I dont have a Rotary Compression checker, and i need to do a compression check tomorrow. I do have a gauge for a piston engine. Here are my questions:
1) which plug do i put the gauge into (best one to use)
2) How do i get the other plugs to not fire and start the engine while im trying to do a check???
3) If all else fails, does anyone know who might carry the right checker, that i can get tomorrow (upstate ny..albany area)
thanks

 

Use a piston compression tester. I personally put them in the lower holes. Remove the EGI fuse from the fuse box underhood.

While cranking hold the air relief valve down and watch the pulses..

 

Sorry to hijack the thread, but I was just curious. I've read varying opinions on what good numbers are from sites and threads on this forum, so what really is good? From rotaryresurrection.com, "115+ is like new, 100-115 is healthy, 90-100 is getting weak(1 year or less in most cases) below 90 could blow at any moment" but is that really true? Has anyone else had similar experience with what he says?

 

I think the mazda manual says 85 or lower is crap and should be rebuilt. Ive been out of touch for like 8 months, so my memory might be a bit fuzzy. It also depends on which series you have and what model (NA or turbo). All those motors had different compression #'s.

 

This isn't true! A normal gauge doesn't have time to get the needle up to the correct reading before the next compression cycle comes around. I keep seeing all these people on the forums getting #'s like 35-35-35 and wondering why. Its because most gauges are fairly slow getting the needle up to the correct reading. Heres how you do it with a piston tester:

1) Warm the car up fully
2) Pull the EGI fuse
3) Insert the tester into the bottom plug hole
4) Have a friend crank it with the throttle full open.
5) Open the air relief valve. Watch the tester for EVEN PULSES. You are not looking for a number at this point because of what I stated above. Just look for very even pulses...there should be 3 in a row.
6) Now close the air relief valve and let it reach a total pressure...this will only take about 3 seconds.
7) This is your compression. If all the pulses from #5 were even, then the number you get in #6 will be the compression all the way around the rotor
8) Repeat with the other rotor.

This is even the way Kevin at Rotary Rusurrection tests them.

-Joe

 

well, I wasnt as elaborate... But I wasnt wrong

Terribly sorry..

 

Didn't mean to offend ya bro! Its just that watching the pulses leads to false readings and I see alot of people here thinking they need a rebuild because of this. Ya weren't completely wrong, and no disrespect was meant

-Joe

 

WOO HOO... I just did the compression check and had solid 120-120-120 on the rear, and 110-110-110 on the front. Almost makes me not want to sell it now....lol

 

Does anyone have a guide on what the compression of a S4 TII should be (1987). I think my above numbers are good, but i want to make sure.
thanks

 

Your compression is damn good. Mine is about 105 on front and rear and I consider that great. Below 85 is boderline for low compression.

-Joe

 

where can i get a rotary compression checker? =)