How to test compression on a rotary engine the easy way
06-12-2013, 07:27 AM
#1
sas
Thread Starter
How to test compression on a rotary engine the easy way
Many people in the past have approached me with information on how to test compression on a rotary engine.
Though the best method is with a proper rotary tester, there is another solution. It's actually very simple.
1. Take a normal compression tester, and remove the valve that keeps the compression in the tube.
2. Remove the bottom spark plug from the front rotor and insert the compression tester tube. Make sure it seals properly.
3. Connect a strobe timing light with angle (degree adjustment) and connect to the trailing spark plug lead on the front rotor.
4. Run the engine for 30 seconds whilst checking the compression using the strobe light. You may have to adjust the degrees to get a true reading. Be careful not to touch the disconnected spark plug lead! (My auto electrician discovered this the hard way, quite a few times....)
5. Note the highest reading and write it down somewhere.
6. Insert the front leading plug, connect the plug lead and repeat this process on the rear rotor.
Note that any reading below 700Kpa is indicative of a problem and an engine rebuild is imminent. Compression above 850Kpa shows an engine that's operating reasonably.
Hope this helps.
PS - Remember to re-insert that compression tester check valve!
Though the best method is with a proper rotary tester, there is another solution. It's actually very simple.
1. Take a normal compression tester, and remove the valve that keeps the compression in the tube.
2. Remove the bottom spark plug from the front rotor and insert the compression tester tube. Make sure it seals properly.
3. Connect a strobe timing light with angle (degree adjustment) and connect to the trailing spark plug lead on the front rotor.
4. Run the engine for 30 seconds whilst checking the compression using the strobe light. You may have to adjust the degrees to get a true reading. Be careful not to touch the disconnected spark plug lead! (My auto electrician discovered this the hard way, quite a few times....)
5. Note the highest reading and write it down somewhere.
6. Insert the front leading plug, connect the plug lead and repeat this process on the rear rotor.
Note that any reading below 700Kpa is indicative of a problem and an engine rebuild is imminent. Compression above 850Kpa shows an engine that's operating reasonably.
Hope this helps.
PS - Remember to re-insert that compression tester check valve!
06-12-2013, 01:15 PM
#3
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What are you doing to prevent the disconnected plug wire from burning out the coil while the engine is running? Having it charging up without a method of discharge will burn out a coil quite fast
What are you doing to prevent the pressure from the fuel combustion from over-inflating the compression score?
Are you accounting for the effectively increased volume (and resulting decreased static compression) by having a tube extending from the plug hole to the sensor?
How are you normalizing for 850rpm? The charts only go to ~300rpm, and the normalization line is not linear, so the math could get complicated?
What are you doing to prevent the pressure from the fuel combustion from over-inflating the compression score?
Are you accounting for the effectively increased volume (and resulting decreased static compression) by having a tube extending from the plug hole to the sensor?
How are you normalizing for 850rpm? The charts only go to ~300rpm, and the normalization line is not linear, so the math could get complicated?
DIY fail.
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