JFR

Alright, this is quite a common topic, I know, I've searched. I just haven't gotten the exact answer(s) I need.

So a while back, I bought a normal piston compression tester, which looks like this...

[IMG][/IMG]

Alright cool. Lets test the compression. So I have read that you don't want the total PSI for each face of the rotor. I've read to hold the valve on the side in, to let the needle bounce for each face. (I also read later to just remove it, but I'm not sure if it's the right valve; I read there are sometimes two valves.)

Okay. The compression I got was 35, 35, 35 for the rear rotor. Front rotor, I got between 33-35 for all three faces. All bounces of the needle were even with each other for each rotor. I read somewhere a while back that those were good numbers. Then I also read that I want numbers like 110-110-110 for each rotor. After reading that the numbers I got show the engine has low compression, I was a little confused because I read different numbers I should get when I test it.

I tested it correctly, unplugged crank- angle sensor, EGI fuse, put the tester in the top spark plug hole( I forget which one is L and which one is T) and floored the accelerator while cranking. This is all following the instructions listed in the Haynes manual.

Anyway, I read that someone else had got similar numbers as I did, all around 35. Then I read more and found out that the low numbers could have been because they didn't completely remove the valve on the side, and instead just held it in, as I did.

I am going to test the compression one more time, but I have a question about the tester itself. Supposedly there could be two valves, but mine only has one shown in the picture above. Is that the valve that I have read about to remove completely? Or is this not a suitable tester, though I'm pretty sure it would be? Well, if it is, how do I remove it? It doesn't just unscrew.

[IMG][/IMG]

[IMG][/IMG]


Sorry for the low quality images, they're from my phone and such a long post for a simple thing to do, I just want to make sure I get this straight so I can go from there.

Thanks,
Jordan

synesthete

You want between 30-35 on each face. Sounds like your motor is healthy. If you are using a tester that has no check valve, It will give you 3 readings for the whole rotor instead of the true compression of that face.

JFR

Hrrmmm.... can anyone explain why I have been reading that I need around 110 on each face or so? I have also been told this too, and that I have tested it incorrectly. Honestly, I think the engine is good, the "psssh's" it makes while testing are strong, even sounds. But hey, I could be wrong.

ticalll

i think you want 70 +

inflatablepets

Please don't post such mis-information. My tester has the Schrader valve removed and I pull almopst 130 PSI per rotor face. If you have 30-35 per face than your car is not in running order.

synesthete

The compression on these things is measured by each face (3 faces per rotor) or as a total compression rating of each rotor. So if you have a piston tester with no release valve than it will crank and keep showing you the total rotor. With a release valve you will see it bounce 3 times quickly showing a reading for each face.

SO
With the proper tester you will get 30+ 3 times each. Close the valve and you get a total. If your tester has no valve it will show you 3 maybe slightly different numbers but they would all be measuring in fact total compression on that rotor. The limit for a healthy motor is 85-90 on each rotor with no rotor or face significantly lower than the others. Rotaries are not high compression motors. If your seeing 3 bounces of 30+ OR a reading of 90 or more you are "healthy" Sorry if this doesnt help. If you were told you should have 110 on each face than that is not being tested the correct way. You have tested it correctly yourself and have good compression.

synesthete

Your not testing it right, and you are yourself posting mis-information. Though you have good compression for the whole rotor, you dont have any idea what each face looks like.

JFR

Thanks. I hope your right. But there are still many people out there that think it should be around 35 and many think it's supposed to be around 110.

gscully

a friend of mine got one of those testers when we went to test his car and the part that you want to remove is at the tip where you screw it into the hole for you spark plug. Both my car NA and his TII were in the 90psi range all round 35 would be really low, unless I'm missing out on something.

inflatablepets

Ummm NO. I got those readings per rotor face. if I left the valve in there I'd have an inaccurate reading. Maybe you should do a bit of research. You need 3 even bounces of 70 PSI or more. If you leave the Schrader valve in, you will get skewed results.

JFR

Yeah, I'm not quite sure myself, either. Maybe I could try a different tester. Though reading several other people having gotten similar numbers, could it possibly be a coincidence the numbers are the same or that my testing is wrong?

pjtj2

iTrader: (3)

By holding the pressure release in you're venting a good portion of each compression "stroke". As the previous post remarked, there is a valve on the spark plug hole insert that needs to be removed to give a more accurate reading.

gscully

I thought the valve just lets the pressure off so if you leave it in you'll get the max pressure (the needle doesn't bounce) instead of being able to see the pressure on all 3 faces with the needle bouncing.

