Bad Apex seals?
11-24-09, 08:50 PM
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Bad Apex seals?
I own a 1987 non-turbo Rx-7 and it has performed flawlessly until recently. I was checking to make sure the timing was set correctly and it was. I finished up and took it for a test ride when I noticed it was running VERY rough. Listening to the exhaust it sounded like only one rotor was firing. I rechecked all the wiring and plug wires - everything ok. My Haynes manual describes a method of checking compression using a standard compression gauge - you just need to remove the shrader valve from the gauge so it drops to 0 psi after every compression event.
Results: #2 rotor indicated peaks of between 80 and 90 psi on every power stroke. The book calls out 85 psi as normal so #2 rotor appears to be ok.
#1 rotor different story. It shows 2 small increases (maybe 5 psi or so) then one reaching 85 psi like rotor #2. The book says this indicates a blown apex seal!
This has me totally perplexed as all I did was check the timing - nothing else. I don't understand how I possibly could have blown a seal with a simple timing check.
I cant remember for sure, but there is a possibility that I might have turned the engine in the opposite direction while finding the timing mark and putting a dab of white paint on the pulley notch. Is it possible I could have ruined a seal by doing that?
If I did rotate it the wrong way, it certainly wasn't more than 1/2 a turn.
The possibility that I may have inadvertantly lunched a rotor makes me absolutely sick!
Any input on this would greatly appreciated.
Thanks
Tom
Results: #2 rotor indicated peaks of between 80 and 90 psi on every power stroke. The book calls out 85 psi as normal so #2 rotor appears to be ok.
#1 rotor different story. It shows 2 small increases (maybe 5 psi or so) then one reaching 85 psi like rotor #2. The book says this indicates a blown apex seal!
This has me totally perplexed as all I did was check the timing - nothing else. I don't understand how I possibly could have blown a seal with a simple timing check.
I cant remember for sure, but there is a possibility that I might have turned the engine in the opposite direction while finding the timing mark and putting a dab of white paint on the pulley notch. Is it possible I could have ruined a seal by doing that?
If I did rotate it the wrong way, it certainly wasn't more than 1/2 a turn.
The possibility that I may have inadvertantly lunched a rotor makes me absolutely sick!
Any input on this would greatly appreciated.
Thanks
Tom
11-25-09, 06:28 AM
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If it ain't broke, don't fix it. What led you to check it in the first place? I'd like to know if turning the engine in the wrong direction (even a little bit) would mess anything up as well. I know setting the timing wrong would be very bad. I think those compression ranges are good, but if the manual says what it does and you did test it correctly then ouch.
11-25-09, 06:14 PM
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Bad Apex seals?
I didn't mention it in my original post because it was not relevant but the reason for checking the timing is that it failed smog at idle only. Thats why I was checking the timing. Actually it was right on the money so I did nothing but put the angle sensor cover back and that was it. Keep in mind the motor was running extremely smooth and quick before this problem, and the engine was just rebuilt by the previous owner less than 25 thousand miles ago.
I have a lot of experience with piston engines but this is my first rotory engine so I have to rely heavily on people with experience and reading a lot. If turning the engine in the wrong direction is a big no no I surely would expect the manual to make it explicitly clear. Especially if turning it just a little bit can ruin an apex seal. I am not driving the car any since the compression for fear I will score the surface of the "bore" (its probably called something else on a rotary).
Also, if an apex seal is the problem - and since its the front rotor - has anyone replaced a front seal seal without removing the engine? In other words - can you remove enough off the front of the engine to remove the rotor in the car? It sure seems like it would be a quicker way to get the job done. Just wondering.
Tom
I have a lot of experience with piston engines but this is my first rotory engine so I have to rely heavily on people with experience and reading a lot. If turning the engine in the wrong direction is a big no no I surely would expect the manual to make it explicitly clear. Especially if turning it just a little bit can ruin an apex seal. I am not driving the car any since the compression for fear I will score the surface of the "bore" (its probably called something else on a rotary).
Also, if an apex seal is the problem - and since its the front rotor - has anyone replaced a front seal seal without removing the engine? In other words - can you remove enough off the front of the engine to remove the rotor in the car? It sure seems like it would be a quicker way to get the job done. Just wondering.
Tom
11-25-09, 08:12 PM
#4
Timing is controlled by the ECU so it might help us if you told us exactly how you were checking timing and why you felt the need to.
If it was indeed b/c it failed smog, then chances are you have an issue with the emissions system - cat, airpump and other controls. Not sure why you think to check the timing for that but I'm unfamiliar w/ piston engines at this point so...
The emission components are described in the Factory Service Manual which you can find in the FAQ threads for the 2nd gen.
Turning the engine in the reverse direction shouldn't cause the apex seal to break. Re-installing the Crank Angle Sensor incorrectly can cause an apex seal to break if you installed it incorrectly and screwed up the timing.
