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Flywheel bolts

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Re: Flywheel bolts

Postby Anonymous » Tue Feb 10, 2015 10:13 pm

Posted by: DL on 16:01:54 12/09/14 Tue

I would prefer the shanks on my flywheel bolts. I would also avoid using a splodge of loctite 620 on ends thread and confine the 620 to the very end of the thread (where it meets the shank) and it would be a tiny drop.

I dont have to go through my reasoning as it is pretty obvious.

On the manual it states that you should use belleville washers. I dont think that would be of any use at all as you would squash them flat at the torques we are talking about. More useful would be thick, hardened steel washers to spread the load.
Anonymous
 

Re: Flywheel bolts

Postby Anonymous » Tue Feb 10, 2015 10:13 pm

Posted by: roger on 08:30:33 12/15/14 Mon

Belleville washers are spring washers and only become effective when they are 'squashed' flat. That is the way it is.

The pre load provided by spring washers prevents the bolt from rotating loose but can serve another purpose in that it can make up for any small settling down of the flywheel after assembly.

To back up the belleville washer 262 was used as a thread locker in earlier engines. Providing the propeller was properly balanced and torqued, flywheel bolts lasted the course. If 620 is used instead, then it should also be used as a thread locker and especially so if plain washers are used.
Anonymous
 

Re: Flywheel bolts

Postby Anonymous » Tue Feb 10, 2015 10:13 pm

Posted by: DL on 13:46:12 12/15/14 Mon

I understand how the belleville washer works. However, IMHO, the ones used on the Jab flywheel are not fit for purpose. They are flimsy and do not seem to match the torque that the hex bolt is being tightened to.

I agree, the bolt needs to flatten the washer, but it has to flatten it to its optimum shape for proper clamping.

all bolts make a tight connection by tightening to the point where its threads just start to deform. Bolts of various hardness, diameter, and material configurations require varying amounts of torque to reach that tightness.
This is the same with Belleville washers.

Therefore, the bolt and Belleville washer must work together, which means that the torque of the Belleville washers should match that of the bolts.

If the torque of the locking washer is exceeded by more than a few percent during assembly, the ability to lock, is destroyed. Undertorqueing, will result in the washer not living up to its function.

After all, all we need to look is at how they are used on Jabiru props. The aim is not to squash it to smitherins but to keep it under tension and give it room to expand or contract as the propellers expends and contracts due to changes in humidity.
Anonymous
 

Re: Flywheel bolts

Postby Anonymous » Tue Feb 10, 2015 10:13 pm

Posted by: roger on 10:11:59 12/16/14 Tue

The belleville washer specs change from one generation of egine to another and some may appear 'flimsy' to you. But if they regain their shape then they are serving a purpose by providing a pre-load to the bolt.

The information that you have quoted from the internet is all good stuff but not relevant as loctite is used as a primary means of preventing the bolts from unwinding. For loctite to work it has to be applied to the threads.

If you do away with the belleville washers and loctite then the engine becomes a good candidate for loosing its flywheel.
Anonymous
 

Re: Flywheel bolts

Postby Anonymous » Tue Feb 10, 2015 10:13 pm

Posted by: DL on 14:09:36 12/16/14 Tue

Roger, my biro spring, regains its shape after torqueing to 8lbs/foot, it does not mean it is suitable for holding a propeller in place.

I research my info as you probably do and the internet is a great source of info as are books and experience. I would be a fool to totally rely on any one source.

The skill is in filtering what is applicable and what is not.

It seems to me that a lot of what I hear has no scientific basis, just opinions, nothing more and nothing less ...
Anonymous
 

Re: Flywheel bolts

Postby Anonymous » Tue Feb 10, 2015 10:13 pm

Posted by: Gary on 19:40:22 12/16/14 Tue

This is the problem with jabs, nothing is set in stone and nothing seems to be the right thing to do, its all hit and miss with the general public being the ultimate design and test engineer, these engines remind me of the early italian mopeds of the 70's, they go great when running but don't last and fall apart due to crap engineering, then needing extensive bodging to put them semi right, i feel that jabiru is just bodging a boat anchor all the time and unfortunately for me and you we have a boat anchor..
I am currently reluctant to change the bolts as no doubt another bodge fix will be around the corner and I believe the LAA is now involved, and a mandate is due, this may have a suitable bodge that has to be carried out before next flight scenario. Think I will wait and see what will happen, will save doing it twice I suppose. I am also not convinced on the supply stock of bolts from jab, would like to see the certification for them before buying to ensure they are correct, not a difficult task. This should be available if the supplier is ISO rated with a good QA management system
Anonymous
 

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