compression test.
01-02-09, 01:52 AM
#1
compression test.
i cant find anything in the faq or by searching although im getting allot of baw and stuff about cars and parts for sale when i search. so can anyone tell me how to do a comp check on a t2 fc iv never done it on a rotary so a little guidance would be helpful. also what is the spark plug wire order starting from top left to bottom right?
01-02-09, 02:49 AM
#2
-Screw compression tester into plug hole (I don't think it matters if it's L or T)
-Remove EGI fuse
-Have someone crank the car while holding it at WOT, hold down the release button on the tester the whole time.
-Watch the tester. You want to see 3 even bounces. Looking at the psi, 115 psi is like a brand new motor, 100s-90s is acceptable, anything lower than ~80 psi needs to be rebuilt soon
plug order (looking straight at the side of the motor):
T1 T2
L1 L2
Also, when searching for something, go into 'Advanced search', Switch to 'Search titles only' and narrow it down to the section you want with the menu to the right of the page. Makes it much easier to find stuff.
-Remove EGI fuse
-Have someone crank the car while holding it at WOT, hold down the release button on the tester the whole time.
-Watch the tester. You want to see 3 even bounces. Looking at the psi, 115 psi is like a brand new motor, 100s-90s is acceptable, anything lower than ~80 psi needs to be rebuilt soon
plug order (looking straight at the side of the motor):
T1 T2
L1 L2
Also, when searching for something, go into 'Advanced search', Switch to 'Search titles only' and narrow it down to the section you want with the menu to the right of the page. Makes it much easier to find stuff.
01-02-09, 08:28 AM
#4
The Compression Testing Post to End all Compression Testing Posts
This is a little better guide.
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/rotary-compression-tester-734840/
Here is jackhild59's methodology for uniform compression test results on a rotary engines
Fully charge the battery. Slow rotation will yield deceptively low results.
Use the bottom spark plug hole; take both bottom spark plugs out for the duration of the test.
Remove the EGI fuse: you don't want the thing trying to try to run.
The throttle should be held to the floor or the throttle plate tied fully open. Failure to do this will yield very low results.
You will need an assistant to operate the ignition (and throttle) or a remote start switch with the throttle tied open.
Ideally the test should be done while the engine is warm. Cold is ok, but warm numbers are what should count. If you test a cold engine, be aware the what looks like an unacceptably low number may actually turn out to be quite all right. There is no hard fast number that will be the difference from cold to hot. Warm will be consistent, cold may not be. If an engine fails the test cold, it may well pass the test when warm.
Crank the engine for about 10-15 seconds max for each test.
There are two different tests to perform on a rotary engine with a piston compression tester! Both tests should be performed separately. Most people blend together the methods and smear the results, leaving a muddy view of the compression state of the engine.
Bump Test:
This verifies that the apex seals are operating properly, ie. not broken or stuck.
Remove the Schroeder valve in the BOTTOM of the compression tester (NOT the side release valve) for the 'look for three uniform bump test'.
Leave the side release valve alone for this test.
Test each chamber front then rear, make notes! Those bumps should be even and somewhere around 60-70 psi minimum.
Compression Test:
This is to test the actual compression in the engine.
Replace the Schroeder valve in the BOTTOM of the compression tester.
Retest each chamber, this time allowing the pressure to pump up to the maximum psi. Write this number down.
PSI should be above 85 psi per the FSM. Lower than this and the engine is in need of a rebuild. This engine will be prone to flood. It may however run for quite sometime, especially if it is NA.
90 psi+ should be enough to run reliably;
95 psi + is great,
100psi+ is excellent.
NOTE: All pressures will tend to be lower with longer hoses and higher with shorter hoses. Experts agree that ideally, the hose should be as short as possible; Best would be if the hose were eliminated and the unit screwed directly into the sparkplug hole essentially with the gauge as closely coupled to the compression chamber as possible.
