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wRrooster

Blown Piston Rings?

10 posts in this topic

Maybe someone can tell me what a blown piston ring in a 4-stroke is like?

I've got an 04 wr450f and have never had a problem with my bike. I shim the valves regularly, but have never replaced the piston or rings. Yesterday, I started to get some popping at high revs, kept riding, started to get the same bog and popping at mid-rpm. Then while trying to get my bike out of the woods, it started dying out at low revs, barely on the gas, then to the point where it will barely start, or dies instantly if it does start. I got it home, after driving a truck into where it died, checked the plug.... it looks fouled, like one of my buddies 2-strokes! My plug had never looked like this, it has always been perfect. I took my carb apart for kicks, it was clean, nothing was blocked. Is the fouled plug from blow-by of the piston rings? If the rings are blown, I thought there would be no compression, which there is at the kick starter. Before I tear my engine apart, maybe someone who has seen this can give me some advise?

Thanks

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CDI or ignition problem? When the CDI went on my old 426 it was popping and running very much like you are describing. Make sure your ground points on the frame are all clean.Try someone else's CDI if you can, to verify that it either is, or is not the issue. Usualy a blown piston will cause alot of blow by out of the breather hose from the valve cover. :thumbsup: WR Dave

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Thanks Dave, I'll look into that. I actually did remove my starter motor the other day, so it could be a wiring issue, but I've been riding for a day and a half problem free until this happened.

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If your rings are gone, you'd be smoking lots, any signs of smoke from the pipe?

It does sound like a gradual spark decline.

have you tried a new plug? sometimes, a plug can do the same thing as it's dying.

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Gradual spark decline is a good way to describe it.

I did put in a new plug when I got home, fired it up and had the same popping going on when I revved it. I didn't notice any smoke out the tail pipe, so hopefully its not a blown piston/ring.

Could a CDI/mis-fire problem cause such a fouled plug? Normally mine is a perfect coffee with cream color, now its got a black electrode and the threads are oily. I don't think its a carb/mis-jetting issue.

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Gradual spark decline is a good way to describe it.

I did put in a new plug when I got home, fired it up and had the same popping going on when I revved it. I didn't notice any smoke out the tail pipe, so hopefully its not a blown piston/ring.

Could a CDI/mis-fire problem cause such a fouled plug? Normally mine is a perfect coffee with cream color, now its got a black electrode and the threads are oily. I don't think its a carb/mis-jetting issue.

Have you put in some bad gas maybe?

Try remember if it started after fill up, I had somewhere like this prob but found out it was some old gas with probably lots of water in it.

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If your rings are gone, you'd be smoking lots, any signs of smoke from the pipe?

My 05 is now smoking and not happy about replacing the rings at such an early age. Something must have gotten past the airfilter? She smokes pretty bad. Going to Pro Tech in Temecula soon.

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If your rings are gone, you'd be smoking lots, any signs of smoke from the pipe?

My 05 is now smoking and not happy about replacing the rings at such an early age. Something must have gotten past the airfilter? She smokes pretty bad. Going to Pro Tech in Temecula soon.

Make sure the breather hoses are clear first. Excessive crank case pressure could cause this as well. Do the cheap stuff first. WR Dave

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Your getting full the is dumped in there, not igniting..then combusts...tehn more dumped in there and no spark....I didnt know that a clogged breatherhose can do that though. :thumbsup:

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After dumping the gas and putting in fresh high-test, new plug, cleaned carb. I took it for a rip and after about 2-3mins of heavy throttle riding, it did the same thing... there was a sharp decrease in power and it was bogging down. The plug is really white (looks way too lean), but I still don't think its a carb issue, especially after just cleaning it, and my jetting has always been spot-on. Valves are also within spec. Besides it being a bad CDI, and I don't want to go buy a new one of those just for a test, I don't know what else this could be? Could a valve not seating properly cause a lean condition and loss of power like this? I've done all the cheap and easy fixes I can think of before replacing expensive parts.

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