JFR

I don't think there is one on mine... and it's a normal piston tester.

oddphella

so what...nobody know the correct way to check compression with a normal tester?

someone should just contact a Rotary "Pro" and see what they have to say...

synesthete

LOL, guys this has been brought up soooo many times. The compression per rotor is between 80 and 120 if your higher than that good for you... The compression per face is only 30-40. You need a tester with a valve that is constantly open to get a TRUE per face reading.

If you can only get it for the rotor, than all you can do is make sure that the reading doesnt change much relative to the face, this would indicate a blown seal on one side.

If your saying that you have 110+ per face than you would have 330+ per rotor, thats ludicrous, youd need alchohol to fuel that. Rotarys are NOT HIGH COMPRESSION. Sorry i know its kinda confusing because there is the good testing method and the good enough testing method, but trust me on this one. If your seeing even bounces of 30+ and a valve closed (retaining pressure) reading of 90+ you are good.

sar

iTrader: (1)

I hate to bust your bubble -You're fooling yourself in saying that you're not providing misinformation - , but rotary compression is not 30psi per face. Stock rotor faces have 9.7:1 ratio in the na s5 9.7*14.7=142psi completely perfect sealed compression.

Multiplying by face makes no sense and is like saying that total compression on a piston engine is the combination of what every piston has. The 6 rotor faces are why many companies/people consider us as 6 cylinders.

The issue here is the testing procedure, the side valve does lose pressure and typically results in number around 30psi as I found in my running car and a friend's car. 30psi air + fuel will not combust very well. Removing the top valve (or plug in side) will result in full pressure readings.

Proper numbers per face are 100-120psi, tested with the top (or bottom) valve removed and not the side.

Turbo23

iTrader: (4)

Its PER face. You should see 3 bounces of about a 70 or higher. Even 70 per face is kinda low. Hence when you see readings saying 0-80-80, that means that you have lost compression on that one face. I would say the best way to know what your seeing is, just take your finger off the tester and let the gauge read. You wont get the 3 bounces, but you should get one reading telling if its above 35. If your that low, look into a rebuild kit.

synesthete

Ok, i was wrong in saying that the high value is the sum of the faces, your right sar that makes absolutely no sense. The simple fact is the guys compression is fine though. Heres the best page ive found on compression testing procedure, and the method i have always used. http://www.rotaryresurrection.com/ro...lder/comp.html

Sorry for adding to confusion

JFR

Okay so 35 sounds low. But say I do remove that valve... it will pretty much show good compression won't it, because I got like 35 on every face for both rotors. And when an engine needs a rebuild, or is blown, usually something goes out like a side seal, apex seal, etc, so if I do have low compression why would all faces show nearly the same number?

Next step... different compression tester I think?

hondahater

iTrader: (2)

the compression ratio of your rotors has nothing to do with actuall compression. High or low compression turbo motors all have the same compression (120 on a perfect motor).

rxspeed87

your a little mistaken
reason why he is prolly getting 30-35psi is cause he was holding the check valve in releasing pressure. hence the REALLY low numbers 30-35 is a dead motor.

if the compression checker has no check valve then what you will see is compression for each face. the check valve holds the pressure it so you see the max pressure and that is it

rxspeed87

if you don't have the release valve chacnes are you don't have the valve that holds pressure in. if you don't have the valve that holds pressure in your going to read a lot higher numbers

how about this I was getting 110 in bounces of three. was not holding a check valve down or anything like that.

I think your doing it wrong buddy

rxspeed87

wrong buddy your the one missinformation on your side. I get three BOUNCES of 110 psi

rxspeed87

incorrect what you need is a tester that HAS NO VALVE. when you ahve the valve and push the button your venting pressure. so therefor your readings are not accurate. you can get readings when you don't have a valve to hold the pressure in there. have you ever seen a true rotary compression tester? there isn't a valve on there to hold down. and they read usually 90-100+psi depending on motor.



no 110+ per face doesn't mean 330+ per rotor.

they don't add up. that's like saying if I have 110psi on one cylinder that means my motor has 440psi on the whole mtor if it is a 4 cylinder and 880psi for the motor if it is an 8 cylinder. just doesn't work that way.

if your valve is still in place when doing the test your doing it wrong. at that point your releasing all your testing pressure. the amount that gets released to atmosphere can vary depending on a fwe things unrelated to the health of the motor. you need to remove the valve all the way off the tester. at that point you can test true compression