Jabiru Engine 2200B flywheel failure

[deadstick]

Here are some images of a friends 2200 fitted in her 24 rego J170, she found this on her pre flight after pulling the prop through and it feeling strange. This engine has as far as Jabiru engines go been fairly good, with only major work a broken through bolt repair, new cam and 'Top end' 278 Hrs ago at 839 TTIS. Looks like the latest configuration of the dowels too...

 

 

 

 

 

[dazza 38]

Another quality product from Jabiru

 

 

[rankamateur]

One of the bolts looks OK, she will be able to use it again anyway!

 

 

[deadstick]

Looks like it flew for a while with a few broken! Given that all are rusted except one freshly sheared bolt. Some are bent to by the looks, wonder if that happened before or after.

 

 

[bexrbetter]

Another quality product from Jabiru

Shirley those bolts were fitted by someone else? I would find it hard to believe shank'less cap screws are standard Jab fare?

 

Oh dear, I shouldn't have looked ... where the hell is Jab's flywheel locating dowel pins????

 

http://contrails.free.fr/engine_jab_flywheel_en.php

 

Some more info ....

 

http://contrails.free.fr/engine_jab_bolts.php

 

Jabiru Flywheel Bolts Important Notice

 

broken bolts

 

Contributed by Anton Lawrence

 

Over the last couple of years there has been an increasing awareness of a problem with the flywheel retaining bolts in the Jabiru 2200 and 3300 engine.

 

The problem is simple enough to identify, the bolts are breaking and have caused in-flight engine failure. The cause has been much harder to identify and has been blamed on loose prop and prop extension bolts.

 

There can be no question that loose bolts in this area will transfer harmonic vibrations down the crank and precipitate movement of the flywheel parts.

 

Examination of the timing gear on engines with broken bolts has identified severe fretting of the gear against the end of the crank, this cyclic movement is the reason the bolts are breaking. The retaining bolts are 5/16th socket cap screws property class 12.9, although some of these are threaded full length, which wouldn’t normally be considered best practice, all the bolts are fracturing on the shear line.

 

12.9 bolts have an ultimate tensile strength of 1220 MPa and yield strength of 1100 MPa, it is normal to tighten these to within 90% of yield; this is to ensure proper clamp pressure of the parts.

 

This would cause the Jabiru bolts to elongate by about 5 thou and is the mechanism by which clamp pressure is maintained.

 

A company in Hamilton, Asseco has analysed this joint and come up with a torque figure of 41 Nm for these bolts with lubricated threads and washer face. I have used the formula from MIL-HDBK-60 and come up with a figure of 43 Nm using the same lubrication and 56 Nm with no lubrication.

 

The Jabiru manual states a figure of 24 Nm for these bolts with out lubrication, it is my belief that this where the problem partly lies. (Jabiru apparently now recommend 32 Nm but this is still almost ½ the maximum preload the bolts can take.)

 

timing gear

 

Contributed by Anton Lawrence

 

The CAA is working on an AD for these engines which will most likely require the bolts to be replaced every 100hrs. It is very important that as part of the replacement procedure the timing gear is removed and inspected, if there is any sign of fretting the part should be replaced and equally important is that the bolts are replaced irrespective of their appearance.

 

Jabiru are now fitting three 1/4 inch dowels into the end of the crank in an attempt to prevent this fretting, any new gear will have holes for these dowels pre drilled. The fitting of the dowels into the crank is a very precise job and should not be attempted by anyone other than a qualified fitter, engineer or toolmaker. Asseco is one company which has already completed ten of these dowel fitting operations, I don’t want this article to appear to be advert for one company or an other, so if you want their contact details you can contact me directly and I will pass them on to you.

 

flywheel bolt

 

© Jabiru

 

In conclusion, if you have an unmodified Jabiru engine of either type in any aircraft type you should immediately have the flywheel bolts and timing gear inspected, if all looks OK you should replace the bolts (reminder, 12.9 bolts should never be reused) and tighten them to between 41Nm to 43Nm using molybdenum grease as a lubricant in the threads and under the head, don’t get any grease on the bearing surfaces. If you use Loctite 620 in the threads and grease under the head you should tighten to 46Nm, Loctite 620 and no grease tighten to 53Nm.

 

If you are going to tighten these bolts to the above figures it is vital the bolt has a ½”diameter minimum hardened washer under the head, if not the bolt will embed into the alloy parts and preload will be lost.

 

Check the prop bolts and prop extension bolts for correct tightening and also check to ensure the extension is running true and the tracking is within 3mm, on some aircraft these have been found to be well off centre. If you have 10mm prop flange extension cap screws installed with Loctite 620, you can take them to 89Nm to reach 90% of yield.

 

I have also checked the torque for the Crankshaft Prop Flange Cap Screws as these have also been found slightly loose, Jabiru recommends 40Nm but these bolts are capable of taking 83Nm.

