compression?? odd readings

Jeff4764 · 09-25-2008, 05:14 PM

ok, so i have an 87 n/a, ive explained this problem before... It starts fine when its cold, but once it warms up it has a hard time starting and sometimes wont even start. I was told to check compression so i bought a tester, (didnt remove schrader valve, just held in relief valve) the pulse is are very even steady pulses and all read the same. Heres the problem, its reading 50 psi every time.. But i was told if there steady and even pulses the compression is fine.. can someone give me some insight.. maybe a different problem the compression

Phoenix7 · 09-25-2008, 05:18 PM

50 is too low. Are you sure you tested it right. That's crappy compression. Normally anything around 80psi means your motor is dying.

Jeff4764 · 09-25-2008, 05:22 PM

im pretty sure i did, i tested both trailing, and pulled the injector and egi fuse and held pedal to floor while trying to turn it over. but if it was bad would the pulses be even

djmtsu · 09-25-2008, 05:54 PM

If it was tested correctly than 50psi is toast. Rebuild time.

I suggest Rotary Ressurection.

87turbo_turtle · 09-25-2008, 06:07 PM

sounds like its time to rebuild

Jeff4764 · 09-25-2008, 06:13 PM

I do believe you guys, but does it sound like i did it right?? and would the pulses be even if compression was bad? could it be in the intake? I have no idea.

classicauto · 09-25-2008, 06:37 PM

Quote:

Originally Posted by Jeff4764

I do believe you guys, but does it sound like i did it right??

Was the engine warmed up when you did the test? Otherwise everything else sounds pretty good as far the tests execution is concerned.

Although those are low numbers even for a stone cold engien that is in decent shape....

Jeff4764 · 09-25-2008, 06:14 PM

and if it was 50 psi would it even start cold.

Phoenix7 · 09-25-2008, 06:17 PM

Take a video of both rotors being tested. 50psi is too low, whether or not the pulses are even (your apex seals intact).

djmtsu · 09-25-2008, 06:25 PM

Just because the apex seals are there, does not mean they are efficient at sealing anymore.

Heat causes expansion, expansion lowers compression.

Jeff4764 · 09-25-2008, 06:36 PM

ok I can do that and post it tomorrow. But does it sound like i did it right...
I tested both rotors on trailing side. the compression tester fitting screwed into the spark plug hole and i pulled both the inj. fuse and the egi. fuse. I had my girlfriend get in the car and push the pedal to the floor, and cranked it for about 10 seconds while i held the pressure relief valve in and got a steady reading of about 50 psi. I will take video, and if you guys can check it out tomorrow and give me some input that would be awesome.

Phoenix7 · 09-25-2008, 06:42 PM

Plus, you can drive it until it can't hold compression. Just don't expect it to go anywhere, fast.

Some people add a bit of premix to raise compression too. If you can't get it rebuilt soon then I'm sure others will chime in with ways to help the motor last a little bit longer.

vex · 09-25-2008, 10:08 PM

You're doing it correctly. 50PSI is fine for checking the apex seal condition, now you need true compression value of the rotor. Do not hold the relief valve and you should get the max number on the compression. I bet you're going to be getting above 100PSI, just a guess though.

http://www.aaroncake.net/RX-7/blown.htm

Jeff4764 · 09-26-2008, 06:58 AM

If i hold the relief valve it will just keep bouncing to 50 psi. If i let go of the relief valve it will bounce a fewtimes and stop at about 95 psi. so if what your saying is right then i am a happy camper.

djmtsu · 09-26-2008, 07:32 AM

Happy that you have compression, but sad that you still have hot start issues.

