Currently, I am trying to determine the health of my engine. My system looks to have many of the symptoms of a damaged inner O-ring which is causing the system to both:

1) Slowly lose coolant pressure over a period of time when the system is off.
2) Pressurize above the AST cap limit forcing coolant into the overflow reservoir.

I will make a separate thread containing the results from my coolant pressure testing, but I wanted to first get some feedback on the compression of my engine.

I remember reading somewhere that a compression test can give some feedback as to if you have a poor o-ring. (There was some combination of results that meant there was a failure)

I used a nice little Mazda rotary compression tester from my friends at Northstar Rotary Rockets and it even prints out a little piece of paper with your results.

I did two tests, one for each rotor. The first test was the trailing plug on the side nearest the firewall. (Not sure if that is front or rear) Car was properly warmed, then let cool for a few mins. Tests were with WOT for 7-10 seconds.



I then tested the trailing plug on the side nearest the front of the car. I see the "hit-hit-drop" "hit-hit-drop" pattern here... what does this mean?




I know that 6 is low and around 8 is what you are looking for. I'm definitely above 6, and below 8. My question is, do these results offer any insight into a possible inner o-ring failure? In addition, do these numbers warrant a rebuild if I have to send the engine away to fix the seal?

Thank you in advance.

-Rotary4tw

 

The variation in the second plot is not good. It looks as if you have a worn/cracked seal and two other good seals. Either way it looks like trouble.

Edit - I'm not too sure that a compression test is a great way to test for O ring failures. A pressure test should tell you if you have a bad O ring.

 

The second graft could be a stuck side seal. One bad apex seal can kill the compression on two sides of a rotor. You just have only one small dip. Do the water steam cleaning method to clean any carbon build-up. Any stuck seals will cause a loss of compression. Then test again later if you want.

 

The engine compression test that you performed measures the pressure generated by the rotor as it turns, which willl tell you how healthy your apex seals, side seals, and rotor housings are.


This is not the same thing as a cooling system pressure test, which will pressurize your cooling system and test to see that it holds the pressure. This will tell you if your cooling system (hoses and coolant seals) is in good shape, or if you have any leaks.

You can borrow this tool from Autozone, if there are any shops near you:
http://www.sjdiscounttools.com/sta12270.html


-s-

 

I was under the impression that there was a compression "pattern" that some how gave insight to an o-ring failure. Even if this is not the case, it's not big deal.

Unfortunately for me I did find the tool you were talking about, and my system both looses pressure as well as over pressurizing after a few mins of running with the tester hooked up to the coolant filler neck.

I'm making a post about them right now...

I will take the information and move forward from there, likely with a rebuild.

-Rotary4tw

 

If there was o-ring failure, the low compression would be noticable on all sides, not just at a specific apex 'point'.

I'm with the others on a possible sticking side seal or maybe a worn apex seal... although again thats usually effective on two sides with an apex seal.

~Kris

 

actually, it cant be a bad apex seal with only one low peak, one low peak has to be a side seal. aa bad apex seal or courner seal will affect 2 peaks, not just one.

 

Very True - I should have looked more carefully .

 

Are you sure that the rest of the coolant system is okay? Have you checked all the hoses for leaks including the turbo coolant hoses? Don't jump to the worst conclusion just yet, it could be something as simple as a blown coolant filler cap.

 

Looks to me like a stuck or broken side seal. Does your engine have any large porting done to the intake ports or is it stock? Sometimes, a large intake port can contribute to broken side seals.... that's why I'm asking.

If the car still runs OK, I might choose not to rebuild it... it's expensive, time consuming, etc.

If you're going to be taking apart the engine to fix another problem like a bad O-ring or something, you can replace all the seals while you're in there for relatively low cost.

 

the 1st graph is o.k. the second graph is a flat corner seal or a stuck side seal...if it was a apex seal you would have 2 chambers indicating low compression readings.

You can try and rectify it by pulling out your fuel pump relay , turn the motor over till the engine starts and burn off whatever gas that`s left in the chamber. Then you pure about 8 oz. of marvel mistry oil into the chamber rotate so it speads evenly leave it for a day or two.

Good luck

 

Andre, how would a corner seal stick that it could only effect one chamber? The MMO is a good idea, hopefully its just stuck and not broken.

Thanks,
~Kris

 

Some top oil like marvel should let you know more about the problem. A little carbon removal wouldnt hurt either.