 

If all these bolts are tightened correctly and all the parts are running true it should be possible to eliminate the problem of broken bolts.

 

When tightening bolts you should tighten to halve the required amount following the tightening sequence, leave for an hour (no longer if using Loctite 620) to allow for local relaxation and then complete the tightening in one movement so as not to get stuck with static friction at a lower level, I have calculated the turn of the nut (5/16 cap screw) from snug tight to 43Nm be only 48deg so take care.

 

loctite 620

 

© Loctite

 

Some notes on Loctite :

 

Jabiru has apparently changed their recommendation of Loctite 262 to 620 for the above parts. 620 is not specified as a thread lock product but Loctite assure me it is good for the job as it has a longer time before cure and higher temperature capabilities, you can download all the data sheets from http://www.loctite.co.nz.

 

Unfortunately you won’t find the friction coefficients or nut factors on these sheets, I have had to dig deeper to get these directly from Loctite.

 

 

[jetjr]

Bex some of this information is very old.

 

Im led to believe someone was fitting aftermarket propellers and prop shaft adapters werent made correctly in NZ, were actually made out of round, caused a run of problems.

 

2200 have much more harmonic problems than 6 cyl.

 

Since dowels and larger bolts fitted problem dissappeared

 

Flywheel bolts are checked every service? BUT have to remove rear coil plate to get to them.

 

Loose or out of track prop can cause this, would feel vibration . Im surprisd how much vibration people think is OK and continue to fly with

 

Really glad it was picked up in preflight.

 

 

[Oscar]

Those flywheel bolts look very suss to me - why the corrosion on them and not on any of the other bolts on the flywheel? Were they possibly re-used and originally from a flywheel that did not have dowel pins, and thus quite possibly cracked before they were installed?

 

 

[deadstick]

Oscar, I seriously doubt jabiru would reuse old bolts. Surely their quarantine is a lot better than that. The info from the contrails site is an interesting read. I change flywheel bolts at every 500 and any chance I get really, equally important though is continual inspection of the prop bolts and balance up front. Any vibe at the prop flange is very large by the time is gets to the rear of the crank.

 

 

[Oscar]

One would certainly hope so! Did Jab. do the overhaul? It just seems strange that there is so much evident corrosion on those specific bolts; I'd assume that you get a fair bit of sea air at Nowra, but there surely has to be a reason why those bolts only have that evident problem. And you're absolutely correct re the prop bolts - was the prop installed with the beleville washer pack? Of course, the other known cause of flywheel bolt shear is detonation, and if the bolts were on that engine when it broke the through-bolt, they'd have likely been cactus..

 

 

[deadstick]

Oscar, if jabiru didn't change this bolts during overhaul then they certainly have violated their own manual. Install of that engine was as per the manual as all ways, inclusive of the propellor. The environment at Nowra is very corrosion friendly and that level of corrosion is not uncommon.

 

 

[deadstick]

Oscar, The stud broke because of incorrect nuts, they have admitted that and warranted that part of the overhaul.

 

 

[jetjr]

Interested in how this plays out keep us informed

 

I did some playing with Carbon props - before Jabiru released theirs - on a 3300, found a good one and fitted it. Ended up testing 3 different ones.

 

I and a number of others was amazed at the smooth running compared to wooden type.

 

Subsequently had access to dynamic balancer and ran this test - showed up as having "severe" imbalance initially, able to reduce to satisfactory level. Cant tell a huge difference but its sure noticable.

 

Point being was there was significant vibration levels even with a smooth feeling prop. Hate to think how bad the wood type would have been.

 

I believe harmonics and vibration levels are inherantly higher on 2200 and proper balancing would be worth the effort.

 

 

[deadstick]

Here's what I achieved on my 2200, to do it I had to balance with two weights separated either side of the low spot.

 

 

 

[jetjr]

good result

 

Are you using washers on hub?

 

I had ongoing problems with tracking on wooden props, used to seem to depend on weather, humidity I guess

 

I am in dry inland but could end up with up to 8mm out of track in fairly short time. That rattles things nicely.

 

Used backing spacers, cardboard, ended up getting new prop under warranty - good service from Jabiru, ran for a couple hundred hours and was doing similar thing again, ended up going to 2 Blade CF and never looked back.

 

 

[deadstick]

I have had no end of trouble with the wooden jab props, same issue as you and delamination, went to the sense inch on the 230 and what a massive difference. The 160 has the jab wood laminate prop, a few minor issues but still tracking ok, spent a lot of time getting the track and spinner true first of all, but have noticed over the years that they like half the weight required spread either side of the light point, giving two nodes. I'm intending on putting the transducer near the flywheel soon to see what the difference is front to back.

