Compression numbers
05-23-09, 07:56 PM
#1
Compression numbers
I felt like I was waiting to hear about a pregnancy test, but I finally broke down and compression tested my TII swap.
Front rotor: 70, 35, 70
Rear rotor: 90, 90, 90
All on a hot engine....
I've had growing problems with smoking exhaust, but not loosing any coolant. Hopefully I don't have coolant seal also.
Front rotor: 70, 35, 70
Rear rotor: 90, 90, 90
All on a hot engine....
I've had growing problems with smoking exhaust, but not loosing any coolant. Hopefully I don't have coolant seal also.
05-23-09, 11:16 PM
#4
Make sure before you rebuild
You may have done a great compression test. You may also look this over and find additional help.
Good Luck!
Good Luck!
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.
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.
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.
05-24-09, 12:07 AM
#5
I used the compression tester plug-n-play. It has about 1ft hose that screws into the spark plug socket. On the gauge side it uses a sleeve that slides back and forth to fasten the gauge. I didn't mess with the valves on it.
I did compression test without holding the button, but can't remember what those readings were...I didn't think they'd be relevant.
Tomorrow I'll use the info you posted to check more.
I've been chasing down problems that may or may not be related to compression.
-sporadic smoking exhaust
-electrical problems: getting low voltage, even after a reman'd FD alt and removing power from all stereo amps (possibly just the factory gauge giving crappy feedback)
-sporadic fuel smell: tested for leaks and haven't found any cause
-most recently a real bad idle: I checked TPS numerous times, tried adjusting screws on TB (fast idle and can't remember the other one), have been checking the BAC, tried moving timing around with CAS. I don't have my A/C belt on and have tried driving with no P/S belt and P/S unplugged. Other than lowering the draw on my electrical system neither A/C or P/S had much effect. Doesnt seem to matter what I do, the car wants to idle at just above zero.
05-24-09, 08:33 PM
#7
Forgot today was my nephew's graduation party...didn't do anything car-like today. But I'm doubting the new tests will turn up numbers that are that different. I'd like to think that one low bump will rise about 40psi with different methodology, but lets be realiastic.
Even with needing a rebuild I'd say I got pretty good life out of a JDM engine. Kudos to Atkins!!
With there being an undriven black vert in the garage I was thinking of putting my TII swap into it anyway. My first RX7 was a black vert and IMHO there are few cars that look better than black verts. Tho I did see a Nissan GT-R the other day. First one I've seen in person, and I gotta say the pictures don't do it justice. Simply a stunning car to look at!
Anywho.....I'd rather have a black turbo vert than red one.
Even with needing a rebuild I'd say I got pretty good life out of a JDM engine. Kudos to Atkins!!
With there being an undriven black vert in the garage I was thinking of putting my TII swap into it anyway. My first RX7 was a black vert and IMHO there are few cars that look better than black verts. Tho I did see a Nissan GT-R the other day. First one I've seen in person, and I gotta say the pictures don't do it justice. Simply a stunning car to look at!
Anywho.....I'd rather have a black turbo vert than red one.
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05-25-09, 03:06 PM
#9
Did more thorough tests today.
Leading plugs both out, EGI out, engine warm, WOT
Shraeder valve out/apex seals
front: 80,50,80
rear: 100+,100+,100+
Shraeder valve in/total compression
front: 110
rear: 120
I'm suspicious of my readings because I'm using a dial gauge and once the gauge starts bouncing it gets hard to read the small bumps. I'm going to look into renting or buying a digital gauge.
Leading plugs both out, EGI out, engine warm, WOT
Shraeder valve out/apex seals
front: 80,50,80
rear: 100+,100+,100+
Shraeder valve in/total compression
front: 110
rear: 120
I'm suspicious of my readings because I'm using a dial gauge and once the gauge starts bouncing it gets hard to read the small bumps. I'm going to look into renting or buying a digital gauge.
05-25-09, 06:41 PM
#11
Better yet, have a proper compression test done with a real rotary-engine compression tester. The 80-50-80 numbers don't sound right. When a single apex seal fails, or is failing, usually two of the compression faces will be affected. For example, something like 100-60-40, or even 100-10-00. Usually don't get 2 faces with the same compression and one with low compression.
Also, in order to compare your compression numbers to those in the FSM you need to normalize the numbers to an engine cranking speed of 250 rpm. Check the information in the FSM.
Also, in order to compare your compression numbers to those in the FSM you need to normalize the numbers to an engine cranking speed of 250 rpm. Check the information in the FSM.
