Proper 2 stroke compression test?

[pat-kdx]

I took the exhaust pipe off my 2000 KDX 200 and looked into the cylinder and noticed signs of blow by on the piston. From that angle the cylinder walls still look good. I want to see if it is time for a rebuild or at least new rings by doing a compression test.

What is the proper method to compression test a 2 Stroke?
1) Open the throttle fully
2) Use kick starter to rotate motor until the compression needle stops rising

Would performing a leak down test yield better results?

The bike is new to me and I am not 100% sure what engine work has been done. The previous owner told me the head was ported and he thought it may have been bored out. He was the second owner. Looking on the Kawasaki website, the spec for my engine states 136 psi. Is this the minimum for this engine or what is shipped from the factory? My tests are showing 180 psi after 7-8 kicks of the starter.

 

[nickyd]

Pat - some blow by is normal - I had a piston in my KDX that had major signs of blow-by. I thought for sure it was time to change it - My compression was still good (around 165psi) but I took her apart anyway - mic'd the piston and she was well within the limits......cleaned the P-valve and put some fresh gaskets and rings in and kept on riding. For what it takes to do a top end on a two stroke, I didn't mind the time (and the few parts - circlips, gaskets, etc) - plus now I have peace of mind that the piston in within the proper measurements and the cylinder is clean. For yours I might tend to ride it through the summer and keep an eye on that compression and maybe do the top end in a few months (dependant upon your riding) - or if it keeps you awake at night, take her apart and mic the parts just to be sure.

 

[bikepilot]

136psi is probably an absolute minimum, I would expect 160 - 190psi on a good motor. You did the test correctly, though I always hold the kill switch or ground the plug as it can damage the ignition system to kick it over without the plug instaled or grouded (the kill switch simply grounds the coil).

Top ends are easy, if you are worried about it, take it apart, mic everything, clean the pv's and put it back together.

FYI - you can have completely worn out rings and pistion and still have good compression. I went far too long on the top end on my 1993 KX250, including a solid 3 weeks of dune riding (8 hours a day, every 7 days a week:)). After all that, the ring gap was much bigger than any of my feeler gauges (Probably around 1/4"), the piston to cylinder cleanance was huge and it was still making 175psi of compression and running strong.