I have a compression tester that has a one-way valve so it holds compression. It is convenient for a piston engine because it keeps building pressure to show you a good peak and it keeps the needle at that peak. Can I use this to get an accurate reading in a rotary? If I cranked it over it would only read the pressure of the best rotor chamber. Do I need an electronic one that's designed for a rotary? Or should I just have someone watch the gauge as I crank it?

Also, what's the best pressure I could expect to get?

the compression gauge usually has a schrader valve somewhere, it can be removed so it won't retain pressure.



on the gauge I purchased from autozone, the valve was in the fitting on the end of the hose that screwed into the spark plug hole, just grab it with some needle nose pliers (or the shrader valve removal tool you find at the tire mounting machine in the typical muffler shop) and unscrew it, counter clockwise like a normal screw... once it's out it shouldnt cumulate the pressures from each 'stroke'.



I was able to set mine where I could see it from inside the car through the windsheild between the hood and the car, it might be easier to have someone around.



expect at least 85psi if it runs well.



people get usually between 90-120 when good, some have reported 150.

To add onto what pengaru was referring to...



You will want to remove the schrader valve to make sure that all three faces of the rotor hold compression. If one apex seal is in bad shape, you will not have compression on two sides of the rotor. However, within this situation, the one good face that is sealing will show up on the compression guage if it is reading and holding peak pressure (schrader valve inserted).



I always try and perform both tests; with and without the shrader valve.



Good luck.



Kyle

you want to take the valve out, and you are primarily looking for even pulses. think of it like a regular compression test but you are only looking for the variation between cylinders



mike

anyone know where to find directions for testing the compression on a rotary??? (im stupid and need help with this kinda stuff)

We need to do a GROUP Buy to get a real Compression Gauge for people to share?



http://www.mazdarx7.com/new_page_3.htm





The cheapest one I could find for a Rotary is:



Which is actually for the Suzuki Rotary motor. Not as nice as the one above, but much cheaper.



http://www.rotaryrecycle.net

Wow. That first guage is nice. I would be interested in something like that after I do some research. A friend of mine is the Mazda Tech at one of the local Mazda dealerships so I'll have to ask him what he uses and thinks of this model. Thanks for the link.



Kyle

I thought you needed a special tester to test the compression in a rotary engine? https://www.nopistons.com/forums/pub...IR#>/dunno.gif

not really.



They have some that record the compression pulses onto paper kinda like how they record your heart rate and such at the hospital w/ink...or like a polygraph test... but you can do it just fine with a normal compression tester as long as you can remove the shrader valve which retains the pressure making it difficult to test each rotor face.

Cool.Thanks! https://www.nopistons.com/forums/pub...#>/biggrin.png