Thought and Observations- Vibrations.
If you experience vibrations, here are a few things you can do.
Make sure when you mount your engine (particularly in a cruiser type frame) that the REAR motor mount is square to the seatpost tube. I have noticed that if you compromise and mount the engine so it "looks about right" a lot of times the mounts actually sit on the tubing (from and rear) at a slight angle. This causes a sharp edge of the mounting surface to butt up against the tubing, causing wear and "fretting".
Use something like PC-7 to "bed in" the mount area, to fill the gap where the front mount is on the front tube. Mix it up (or any "putty type" epoxy) and put it on the mount, wrap the tube in plastic wrap, and install the engine. Don't tighten it very much, just enough to get some of the epoxy to sqeeze out. Let it set up and then remove the engine, plastic wrap, and then remount it.
I use this technique and go one step further by placing a sheet of lead between the PC-7 and the tubing, and again between the "U" shaped "clamp" and the tubing- front and rear....MMMMMmmm smooooth.
Some folks use a rubber material in the space I'm talking about, but it only works for awhile, then is cut through by the mis matched parts, or worse, if it's too soft a compound, it worsens vibrations.
For bar vibration, if you have a gun shop near you, get some lead shot (doesn't really matter what size) and fill you bars with it, works great, cost a little though. If you want to go nuts and have access, fill all the tubes of your bike with lead shot.
Make sure your chain is not too tight, it make the bike vibrate if it is, and so does an untrue sprocket.
I personally have found that using thick weatherstripping on the underside of the fenders (if you use 'em) and the inside of the chaingard also helps to stop vibrations and noise very effectively. Clean your surfaces with rubbing or denatured alcohol before you stick on the weatherstrip.
Finally, balance your wheels, you would be surprised at how much "vibration" comes from untrue and un balanced wheels.
Thanks for listening,