250-500cc loose motor mounts causing vibratio? or caused BY vibration?

Last race, my 300 started vibrating pretty bad, bad enough that I was wondering if it was going to blow up. By the end of the race it was very noticeable either under acceleration or under engine braking. At steady easy throttle it was fairly ok. I nursed it home carefully and figured i'd better take a look at the motor, thinking rod bearing or main bearings. As I started to tear it down I discovered that the upper motor mount was very loose. So my question, do loose motor mounts make vibration noticeably worse?

The bike has 160 hrs or so on it, so i'm still going to replace the piston and take a peek at the cylinder and wiggle the rod around and stuff. I pulled the magneto cover and there didn't seem to be any play in the flywheel tho.

Yes, they will make it feel like your bike is coming apart.

Yep they made my son's TC250 feel like it was comming apart. I replaced the nuts with the teflon lock nuts.

I had the same thing happen due to motor mount bolts and it sucked. A little loctite fixed it.

So i put it back together, and rode it hard over the weekend. seems to be good as new. I'm glad i didn't take the bottom end in to the fix it guy.

I have a wr 250 06 and it vibrates also but havent checked bolts yet, do they vibrate much when all bolts are tight. Coming off a ktm 520 to the WR just wondering whats normal

I don't think the vibration is bad on the 250, but I can't compare it to a 520 either. Never rode one.