Engine mounting bolt sheared

Jeff Vaughan · #1 05-13-2023, 02:36 PM

This is why we do inspections. While doing my condition inspection I found the M10x110 engine mounting bolt was loose when I went to check the torque. Well it wasn’t just loose it had seared off on the case. Not sure how this can happen but it is going to be a Bitch getting the 1-1/4” rest of the bolt out of the case. Total Time 320 hrs
https://vansairforce.net/community/a...1&d=1684010036

Jcurry · #2 05-13-2023, 02:56 PM

Thanks for the heads up Jeff!

KeithO · #3 05-13-2023, 04:34 PM

With such a long length maybe there is a resonance problem ? Might try putting some silicone around the mid point of the unthreaded shank, that may damp vibrations and prevent it breaking. Tracy Crook had this issue with the long bolts used to hold the rotary engine layers together.

PaulvS · #4 05-13-2023, 04:48 PM

Good thing you caught it.

Does the case need to be split to get it out?

scsmith · #5 05-13-2023, 06:11 PM

To get bolts like that, I use a gradual, escalating approach.

Start out grinding a screw driver slot in the end with a Dremel wheel. Make the slot big enough and deep enough to get a screw driver that is the full width (10mm)?

Usually it will just screw right out with a screw driver because there is no longer any pre-load tension in the bolt. Try putting a Crescent wrench on the flat blade of the screw driver to get more torque.

If that won't work, next try drilling a medium-sized hole in the end for an Easy-out. It is probably a fairly hard bolt (Socket-head cap screws are usually the equivalent of SAE grade 8 or better), but it will drill ok in the middle, low RPM, high pressure.

If an easy out won't get it, the final step is to drill out the bolt in successively larger steps until you are almost at the thread tap size. From there, sometimes you can grab the end of the thread and pull it out with needle-nose pliers, letting it unwind like a coil spring.

Finally, chase the thread out with a tap. It is really important to get the tap started into the original thread though.

"Every 20-minute job is one broken bolt away from becoming a 2-day ordeal."

bobg56 · #6 05-14-2023, 06:50 AM

Looks like another SB or SD coming soon.

Jeff Vaughan · #7 05-14-2023, 09:30 AM

Thanks Steve for your removal hints. The broken part of the screw is approximately 80 mm in the hole. Ugh
Looks to me that this bolt goes all the way through one side of the case then into threads in the other half. This is in direct line with the hole for the other side engine mount screw which is only 30 mm in length. Just a thought that Rotax saved a manufacturing step by only threading one side of the case needed in the long 110 mm screw on the one side to go all the way into the other half.
Maybe not the best decision on their part if that’s what they did.

Mel · #8 05-14-2023, 10:07 AM

Quote:

Originally Posted by Jeff Vaughan

Thanks Steve for your removal hints. The broken part of the screw is approximately 80 mm in the hole. Ugh
Looks to me that this bolt goes all the way through one side of the case then into threads in the other half. This is in direct line with the hole for the other side engine mount screw which is only 30 mm in length. Just a thought that Rotax saved a manufacturing step by only threading one side of the case needed in the long 110 mm screw on the one side to go all the way into the other half.
Maybe not the best decision on their part if that’s what they did.

If that hole goes all the way through, is there a chance that you could remove the opposing bolt and drill the broken bolt from the other end? That end of the bolt will be smooth and easier to keep the drill centered. Maybe use a transfer punch to start. And the right hand turning drill would help unscrew the broken bolt.

subpar_bucker · #9 05-14-2023, 01:23 PM

Did you do the nose wheel upgrade? I was thinking you could maybe get a collar made like the ones used to match drill the new nose gear. The idea being you have a 1" or 2" metal rod that's the same diameter of the existing hole, with another, smaller (e.g. #40 or #30) hole down the center of the rod. This would ensure that when you try drilling into the remaining portion of the broken bolt, the hole is centered and squared.

It really sucks that you ran into this issue!

cactusman · #10 05-14-2023, 01:36 PM

Just out of curiosity how often do you re-torque those bolts? I remember the initial issue of them coming loose, I put a little loctite in when I installed them. So far so good.

The old dual carb 912 vibration machine strikes again. Need to figure how to turn it into a brass cleaner.