Did a compression test today with a piston tester. Front and rear housings both had 3 even bumps of 35...with the release valve held it...and with it not held it it would pump the gauge up to about 100 or maybe a little over....is this normal or did i not do it right? engine was warm and throttle held open...

 

Sounds pretty normal to me...

 

If the compression for each face of each rotor is really 35 psi, your engine is toast. Have a proper test done with a proper compression tester before you make any drastic decisions, however.

 

car runs perfect so im guessing its not 35....best running TII ive ever had!

 

fixed!

 

Too bad you don't know what you're talking about. "Overall" compression is meaningless in this engine. Ya gotta know the compression for each individual rotor face in order to evaluate engine health.

 

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A piston tester is NOT appropriate to test a rotary engine.

With the release valve held in, you will not see the true pressure of the rotor face.
With the release valve in normal position, you will not see the three faces individually.

There is no winning way to use one and get an accurate picture of how the engine is performing. You're better off saving your cash on the tester and removing the leading spark plug and listening the the air pulses... Or if you've got cash, get a tester...

The best alternative is to find your local dealer that has a tester or find a local rotor head that has one.

 

And why is that? From my understanding with the release valve held in it becomes just like any other pressure tester. The only difference is that it lets the pressure escape through the valve so the readings must be taken quickly. The reading is probably lower since the valve is open allowing some pressure to escape but still closer and more useful from a diagnostics standpoint than listening to the pulses...Last time the test on my engine I got 105psi for every face which is normal.

 

well my local mazda dealer wants 267 dollars for a compression test and says it take 2 days to do it!! so thats no option i just borrowed my friends tester and did it... i kno its not the right or most accurate way but still 267 bucks!

 

Proper compression test procedure using standard tester. HERE
Having the valve open will tell you if you have even pulses on each rotor face.
Having the valve closed will tell you the compression itself.

How is this not better than listening with your ear?
Get a brain morans!

 

ussually u can remove the shrader valve at the end of the tester that screws into the motor, and be able to watch all 3 full bounces,

that way u dont have to hold the release valve open and wathc small bounces, and only see 1 full bounce with it not open.

 

i had 3 even pules with it open and it pumped up to just over 100 closed so good to go!

 

When did a conventional compression tester ever become an unacceptable method? Its been used by thousands for a long while now. I think the problem lies in the fact that there's a procedure to follow and when people don't follow it they get incorrect readings so they blow the whole thing off as wildly inaccurate.

 

lol yeah most people i know that say its no good to use, cause they arnt using it right, lol ive tested 10+ engines iwth a wide variety of results ranging from very crappy high milage to brand new engines.

 

Hmmm, first of all it's MORON.

Second, take a look at the attached graphic. This is from a compression test of an engine with one failed apex seal. As you can see, with one bad apex seal, two faces are reading low but one is showing reasonable compression of ~107 PSI. Now, if using a conventional compression tester, with the schraeder valve removed or the button held in, on this rotor housing, you would likely get one decent bounce and two that are considerably less. Agreed?

Then if you let the compression build by not releasing the pressure in the conventional tester it will build to ~107 PSI. Does that mean the compression in this housing is at an acceptible level? I don't think so.

BTW, you might want to ask Banzai which compression tester system they use.

 

Well if you hold the valve open you won't see even bounces.

 

Sarcasm... look it up!

... And yes, I am still right and you are wrong.

 

You'll still see that compression is wrong. There's entirely too much emphasis here being placed on overall compression. Its the bounces. Overall like stated will simply be the strongest face of the rotor.

 

correction sir you are WRONG and he is right you CANNOT use a piston tester you will NOT get the correct readings.. period the end theres really no argument over it

TwEaK

 

When I checked mine I took the shrader valve outta my dad's snap-on tester when I tested the current motor in my 7. Don't remember what it read but it gave me a general idea of the health of my seals. I just look for good or bad when using a piston tester.

 

You morons are all arguing semantics.

If you see three equal bounces with the piston tester held open, then the average number is a good reference. If you see anything BUT three even bounces, then the average number is irrelevant.

 

i've tested tons of motors with piston testers you don't need to know the exact compression numbers to know if you engine is good or not..a side seal went out on my turboII checked it with a piston tester it showed around 37 on two faces and zero on the other this is how i knew it was a side seal. three even pulses on a piston tester and your good to go unless its showing very low compression on each face.

 

Obviously using a piston tester isn't ideal... but it is much better than no data at all...

 

Farberio nailed it.

 

From your link:


Reading the whole text of a link is good.

Key points as to why the test is not appropriate have been emphasized.
1.) Reading will be artificially low due to pressure bleeding off.
2.) Reading must be taken while needle is bouncing around.

A peak and hold gauge might be helpful, however, rotary specific testers are so cheap that anyone can buy one. I own one. It was approx $250 plus shipping.

Contact TwistedRotors on here for one...
http://www.twistedrotors.com/

Or swing by my house with an acceptable form of payment a spark plug socket, and a ratchet... Acceptable payment can be any one of the following:
-US$20
-One case of Yuengling (You may partake as well.) or any microbrew so long as it's not an IPA.
-Two 2/3lb burgers from Five Guys or Fuddruckers... (One with Jalapeno cheese, lettuce, tomato, pickles, onions, shrooms, BBQ sauce, a shot of Ketchup, mustard, and mayo on it... The other one gets whatever you want on it. You eat it.)
-Extra Large Pizza (Preferably Hawaiian, but whatever works, so long as there's no Anchovies.)

Payments may change based on how hungry I am or how much time I have to kick around.

See above. You can get unlimited compression checks for you and your friends for that price... If you sell your RX-7, you can use it to test a new one. If you get out of the game entirely, you can recoup some of our cost by reselling the used tester.

In addition, the use of it does not take two days. It takes about half an hour... Including time to polish off a beer and bullshit around.

Never said it was unacceptable. It's not appropriate.

-The data you get from it is not 100% accurate.
-It requires modification of the tester.
-The procedure must be strictly adhered to.

In addition, there is a variable.

What if I press my schrader valve harder than you press yours...
My readings will be lower and drop faster than yours...
Up until I actually press hard enough to cover the schrader valve completely with my thumb, then we go back to my values not dropping as fast or at all if the engine is bad enough.

Compression results also vary based on RPM... A bad bearing, thick oil, or an old battery, battery cables, or starter can throw the results off a bit.
Collecting your RPM numbers along with the test results is helpful.

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