I cant find any information on the results from a compression test. Yes i have searched. Anyone got a site or have a topic here on the forums about the results?

 

I've always heard below 80 the motor needs a rebuild, 80 - 90 the motor probably has under a year, 90 - 100 is OK but not great, above 100 you're good to go.

Not to thread jack, but can some one PM or post a step by step process to compression checking a rotary?

 

Hopefully my way isnt wrong and correct me if so.......I got what i believe is a piston compression checker. Take off one spark plug and the related wire. Put the compression adapter inside the spark plug hole and connect everything up. Now this is way easier with 2 people so try and get someone else to help. Crank the motor over a few times and keep a close eye on the needle bouncing up to the same psi mark. Repeat the needle bouncing 3 times or more. Take out the tester and reinstall the spark plug and wire. If you disconnect all the wires and spark plugs at the same time, i think it can effect timing so i wouldnt recommend it.

 

Removing the plug wires effects the timing??? Don't think so..... Just yank the egi fuses to make sure it doesnt fire. As long as you dont mix up the wires you're fine.

 

pretty much yup, make sure the accellerator pedal is pressed all the way down . Take the check valve out of the comp tester gauge and look for 3 evenly spaced readings. Timing though?

john ny

 

Dunno just what i heard. what i mean about that is dont take out every spark plug and every wire at the same time. If this isnt true ima be pissed cause it was a hassle.

 

Yea, you take out the top plug in each rotor. the bottom plug remains for the test.

 

Ok for the test do I test both the trailing plugs, or do I just need to do it for one?

So this is my understanding on how to do it:
1. Remove 1 trailing plug.
2. Screw compression tester into spark plug hole
3. pull egi fuse
4. turn over engine
5. The 3 bounces are your compression reading for each rotor? or for just one?

 

The 3 bounces is just basically a triple check that the reading is correct and that all are the same. If there slightly off i dont think it matters a whole lot but if theres a huge difference then yea theres something wrong....

Anyways, anybody with links on the psi reading ratings?

 

ehh... the 3 bounces are for each face of the rotor. The FSM and Hayes manuals give specs for the Mazda SST, so they are slightly different than a piston engine compression tester

 

Slightly? One is measured in PSI, the other is on a scale of 1-10.

Also, even if removing all the plug wires changes the timing (which it doesn't) the timing doesn't matter at all for a compression test. There is no physical way to change the intake or exhaust timing with the engine together, and it shouldn't even be sparking in the first place.

 

Just to clear things up, the FSM gives values in kg/cm^2, AS WELL AS PSI, and kPa. The Mazda compression tester displays in kg/cm^2 (range of 0-10).

I was saying that values taken with a piston compression tester cannot be compared to values taken with the Mazda tool.

 

Yeah. I honestly don't even know if its exactly 1-10, but its something like that.
Anyway, the figures quoted near the top are pretty accurate. 100+ is very good, 90-100 is pretty decent, 80-90 is marginal, and below 80 is a ticking time bomb.

 

Alright so the psi ratings are known to me now. I'm not at all aware though if you do 3 needle jumps and say for example it reads 95, 90, 100 would that be a problem?

 

No, that's alright. As long as they're close, and 90+, you're okay.

 

Alright, thanks alot for your help.

 

hmmm, so people refer to the manual but most have missed a part were is sayes that rotaries and pistons are different. you can not use your convention piston enginecompression tester. if you do at least remove the shrader valve. This is because pistons dont have the constant power stroke like a rotary. If the shrader valve is left in your reading is just going to show the best face. One rotor chamber may have **** compression and the others may be good. But with the shrader valve in your not going see this. This still isnt as good as the mazda compression tester but hey for like 30 dollars its definitly the better deal. Also remove fuel. disable ignition and only remove the top plugs. They both must be removed while testing unless its a 12a. Bottom plugs stay in and have the throttle held open.

 

How do you remove the Schrader valve?