Four years on … and I noticed the starter was a little sluggish after a month of idleness … this could simply be the battery needs charging but, give they are basically motorcycle batteries and 4 years stuck outside cranking a 2,200cc engine every so often .. it’s not worth the hassle .. which I sort of live with when a bike battery starts to go dickie …

The replacement battery comes in a 5.3kg

I replaced the front one in about 30 mins … you have to be a bit athletic as it involves head first into the front cockpit for about 15 mins .. undoing and separating cables ..,then undoing the clamped securing belt …

Just bought the new rear one today and … will either cut away the Oratex at a joint overlap .. as per last time … or.. as Lars from Oratex ..if I can put a larger access panel ..bigger than the standard O rings … or a zip … of just a removable panel

So … the saga continues … having got them out as simple as … well simple … !

The new bolts just dont seem right …. I should qualify that ….

A couple don’t appear to want to ‘grab’ …. further investigation …and the new bolts are only 1” long 5/16” thread … the old ones are 1 1/4” long … on checking it looks like Jabiru recommend the longer ones .. especially as a double washer Nordloc on the new bolt effectively reduces the usable length even more

Further research on the torque setting this evening … the below from an Australian posting

Jabiru Flywheel Bolts Important Notice.
Anton Lawrence RAANZ Tech Officer
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, Assesco has analysed this joint and come up with a torque figure of 41Nm 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 43Nm using the same lubrication and 56Nm with no lubrication. The Jabiru manual states a figure of 24Nm for these bolts with out lubrication, it is my belief that this where the problem partly lies. ( Jabiru apparently now recommend 32Nm but this is still almost 1⁄2 the maximum preload the bolts can take.)
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 1/4inch 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. Assesco 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.
In conclusion, if you have an unmodified Jabiru engine of ether 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 1⁄2”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.
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.

Check for signs of fretting … fretting being where any chance of movement between faces causes the facs to rub against each other … wear indication would be a sign of slackness in the fitting

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Just ordered the last bits for the 100 hour service and prep for the ferry flight back to the U.K. …

I’m currently stuck at home due to enforced quarantine after a 4 day trip to the U.K. so .. to save me from going mad in 1 room … I’m getting the planning ready … the new Flywheel boats just need torquing up to 39nm Tehran everything can go back in for a ground run and test ….

Mags have been cleaned whilst out and new plugs will be going in

Carburettor has been drained and inspected for any debris in the bottom .. absolutely spotless as I have a micro Andair inline filter

The route I plan won’t be my normal head 360 then 020 to overfly Goodwood … any degree of headwind against such a draggy aircraft would put me on fuel limits before the South coast was reached … so plan is far more interesting

Once we get French landing clearance the route will be Jersey, Caen, Deauville, Abbeville, Le Touquet, Headcorn or Lydd, Southend ..maybe … then onwards to wherever we buy the house

I would like to overnight in Abbeville if lockdown allows … so cool to park your ‘plane next to a low hedge .. hop over to your room and restaurant….

So .. the moment of truth .. after a couple of tentative attempts at removing the flywheel bolts which were stuck super super fast and hard I felt we were facing the inevitable sheared bolt and then engine out and weeks offline

Mike F .. my long standing engineering guru was practicing removing loctite secured bolts in his workshop and a mate of his popped by and said .. you don’t want to do that … you should use the tool ive just got !

Enter Darryl Morris owner of Morris marine and motors at la Collette St Helier .. with his awesome induction heater

We unwound the entire wire extension lead .. or it melts in a could gooey mess if you leave it wound up ! .. the show head was very precise and could easily be placed on a single flywheel bolt head.

The machine is set to 140′ C and touched onto the head and the button pressed …

20 seconds later we removed the probe and eased the 1/4″ socket Allen and lo and behold we had movement… gently and slowly we eased the first one out to check state of thread and washer

All looked fine … now realise the new bolts are shorter by around 6mm or so … we put the first NEW bolt in place with its new nordloc washer … it stiffened at about 75% in so we withdrew to check..

Looks like it would be wise to tap out the hole once each old bolt is removed..

All bolts slackened in about 10 mins !

