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If your 3300 has done 500 hours or more, it's time to change the flywheel bolts! I almost learnt the hard way (bolts snapped whilst at idle on ground) if they snap in the air, it's very messy. The torque test of the glued in bolts is rather useless. The bolts tend to break above the lock tight or the head. Getting them out for the new Nordlock washer setup is an interesting procedure. Leave it to the experts. Exhaust valves and flywheel bolts, the two items in a jab motor that can ruin you day real fast.

 

 

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Why is that, jetjr? Are the non-jabiru props less well balanced, or heavier, or what?

 

I do know of a case where the pilot was trying out a 3 bladed Bolly and it shed a blade, but this is a different story.

 

 

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Yes very different story

 

Ask Rod...... re non jab props and bolts, just another push to keep owners locked into Jabiru parts

 

Its like every 50 hrs or 12 mth I think

 

 

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Yep youre right Nev, 4 cyl had problems with carbon fibre props. Just now theres admission about harmonics being a problem.

 

How can you be liable for something That been modified and how does more frequent bolt replacement solve the problem?

 

 

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More frequent replacement does not solve the problem. What it does is make the defect less likely. Non Jab props are not necessarily worse than the real thing, but Jabiru cannot be responsible for them, so replace at short intervals should reduce the risks.

 

 

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What defect is that and what is the cause?

 

Yet to see anything that indicates prop is related to flywheel bolt problem

 

Some evidence its related to starter torque

 

 

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Jabiru now supply a two bladed composite prop for the four cylinder engine. They no longer supply a wooden prop as standard. When they rebuilt my engine after my mishap they supplied a composite 'scimitar' prop. Don't know if that is a make or style?

 

 

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Its a blade design, built by Bolly from fibreglass

 

You can buy same thing with different/better hub from bolly but its non approved......so needs new flywheel bolts every year

 

 

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The flywheel is supposed to be held from moving by clamping action rather than drive by the bolts in shear. Once loctite has been used how do you retension them? If they move they will shear bolts and/or wear the threads oval. in the crank end. Nev

 

 

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I've wondered if it would be better to put the loctite on the face of the flywheel and NOT the bolts. This should glue the flywheel and stop it moving at all.

 

And you would be able to retension the bolts easily. You could check the effectiveness of the loctite glue job by removing the bolts and seeing if the flywheel was still fixed there.

 

I may do this to mine unless somebody comes up with a good reason why not.

 

 

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I've wondered if it would be better to put the loctite on the face of the flywheel and NOT the bolts. This should glue the flywheel and stop it moving at all.And you would be able to retension the bolts easily. You could check the effectiveness of the loctite glue job by removing the bolts and seeing if the flywheel was still fixed there.

I may do this to mine unless somebody comes up with a good reason why not.

The principle is based on clamping force. If the clamping force is enough, the flywheel can't budge; I'd suggest that's well above loctite's shear point.

Once the clamp tensions ius lost and there's the slightest movement, it becomes cumulative.

 

I'd be having a bolt and thread test done.

 

 

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Do some numbers on torque load from starter, zero to 750 rpm in less than a second.

 

Bolt and other problems issues largely on L2 serviced aircraft in flight training.

 

Camit engines have a different setup again of flywheel attachment and lighter flywheel

 

 

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Yep, Ian has one setup like that, but its experimental and no doubt had some issues of its own

 

Current setup looks much improved and provides big increase in clamp force i believe.

 

They also take load off the flywheel by lightening and belt drive alt and removing generator components off flywheel

 

 

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Dear all, my experience of the 3300 engine flywheel bolts is disappointing. My engine sheared the bolts (luckily on start up) despite the 100 hour torque checks as detailed in the engine manual, however I was always of the opinion this was a waste of time as simply checking how tight the loctite is holding the thread is futile and a torque setting of 24ft/lb was far too low for this type/size/application of bolt (my own calculations concluded these bolts will take over 60ft/lb (dry thread) before over-stress / distortion). This all happened before the revised engine manual (June 2016) recommended “do not use loctite, use Nordlock washers and torque to 39ft/lb”, this can only be perceived as an “admission of guilt” by Jabiru as they knew fine well they had a problem and needed a quick fix.

 

Luckily I had a spare low hour (380 hours with new valves / seats) 3300 engine in storage and decided to fit this engine rather than having the hassle of removing 6 snapped bolts buried in the end of a crankshaft – this is a job for another day. Needless to say prior to installation I replaced the flywheel bolts in the spare engine as the latest engine manual and bulletin. Where things get interesting was the tightness of the existing bolts in the spare engine, I used a torque wrench (old fashioned dial indicator not a modern click-stick) to remove the old bolts and was concerned to discover all the bolts came out easily with a torque pressure of anything between 5ft/lb and 20ft/lb, one can only conclude that none of the bolts were providing adequate compression tension between the flywheel and crankshaft so things could have started to move, the bolts shear-stress and snap. Many people also overlook the fact that the starting torque and forces these bolts sustain during start up is similar to whacking the flywheel with a hammer every time the starter motor engages.

