compression on YZ 250

[fabbo]

Hi Guys

Does any one know what the compression should be on a stock standard 2001 yz 250. in PSI


I had the bike tested today and it registered 175 psi. The manual says 9.1 to 10.6 to 1 what ever that means in psi ?
The bike is still on the original piston and rings! and starts and runs really well.

Would appreciate any feedback

Thankyou 

[ford832]

You're too low.Given the age you're due for a piston/rings.You'll be surprised how much power you'll pick up.220-230 is a good number.Best replace it before things go boom.Make sure you hold the throttle wide open and kick until it won't go any higher when you check it.

[fabbo]

Thank you for the confirmation

Fab.

[Coop]

A 250 two stroke should be in the 170-240 range. So I wouldn't say 175 is low enough to go boom like Ford said, but you are getting close.

Did you test the bike cold or warmed up?

[fabbo]

it was warmed up and the spark plug could be touched and was only warm.
Q. what is the difference between hot and cold?

[SachsGS]

In a plated bore engine if you let the piston go too long (piston slap) it will start to pound off the nickasil. Usually the damage will start around the exhaust port.

[G-MONEY]

Top ends are more affordable than top ends plus cylinder repairs and a crank.

[evo550]

If you are trying to determine whether you need to replace the top end, I would also advise having the piston measured up as well.
Compression test will only give you some of the story. A new set of rings on a old flogged piston will give you an accpetable compression reading, even though the piston is about to drop the skirt. As sachs mentioned.
And if you replace the piston also replace little end bearings and pin. The whole set up is only as strong as the weakest link.

[admiral]

your elevation level will also effect compression ie. higher elevation = lower compression and vise versa