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Rotax 914 head bolt failure


SDQDI
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Just thought I would share this story as I have a few minutes to type it out.

 

On the 10th of may we had a fly day at YQDI it was a beautiful day with mild temps and a high cloud base which pretty well kept the thermals away, I did the 3nm trip from home to YQDI at around 9am. Was great meeting new people and was a friendly relaxed atmosphere.

 

After lunch once things were finishing up I took a pilot neighbour for a local flight basically to have a look around and to see where his son was picking some cotton. Once we were heading home cruising at about 73 or 74 knots with everything nice and smooth I heard a slight noise which sounded like a rivet popping, passenger also heard it but thought it might have just been a patch of rough air, I immediately slowed to 60 knots as a precaution worried at the time that it could have been a wing stay bolt (it's amazing how much stuff goes through your head) all my temps were cool as usual and the engine was still purring like a kitten. We returned without further noises or incidents for a slightly bumpy landing (my specialty) at YQDI.

 

A thorough check of the airframe revealed nothing, no missing rivets, no loose bolts, no excessive movement everything looked good. It wasn't until I checked the engine that I found the problem. Firstly the nut was missing off the top front of cylinder number 1, the reason for this was the bolt at the other end of that stud had broken and the noise was that bolt head hitting my cowling with enough force to make a little impression in it.

 

So after contacting Ole and filling out all the required incident report forms (I spoke to Darren and he said they are well on the way at RAA to getting the incident and accident form set up as an online form similar I guess to the atsb one) rotax was very helpful sending all the bits to Ole and then he flew out on Friday morning and did the necessary repairs. Went for a fly Friday afternoon with no problems so am a happy boy again.

 

I will try and attach some photos, the helpful people at bert flood said it wasn't the first one that had done it so thought I would post this up here so people know what to look for.

 

Engine had 60.7 hours on the clock

 

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Guest Maj Millard

First one I've ever seen fail on any 912, over torqued perhaps at some stage ?....................Maj....

 

 

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There is always the chance of a fault in an item such as this. The QA process reduces it but doesn't guarantee 100% unless you test each one. In a critical part I would like to do this if the nature of the structure allowed it. Rotax probably have a few suppliers... Nev

 

 

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Yep could be plenty of reasons for it like I said it wasn't the first one that had done it so no doubt they are investigating as to the cause whether it was a bad batch of bolts or like maj said over torqued, they haven't told me I'm a rough operator yet lol

 

I'm pretty sure that the other problem bolt/s was also a 914, and from what I could gather it was the exact same bolt that had failed.

 

All in all it wasn't a very dramatic experience the engine still ran perfectly and the service from Ole and Rotax was well above what I expected I have no complaints at all:thumb up:

 

 

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Them there bolts are actually quite sophisticated - brittleness is the enemy of high-strength alloys, and various process stages - the original alloying, forging, forming, plating, and any straightening - can predispose a bolt to failure, or simply increase its sensitivity to over-torquing. I wonder how much the bolt size increased from the 80-hp 912 to the 914?

 

 

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Guest Maj Millard
Them there bolts are actually quite sophisticated - brittleness is the enemy of high-strength alloys, and various process stages - the original alloying, forging, forming, plating, and any straightening - can predispose a bolt to failure, or simply increase its sensitivity to over-torquing. I wonder how much the bolt size increased from the 80-hp 912 to the 914?

Probabily not at all...the 914 is the 80 HP (low compression) with a turbo attached...same case as the 80 HP......the 115 HP is achieved with 35 HP produced at the top end............Maj.....

 

 

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Probabily not at all...the 914 is the 80 HP (low compression) with a turbo attached...same case as the 80 HP......the 115 HP is achieved with 35 HP produced at the top end............Maj.....

err, from the TCDSs the old 81 hp was 1211cc, the 99hp was 1352cc... same stroke... thought the 914 was a blown 1352cc?

 

 

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