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Hi everyone, I'm brand new to the forum. I'm trying to solve a problem with my girlfriend's 2005 300ex. Some history for the quad. Rebuilt top end about 3 years ago prior to purchase. She has never changed the oil once. Double checked by a trusted friend. Recently it started losing power and eventually the cam chain jumped off the crank. Sloppy loose. It also ruined the chain guides and pieces were laying in the bottom of the case. Just the small rails on the sides of the guides. These were replaced with OEM parts. I have read here that most likely it bent a valve. I did not notice any contact marks on the piston and the valve seats were not leaking at all when checked with starting fluid in the intake and exhaust ports. I ordered a cheap chain online. Maybe a mistake. The chain was very tight on install without the tensioner in place. It did not seem to seat in the cam gear all the way where as the old one was so stretched that i could pull up on it between a dozen teeth on the cam sprocket. I was able to install it and re install the tensioner after inspection. I set the timing, adjusted valve lash, put in fresh oil and it fired right up. Seemed like it was going to be great. Sat there idling like a champ. I told her we needed to limp it around in the yard a little to let things settle as she wants to go riding this weekend, and she likes the rev limiter a little too much sometimes. So i started across the yard and as it warmed up a little i noticed a noise from what seemed like the top end. I stopped and it went away. I rode it for another couple minutes and the noise came back louder. Almost sounds like something hitting the valve cover. I shut it down and pulled the valve cover again thing i didn't tighten the cam sprocket bolts and one backed out. I was wrong. Everything looked good and nothing out of place. his sound was much louder than valve rattle and sounded like something was breaking or going to break. rotated the motor by hand without the valve cover on and all seems well with the chain and cam. Install the valve cover again, rechecked the lash, and started back up. Idles just fine with some very quiet valve noise. Rev up a bit and nothing seems wrong but after warming for a couple minutes again i hear this loud noise like something is out of place making contact with something else. Shut down immediately. At one point before this happened i did notice loss of power. Is it possible that a slightly bent valve would not show its ugly head until after warm up and expansion of metal parts. Maybe binding in a guide and sticking some. I'm not a professional mechanic but i have experience with setting timing, shimming valves etc. Thank you all in advance for any help you can offer.
 
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