Compression test?

[mike-evans]

Borrowed a compression gauge and want to do a compression test on my 01 yz 250. Never done one before, is it as simple as removing plug, screw in tester, throttle wide open and give it a good kick, and check reading? What reading would mean all is good?

 

[julien_d]

Kick and keep kicking until the gauge stops going up. A good reading depends on the compression specs in your service manual.

 

[Brandon H.]

I really don't like compression test at all. How high of a reading you get depends on how fast you can kick your bike really.

I would do a leakdown test, kill a bunch of birds with 1 stone.

 

[whenfoxforks-ruled]

Doing 1 now is just a ball park test of your top end. And that will vary with how accurate the gauge is, and if the test is abused. If you test it fresh, and keep checking it periodically, a drop can show when the rings fail. Maybe? No, second the leak down test. Vintage Bob

 

[mike-evans]

I've heard of a leak down test, but don't totally know what it is and what it proves? Is it something I can do myself?

 

[whenfoxforks-ruled]

Do a search here or google. You can buy 1 from motion pro, or put 1 together yourself. The 1 from motion pro comes with instructions! Vintage Bob

 

[mike-evans]

ok, so I been searching the net and what I understand is, u blank off the inlet (carb), outlet (exhaust flange) and powervalve pipe, plug a correct size fiting into the sparkplug hole with a pressure gauge inline, and pump around 6psi in and monitor a leak (if any) and find where leak is...

 

[Brandon H.]

Thats how you can find a leak yes, you can use soapy water in a spray bottle spraying it on sealed surfaces. If you find any bubbles, you gotta leak.

As for testing the top end, I am not sure. Someone who has done it will chime in I am sure.

 

[YZ__rider]

Im not really sure how accurate the compression tests are. It seems to depend most on the accuracy of the tester, which vary. I have had mixed results.

 

[whenfoxforks-ruled]

6psi may be too much. Seems I heard 4~5? It will leak new, its a timed release deal. If it leaks in so many seconds its trashed. Measuring the top end for coolant leaks, do not go over what the cap is rated. Vintage Bob

 

[Beuford]

A leak down test will not tell you anything about the condition of your rings.
It will help for gaskets and seals.