05-25-09, 07:34 PM
#12
Rotary Enthusiast
Better yet, have a proper compression test done with a real rotary-engine compression tester. The 80-50-80 numbers don't sound right. When a single apex seal fails, or is failing, usually two of the compression faces will be affected. For example, something like 100-60-40, or even 100-10-00. Usually don't get 2 faces with the same compression and one with low compression.
Also, in order to compare your compression numbers to those in the FSM you need to normalize the numbers to an engine cranking speed of 250 rpm. Check the information in the FSM.
Also, in order to compare your compression numbers to those in the FSM you need to normalize the numbers to an engine cranking speed of 250 rpm. Check the information in the FSM.
05-26-09, 01:46 AM
#13
Looks like we're both in line for a rebuild!! Gonna do some more research and testing. We'll see what comes of it all.
When I first started getting suspcious from all my other symptoms I stopped in my local Mazda dealership to ask how much a compression test would be....something like $150. I may end up doing that before I resort to rebuild. I'm also going to call around to see if any local shops can do rotary compression tests. But from past experience the only rotary techs in town work for Mazda. I would love to get a professional opinion though.
I don't trust the little experience I have. The rear rotor has very even consistent bumps which make it very easy to read the gauge. The front rotor bumps are not so even but the bumps happen so fast it's hard to determine exactly what to read. I'd love to find out I can rent a rotary compression tool locally....but Southern Indiana is...well small. Probably the best I'll find is a digital.
I still need to read the FSM on it, just been too busy to stop life long enough.
Thanks for the advice, I've got some reading to do. Any pointers in the right direction is appreciated.
If I decide I want the TII swap in the black vert I'm probably leaning towards doing my first rebuild, to an extent, regardless of what more precise testing turns up. I feel like I've cheated death for having the engine put in without a rebuild. If the engine is coming out for the swap the timing is right for a rebuild. I've been itching to do my first rebuild ever since I caught the performance bug...this might just be the excuse I've been looking for.
Now I just need to start whoring myself to pay for my car dreams!!! Hell maybe I can start our own "pay for my car" prostitution ring??
Better yet, have a proper compression test done with a real rotary-engine compression tester. The 80-50-80 numbers don't sound right. When a single apex seal fails, or is failing, usually two of the compression faces will be affected. For example, something like 100-60-40, or even 100-10-00. Usually don't get 2 faces with the same compression and one with low compression.
Also, in order to compare your compression numbers to those in the FSM you need to normalize the numbers to an engine cranking speed of 250 rpm. Check the information in the FSM.
Also, in order to compare your compression numbers to those in the FSM you need to normalize the numbers to an engine cranking speed of 250 rpm. Check the information in the FSM.
I don't trust the little experience I have. The rear rotor has very even consistent bumps which make it very easy to read the gauge. The front rotor bumps are not so even but the bumps happen so fast it's hard to determine exactly what to read. I'd love to find out I can rent a rotary compression tool locally....but Southern Indiana is...well small. Probably the best I'll find is a digital.
I still need to read the FSM on it, just been too busy to stop life long enough.
If I decide I want the TII swap in the black vert I'm probably leaning towards doing my first rebuild, to an extent, regardless of what more precise testing turns up. I feel like I've cheated death for having the engine put in without a rebuild. If the engine is coming out for the swap the timing is right for a rebuild. I've been itching to do my first rebuild ever since I caught the performance bug...this might just be the excuse I've been looking for.
Now I just need to start whoring myself to pay for my car dreams!!! Hell maybe I can start our own "pay for my car" prostitution ring??
05-28-09, 04:07 AM
#14
Nothing new to report. I'm in the process of moving into a better apartment and all my time has been eaten up shopping for places to live. I'm a bit OCD and even though I have a place I can move to this weekend....there is always something better out there...if I just look for one more day.......
I've googled rotary compression tool rental and come up empty. Though I could buy one for about $600 on the low end.
Anyone intersted in an authentic MS hoodscoop with documents to prove it's authenticity?? I may need to sell it to fund my rebuild. <tears and whimpering>
I've googled rotary compression tool rental and come up empty. Though I could buy one for about $600 on the low end.
Anyone intersted in an authentic MS hoodscoop with documents to prove it's authenticity?? I may need to sell it to fund my rebuild. <tears and whimpering>
05-28-09, 08:35 AM
#15
http://rotarydiagnostics.com/pricing%20combined.htm
05-28-09, 01:43 PM
#16
Actually, you can buy one here for $369 shipped.
http://rotarydiagnostics.com/pricing%20combined.htm
http://rotarydiagnostics.com/pricing%20combined.htm
I've been too busy looking at apartments to do much of anything. But I decided on a place today. If I start moving in this weekend (provided I can get a Uhaul on this late of notice) then I won't have time to mess with it much till I'm settled in some. If I'm waiting till next weekend for the move then I have some time to at least make some calls for rental tools and do some reading on things related to blown apex, side seals, etc.