 

My advice for anyone with the early 6 x 5/16” bolts is:-

 

1 – If you haven’t replaced them (regardless of engine hours) replace them now using latest method.

 

2 – Make sure you don’t have starting problems if you do “sort it”, every clunk of the starter strains the bolts.

 

3 – Check the bolts every 50 hours run maximum and any movement, doubts or concerns replace all of them with new including new Nordlocks, and check the flywheel and crank at the same time for any unusual marks or signs of movement.

 

4 – Replace the bolts every 250 hours and inspect the old ones with UV/dye for any traces of stress, wear or unusual marks. Anything untoward investigate for crank or flywheel problems, and ware or elongation of the flywheel and crankshaft holes and threads..

 

Stick rigidly to the above and you shouldn’t encounter a failure, high maintenance it may be but better than looking for a field in a “glider” at 3000ft.

 

My opinion of the theories concerning propellor types, harmonics, etc carry little weight, if the prop is balanced and the engine isnt "shaking out of the airframe" it's highly unlikely it will cause the flywheel to "vibrate off" and snap 6 bolts. I use Sensenich and always have - they certainly know more about propellers than most.

 

I have personally lost all confidence in the Jabiru engine and in the process of ordering a Camit engine as, it certainly appears, Camit have addressed all of the flywheel, head, piston, rocker gear, valve and lubrication problems Jabiru engines all appear to encounter around the 400 + hour run time.

 

 

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As often (correctly) stated the flywheel is held by clamping force. Once it starts to move it will degrade the clamping and the bolts are subject to sheer and as things get worse , bending loads, and wear of the threads. The starter MUST be a factor, the way it engages, but don't write off other twisting going on causing torsional vibration you cannot feel. You have, in effect a flywheel both ends of the crank in those engines. There will be undamped harmonics. Never a good idea. Nev

 

 

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Hi Nev, yes every crankshaft, whether it be a 2 cylinder horizontally opposed or a straight 12 cylinder engine, will be subject to an element of torque reaction or "crankshaft wind-up" as it was called in the old days, however when the engine is designed this is, or should be, compensated for. Regardless of application (aero, auto, generator, marine, etc) all engines will have an element of load on both ends of the crankshaft and there will never be equilibrium due to "drive end" heavy load and "auxiliary end" light load, therefore unwanted harmonics (especially from a propeller) and opposed forces trying to shake or pull things apart will always be apparent - it is the designers job to engineer and compensate for this.

 

Camit appear to have addressed this via a rubber drive belt and larger alternator in effect increasing the load and drag on the "auxiliary end" of the crankshaft and providing a damping effect due to frictional losses with in the drive belt and pulleys, however they (and Jabiru) still offer the internal wound coil alternator so they must be pretty confident they have "engineered out" this problem by increasing the bolt size from originally 1/4" to 5/16" to 3/8", adding two additional dowel pins, a starfish to increase the grip surface area, increased the torque (gripping force) of the bolts and different lock washers.

 

If they had done all of this in the first place I have no doubt we, and others, would not be having this conversation. This is certainly not intended as a criticism of Jabiru because had they "over-engineered" everything from the start with huge bolts, brackets, fixings, castings, thicker materials etc, the conversations people having now would be "don't bother with a Jabiru engine they weigh half a ton!" - sometimes a manufacturer just cant win or do right for doing wrong, however they will always be judged by the their customers / potential customers on how they "react and rectify" when a problem is encountered.

 

 

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A few points re CAE offering

 

40 amp altenator places very little load at startup, yet belt drive can dampen harmonics when running. Not so for old setup and the new 15 amp version which have load always

 

Different pistons and barrels and inhibitor reduces cold friction. Evident by hand prop check before start, much easier.

 

Camit use different flywheel attachment altogether, a threaded lock plate as I understand it. Flywheel is much lighter too.

 

The reported starter cause is likely as we use high powered starter, the engine needs high speed to start. Forces are huge.

 

Jabiru have had many attempts at fixing the problem, bigger bolts, dowels, loctite, starfish, now nordlocks. Still he cause hasn't been identified.

 

 

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  • 3 years later...

Put your starter drive behind the prop. Crude but effective. CAMIT did this (near the end) Starter engagement is like an impact driver. Pull (manual or solenoid) and then rotate (energise) ones are better.

You can't feel torsional HARMONICS It's NOT like a torque wind up. ALL engines have periods where it's happening. Even turbine engine drive quills destroy themselves at the wrong output settings for longish periods with "chatter" in the quill. In those situations you avoid near zero torque settings. In pistons there are "don't use" RPM settings which would change with a different prop.. Nev

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