2nd Generation Specific (1986-1992) 1986-1992 Discussion including performance modifications and technical support sections.

Help confirming blown motor.

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Old Jan 25, 2022 | 06:17 PM
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cactuscactus's Avatar
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Help confirming blown motor.

Hey so I did another compression test today. I had done one before and thought I had good numbers. But I believe i did the test incorrectly previously. Here are the steps I took for this test.
1. Warmed up motor.
2. Removed Schrader valve from compression tester.
3. Taped down air release pin on compression tester.
4. Attached tester spark plug holes for both rotors and tested individually.
5. WOT, cranked about 15 seconds per rotor. (I used L1 for the first test and T2 for the second).

I uploaded a video of my results. Thanks for the assistance

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Old Jan 25, 2022 | 07:31 PM
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The needle on rotor 2 has two little bounces then a bigger one, that points to a bad apex seal or one that's stuck.
Testing compression this way won't give accurate numbers but even bounces are what you're looking for.
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Old Jan 25, 2022 | 08:00 PM
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Originally Posted by j_tso
The needle on rotor 2 has two little bounces then a bigger one, that points to a bad apex seal or one that's stuck.
Testing compression this way won't give accurate numbers but even bounces are what you're looking for.
So a while back when I tested without the release pin taped down I read about 105 psi per rotor. But I didn't have the pedal at WOT so I'm not sure how accurate those readings were.
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Old Jan 25, 2022 | 10:05 PM
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With the release valve closed it'll read the highest compression of the 3 rotor faces, without the pedal down it'll read lower since the engine can't suck in as much air.
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Old Jan 25, 2022 | 10:32 PM
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Originally Posted by j_tso
With the release valve closed it'll read the highest compression of the 3 rotor faces, without the pedal down it'll read lower since the engine can't suck in as much air.
Hey thanks for the info. That's good to know. So with one weird apex seal. Got any ideas on what path I should take forward with this motor?
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Old Jan 26, 2022 | 06:20 AM
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Originally Posted by cactuscactus
Hey thanks for the info. That's good to know. So with one weird apex seal. Got any ideas on what path I should take forward with this motor?
It's hard to know until you take it apart.

IMO you're in luck though, you caught it before a seal let go and damaged anything else. A rebuild is always a bummer but at least you're likely to find re-usable housings and irons.
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