NOTE 2: In general, Turbo II's will be lower numbers than NA, S4's will be lower than S5's.
NOTE 3: This write up is a compilation from several authors, Reted, Kevin Landers, Aaroncake and others combined, clarified and hammered into one place. The intent is to create consistent documented methodology in one place so that the newbs and accomplished alike can agree on the results.
Here is jackhild59's methodology for uniform compression test results on a rotary engines
Fully charge the battery. Slow rotation will yield deceptively low results.
Use the bottom spark plug hole; take both bottom spark plugs out for the duration of the test.
Remove the EGI fuse: you don't want the thing trying to try to run.
The throttle should be held to the floor or the throttle plate tied fully open. Failure to do this will yield very low results.
You will need an assistant to operate the ignition (and throttle) or a remote start switch with the throttle tied open.
Ideally the test should be done while the engine is warm. Cold is ok, but warm numbers are what should count. If you test a cold engine, be aware the what looks like an unacceptably low number may actually turn out to be quite all right. There is no hard fast number that will be the difference from cold to hot. Warm will be consistent, cold may not be. If an engine fails the test cold, it may well pass the test when warm.
Crank the engine for about 10-15 seconds max for each test.
There are two different tests to perform on a rotary engine with a piston compression tester! Both tests should be performed separately. Most people blend together the methods and smear the results, leaving a muddy view of the compression state of the engine.
Bump Test:
This verifies that the apex seals are operating properly, ie. not broken or stuck.
Remove the Schroeder valve in the BOTTOM of the compression tester (NOT the side release valve) for the 'look for three uniform bump test'.
Leave the side release valve alone for this test.
Test each chamber front then rear, make notes! Those bumps should be even and somewhere around 60-70 psi minimum.
Compression Test:
This is to test the actual compression in the engine.
Replace the Schroeder valve in the BOTTOM of the compression tester.
Retest each chamber, this time allowing the pressure to pump up to the maximum psi. Write this number down.
PSI should be above 85 psi per the FSM. Lower than this and the engine is in need of a rebuild. This engine will be prone to flood. It may however run for quite sometime, especially if it is NA.
90 psi+ should be enough to run reliably;
95 psi + is great,
100psi+ is excellent.
NOTE: All pressures will tend to be lower with longer hoses and higher with shorter hoses. Experts agree that ideally, the hose should be as short as possible; Best would be if the hose were eliminated and the unit screwed directly into the sparkplug hole essentially with the gauge as closely coupled to the compression chamber as possible.
NOTE 2: In general, Turbo II's will be lower numbers than NA, S4's will be lower than S5's.
NOTE 3: This write up is a compilation from several authors, Reted, Kevin Landers, Aaroncake and others combined, clarified and hammered into one place. The intent is to create consistent documented methodology in one place so that the newbs and accomplished alike can agree on the results.
01-31-09, 08:12 PM
#5
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compression
so i checked the compression on my turbo swap car today . i did use a tested with a foot and half hose probably not the best idea . with the schrader valve in w/o the upper valve released it bumped up to 40psi .with the valve closed it was at 60 psi .
Now should i have had the gas depressed ? when i did the test both rotors where the same pressure .
according to the seller this motor was rebuild by kevin lander and has about 30 hours on it .
if anyone has any input please feel free to post on it i'm stumped can't get this thing to run for the life of me .
Now should i have had the gas depressed ? when i did the test both rotors where the same pressure .
according to the seller this motor was rebuild by kevin lander and has about 30 hours on it .
if anyone has any input please feel free to post on it i'm stumped can't get this thing to run for the life of me .
02-01-09, 12:30 AM
#6
Are you doing it at ~250rpm where it is supposed to put out those numbers? If the battery is low then you will spit out lower numbers...You should have the gas depressed to let more air into the engine although it won't make THAT big of a difference. The engine is supposed to be warmed up too, I normally see ~20psi less when cold. Make sure you have the hose screwed in as tight as you can get it with your hand. Its weird that both rotors have low compression..I think you're leaving something out.
