not able to tell wich face of the rotoor i am testing.

So how do ou remove the check valve in the piston compression tester?

I will have to test this again

Hybrid.

great point!!!!!!!!




hybrid

First of all, all compressors tester gauges are not created equal.
What could be "great" on one tester (i.s. 120psi) could be "marginal" on another tester (i.e. 100psi).
So which is more accurate?

Even the official Mazda rotary engine compression tester needs to be calibrated.

This is why you should stick to one gauge that you know well.
Over several engines, you get a very good idea of what is "good" and what is "bad".
A lot of these compressor testers (that thread into the spark plug holes) have o-rings on them; a bad o-ring can drop the numbers into the marginal or "fail" ranges.
Having a loose fittings can do the same...
Having a leak in the hose can do the same...
Not threading the fitting properly into the spark plug hole can do the same...
Get the picture?

I use these things to get a *general* idea of what the engine is like.
I don't care of the engine pumps out 115 psi versus 105psi - this difference isn't THAT bad.
I think people are getting too hung up on high numbers.
Remember, Mazda spec allows a *20psi* variance between front versus rear - thus, an engine pumping out 120psi front and 105psi rear is OK in Mazda's book.
What I look for is variance between rotor faces and BIG differences front versus rear.
Significant variances between rotor faces can expose a cracked / damaged / stuck apex or side seal.
Big differences front versus rear can expose a "blown" rotor.
Of course, an abnormally low front and rear test can mean a totally junk engine.


-Ted

Thank you for your insight on that Ted. I suspect that the LENGTH of the hose makes a difference as well. I am sure that I will get a different PSI max with an 18" hose vs. a gauge threaded directly into the spark plug hole.
With the 'bounce' part of the test, the damping of the individual gauge will make an enormous difference in the psi of the bounce-what is important here is that the bounces are relatively uniform, not what PSI the bounces attain.


This testing can accurately identify the following:
1.) Blown apex seals/side seals.
2.) Compression uniformity between rotor faces.
3.) Relative compression between front and rear rotors,
4.) Extremely low overall compression, ie. a worn out motor.

What it cannot do is the following:
1.) Tell you if the motor is fragile, i.e. 'about to pop'.
2.) Tell if an engine is in really excellent condition.
3.) Tell you relatively fine differences between the faces on a rotor.

And we didn't even go into the cranking speed calibration.