Awesome machine .. thanks so much Mike AND Darryl !

An old bolt out … about 6mm longer than the new ones … also you can see the old Loctite on the end threads

it’s going to take a while to get the shaft holes cleaned properly … the hole in the back end of the crankshaft is about twice the depth of the bolt .. but getting the new ones in really tighten early because of the residue on the thread … going to tap gently just to clear half turns at a time of the thread

Cut off a few cable ties to free some of the cables that were tied securely to the spider …

Labelled some of the cables for later re join

Slackened the 4 bolts securing the spider to the backplate … capturing the small 8mm nuts at the front end and their washers so they can be returned to the same position

Some of the supporting plinths stayed in position so easing the spider out ‘square’ was tricky … taking care not to pressure the alternator stators

The port mag decided to stay on its plinth so removed it in situ and can separate away from the engine bay. Having released the alternator pair of charging cables slipped through the centre hole and the spider could be lifted away. Boy, the magnets are strong and take some pull to get the unit out.

Wih the stator out .. you can now, finally see the 6 x 5/16 bolts that secure the flywheel in position

Now the job of locating a good quality Allen socket head to get good purchase on these … after considering whether to try the pencil flame idea of pre heating

Pre planning the 100 hour engine check …

Its done just under 95 hours … at very varied power use .. which the manufacturers recommend .. ie don’t drone around at the same RPM hour after hour as the pistons glaze the bores …

(Update .. just cross checked my log book and engine run hours with my Hobbs entry and Hobbs is 99.25 … so time to stop and do this…. New bolts arrived 26th Jan 2021)

This has been a great workhorse .. hauling lots of small, medium and Large ! People around .. and also purring around at 5,000’ on very low RPM .. then nice fast turns with smoke and eager passengers who like to see the world on its edge ..keeling around on a wingtip ..

I’ve religiously changed the oil every 25 hours …after the first 25 .. you can go to 50 hours between changes but it’s so cheap AND a really easy way to make sure nothing is going awry over time …

Anyway … it’s 99 hours now .. so time to plan a usual oil and plug change but also … there is a service bulletin that states you should check and change the 5 bolts that hold the flywheel in place.
The great session I had at Skycraft last year showed how closely clustered these bolts are … they bolt directly into the rear face of the drive shaft.

They need initial checking to see if any have worked loose before they are all replaced with improved design and improved Nordloc washers.

In the early days, Jabiru had problems with these earlier bolts sometimes failing. A bolt failing on a flywheel as you might imagine pretty quickly adds strain to those remaining and your flywheel starts to think about other trajectories !

Not sure who it was … but years of clever research was published recently … and the LAA published in their regular magazine … Bizarrely.. it turns out that the recommended cruise RPM of around 2,700 RPM sets up harmonics in the assembly that is detrimental to these bolts !

THIS replacement is purely precautionary … but wise …

update 23 Jan 2021

Had a look at the back end of the engine today .. to see what the back of the ‘spider’ looked like .. turns out I can’t see the bolts .. but see a splined end .. so guess it’s a spider off and then release the splines mount ..

I asked Dave Almey from Skycraft what the spine end was for … apparently it’s so that you can add a drive shaft to drive a vacuum .. if you use vacuum instruments … learn all the time) .. thanks v much for quick response Dave

This excerpt from the LAA magazine mentions the detail around removing previous bolts … that were secured with Loctite … and recommends pre heating to break that Loctite … vs … with Nordloc washers NOT to use Loctite PLUS differing torque settings

Will be interesting to see how you can “apply heat to the thread and not the head of the bolt” when zero thread is actually visible … it ALL being in the body of the drive shaft 😊

At last … after searching and sub referencing different Jabiru docs I have located the different torque settings associated with Nordloc washer on the cap screws … bolts .. for the flywheel …. 39nm

Great flying conditions.. cold .. but clear .. and some moody clouds thrown in …

Problem at the threshold just before take off … finally full and free movement check and spotted a loose inspection disc over my head … quick call to tower .. shut down at the hold .. unstrap .. lift out of seat .. slide panel back into position and restart .. 60 seconds … ready to go …