broken motor mount bolt

[Slyfox]

I thought I would share an experience I just had. while doing my yearly inspection, I found a broken bolt for the motor mount. I sunk. at first I thought it fell out. I looked closer and it was broke clean off. the location was the left upper rear. I removed things to get the mount off. intake, water hose to cylinder. looking at it, it wasn't going to be fun. it was broke off about an 1/8 inch inside flush, not only that the cylinder was in the way for a straight on attack. I took a carbon burr and did the best at putting a nice debit and a nice spot to center punch, which I took a long flat punch and put a point on it. center real close now.

now to understand this the original bolt is a 10mx1.5x50. 10.9 grade. so it is hard steel. I than got some drill bits that were 8 inches long. now I can get a straight shot with no bend. didn't have to remove the cylinder. I used a 3/16 bit and got about 1/8 cut. than I took my extractor and tapped it in and than took a 1/2 wrench and carefully started turning, tight at first and than it came out. feeeeew I was done getting that out.

next step installation. I read a bulletin I found online for a skyranger. lots of good information, seems they are having a bunch of problems with this very bolt breaking. had in there to install a new 12.9 tensile strength bolt and torque to 27ft lb. also they mentioned grinding down the fins on the cylinder so there would be a better straight on with installing the bolt, so I did that.

to install this side on my 4 it also took two washers to make things center for a good install with the rubber mount against the block. so I put to washers there. nice line up and install. I checked all other bolts for 27ft lb and found the lower bottom on the same side loose. so now that's tight.

I guess what is needed is for everybody to check these mount bolts and torque them good. I now have a stronger bolt on that location. I have the 912uls. I do fly hard, I have a medium IVO prop and hang on the prop for landing short field. plus hit it hard on take off. I'm sure that doesn't help for this type of thing.