Broken cylinder head bolt 912is sport

Thought I might report an issue I just experienced. I decided to take off all the cowls for a thorough inspection prior to a planned extended inland camping trip in a few weeks time. The first thing I noticed was a nut missing off the top fwd stud on NO 1 cylinder. Interesting. Rang my friendly Rotax man who suggested I look on the opposite side of the engine and sure enough, there was a 'hole' where the head of the bolt/stud should be! This one goes right through the block and out to the other side with a locating nut/ferrel that is designed to spread the load over the whole length of the bolt/stud. Apparently the stud had snapped, on end vibrated out and went to earth (a God's Must Be Crazy moment!) and the nut on the other end following. One length of stud remained as it was restrained by the nut/ferrel arrangement.

I was assured that no damage will be done unless I decided to put on new nut on the remaining thread and tighten it. Glad I phoned for advice.

Anyway, the good news is that Rotax came to the party and covered 8 hours travel, labour and parts to fix it all as it is 'a known issue', even though my engine has approx. 400hrs on it after 2.5 years. I was also informed that Rotax have developed a new gearbox for the 912is Sport that is know to develop issues (I have already had to have a repair done at 150hrs). Apparently any problems post July will result in owners getting a new gearbox rather than a repair. On both counts I take my hat off to Rotax for nice service.

cheers

ross

Happy to hear no major damage. Good catch Ross. Very good catch.

Thanks for the heads-up mate. I'll be sure to keep a good eye on mine when I eventually get it......although by then gearboxes will be a thing of history as I'll be using the Rotax photon engine :)

Yeah, i was luck to catch it here and not in the middle of OZ in a few weeks! Interesting to hear from the Rotax guru that it could probably keep going for long time without damage - only damage would occur if someone saw the nut missing and put a new one on and tightened it without realising the stud goes right through to the other side. We haven't got any of the Rotax maintenance courses for the 912is sport here in OZ as yet but I think it would be a really good investment of time to attend one with an expert to understand the intricacies of these engines - I have not problem with the general maintenance but this sort of knowledge is a step above my pay scale!
cheers

r

Really good idea on your part to do that check before a long trip. Can’t imagine the grief if you had engine issues in the middle of the Simpson desert or other similar places. Congrats on some good planning. Also, I’m currently in the UK, returning for most of June then in the USA early July .... flying with S&R in the backcountry. So if you’re passing through on your way to the centre in June, give me a call and if I’m up north building, be really great to see you and Gayle again and brag about my progress !!

Ross,

I'm still trying to understand how the bolt/stud and locating nut works and how adding a new nut would affect it... Can you explain this a little more?

Thanks!

George

I think it would best explained by a Rotax tech George - I am not much good beyond changing the oil - but he stressed on the phone 'Don't put a nut on it and fly!, it will cause damage!" and he did show and explain it when fixing it but in one ear and out the other. I do remember him explaining that the rather long stud/bolt is designed to spread the load evenly over the hole length - however that doesn't answer your Q

cheers

ross

Ross,

No worries! Just curious.

George