broken motor mount bolt

[Slyfox]

I will preface this with I am not an engineer, nor do I play one on TV... however, if you replace the broken bolt with one that is harder than that specified, there are several considerations. First, harder bolts are usually more brittle and will fracture. Another consideration is with a harder bolt so it won't fail, will the case then fail. I would rather check and replace bolts that have a case crack.

Just thinking... Ralph

I took into consideration a bulletin for the skyranger so I felt I was ok by going from 10.9 to 12.9. I really think this bolt got loose because the one below was loose. so check this one often is my advice.

[herman pahls]

I also fly a 912ULS in a model 4 Kitfox.
I did not build it.
Does anyone have a photo to show the location of the broken bolt.
Thanks

[Slyfox]

I did find what broke that bolt. I had a vibration at 3000 rpm. I've been trying to chase it down. I cleaned the spark plugs, checked the floats, checked and cleaned out the mid range jets. while I was running it after all the carb work, which also included checking to make sure the clips were on the 3rd from the top. I noticed the spinner bouncing around big time at 3000 rpm. today I tore into it and got the spinner nice and centered to the prop. wow, nice and smooth now. hardly any vibration at the 3000.