VIDEO - Compression Test
 

I recorded my compression test. From my limited knowledge and understanding, it looks really good with consistent 105psi pulses on both rotors. Take a look and see if I'm missing anything.

Comments appreciated.

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This photobucket version may be clearer
 

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looks good to me! if thats a tii engine thats nice and strong

Thanks. Yes, it is a Tii. I'm still struggling with it not running well so I'm being anal about the basics. Clearly the 105+ reading is goodness and I dont see any signs of "skipped beats" but getting experienced eyes on it seems a good idea.

If I can eliminate any chance that the rotors and seals arent happy campers, then I dont have to worry about pulling the engine. No sense screwing with phantom vacuum leaks, bad grounds, malcontent TPS adjustments, retentive injectors, manic BACs or all the other crap if the 3 major moving parts of a rotary are f'd up!

Thanks again, DJ. I'm guessing that with 60 views I'm not misreading the pulses on the gauge and so I'm good to go on that front.

Thanks guys.

What was the engine cranking speed? Can't really evaluate the numbers unless you normalize them to the Mazda quoted spec of 250 rpm. If the engine is turning significantly faster than the 250 rpm, your numbers will be higher than the Mazda spec. And vice versa for a slower engine cranking speed.

However, you can come pretty close to 250 rpm by doing the following. Fully charge the battery, remove only the leading plug from one housing--leaving the other 3 plugs in place. Run the test on that rotor, then reinstall the plug, remove the plug from the other housing and run the test on that rotor. Again, with the other 3 plugs installed. The engine cranking speed will be very close to 250 rpm and your numbers can be directly compared to the FSM spec.

So the only difference between what I did and your method is that I left both leading plugs out. Any idea how many PSI that would translate to? Given that I was at 105+ (this is a newly rebuilt engine) do you think the drop would be material?

Shouldnt it be 35 psi puffs and 105 total? im befuddled.

I'm using Aaron Cake's procedure which you'll find here. In it he says "You are not looking for excellent numbers, just three even bounces above 70 PSI."

No way to know without knowing the engine cranking speed at the time of the test. However, assuming your battery was fully charged, and the open plug holes, the engine cranking speed would likely be well above 250 rpm. In which case the numbers normalized to 250 rpm would be lower, but probably still in the acceptible range. The important thing is to have relatively even pulses for all 3 faces a rotor, and similar numbers for both rotors. In that sense, your engine seems to be in good shape.

Good good! Thanks. Yes, the battery was fully charged.

So coming from "Compression Tester Man", I'm going to mark the short block off the list! :icon_tup:

Yup looks good.

nice video, i was never quite sure how to test and this helped

I don't think the number you are claiming is accurate, because of the damping (or lack of it) on your gauge. I also don't think this number is all that relevant anyway. You just want to see uniformity. The compression looks good at this point, you just are not quite finished with the evaluation.

You now need to do the second part of the test. Replace the bottom shraeder valve and do the pump up test. Allow each rotor to pump the gauge up to the maximum it can attain. This will tell you the ultimate compression for each rotor. This number will be meaningful.

If they both pump up to 105 psi, then you have real peach!

Good luck!

RX-711, glad you found it useful. Guess I have to add step two to the video now!

Ok, Jack. I'll do that. I wanna be peach!