09-25-2008, 05:14 PM	#1
Jeff4764 Rotary Fan in Training Join Date: May 2008 iTrader: (0) Posts: 40 Rep Power: 0	compression?? odd readings ok, so i have an 87 n/a, ive explained this problem before... It starts fine when its cold, but once it warms up it has a hard time starting and sometimes wont even start. I was told to check compression so i bought a tester, (didnt remove schrader valve, just held in relief valve) the pulse is are very even steady pulses and all read the same. Heres the problem, its reading 50 psi every time.. But i was told if there steady and even pulses the compression is fine.. can someone give me some insight.. maybe a different problem the compression

09-25-2008, 05:54 PM	#4
djmtsu My minds tellin' me no... Join Date: Feb 2008 Location: Murfreesboro, TN iTrader: (10) Posts: 4,043 Rep Power: 21	If it was tested correctly than 50psi is toast. Rebuild time. I suggest Rotary Ressurection. __________________ 1976 Mazda Cosmo RX-5 1976 Mazda Cosmo RX-5 2003 Toyota Tundra TRD 2015 Toyota 4Runner SR5

09-25-2008, 06:07 PM	#5
87turbo_turtle Rotary Chic Join Date: May 2008 Location: New Holland, SC iTrader: (0) Posts: 232 Rep Power: 17	sounds like its time to rebuild __________________ Turtle Yes I am a girl and I will kick your butt. Prove yourself.

09-25-2008, 06:25 PM	#10
djmtsu My minds tellin' me no... Join Date: Feb 2008 Location: Murfreesboro, TN iTrader: (10) Posts: 4,043 Rep Power: 21	Just because the apex seals are there, does not mean they are efficient at sealing anymore. Heat causes expansion, expansion lowers compression. __________________ 1976 Mazda Cosmo RX-5 1976 Mazda Cosmo RX-5 2003 Toyota Tundra TRD 2015 Toyota 4Runner SR5

09-25-2008, 10:08 PM	#13
vex RCC Loves Me Not You Join Date: Jul 2008 Location: Influx. iTrader: (6) Posts: 2,113 Rep Power: 19	You're doing it correctly. 50PSI is fine for checking the apex seal condition, now you need true compression value of the rotor. Do not hold the relief valve and you should get the max number on the compression. I bet you're going to be getting above 100PSI, just a guess though. http://www.aaroncake.net/RX-7/blown.htm __________________ The Official FC Radiator Thread My Project Thread: Cerberus CCVT Virginia Rotary Group Last edited by vex; 09-25-2008 at 10:17 PM..

09-25-2008, 05:22 PM	#3
Jeff4764 Rotary Fan in Training Join Date: May 2008 iTrader: (0) Posts: 40 Rep Power: 0	im pretty sure i did, i tested both trailing, and pulled the injector and egi fuse and held pedal to floor while trying to turn it over. but if it was bad would the pulses be even

09-25-2008, 06:13 PM	#6
Jeff4764 Rotary Fan in Training Join Date: May 2008 iTrader: (0) Posts: 40 Rep Power: 0	I do believe you guys, but does it sound like i did it right?? and would the pulses be even if compression was bad? could it be in the intake? I have no idea.

09-25-2008, 06:14 PM	#8
Jeff4764 Rotary Fan in Training Join Date: May 2008 iTrader: (0) Posts: 40 Rep Power: 0	and if it was 50 psi would it even start cold.

09-25-2008, 06:36 PM	#11
Jeff4764 Rotary Fan in Training Join Date: May 2008 iTrader: (0) Posts: 40 Rep Power: 0	ok I can do that and post it tomorrow. But does it sound like i did it right... I tested both rotors on trailing side. the compression tester fitting screwed into the spark plug hole and i pulled both the inj. fuse and the egi. fuse. I had my girlfriend get in the car and push the pedal to the floor, and cranked it for about 10 seconds while i held the pressure relief valve in and got a steady reading of about 50 psi. I will take video, and if you guys can check it out tomorrow and give me some input that would be awesome.

09-26-2008, 06:58 AM	#14
Jeff4764 Rotary Fan in Training Join Date: May 2008 iTrader: (0) Posts: 40 Rep Power: 0	If i hold the relief valve it will just keep bouncing to 50 psi. If i let go of the relief valve it will bounce a fewtimes and stop at about 95 psi. so if what your saying is right then i am a happy camper.

09-26-2008, 07:32 AM	#15
djmtsu My minds tellin' me no... Join Date: Feb 2008 Location: Murfreesboro, TN iTrader: (10) Posts: 4,043 Rep Power: 21	Happy that you have compression, but sad that you still have hot start issues. __________________ 1976 Mazda Cosmo RX-5 1976 Mazda Cosmo RX-5 2003 Toyota Tundra TRD 2015 Toyota 4Runner SR5