Compression Testing - Late Model KTM Two Strokes

[@oasis618]

I never thought about the thread length of the test hose changing the volume and compression reading before. Great info!

[@offroadrepairman]

The hose has volume too 💡💡

[@slaverace1]

The hose volume is not relevant because the hose has a one-way valve at the base of the hose.

[@markbuckholz3184]

Remember that both elevation where you test and how long the hose is on your compression tester will change ultimate numbers you get on a particular compression test. Always good to baseline your bike when it is in perfect condition, and then you can look at the relative change as things wear. Thanks Jeff for the great video! And always good to ground the spark plug and/or make sure the kill button is depressed, will help reduce the chances of the energy from the ignition system not being dissapated by an ungrounded spark plug wire.

[@slaverace1]

Hello Mark: Thanks for your comment. The hose for the gauge has a one way valve (similar to a Schrader valve) in the threaded end of the hose therefore making the hose length inconsequential.

[@mototrials582]

​@@slaverace1not if the hose has any expansion under pressure. Likely,the longer the hose,more expansion, showing slightly lower numbers.

[@slaverace1]

@@mototrials582 Seems like you just want to be right, so you win! I'm going riding.

[@gc3937]

Thank you Jeff. All your videos help a lot!

[@slaverace1]

Glad you like them!

[@jclips999]

I bout a $20 compression test on Amazon to test out our Yz65 the recommended psi is 130 and the gauge read only 80psi so I thought time for a top end! Well after replacing top the same gauge read even less psi! Your advice on a quality gauge with a 3/4” length adapter surely is great information thank you! Those readings really bothered me until I saw this video!

[@mototrials582]

Did you do break in ride to seat the rings before testing compression?

[@ponydown418]

Thanks Jeff as always.

[@slaverace1]

You are very welcome

[@offroadrepairman]

The volume change because thread length in combustion chamber is irrelevant to getting an accurate pressure reading. The hose that you threaded into the cylinder has volume also. That’s why it takes many rotations to achieve the maximum pressure reading.

[@slaverace1]

Hello: Using the correct hose with 3/4" threads IS relevant to achieving an accurate measurement. The hose volume is not relevant because the hose has a one-way valve at the base of the hose.

[@motoxposse]

Jeff what’s your feelings on also pushing the kill switch so ignition is grounded ? Years ago this was supposedly a must do to prevent ignition damage 🤷‍♂️

[@slaverace1]

Hello: I should have put that and other info in the video. Might need to re-do the video.

[@Mostviews111]

You didn't ground the plug.

[@mikaelheed595]

My 250sx 2024 hade 205 psi at 0h.

[@redhill3282]

Thanks Jeff At what psi reading would you recommend a rebuild?

[@slaverace1]

Hello: I don't use compression readings to determine when it's time for a rebuild because often the piston/cylinder clearance is beyond spec before the compression declines. Most guys do top end rebuilds at around 125 hours. I like my engines fresher than that so I do rebuilds at 75-80 hours.

[@codyhall1091]

I thought they threw a check engine light for cranking it without the fuel pump connected??

[@slaverace1]

Hello Cody: Mine does not throw a code.

[@mototrials582]

Dang, those are some high compression foot pegs!

[@rafy600]

Jeff, do you know if a Sherco 300 2023 uses the same procedure. I'm asking because I checked mine with 3 different heads at sea level in Texas and got I believe 125 on all 3

[@slaverace1]

Hello: All 2 strokes use the same procedure. You either have 3 heads with the same volume or a poor quality or faulty gauge.

[@rafy600]

@slaverace1 thanks buddy, it has to be the gauge the heads are all from S3

[@Tacoexplorer]

You have a high compression head on it? Or medium?

[@slaverace1]

I ride from 7000' to 12,000' so I use the TSP "high" insert.

[@Mostviews111]

Test it with with the shorter threads wont even show a noticeable difference.