 

 

[Oscar]

Oscar, if jabiru didn't change this bolts during overhaul then they certainly have violated their own manual. Install of that engine was as per the manual as all ways, inclusive of the propellor. The environment at Nowra is very corrosion friendly and that level of corrosion is not uncommon.

Absolutely agree, new bolts are the requirement in the repair manual. There has to be a reason, but perhaps it is just buried somewhere.

 

 

[deadstick]

Don't understand what you mean by the "perhaps it's just buried somewhere" do you mean in the design?

 

 

[Oscar]

No, not really - with the dowels, the larger bolts and the steel starfish arrangement, I am under the impression that flywheel bolt failure is now a rare occurrence - sufficiently so that one should be looking for a specific cause of this specific failure. The 'buried' reference is to the fact that a number of things could cause such a failure, including a bad batch of bolts, installer error, prop imbalance, an occurrence of detonation etc. - even someone hitting the starter while the prop is turning. If you have a close look at the photo showing the ring gear, there is a badly chewed-up set of teeth just to the left of the 6 o'clock position, with the tooth just to the left of the trigger plate looking badly bent and the one two further around appearing to have the top snapped off.

 

 

[deadstick]

Just looked at the original pic, lot clearer. No chewed up teeth or tips missing. There are lots of hypothetical causes but given the statistics of failure previously probability dictates the cause is the same. It will happen again and again and again until the engineering is robust enough to cancel out the cause when it presents. Interestingly the engineer said the dowels were still ok and straight, so I would think torsion ( detonation, power pulse, prop stile etc) wasn't the cause. Some sort of harmonic and bolt stretch due hammering would be my stab, and it's just that... A guess, it's certainly above my pay grade!!!

 

 

[Oscar]

Well, I guess replacing six bolts every few hundred hours is cheaper than having to buy new Rotax crankcases. However, it shouldn't be happening, though I think it's a bit of a stretch to extrapolate from the earlier design problems to assume the latest iteration has the same failure rate. That said, we are going to the new CAMit alternator which assists in smoothing the crankshaft harmonics and I do not expect to have any problems with the flywheel bolts.

 

 

[deadstick]

Lol, I didn't expect to have any of the failures I've had. Good luck with your project mate .

 

 

[Oscar]

Which is a completely reasonable position! (and I appreciate the hopeful note - a great many hours have already gone into our project, in airframe mods, repairs and general refurbishment as well as the engine rebuild and work still in progress on oil and airflow cooling improvements - the EO itself runs to 14 pages and it isn't complete yet - and that's without the test reports etc!).

 

The whole thing is, there's never been a sufficiently detailed compilation of the actual causes of failures to really get a full handle on why what happens, happens. Nobody would argue that Jab. engines aren't finicky, nor that there haven't been design problems - if that were not so, then what CAMit are doing would make no sense. However, the very lack of application of forensic-style examination of causes (and I am entirely comfortable with saying that Jabiru themselves have not assisted as well as they could in establishing the real causes, preferring to scuttle behind 'operation' too readily) has meant that many people have lumped the 'failures' into convenient large boxes, all tending to be labelled 'fundamental design flaws'.

 

Frankly, neither 'side' of that situation has been of very much use in furthering the useful development of the engines - and I think that any reasonable person would see that as a bloody shame for the owners and operators just as much as for the factory. Jab. engines have some very desirable features - light weight, simplicity and economy being the leading ones - and some far less than desirable ones. They are, without a shadow of doubt, the 'weak link' in an otherwise rather admirable aircraft in terms of initial purchase and operating cost, reliability, primary and secondary safety and mostly just a damn good combination of attributes.

 

I don't believe that CAMit would persevere with the Jab. engine as the basis for its improvements if it did not understand the problems and believe in the solutions it has developed. I think there are going to be some rather happy campers coming away from Natfly who have talked to Ian Bent and seen the work that has been done.

 

 

[deadstick]

Seriously thinking of attending Natfly, 2.1 nil wind from my place, but that's got a bit of tiger country in it, so I may well fly an arc, paddock hopping all the way. Is your project an ex engine, hard landing by chance? ( pm )

 

 

[Oscar]

Certainly is! EFATO, overturn, fin smashed, one wing attachment ripped out, damage to both wings (replaced). Compounded by obvious extra damage through ham-fisted retrieval. Through-bolt failure...

 

However - and I say this in all sincerity - this was another aircraft that shows a history of engine problems that suggests a major amount of 'unsympathetic' operation (training fleet most of its 3700-hour life - and when we dismantled the engine, there was evidence that it should NOT have been rebuilt.) Altogether too much evidence of it having been poorly maintained - engine and airframe alike. Some minor repairs that were signed-off by an L2 that are a bloody disgrace. It says heaps for the basic durability of the airframe that it continued to do its duty.

 

 

[deadstick]

Hell! were you on board? was it Mittagong? memory is foggy... Hmmm yes, there are L2's and there are L2's, its like any industry.