05-28-09, 05:59 PM
#17
Actually, you can buy one here for $369 shipped.
http://rotarydiagnostics.com/pricing%20combined.htm
http://rotarydiagnostics.com/pricing%20combined.htm
05-29-09, 12:36 AM
#18
RX-7s are reliable.
There's actually a few options for rotary engine compression testers. TwistedRotors has developed a hand-held tester and is currently selling it in a Group Buy on RX8club.com for $230 shipped in the U.S. Here's a link to the Group Buy:
http://www.rx8club.com/showthread.php?t=172238
Or you can go to www.TwistedRotors.com for more information.
~Angel
http://www.rx8club.com/showthread.php?t=172238
Or you can go to www.TwistedRotors.com for more information.
~Angel
06-02-09, 02:53 AM
#20
There's actually a few options for rotary engine compression testers. TwistedRotors has developed a hand-held tester and is currently selling it in a Group Buy on RX8club.com for $230 shipped in the U.S. Here's a link to the Group Buy:
http://www.rx8club.com/showthread.php?t=172238
Or you can go to www.TwistedRotors.com for more information.
~Angel
http://www.rx8club.com/showthread.php?t=172238
Or you can go to www.TwistedRotors.com for more information.
~Angel
The computer has blown up from a failing graphics card being upgraded, to me frying the motherboard do to my own carelessness, to needing a new cpu that is compatible with the new motherboard, to upgrading the psu to make sure I have the watts to push everything. It's been a true murphy's law headache and expense.
In fact I'll start a non-car related thread about it in the lounge...maybe tomorrow at work.
06-13-09, 12:59 AM
#24
Best News I Could Imagine
I finally had some time to tinker with my car. Nothing has changed with compression testing. I called about renting a digital compression tester and local tool renters don't have them. I'm going to call around to Autozone and the rest of the major chains. They do some tool rental.
BUT I couldn't be happier, I seem to have fixed my horrible idle. I swapped a CAS that I have had lying around. While doing that I find that my harness for the CAS is all gunked up. Spilled oil from the filler neck had run down onto it. The oil was bad enough that it had worked it's way into the contacts. I cleaned it up real good with some electric cleaner. WAAAA LAAAA!!! Smooth idle, acceleration, etc. Not sure yet if it was the gunked up harness or the CAS.
It was a quick swap before heading to work so I've only driven the car to and from work. The idle is sitting a little high (1000 RPM). But I'll mess with the timing, TPS and such tomorrow.
Obviously the compression numbers are still a concern, but at least my DD isn't sputtering and wanting to stall. The potential rebuild doesn't seem nearly as immediate.
BUT I couldn't be happier, I seem to have fixed my horrible idle. I swapped a CAS that I have had lying around. While doing that I find that my harness for the CAS is all gunked up. Spilled oil from the filler neck had run down onto it. The oil was bad enough that it had worked it's way into the contacts. I cleaned it up real good with some electric cleaner. WAAAA LAAAA!!! Smooth idle, acceleration, etc. Not sure yet if it was the gunked up harness or the CAS.
It was a quick swap before heading to work so I've only driven the car to and from work. The idle is sitting a little high (1000 RPM). But I'll mess with the timing, TPS and such tomorrow.
Obviously the compression numbers are still a concern, but at least my DD isn't sputtering and wanting to stall. The potential rebuild doesn't seem nearly as immediate.
06-13-09, 08:09 AM
#25
Great news. There may be lots of carbon build up due to the misfiring and incomplete combustion at the root of your compression test woes.
Maybe you should do the water trick to clean everything out?
Everyone jumps in and says rebuild/popped seal way too soon. Everyone want so be the first to internet diagnose your 'blown engine'. That is one reason I compiled the compression testing info.
You may still need a rebuild, but a rebuild would not have solved your stumbling idle and smoking problem. Careful observation and troubleshooting is the key.
Good Job.
Maybe you should do the water trick to clean everything out?
Everyone jumps in and says rebuild/popped seal way too soon. Everyone want so be the first to internet diagnose your 'blown engine'. That is one reason I compiled the compression testing info.
You may still need a rebuild, but a rebuild would not have solved your stumbling idle and smoking problem. Careful observation and troubleshooting is the key.
Good Job.