Jump to content
Sign in to follow this  

Compression test, dry?

Recommended Posts

Is it ok to run a compression test without any gas/oil (2 stroke) or tranny fluid in the bike? I"m just wondering because I put transmission fluid in but had the gas tank off and carb was dry. I had 136psi which seems low, considering I just put a new topend in.

Share this post


Link to post
Share on other sites

You can give it a squirt of oil. You did give it some oil at assembly.....I hope. What is your elevation? I had about 160 on a fresh bore/stock uncut head at 2000 feet.

Share this post


Link to post
Share on other sites

I always try it dry. Then put a lil oil in the cylinder to see what the compression is. With the oil it should go up some.

Share this post


Link to post
Share on other sites

Yes I oiled the cylinder and rings before assembly also had the throttle wide open. 3300 feet. Higher elevation = lower compression right?

its been about a week since I put the piston in though. . . .

Share this post


Link to post
Share on other sites

Seems a bit low, but it could be a mix of higher elevation and your gauge. That will be plenty to run. It should come up a bit soon.

Share this post


Link to post
Share on other sites

So after I break in the piston and the rings "set", I should expect higher compression reading? My old 04 125sx gave 150-154psi, something doesn't seem right......

Share this post


Link to post
Share on other sites

that seems pretty darn low. I had 180psi on my cr250 and it had a reasonable amount of hours. You may see a slight increase with a warm motor, but not much. PUtting oil down the sp hole will give you a falsely high reading imo.. It doesn't matter that there is no trans oil, a 2t connecting rod is lubed by the premix as it comes in from the carb. I would check it after you run it a bit, but sure seems low. I assume you did kick hard a few times, not just once? Kick till it doesn't go up, then watch the gauge to see that it doens't bleed off, it should hold that psi a long time.

Share this post


Link to post
Share on other sites

Don't sweat it if you can't get to the numbers of the sea level guys....run it, it will be fine.

Share this post


Link to post
Share on other sites
So after I break in the piston and the rings "set", I should expect higher compression reading? My old 04 125sx gave 150-154psi, something doesn't seem right......

Get it broken in first. Are you using the same gauge as with the old '04?

Share this post


Link to post
Share on other sites

My 250 went up 25 psi after break in. You should expect something similar with the 125.

Premix oil not only lubes everything, but it also aids in ring seal.

I had a 125 that would get around 120 psi with a new piston, but it ran well. My 250 gets around 230 psi.

Also note the gages may be different for all people. Run to oreillys and rent their compression tester. This will allow you to verify your numbers to see if your compression tester is still accurate.

Share this post


Link to post
Share on other sites

Its the same compression tester as before

I kicked it 10-15 times

I'll break it in and test again.

I have O'reillys right down the street so I'll check out their compression tester.

Thanks guys

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×