Compression test?
 

Hello,

NOOOOOOOOOOBbbbb question....

Can a compression test be done on the RX-8? If so is it exactly like a compression test for a piston engine? If not how do they do it/how does it differ?

This sounds weird I know, I am confirming (or not confirming) what a dealership is telling me.

Thank you,

Brian

You dont exactly have to do it at a dealership, as long as the shop you go to has the right equipment its all good.

usually a compression test will cost just 1 hour of labor, but make sure u do it at a dealership who knows what they're doing, not just give you some numbers so you can walk away.

Each rotor has 3 faces so that each housing needs to give 3 figures. A standard compression guage has a schrader valve that holds peak values so this would not satisfy the needs of a rotary compression test. You need to be able to see if the succeeding face has lower figures. The elctronic units that MAZDA have can properly account for the 3 numbers and also provide cranking rpm which is very important in a compression test but even more so with rotaries. There are many things that can be garnered from a proper test on a rotary, for example: 2 low figures and a high figure represent a single bad apex vs one bad number would more likely be a side seal.

I sometimes will even use a standard compression guage with the valve removed and we also use the old 70s guage that plots a graph on paper.

Paul.

Paul,

Thank you VERY much. That is EXACTLY what I was looking for.

My issue is I drove another same year/model/tranny/port engine car without mods. Mine (both I and the other person thought) seemed much "weaker" and slower (even at higher RPMs). So I take it to a local stealership who I have had work done at without an issue several times. They tell me they can NOT do a compression test, it does not work that way. So I call another dealer and talk to the service manager and head mechanic briefly. They were confused by the first dealers comments.

I have to pick my car up today so I can go out of town. However Monday I will take it to the "other" dealership and ask them to look into it.

I did take it to a local tuner shop and had a compression test done a few weeks back. They stated two cylinders were running around .75. They stated I might want to take it to a dealership to have it checked out. So I did and then I entered the twilight zone.

It sucks not knowing what to think :(. Hence my OP.

Thank you again,

Brian

Quick and easy test
 

This is the shade tree version of the compression test:

Remove the coil trigger wires (you don't want the engine to start or Taz you)
Remove the trailing plugs (the top ones)
Place a finger over a trailing plug hole to seal it.
Make sure you are not near any rotating parts.
Have a buddy crank the car.
You should hear even sounding noises, if you hear loud, soft, soft you should let the dealer check further.
Check both rotors.

Good luck, and be careful.

Just undo the ESS plug...it's easier than all the coil plugs and does the same thing :)
sounds kinda like a "butt dyno" though :lol2:

this is the least expensive "proper" rotary compression tool that I know of, assuming you already own a laptop computer:

http://rotarydiagnostics.com/

that'd be a nice one to have:ylsuper:

wow,

your posts suck!@! ;)

good job.

beers :beer:

just doing my job ... :kiss:

I have one of those. It rocks.

Actually, you can run this system on any Windows computer--desktop or laptop--under Windows 2000, XP or Vista operating systems. And you can locate the computer up to 16 feet from the tester using a USB cable w/o supplemental power. With a powered USB hub, that distance can be increased significantly.

In addition, at least one user is running the software on a Mac using the Parallels, Windows emulation program (http://www.parallels.com/).

Larry
http://RotaryDiagnostics.com

While we're on the subject, this is an example of what you hope to see when doing a proper compression test.

If you use the above described device, yes.

Sealing goodness :Peace:

any chance I can get a publicity discount :angel:

How about this:

http://www.mazdamaniac.com/images/misc/comptest.jpg

He he! Look us up in the vendor area at SEVENSTOCK XI and I'll see what I can do.:)

how much would the dealer charge for a compression test...
got the 8 about 2 months ago and would like to kno if everything is ok

My guess would be $80-$100USD at the dealer and perhaps a bit less at an independent rotary shop. Where are you located? Call a few shops and ask.

NY, lower westcher county/ I've only been in one dealer around here so far// they are pretty expensive
asking me $220 for a set of spark plugs, which I found online or $25 each =]

2 cylinders???

Don't think I can make it, but I'm standing on the edge of the purchasing cliff. All I need is a small push .... :eyetwitch

How many quarts of oil did you put in the chambers to achieve those numbers? :Eyecrazy:

just j/king :kiss:

lol

Those were just after the engine hit operating temp for the first time.
I've put about 4k on the motor now - all at high boost, high temps and fairly high stress - so it is time to do it again.