If you pull the engine apart to replace an apex seal (which is the equivalent of a piston ring, you will need to replace the other soft seals (oil and water) b/c they will inevitably get moved and dislodged and won't seal properly again. If you are mechanically inclined, the rotary is pretty easy to rebuild and there are a few videos that can guide you through the process.
If it was indeed b/c it failed smog, then chances are you have an issue with the emissions system - cat, airpump and other controls. Not sure why you think to check the timing for that but I'm unfamiliar w/ piston engines at this point so...
The emission components are described in the Factory Service Manual which you can find in the FAQ threads for the 2nd gen. Turning the engine in the reverse direction shouldn't cause the apex seal to break. Re-installing the Crank Angle Sensor incorrectly can cause an apex seal to break if you installed it incorrectly and screwed up the timing.
If you pull the engine apart to replace an apex seal (which is the equivalent of a piston ring, you will need to replace the other soft seals (oil and water) b/c they will inevitably get moved and dislodged and won't seal properly again. If you are mechanically inclined, the rotary is pretty easy to rebuild and there are a few videos that can guide you through the process.
11-26-09, 02:43 AM
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gracer7- thanks for reply. I am encouraged by your comment that turning the engine in reverse direction shouldn't cause apex seal to break.
I didn't want to get into detail on why I was checking the timing because that is a whole different problem and I didn't want to get sidetracked - but here it is.
Emission failure at idle only prompted me to check the timing with a timing light to verify it was correct (Haynes manual suggestion). Using the leading edge plug wire for #1 rotor the pointer was dead on with the white notch on pulley. Changing the timing light pickup to #1 Trailing edge spark wire however did not show the red pulley notch as the book said it should - it was still pointing at the white mark. My conclusion is that the leading AND trailing spark plugs are firing at the same time. I was checking inside the angle sensor to determind if I could figure out why. Please note: I have NOT changed anything inside the Angle Sensor NOR have I removed or tried to alter the angle sensor position. My purpose was only to LOOK to see if I could see anything obviously wrong. I noticed that once the pointer on the engine was on the white notch, one of the top two rotating magnets was painted white and pointing directly to a white mark on the pickup coil. That made sense to me so I screwed the top back on and thats all I did. It was at that point that the engine ran very rough and I then proceeded to the compression test I talked about in my first post.
The engine was running very rich as indicated by black sooty spark plugs so I wil try some new plugs and see what happens.
I live in Reno now and so far have not found one mechanic in this entire town that works on Rotary engines. The Mazda dealership service manager said the plugs were oil fouled and I needed a new engine (they do not do rebuilds). I have done enough racing in my early years to know the difference between oil fouled plugs and carbon fouled plugs. So much for the dealerships expertise.
Any thoughts on what may cause a rotor to appear to have low compression if the problem is not a seal.
Thanks for all the comments and suggestions.
Tom
I didn't want to get into detail on why I was checking the timing because that is a whole different problem and I didn't want to get sidetracked - but here it is.
Emission failure at idle only prompted me to check the timing with a timing light to verify it was correct (Haynes manual suggestion). Using the leading edge plug wire for #1 rotor the pointer was dead on with the white notch on pulley. Changing the timing light pickup to #1 Trailing edge spark wire however did not show the red pulley notch as the book said it should - it was still pointing at the white mark. My conclusion is that the leading AND trailing spark plugs are firing at the same time. I was checking inside the angle sensor to determind if I could figure out why. Please note: I have NOT changed anything inside the Angle Sensor NOR have I removed or tried to alter the angle sensor position. My purpose was only to LOOK to see if I could see anything obviously wrong. I noticed that once the pointer on the engine was on the white notch, one of the top two rotating magnets was painted white and pointing directly to a white mark on the pickup coil. That made sense to me so I screwed the top back on and thats all I did. It was at that point that the engine ran very rough and I then proceeded to the compression test I talked about in my first post.
The engine was running very rich as indicated by black sooty spark plugs so I wil try some new plugs and see what happens.
I live in Reno now and so far have not found one mechanic in this entire town that works on Rotary engines. The Mazda dealership service manager said the plugs were oil fouled and I needed a new engine (they do not do rebuilds). I have done enough racing in my early years to know the difference between oil fouled plugs and carbon fouled plugs. So much for the dealerships expertise.
Any thoughts on what may cause a rotor to appear to have low compression if the problem is not a seal.
Thanks for all the comments and suggestions.
Tom
11-26-09, 11:35 AM
#6
OK. I can't comment any further on 2nd gen related items since it has been many years since I've owned one. I'll wait for a 2nd gen guy to chime in or feel free to Pm one of the regular 2nd gen (FC) guys you see on here.
The title of your thread isn't descriptive enough to attract the right people.
If you go to the Regional section and post up looking for a mechanic or a knowledgeable local guy, I'm sure you'll get some responses. There is at least one guy from Reno on here.
The title of your thread isn't descriptive enough to attract the right people.
If you go to the Regional section and post up looking for a mechanic or a knowledgeable local guy, I'm sure you'll get some responses. There is at least one guy from Reno on here.
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