rebuild or not rebuild

Hey guys I have a couple of questions. First off i have a 2000 WR 400, and it has a lot of miles on her, my brother had it before me and used it on the track a couple of times, and i am just a trail and hill climber freak. But anyway i don't have the money to go out and buy a new bike but this is my question, i have a weird noise coming from the left side of the motor, i talked to one of my friends and he says that it could be my cam coming loose? is that possible, or i should say common. It is like a clinging noise like metal parts vibrating together. I mean i don't really beat my bike but i do use all the power she will give me. So i am not sure what i should do, should i bore it out and rebuild the motor or should i just try and pay someone to look at the bike and give me their two cents on what might be wrong with it. I have kept up on all maintence, but just am not sure what i should do next. Thanks for the help. :)

Could it be pinging from using low-octane fuel? My opinion is that it's probably valve clearances that are out of spec. by a lot.


I would start by taking the valve cover off and checking clearances on all the valves. Valves get louder as they get looser, but valves typically tighten over time. Look at wear marks on the cam lobes. Check all the cam bearings for free play. It might be time to invest in some Kibble White valve springs and a new piston and rings. If you decide to replace the piston might as well put in a new timing chain. It takes a lot more work and money to bore out to 426 and the power increase in minimal. A properly jetted 400 will still try and pull your arms out of your sockets just like a 426 and 450. Your bike as steel valves which are known to be very durable in comparison to titanium valves.

I would check valves and rebuild if necessary. Wouldn't bother boring it out,a s there is plenty of power with a properly set up motor. There are lots of technical resources to help you in the T forum. I have used them and they are easy to follow. Don't waste your money having someone else do the work, unless you just don't have the time or inclination.

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