Compression test

[agermaney]

Hi, Ive been a casual RX fan for many years but the urge to buy is now reaching a climax. After several weeks of browsing this forum I took the plunge last night and joined.
So hello to everyone, from your latest newbie.
I\'ve found many answers to my queries on this site and it will take many more hours to get through all the interesting info.
My entry question is in regard to compression testing. Why is it necessary to keep the guage\'s non return valve button depressed while cranking the engine and observing the reading?
I\'ll probably feel a right pratt when I get the answer but that\'ll teach me to think a little longer before jumping in.
Anyway, with ice broken, I\'ll look forward to enlightenment (is there a spell check on this?) from what is definately an elite bunch of guys.

Andy.

[probedb]

Welcome to the forum! I\'m a newbie round here and have only just started saving for an rx

[agermaney]

Thanks for the welcome probedb.
I think I may have twigged regarding my compression test question.
Is it because if only one tip seal has failed, the remaining two will still pump the guage up as there will still be one effective chamber?

I need to think harder next time.

Andy.

[MillSpeed]

When testing a rotary with a standard compression tester, you\'ll be getting three discreet compression figures per rotor i.e. one for each rotor face. If you don\'t hold down the non return valve, you\'ll just get a reading for the first face. With the non return valve held down, the gauge will bounce as each working chamber reaches TDC on the compression stroke, if you\'re quick enough you can see the max compression that each face is achieving.

[agermaney]

Thanks MillSpeed.

Andy.

[MillSpeed]

No probs mate :wave

[MillSpeed]

Oh yeah, just to add...if you have a cracked apex seal you\'ll get a zero (or close to zero) reading from two of the rotor faces as the air in the chamber on its firing stroke gets forced through the broken seal into the neighbouring chamber. If you have a broken side seal then you\'ll just get a poor reading on one of the faces.