Whats the procedure to check compression on RX

[Him]

What shall be done to do a proper compressioncheck on an RX?

Shall all the coils be desconnected? Throttle, what position? Shall I manually lift the throttlevalves? How high should the compression be? Shall the engine be cool or warm?

TIA

 

[nhrxrider]

I don't have a FSM, but as an auto technician, I just used a generally accepted procedure, slightly modified for this particular engine:

• 
  Run the sled long enough to warm up to normal operating temp. Don't just let it idle...that gives an uneven temp. Try to ride it around your yard a while to get a true "trail" temp.
  Completely remove all of the coils. On many new coil designs, if they are left hooked up without being able to ground through the plug, they can burn up.
  Remove all spark plugs
  Thread the compression gauge into the first cylinder
  Use something to hold open all of the vacuum valves (I used my fingers, but this may not be the best way)
  Push the throttle all the way open while cranking the engine

I was able to do all of this myself by using one hand to hold the valves open, my other to operate the key, and my arm against the throttle. Just put a rubber band or clamp over the throttle or have someone help you to save the juggling.

Repeat this for each cylinder. Let us know your results...I'm curious what others have come up with.

Jim
[/list]

 

[Him]

I did a quick test yesterday, but that was with a cold engine, throttle at idle and the valves closed. I had to create an 'adapter-pipe' with a plug and a 13cm long pipe welded to it. The inner diameter of the pipe was 10mm so that would lower the compression but my concern was if the compression was different between the cylinders.

With a warm engine, throttle & valves fully open and a correct instrument I guess that the numbers would be much higher. I didn't take a second test, but I shall do that later with warm engine and the most important thing: Not by myself, to few hands...

Readings:
Cylinder #1 7.2kg
Cylinder #2 7.0kg
Cylinder #3 7.3kg
Cylinder #4 7.5kg

 

[Skydog]

What is that is PSI??

 

[LazyBastard]

Er... kg is a unit of MASS and has absolutely no relation to pressure, unlike the POUND, which is a unit of force. The metric unit for pressure is the Pascal (Pa).

 

[LazyBastard]

In order to get an accurate reading, you need to put a one-way valve at the tip of the... sparkplug.

 

[Him]

I borrowed a correct tool for the job, and I think I got somewhat more
correct readings. And LB, sorry for telling the wrong unit, the unit now is
in BAR.

It was done on an cold engine, throttle at WOT, walves fully open.
I dunno how the readings would change on an fully warm engine.

Cylinder #1, 13.3 bar
Cylinder #2, 13.3 bar
Cylinder #3, 13.0 bar
Cylinder #4, 13.2 bar

To convert it to you're favorite unit, use http://www.matweb.com/tools/conversion.asp