Topic: Compression test question

[zoo mob]

Any reason to pull all of the plugs at once? It was suggested that I do this over at KZrider, I've always pulled them one at a time, any difference? Also, I'm assuming having the exhaust off won't make a difference in the readings correct?
Thanks

[750goes]

All plugs out will give a better reading per cylinder, as when cranking you are ignoring the other cylinders if there is no resistance to compression ie  no plug in the hole..

[eurban]

The readings that you will get from a compression test will be affected by many things other than the actual compression of the the cylinder being tested.  Your procedure for testing is one of them.  The internal volume of the compression tester is another (this one can make a huge difference in a small engine; read TwoTired's posting in the "tricks and tips" section).  Proper testing procedure typically involves: fully charged battery and properly functioning starter, all 4 plugs removed, throttle held wide open or carbs removed, good seal to the cylinder head.  The most important thing is to be consistent in the testing of all 4 cylinders.  In your results, you are looking for consistent numbers between your cylinders, more than comparing absolute values to those in the books.  

[cycleman]

Most compression testers on the market are designed for auto engines, bigger displacement.  Therefore the readings on a bike engine will not be totally accurate.

As previous poster has noted, all readings should be close to each other. 

I've never really been a fan of doing a compression test just for the hell of it.  They are meant as a diagnosis tool and they usually confirm the obvious.  If you've got blow by, down on power, fouling plugs etc, then you'll know you've got a problem and the compression test will probably show you the offending cyclinder ( which you already new - the one with the fouled plug.)

If you do the test and find one cylinder is down 10-15 lbs you are going to worry about it and make it into a real problem ( in your mind ).  When in reality the engine will run a very long time.  If it ain't broke don't fix it.