Broken Motor Mounts
- Thread starter smerch69
- Start date
So what....did the bolt break or did mount break at bolt hole? Or did the actual mount bracket break, if the first happened then I would suspect a loose bolt causing stress on motor mount, if the latter, then I would figure a combination of vibration and metal fatigue to be the culprit. Of course there's always the "shit happens" explanation.
they broke off of the frame
how does the one holding the head look? and how does the hole in the head mount look? Usually when you get breaks it is due to uneven pressure or loose mounts letting the frame flex on hits and landings. those can, believe it or not wear out head and base gaskets from movement. One of the reasons some of us like the oringed heads better. your vintage of rig is one that I have yet to see break a motormount like you are describing. By all means when you get it welded make sure it is a two sided weld, and if at all possible complete the outside weld with the engine in place and the bolt torqued to spec. The frames are made of pretty mild steel contrary to popular belief and don't require any tricks to speak of, but you want them to go together with as little stress as possible to prevent that from happening again.
what I have done when the mounts end up misaligned and broke again after a "fix" is to use a washer that fits the bolt well and weld it over the old hole. that sometimes means overboring the hole in the mount. That way you can make the repair fully compatible with lining up with the other holes. dont miss checking out the bushings where the swingarm pivot goes through the engine. seldom is that a problem, but it can be. yours is a really well designed frame, unlike some yellow and green ones were of the past.
Still no photos I'd like to see what it looks like
They DO look like they ran awhile loose! Those look easy to gusset the back when welding it up so that it is stronger. it won't show and look ugly either. Just put the engine back in, bolt it up and torque it before you weld the outside of the crack. you will probably want to leave the washer off. the heat from the final weld will make the stress less fit possible. when i do that one I do it about 1/4 of an inch and skip about that much, let it cool do it again etc. that way the whole thing isn't so apt to try to change shape on cooling if it never gets too hot.
I think I would measure the motor and use all thread across the frame with nuts to lock it into place, then weld. Everyone has a way to do it, but yah, I have never seen any of mine in that bad of shape.
Good luck.
Good luck.
Those were pretty far past anything I have seen from that frame, too. Bikes are so much better and have been in the last 20 years that we see so many of them being used and used often for much longer now. We used to get a new bike or fresh frame and slide the axle as far to the front as we could and measure from the front axle to the back, or to the swingarm pivot or both. then from the swing arm pivot to the shock mount(s). 6 months and 15 to 20 races you could do it again and think you were measuring a different brand nearly. About 1990 for red and blue you quit seeing that so much.