Preventing and repairing broken engine lugs on slabby SevenElevens

There have been several reports of broken lower-rear engine mounts on SevenElevens with GSX-R750F/G/H frames.
The pictures on the right show a bike with such a broken frame lug.


I suspect this being caused by either two reasons...

a.) over-tightening of the lower-rear engine mount which stresses the lug
b.) the early GSX-R750 frames use a 10mm bolt whereas the later bikes all use a 12mm bolt, so there's a 2mm slack.

This page shows how to repair/weld the broken lug and how to fill up the slack in the engine mount.

You should make sure that the engine+bushing fit exactly between the two lugs (=without any play) and not over-tighten the bolt so that it compesses the soft aluminum bushing and stresses/bends the lug (use Loctite!).



To ensure proper strength of the repaired lug, full material thickness needs to be restored and sharp edges prevented.
Leave the engine side of the lug untouched to be able to position the broken-off lug correctly.
To fill up the slack in the engine mount I used a piece of 12x1mm copper pipe which is easy to obtain at any hardware store.

The pipe needs to be as long as the engine mounts (on the picture it's sticking out).
Here it's placed correctly and the engine won't be able to move under high loads anymore.
The picture on the right shows the idea of an adjustable spacer by "PoPs"...

"The mod I did to solve this problem was to produce an adjustable spacer out of a big bolt (M20?) and nut to replace the aluminum spacer. In that way, when engine, new spacer and bolt are in place, I can adjust the threaded spacer to take out all the clearence. Only then did I tighten the engine bolt. It made for improved handling too as in this way the engine can be really squezed insted of all bolt force just bending the lug.
It's very much the same idea that is used in the post 89' frames (if memory serves me) where you have an adjuster to take of the slack between the frame and the swingarm bearings so that when you are tightening down the long swingarm spindle bolt you are not bending the frame itself to close the gap.
This idea is being used now on the engine mounting bolts of many new bikes. Seen it on on the new SV1000 for instance. Basically it was just a big bolt (M17?) a nut and a washer to spread the load. The finer the thread the better as you'll get finer adjustment. If you want to get fancy you could machine a washer with a step as shown. It also made for very easy engine mounting as you could leave the adjuster closed when feeding the engine in and open it after everything is in place. "