2018 XC300 horrible sound?
 

https://youtu.be/YYyDUmWL-2M

What on earth is this sound coming from?

I have not been able to get the flywheel off because of lack of acceptable tool.

I have good compression, measured by stroke resistance on the kickstarter.

The FW bolt is torqued to 40Nm but I can't check crank play or not torque until I can cobble a tool to get the FW off.

The noise is barely a flutter until the bike reaches operating temp and then it becomes horrible.
It "feels" like there is more violent vibration once the noise reaches the levels in the video.

Thank you

I'm guessing it's power valve or power valve linkage.

I've heard of the power valve actuating arm vibrating on the crank case.

Could also be something is loose on the power valve mechanism and the power valve is just flapping around.

First thing I would do is remove the right side power valve cover and run the engine, see what you can see.

Could also be a snapped piston ring but I doubt it as you say you have good compression. How many hours do you have on your piston kit?

It would be worth removing the exhaust and looking up the exhaust port with a torch, look at the piston/rings and also see if the power valve looks OK.

Fingers crossed it won't be anything too serious or expensive. :)

Best of luck and keep us updated. Dave.

60-80 hours on the piston.

I had a stick pull the wire out of the hour meter at some point and I'm not sure how long it took me to notice.

Go to the power valve, the linkage is suspect I had some similar issues and it was the power valve sticking closed. Just out of curiosity how many turns is your power valve at?

Power delivery seems consistent through the throttle range when the noise is present. Bike also has good power delivery before the noise appears. Noise doesn't seem to appear until the bike is ridden under load for a few minutes.

IIRC the PV screw is set at 1 3/4ish as it sits.

Yes, the more I think about it, it sounds like something power valve related.

If it was a snapped ring you'd hear a rattle at idle.

Good luck, Dave.

Can't help, but love the expression on your son's face at the end!! such a typical "... why are you bothering with this, it still runs, we could be riding...??" look

True... :D :D :D :D :D

LOL,

The video is doing the WHOOMP WHOOMP cyclic sound and vibration little justice. Especially when I was so frustrated I laid on the pipe for a solid 100yds just trying to see if I could make it let go.

That's my riding buddy's kid. He actually said something like "Holy crap, I thought that thing was going to explode coming down the logging road. What's wrong with it." My kid was gone by then but he was definitely the whatever, lets just ride guy.

Hopefully it's not too serious, won't cost too much time or money to fix and you'll be back on the trails again soon! :)

Keep us updated, all the best, Dave.