Compression test--good? bad?
07-27-09, 03:23 PM
#1
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Compression test--good? bad?
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07-27-09, 03:42 PM
#5
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Front: 35psi (release valve held open), 120psi overall reading (release valve closed)
Rear: 34psi (release valve held open), 115psi overall reading (release valve closed
Rear: 34psi (release valve held open), 115psi overall reading (release valve closed
07-27-09, 03:48 PM
#7
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290,xxxkms on the chassis. i finally got around to checking the compression of the motor because i was unsure if the motor had original kms on it or not. not bad for an s5 for 600 bucks! person was selling it because the transmission was stuck in reverse, but it was a free, effortless fix 
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07-27-09, 04:04 PM
#10
im confused.. you guys are saying 35psi is good? a good motor pulls around 90-100 at the low end.
try doing a proper comp test though. take out the valve in the end of the tester and retest. valve closed test doesnt mean **** about anything.
try doing a proper comp test though. take out the valve in the end of the tester and retest. valve closed test doesnt mean **** about anything.
07-27-09, 04:09 PM
#11
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no were looking at the 120/front and 115/rear. read closer dude.
my TII has 90/front 80/rear so my motor is tired.
but it still pulls hard though so iam happy
but remember i also have lower compression too. so ill rebuild mine in a few months
my TII has 90/front 80/rear so my motor is tired.
but it still pulls hard though so iam happybut remember i also have lower compression too. so ill rebuild mine in a few months
07-27-09, 04:13 PM
#12
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Yeah, I was pretty happy with the buy. Stevensimon, check rotaryressurection. I doublechecked there when I used the piston engine compression tester.
Here are some pics of my car:
Here are some pics of my car:
07-27-09, 06:29 PM
#16
+1
Anyone who thinks 35 is good, go take the schrader valve out of your compression tester and watch the needle while your motor turns over (pedal to the floor).
To the OP, make sure you followe the writeup on the aforementioned site properly. You should be seeing at least 75psi per bump.
Anyone who thinks 35 is good, go take the schrader valve out of your compression tester and watch the needle while your motor turns over (pedal to the floor).
To the OP, make sure you followe the writeup on the aforementioned site properly. You should be seeing at least 75psi per bump.
07-27-09, 06:57 PM
#17
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.
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.
07-27-09, 07:05 PM
#18
Actually, you should read it yourself. http://www.rotaryresurrection.com/2n...ion_check.html
Not all testers have a schrader valve to remove, and most have a bleeder button you can press to vent pressure between bumps.
Not all testers have a schrader valve to remove, and most have a bleeder button you can press to vent pressure between bumps.
but in any case. as long as it runs well then be happy.
07-27-09, 07:24 PM
#19
There's something odd with your tester then. The needed drops towards 0 between pulses, right (w/ the valve open)?
Forget what I said before about adding them up. I forgot the air gets partially vented, so the 30-35 psi figure is pretty useless except to tell you that you have compression on each face. It's only part of the pressure. But with the valve closed, you will see the highest compression of the 3 faces. They're usually (or hopefully) about equal anyway. There's nothing wrong with your engine; 110psi is great. My current engine has 110-120psi on all faces.
Forget what I said before about adding them up. I forgot the air gets partially vented, so the 30-35 psi figure is pretty useless except to tell you that you have compression on each face. It's only part of the pressure. But with the valve closed, you will see the highest compression of the 3 faces. They're usually (or hopefully) about equal anyway. There's nothing wrong with your engine; 110psi is great. My current engine has 110-120psi on all faces.
07-27-09, 08:43 PM
#21
Yeah I've always been confused by this. 35psi per face doesn't sound right at all. My 202k-mile S4 n/a makes about 90psi per face on a conventional tester with the valve held open. It seems like 30-ish psi on each face wouldn't even be enough to ignite the intake charge. 
07-27-09, 09:11 PM
#22
Stevensimon/Stanello, etc:
How can you guys have such high readings while holding the air vent/release/shrader valve open? What write up or source are you using for your testing?
How I've learned to do it (fc3s or wankel.net or something)...
When you have the valve open, you're not looking for a reading above 90PSI - you're looking for even bounces, that's all. It will show you if all the chambers are sealing. Because the vent/release/etc. is open, part of the pressure is being lost. Three even bounces - good. Two even, one low - side seal bad. Two low, one higher, apex seal is bad/lost. No?
When you leave the air vent/release/shrader (closed), you're looking for a steady build up op pressure, and should end up with a min. of 90PSI.
How can you guys have such high readings while holding the air vent/release/shrader valve open? What write up or source are you using for your testing?
How I've learned to do it (fc3s or wankel.net or something)...
When you have the valve open, you're not looking for a reading above 90PSI - you're looking for even bounces, that's all. It will show you if all the chambers are sealing. Because the vent/release/etc. is open, part of the pressure is being lost. Three even bounces - good. Two even, one low - side seal bad. Two low, one higher, apex seal is bad/lost. No?
When you leave the air vent/release/shrader (closed), you're looking for a steady build up op pressure, and should end up with a min. of 90PSI.
07-28-09, 12:41 AM
#23
Furthermore, a couple of factors can affect your readings:
Battery - make sure its fully charged
Throttle - make sure its open fully (pedal to floor)
Engine Temp - Cold compression tests may be misleading
one source: http://www.aaroncake.net/RX-7/blown.htm
When you have the valve open, you're not looking for a reading above 90PSI - you're looking for even bounces, that's all. It will show you if all the chambers are sealing. Because the vent/release/etc. is open, part of the pressure is being lost. Three even bounces - good. Two even, one low - side seal bad. Two low, one higher, apex seal is bad/lost. No?
I guess... But whatever number u end up with is going to be the highest reading of all faces. Assuming that they're all pretty close, its not really a big deal, but its not the most accurate way.
07-28-09, 12:50 AM
#24
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i dont mean to thread jack, but since we're on the subject of compression test. doing a wet compression test on a rotary tell anything?
i know the purpose of a wet test just curious on what type of reading you would get.
i know the purpose of a wet test just curious on what type of reading you would get.