02-01-09, 02:13 AM
#7
yet another rx
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compression
yeah just with the starter . i can't get the damn thing to fire the guy i bought it from let it sit with fuel in it for almost a year . so i cleaned everything totally out and put in new fuel new leading plugs and it fired . but then it wouldn't go over 4k rpm so i double checked air leaks found none . so i changes the injectors now i can't get it to start .
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02-12-09, 04:48 AM
#8
yet another rx
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compression
you know i tried again with funk the other day with the shrader valve in a i got up to like 65 psi with the release valve closed the throttle open.
but i did have the leading plug in on the rear rotor . wondering how much you think the foot and 1/2 hose would lower the pressure ? even stranger both rotor pressures where dead on to each other.
but i did have the leading plug in on the rear rotor . wondering how much you think the foot and 1/2 hose would lower the pressure ? even stranger both rotor pressures where dead on to each other.
06-22-09, 09:57 PM
#9
I did a compression test tonight and I'm concerned that I may have did it wrong. On my compression gauge, I can't get to the Schraeder valve and the hose is 24" long. Here's what I got on a cold engine (s4 GXL with 96k on it and no rebuilds, using leading plug hole with trailing plugs in place). I did get the hose in as tight as I could (hard angle), but it felt like it was too easy to break it loose afterwards and I think that might contribute. Here's the results that I got on both rotors, as they were dead even.
35psi with the release valve held in, 3 even bounces per rotor
80psi for each rotor, not touching the release valve
Does this sound correct and healthy? I read KhanArtist's post and if what he says is right, it would be around 100psi when at proper temperature. And assuming that my gauge's hose is too long as well, that would mean I'm well within the healthy range. Could someone please double-check me on this? I just want to make sure that I know my engine is in proper operating condition before I start planning for forced induction.
35psi with the release valve held in, 3 even bounces per rotor
80psi for each rotor, not touching the release valve
Does this sound correct and healthy? I read KhanArtist's post and if what he says is right, it would be around 100psi when at proper temperature. And assuming that my gauge's hose is too long as well, that would mean I'm well within the healthy range. Could someone please double-check me on this? I just want to make sure that I know my engine is in proper operating condition before I start planning for forced induction.
06-22-09, 11:09 PM
#10
Compression Tester Guy
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Getting 3 even bounces sounds like a good start. 2 feet of hose will greatly reduce the reading you're getting.
Unfortunately there is no way to guarantee your engine is healthy based on how those numbers were achieved. A proper rotary engine compression tester should be used. RPM and dead volume need to be accounted for when testing compression on our cars and that's just not something you can do with a piston checker.
-John
Unfortunately there is no way to guarantee your engine is healthy based on how those numbers were achieved. A proper rotary engine compression tester should be used. RPM and dead volume need to be accounted for when testing compression on our cars and that's just not something you can do with a piston checker.
-John
06-23-09, 01:18 AM
#11
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N/A all the way
you say you changed the fuel injectors... make sure you plugged them back in right... because your secondary injectors don't open until 4000rpm... if those plugs are pluged in your primary injectors your engine will have a hard time starting... and if you do get it started you'll have to keep it constantly floored to keep it going... idling at 4000rpm... secondaries will be dumping fuel high up in the manifold for no good reason... a haynes manual will show you which color wires feed the proper fuel injectors (in the back of the book). FP (front primary), RS (rear secondary) and so on...
05-21-10, 10:34 AM
#13
You will need the starter to be attached on the tranny and a strong battery and know what you are doing
EDIT:
Take a look at this vid, it was me doing a compression test on an engine laying on the ground, you can see that the rear rotor reaches 90psi but looks like the front rotor has a blown seal or stuck maybe
http://www.youtube.com/watch?v=XcsyQuQs1Vo
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