ORIGINAL: Truckracer
I wouldn't tolerate that kind of flex and don't especially care for any of the molded mounts. Hanger 9 makes a decent universal aluminum mount at a fairly good price. These have worked well for me in the past and are the same as supplied in many of their ARFs.
Yes, a flexible mount can be very hard on your muffler and airframe.
Guys, it's not like the engine is jumping around while running at all. Mine isn't moving around at all actually. I can though, grab the prop and move the engine visibly, as seen by looking at the spinner - cowl gap.
Regarding solid mounting, Dubro supplies a mount I see a few guys using - that uses rubber bushings? How is it that those mounts work, when you're suggesting a nylon mount that allows some movement will not? Not following that logic, but I could darn sure be missing something! Don't forget, we're using beam mounted engines here!