rxspeed87

then somebody needs to fix his page cause he is confusing and missleading people like you who are t hen trying to mislead other people

synesthete

^^WTF 5 posts to say the same thing!

Just let it rest for christs sake, someone already said there are different numbers you can get depending on tester and procedure. I already said i was wrong in stating that 30-35 psi was real compression per face. Regardless 30-35 psi per face has been my results on 2 different healthy rx7s. And tell me this... How is the amount of pressure blowing off going to change on the same tester, why would their be any difference its plugged into the same spark plug hole? All your looking for is even bounces and a compression of over 90 for each rotor.

Icemark

synesthete please do not post in this thread anymore. Your answers are clearly wrong and you don't understand the subject matter.

To clear things up.

When compression checking a motor, the motor should be warm, and the throttle should be fully held down while cranking at 500 RPM.

You check each rotor face. In an ideal world you would have a compression check like this:
120-120-120 or higher on each face.

Each face would show a full compression.

If you have a compression check of any face under 80 the motor needs rebuilding (although myself I consider anything under 90 psi as needing rebuilding as the parts are near failing, but probably have not worn out anything too expensive at that point.

a compression check of 90-30-90 would show a blown side seal

A compression check of 30-30-90 would show a blown apex seal

synesthete

So your telling me that both my rx7s are blown on all 6 faces, even though they run great, and the posters motor is blown even though he believes it is healthy..... And rotary resurection lies about the numbers you will see. I may be confused on what im actually measuring but at least im not screaming rebuild to someone with a healthy motor.... I concede this argument, no more posts from me.

Icemark

The key is you are only doing half the test if you are following Kevins write up:

You were holding the valve on an piston compression gauge... not letting the valve out.

So again, it points to you didn't know what you were doing

So to further clarify the simple subject:

Holding the valve in you are looking at the differences between rotor faces, letting the valve out you are looking at actual compression. Holding the valve in and seeing 30 PSI is nothing, and only half the test. That only shows the difference between rotor faces and not the actual compression

synesthete

Actually i've been saying to do both. And with both compression testers i've used if you dont hold the valve open you get 1 reading only, little or no bounce at all.

I think i lost my credibility when i said the rotors compression was total of the faces, I can understand that, sorry for my ignorance, but as far as i know that was only mis-information i posted. But i apologize for the confusion.

Icemark

Of course this is why I say use a rotary compression checker or build your own.

Piston checkers are easily mis-understood when doing a check on a rotary motor.

inflatablepets

Thats because you got

JFR

Okay, so the numbers I got show that I DO NOT have a blown motor, right? They do show that the compression could be low, or it could not be low, because I need to test it without holding the valve in? Am I getting this right? If so, how come when I don't hold the valve in, I just get like 110 and not like 110-110-110? Is that because I don't have the other valve on my tester to let the needle fall back down or because technically, it is for a piston motor?

So what I need to see after knowing that it's not blown, is like 110-115 without holding the valve in? And that's it?.... Good motor?

rxspeed87

sorry I will make what I was saying a little more clear. different testers depending on how big their bleeder valve is can vary the amount of the reading.
so you tested a good motor on 35psi doesn't mean that is the best way to do the test.
you want even bounces your right. and your right you want them over 90. but if you are holding the valve open that is releasing pressure. if the pressure gets released it never makes it to the tester. therefor you really don't know what pressure your motor is really making cause there is so much pressure being bled out to the open air that doesn't even get tested

rxspeed87

and if anything icemark wouldn't a tester without the valve in there in the first place be the best method?

rxspeed87

that valve is just a one way valve. once the motor pushes air into the tester the one way valve holds it in there and doesn't release the pressure till you push the button. most of the engines out there are piston engines and you really are testing only one cylinder, one piston and so forth. this way with that valve in there you take out your spark plug screw in the tester go into your car and crank it then come out and read what it says. makes life easy if you want to do something like this on your own. if that valve wasn't there you would need someone watching the meter as you crank so it would require two people. remember we in america are lazy . now since it is a one way valve though and holds that pressure in the tester itself it can only read peaks and that is all. but when you have someone crank on the motor and you hold the valve in not all your pressure is going to the tester. most of it just squirts out the valve and you only read 30 psi. that 30psi means nothing for the health of the motor. only thing it might SEMI be usefull for is making sure yuo have even pulses but even that I would be leary of being that most the pressure just gets released to atmosphere bypassing the tester. best test would be to remove the valve all together and make sure you have even pulses then. this way you should read much higher numbers and be more accurate as the full pressure should be pushing againt the tester. also since the valve isn't in there the pressure will get released again as the rotor moves away from the spark plug on what would be the power cycle of the engine.


icemark I do have a question for you though. as far as the tester goes since I haven't had a chance to really try this yet. when using a tester for a piston motor with the check valve removed vs with it in there how much of a difference should peak pressure be? I know at least with a piston motor using the valve it takes a few cranks to actually get a peak reading. which one would be best to go by for the peak?

RETed

Holy crap, we got people that don't understand the concept of "pressure"?

http://fc3spro.com/TECH/FAQ/compress.html

Sorry for the late reply, but I just got around to reading the PM from the original poster...


-Ted

Icemark

Yes, that is what I use.

Also as Ted reminded me, (and I didn't post before) compression should be checked in the trailing plug holes. Yep the "T"op spark plug holes.