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2006 crf250r lacks compression ...still!

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bike lacked compression so I threw in a Wiseco piston and there's still no compression when I try kickstarting. I just checked my valve clearances and they're good.

Does anyone know a good way to check if there's a pressure leak through the valves?? Any other possible problem?? Any info would be greatly appreciated, thanks!

info on the bike: I've had the bike less than a year and it recently had less compression every ride. Eventually I could only bump start it. Now it wont even do that. Carbs good, engine's getting fuel, and just replaced the spark plug and its got a good spark.

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Have you ran a leak down test or a compression test? If not, it's a real good place to start if you truly think it's lacking compression.

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thanks charlie c. i dont have a leak down tester and I dont really know where to start now without one. I've heard of running compressed air where the spark plug goes but dont know anything about it.

and yeah, i thinks its a lack of compression still. I just compared it to another 06 crf250r to make sure and the difference is night and day.

I was hoping someone could guide me in the right direction?... I honestly dont know what my next step should be. Thanks in advance!

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You should be able to go down to the local autoparts store and pick up a leak down tester. I think they're about $30-$50. Take your spark plug with you so you can be sure that they have the right size for the plug hole. If you can't find one, at least pick up a compression tester to see what type of pressure you're building up.

Has that bike overheated quite a few times prior to your lack of compression issue? Because you installed a new piston, I can rule that out for the most part, but is it installed correctly? The larger cutouts on the piston go towards the intake side. I've read about people installing them backwards and bending the valves which would cause low compression. A distorted or heavily grooved cylinder would also cause an issue. I have a feeling you're going to be tearing it down regardless.

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Thanks! Bike never had a problem with overheating. the old cylinder had signs that a lot of dirt was getting in though.

and ive done a few pistons before and im pretty sure that everything was installed properly. and yeah, I double checked that the piston was in the right way before I installed it.

I'll see if I can borrow a compression tester and ill see about buying a leak down tester soon. thanks!

what will the leak down tester show? just if and how much it is leaking? whats the best way to locate/diagnose the leak if it is leaking?

thanks!

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Thanks! Bike never had a problem with overheating. the old cylinder had signs that a lot of dirt was getting in though.

and ive done a few pistons before and im pretty sure that everything was installed properly. and yeah, I double checked that the piston was in the right way before I installed it.

I'll see if I can borrow a compression tester and ill see about buying a leak down tester soon. thanks!

what will the leak down tester show? just if and how much it is leaking? whats the best way to locate/diagnose the leak if it is leaking?

thanks!

Off the top of my head, I can't remember. I'll have to look when I get home. It has to hold a certain amount of pressure for a certain amount of time. The instructions that come with the leak down tester should have that.

Timing is also critical like samras121 said. I automatically assume that it has already been checked.

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If your sure about the timing, then the other possibilities will require disassembly anyway. if you pull the head, 1 way to check valves is to spray carb cleaner or WD40 into the ports with the head level like it's on the bike. if it flows through to the chamber side, it's leaking.

1 way to give an indication on cylinder/rings or valves before pulling it down, is to put a little crank oil in through the plug hole. if comression goes up, then it's the rings or cylinder as the oil leaks by slower than air. if it stays the same, it's gonna be valves or head gasket.

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If your sure about the timing, then the other possibilities will require disassembly anyway. if you pull the head, 1 way to check valves is to spray carb cleaner or WD40 into the ports with the head level like it's on the bike. if it flows through to the chamber side, it's leaking.

1 way to give an indication on cylinder/rings or valves before pulling it down, is to put a little crank oil in through the plug hole. if comression goes up, then it's the rings or cylinder as the oil leaks by slower than air. if it stays the same, it's gonna be valves or head gasket.

wow, thanks! Makes perfect sense! never even heard of this before but I'm gonna be doing it with my crf450 pretty soon too as it seems to have lost some compression too. Thanks!

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bike lacked compression so I threw in a Wiseco piston and there's still no compression when I try kickstarting. I just checked my valve clearances and they're good.

Does anyone know a good way to check if there's a pressure leak through the valves?? Any other possible problem?? Any info would be greatly appreciated, thanks!

info on the bike: I've had the bike less than a year and it recently had less compression every ride. Eventually I could only bump start it. Now it wont even do that. Carbs good, engine's getting fuel, and just replaced the spark plug and its got a good spark.

When you replaced the piston you took off the cyl head right.You should have check the valves for leaks.The simplest method to check is to fill the intake & exhaust port with a brake cleaner and look at the valves if there are leaks or seepage.If you see a small seepage just try to tap the valves slowly to see if a dirt is causing it.Wipe it this time it should be dry if not there go your problem.

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Off the top of my head, I can't remember. I'll have to look when I get home. It has to hold a certain amount of pressure for a certain amount of time. The instructions that come with the leak down tester should have that.

Timing is also critical like samras121 said. I automatically assume that it has already been checked.

haha nice. it was just something that popped into my head. im not the best with four stroke motors but im studying to be a mechanic. thanx for the confidence boost. lol

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