Bought a compression gauge but I got no reading on the TB 250. The gauge reads from 10psi, but I got no reading. After some head scratching, I saw in my Clymers manual for SP 500 that "the compression cannot be tested with a gauge on this engine due to the compression release mechanism within the camshaft." Is this the same on the 2-stroke Trail Blazer 250? My SP 500 book says to put my finger over the spark plug hole, then crank the engine. "If you feel pressure, it's got enough compression to start the engine." Doing this I feel strong pressure. still stumped.

 

Intresting..my 2000 needs 115psi..Anyone with an older TB know???

Chances are, you just found your problem...I don't think the TB's engine is that much different from your to mine..

 

Just to confirm, I should get readings of 100+psi on the TrailBlazer 250, right? This one is a 1997 I think (SER#97-02387 . . . is the 97 the year?). Is anyone sure that my low reading on the new compression gauge is real, or does this ATV have a compression release mechanism within the camshaft, like the SP500? Thanks. I just want to be sure before I start trying to figure out if the poor compression is rings, valves, gasket, or ??

 

I don't think 2 strokes have compression release mechanism..mine don't

 

the 250 engine is soo small u dont need a compression release to start it. but on the 500 you do since its such a big piston.

 

Hey guys, 2-cycles dont have compression releases. Well, at least the polaris atv's.Some older super compression chain saws had them. Since the 2-cycle has a narrow squish area above the exhaust port, a compression reading can be hard to get. make sure your fitting is snug, hold the throttle wide open, and turn the motor over as fast as you can until the gauge peaks out. That will be your compression reading. A helpful hint on 2-cycle starting if you think the compression is low, pour a capful of motor oil into the plug hole and either recheck compression, or try to start it. It wont last long, but it will boost compression just long enough to start it, if it is low. Although from what you were saying about it recranking after a couple of days of sitting, seems like that might not be the culprit. A 97 model would be iffy on rings unless it has alot of riding time on it. Hope this helps,Bubba

 

you want about 110psi of pressure.
anything under 90 psi and it backfire and be extremely hard to start.
and anything below 75psi, it won't fire.


now if you had anykind of decent compression, placing your thumb over the hole and cranking it, will blow your thumb off no matter how hard you try to press down.


2 stroke don't use camshafts,like four strokes.
and compression release mechanisms don't release all the pressure, just a frction of it, to make it easier to turn over, yet have enough psi to fire.

the 250 engine don't have a compression release....but..the 400 2 stroke pllaris engine does, in the form of a small hole drilled above the exhaust port.


if you said it ran fine for awhile untill it shut down, and now it won't start, i would suspect it had a lean condition, and seized the piston a few times, wich should also warrent a carb rebuild if indeed you have low compression.(not to mention a top end rebuild)

 

The "Compression release" is a small hole on the 400cc two strokes above the exhaust port. It is there to lessen the strain on the starter motor when cranking the machne over. Even at idle the hole is irrelevent due to the speed of the piston. On the four strokes there is a mechanical release that lifts one of the valves slightly on starting. You shouldn't have either on a 250 two stroke.

If you aren't getting any compression, more than likely it's either a blown head gasket or a seized motor (rings stuck in the piston). Either way, it's time to tear the motor down.

 

Thanks for your help, y'all. It looks like a complete top end rebuild. Ugh!
Anyone know where I can find a manual that will help with tis 97 TB 250?