Two Stroke Motocross
Two Stroke Motocross Forum => General Two Stroke Talk => Topic started by: YZ250 on July 22, 2010, 04:10:20 PM
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I was wondering, is it possible, by pushing or slowly kicking the kickstarter down, to estimate how much life or compression your engine has? Just recently while trying to sell my kx100, the man i was trying to convince started to push the kickstarter down with his hand. He said he was checking the compression. Is this, at all, a good way to check your engine life/compression?
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Well, I would question how accurate you could possibly be in determining anything this way, but it'll definitely tell a buyer if the motor's blown. If it's got compression - some compression - that's another thing to check off the "is this guy bending me over on this deal?" checklist. But as a way to determine how many hours the motors has left or whatever, I'd be hesitant to rely on something so subjective unless you've got a big grey beard.
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It takes a minute and a half to screw off a spark plug and screw on a pressure gauge, i'd go that route. I mean all engines have a minimum psi they should be at. If the engine should be at 110psi, then 95psi by hand might feel acceptable when in fact it isn't
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My best friend buys literally hundreds of bikes and has many years of experience in repairing, restoring and rebuilding motorcycles. Yes, he can tell how badly worn a bike is by kicking the kick starter slowly.
Once the machine is running, he hears things that many would not. It comes from experience and interaction with thousands of machines in your lifetime.
This is not to say that a beginner or even someone with years of riding experience could do this but it is possible.
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Exactly. Unless you've got a ton of experience with that kind of thing, which I most emphatically do not, I wouldn't trust the kickstarter compression test beyond, "Does it have compression at all, YES / NO."
With that said, I guess I feel compelled to brag that the 120 feels crisp as a winter morning when you move the starter by hand. :D
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Not only will kicking the engine over by hand give you an idea about the condition of the engine, the sound will also give added information re: whats going on in there. A healthy "ka-donk" means compression is still healthy and the piston still in close proximity to the bore.
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I've done it to get a feel, but if I go look at a running bike I will take my compression tester with me to know for sure. Generally I prefer basket cases so I can rebuild it how I like and know the condition of ALL the parts. (Off topic: I'm trying to close the deal on a '79 RM250 bc for $75, but I am second in line so I may miss out).
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This may sound wierd but I do the same thing. I am listening for the air rushing by the rings and the rate of the stroke compared to the time it takes for the stroke.What I mean is its like a top end leak down test, charge the cylinder and see how long it holds.Listening to and engine run detecting piston slap is another thing you can pick up along the way. Jetz is really going to love this but placing your hands upon the crankcase (wearing gloves) you can detect vibrations worn crank or wrist pin. That is some voodoo shit right there!