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Flywheel Bolts

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Flywheel Bolts

Postby sunlot2001 » Mon Dec 03, 2018 7:49 pm

I was reading a safety article in the latest LAA mag, where they recommend using Nord Lock washers beneath the six socket cap head bolts - and NO Loctite. My engine is serial No.3777 which has the 3/8" bolts but they are factory-bonded with a very strong Loctite (grade 620).

The factory procedure for removing these bolts recommends applying heat to soften the Loctite - either by a pencil gas torch or a heat gun. This worries me because I would need to be careful not to accidentally anneal the heads of the screws. I imagine it would be best to apply MODERATE heat for a long time to allow time for the heat to conduct down to the screw threads?

Also I would imagine that some very high torques are needed to break out the bolts and if someone holds the prop for me - is there a risk of twisting the crankshaft?

I'm just hoping there might someone out there who has already tackled this task on a similar engine configuration to mine? Any advice would be much appreciated.

Best regards,
Pete
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Re: Flywheel Bolts

Postby Steevo » Wed Dec 05, 2018 11:44 am

I did these on mine a few years ago and it was not as bad as the manual makes it sound.

First off, although 620 was used, it does deteriorate over time. I applied a little bit of heat to mine and they came out fairly easily. I did it on my own and did not have anyone holding the prop. There would have to be a huge force to do any damage to the crankshaft, you would struggle to do that with just a socket set.

Just direct the heat to the side of the screw where it meets the flywheel. It doesn't actually take that much. As long as the cap screws are not snapped already or at breaking point, you will be surprised how easy they come out.

I am sure there are a lot of horror stories out there of things not going to plan, but the ones I have seen done and done myself have never been too bad. Just work them one at a time. If you do take them all out at once, then make sure the prop is not turned in any way otherwise you will put the timing out. I did mine one at a time and then torqued them all up when all the old ones were out and the new ones in.
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Re: Flywheel Bolts

Postby PKnight » Wed Dec 05, 2018 5:46 pm

I must admit that I am nervous about the possibility of breaking these bolts on extraction. I wonder if a large soldering iron would give a more controlled heat to melt the Loctite while minimising the risk of shearing the bolts through over-heating. Anyone tried this approach?
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Re: Flywheel Bolts

Postby sunlot2001 » Wed Dec 05, 2018 7:09 pm

Thanks Steevo and Peter for your comments. I was only going to use one of those little pencil-flame torches that you can use for cooking (only about a tenner off of EBay) - plus I was going to use a temperature probe to make sure I don't soften the screw heads. I've read that a grade 12.9 bolt is ok up to 250 deg C.

Also, I appreciate that it's vital not to upset the timing if all the bolts are removed - but I'm tempted to remove the flywheel to make sure that the joint faces are thoroughly de-greased.

But it certainly doesn't sound like the nightmare job I had imagined!

Thanks again,
Pete
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Re: Flywheel Bolts

Postby diablo » Wed Dec 05, 2018 8:20 pm

Very unlikely you will get anything near 250C. Flywheel is aly and very good at dissipating heat. The chances are that 620 will have softened up and bolts will be easily removed. As steve says, take them all of but one. However, if you are careful there will be little chance of screwing up the timing. You can cut or file groves lengthwise on one of the old bolts and use it to clean up old 620 from crank threads or use a 7/16" tap.

I pioneered the use of nordlock X (Belleville nordlock washers) in the UK and flew with them for three years without problems (around 65 hours) obtaining manufacturers and LAA approval. I tested torque of bolts at 1,2,5,10,20,25 and 50 hours. They did not slacken off an iota! Following my testing, Jabiru implemented nordlocks on their builds.

If you need nordlocks, I have still have some. I suggest you also replace the 1/4" washers on exhaust port on heads nordlocks as the original flat washers to pretty much zilch and bolts securing manifold have a tendency to come loose!
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Re: Flywheel Bolts

Postby sunlot2001 » Wed Dec 05, 2018 10:54 pm

Hi Diablo,

I've got a 3/8" UNF tap to clean out the tapped holes (my flywheel bolts are 3/8" UNF - the engine is serial No.3777). I've purchased just the standard Nord Lock washers (I couldn't find a quick source for the Nord Lock X in the 3/8" size - but I can see the "X" version has an advantage in severe applications).

I guess I'd be OK with standard Nord Locks for now - the Jabiru Engine Manual doesn't seem to mention the "X" version?

Thanks for the tip re-Nord Locks on the exhaust manifold - it makes sense.

Best regards,
Pete
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Re: Flywheel Bolts

Postby Pops » Fri Dec 07, 2018 2:54 pm

Dino - or anyone else - can you advise of a supplier for small quantities of Nord-lock X 1/4" washers?

Also

The Jabiru manual refers to using either Brighton Best 1960 or Unbrako bolts for the flywheel - can anyone advise on alternatives that are the right quality or someone who can supply ?

1300 hours on my early SK now and not had a problem with the bolts - did have the engine TBO at 900 hours by Gary Cotteral just in case but he rebuilt it with 1/4" flywheel bolts as his view was that upsizing the bolts didn't help - seems that the La agree! However I do want to do the washer mod at next inspection

Thanks

Paul
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Re: Flywheel Bolts

Postby sunlot2001 » Sat Dec 08, 2018 8:30 am

I tackled the flywheel bolt job yesterday. Despite the Loctite 620, they came out without too much of a struggle - even without the application of heat. I used a quality hexagon bit adapter and a breaker bar - but the torque applied wasn't all that excessive - certainly there was no risk of snapping off the heads of the bolts.

One thing concerned me though - the thickness of the 3/8" Nord Lock washer is 2.5mm where the existing washer was very thin - maybe only 0.7mm. As a rule of thumb you need 1 x the bolt diameter of thread penetration. Unfortunately I didn't have a means of measuring this at the time (but it looked a bit marginal). So I'm considering going from 3/8"UNF x 1" to 3/8" x 1-1/8"UNF. These are available from Tools Today in the Brighton Best brand at £34.39. Obviously, I'll need to run a tap down the holes and then check that the bolt doesn't "bottom out".

The other point was regarding the Nord Lock washers. I bought my standard NL3/8" washers from Threadrive Components Ltd, but I'd quite like to upgrade to the superior "X" series version (NLX3/8") - I can't find them on their website. Has anyone found a source for these?

Best regards,
Pete
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Re: Flywheel Bolts

Postby Pops » Sat Dec 08, 2018 6:16 pm

Interesting that your bolts are 1". The engine manual for my early engine state that the 1/4" bolts used are 1 1/4" long. I'm intrigued now to find out what length mine are when I remove them. I'll be ordering various lengths just in case!!

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Re: Flywheel Bolts

Postby diablo » Sat Dec 08, 2018 8:04 pm

Paul is spot on, flywheel bolts are 1 and 1/4 " not 1". I have both 3/8" nordlock X and 1/4" nordlock in small quantities ... pricing info including domestic and international postage in classifieds section.
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