drakesword

So i just tested with my newly acquired compression tester from advanced.

Just on the top plugs i get about
front 33 per face 100 psi total
rear 30 per face 90 total.

About to do bottom plugs

sharingan 19

iTrader: (16)

why?

drakesword

just wanted to see if it was any different but it wasn't. When we put the gas peddle to the floor however, it was 35 per face and 120 total.

Did i read wrong or is it s'posed to be 90 psi per face. The seals seem fine as all of the faces are equal in pressure, unless there are no seals lmao.

farberio

iTrader: (7)

It should be 90 psi per face.

A piston compression tester has to be modified to work on a rotary, did you do that?

drakesword

probably not. . . what mods do i have to do?

farberio

iTrader: (7)

I don't know of the top of my hand, so you will want to search this one.

drakesword

I couldnt find anything other then to bypass the valve which i did by holding the button. The seals shouldn't be shot because the engine is s'posed to have about 30 - 35k miles on it. I will call the dealership to find what info they have on when they replaced the engine. If it wasn't replaced like the previous owned stated i'm going to his house for a little chateroo.

need RX7

iTrader: (4)

If the tester has a check valve with a button you press to relieve pressure, hold it down the whole time while cranking. You're looking for 3 even bounces of 85 psi or above. The numbers should all be close to each other, if 2 are drastically lower than the other, you have a stock or blown apex seal, if 1 is drastically lower, you could have a stuck side seal. If all 3 are very weak, you could have 2 or even 3 blown or stuck apex seals.

drakesword

i think its more likely theyre stuck then blown. So anyway to unstucked them without opening her up? Maybe a shitload of seafoam sitting overnight . Id rather avoid the "ATF trick".

need RX7

iTrader: (4)

I've heard marvel mystery oil works pretty well.

Go48

iTrader: (7)

As others have said, you can't just use a conventional compression tester on a rotary engine without removing the schrader valve or pressing the little button on the side of the gauge while cranking the engine. By watching the bounces you will get an approximation of the compression for each face as the engine turns over. If you get bounces of 30 psi when doing the test correctly, that is very low compression.

A total compression which you obviously arrived at by building to a total pressure after cranking the engine for several revolutions is meaningless in this engine. And, also as said, you will not find a significant difference in compression readings between the trailing and leading plug holes.

drakesword

yea thoes readings were from holding the button down. I think the seals may be sticking/stuck so the engine is currently bathing in a can of seafoam and mmo. Ill wait 24 hours and retreat then wait another 12 hours. If i dont see anything different ima take it to my mechanic to use his tester to confirm my 35/30 readings. Finally if its still low then i guess its rebuild time when i have the money. Shame on such a young engine.

platinumyama32

drake.. your safe.
some people through out the wrong advice.

taken from RotaryResurrection.com

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.

drakesword

so my results were in the ok range? Well the engine is going to be sparkling tonight.

Black Knight RX7 FC3S

iTrader: (7)

I always take out the check valve so I dont have to hold down the relief button.

platinumyama32

yes, your motor's in good condition.

the seafoam you just used to remove the built up carbon will only help things.

alexdimen

iTrader: (13)

You don't have to modify the tester, as pointed out above.

drakesword

well i dont understand why, maybe someone could explain, why a pressure reading varies from piston reader to rotary reader. In my mind 1 psi is the same no matter the container; tire, air tank, piston, and cylinder.

kenn_chan

a piston engine tester is designed for one cylinder, a rotary tester meaures the differences of each face and records them for comparison. Check out the thread I got running on a compression tester I just bought. it rocks.

Ken

Go48

iTrader: (7)

Glad to hear you like it Kenn! Now do you want the other 3 Acquisition Units for that 4-rotor you will some day build.

Larry

mazdafaacka

I just got done testing my motor with a standard comp tester minus the schrader valve.


Cold motor, WOT, CAS disconnected as per instructions from FSM.

According to the FSM, you leave the bottom two plugs installed while your testing the top two and then install the top two while testing the bottom two holes.

I had similar results on all holes. 3 even bounces of 90-95psi leading, trailing per rotor.

I believe this is the correct way of testing with the piston comp tester. Maybe you need the other plug in place to get an accurate reading, I would think that with both plugs removed per rotor that it wouldn't be able to squish the mix and therefore provide very low psi readings.

Motor has 109k on it.