What About No Loctite?

[Bruce Tuncks]

Thanks Mike thats a deal. I'll order the new screws.

 

And I think you have explained why the loctite on the flywheel should not be omitted: How about this...

 

(1) The flywheel bolts must have clearance or you couldn't put them in.

 

(2) Friction of the clamped faces is not enough to prevent slippage of the flywheel under the inertial forces of crankshaft pulsations.

 

(3) The loctite is there to FILL THE GAPS so the flywheel doesn't have a hammering action under these inertial forces given the clearance the bolts have in their holes.

 

Is that what you were getting at?

 

 

[AVOCET]

Yes thats about it , and also ide be reluctant to go against jabs recommendations ( regarding loctite )

 

Ive got the 620 , but no primer .

 

Give is a call when your ready .

 

Mike

 

 

[jetjr]

I thought loctite was used simply to avoid lockwire. There are places on Jab like prop flange bolts where lockwire is simply too hard.

 

Certainly requires care to be used correctly.

 

Also cant check tension with wire in place either.

 

Some of the other makers wouldnt have had loctite available when they were designed, also carry bigger bolts, heavier components and more torque. Ease of maintenance is as important as weight. Not so in aircraft.

 

If the flywheel bolts are broken youll know it pretty quick with a torque wrench. Replacing them is a PITA

 

 

[Downunder]

I wouldn't say loctite is like safety wire. Loctite plays an active roll in the retention of the bolts (like a spring washer or nyloc nut) where as safety wire is there just in case and really should never have a load on it.

 

 

[old man emu]

I can't remember what the thread on these flywheel bolts looks like.

 

If it is a coarse thread, then the metal the bolts are going into is "soft", like aluminium, cast iron or alloy. When the were initially fitted and torqued up, there would have been damage to the threads into which the screw was going. That is the way screws/bolts work. They get tight by distorting the material they are screwing into. This also happens to the bolts as they tighten. If you take the bolts out, you are left with a minutely "stripped" thread, so that the next time a bolt is screwed in, it is going into an over-sized thread. That's why it would be a good idea to at least replace the bolts each time they come out.

 

This all begs the further question: Why are the flywheels being taken off? The only reason I can see for removing a flywheel is to replace a toothless ring gear.

 

Old Man Emu

 

 

[Sloper]

Goodaye all

 

The correct Loctite has its uses, we use a bit reassembling truck components, used components that is.

 

As threads are touqed the threads distought and the bolt stretches, loctite allows the reuse of the bolt.

 

Would l use it for aircraft flywheel bolts?, l would go with the manufactures suggestion when using new bolts that l would fit.

 

Bolts are cheap insurence.

 

This also begs the question where are the dowls that would take some of the load and ensure the flywheel is put back in the correct position for balence?

 

If no dowls l would make sure the flywheel goes back in the same position.

 

regards Bruce

 

 

[Keenaviator]

I can't remember what the thread on these flywheel bolts looks like.If it is a coarse thread, then the metal the bolts are going into is "soft", like aluminium, cast iron or alloy. When the were initially fitted and torqued up, there would have been damage to the threads into which the screw was going. That is the way screws/bolts work. They get tight by distorting the material they are screwing into. This also happens to the bolts as they tighten. If you take the bolts out, you are left with a minutely "stripped" thread, so that the next time a bolt is screwed in, it is going into an over-sized thread. That's why it would be a good idea to at least replace the bolts each time they come out.

 

This all begs the further question: Why are the flywheels being taken off? The only reason I can see for removing a flywheel is to replace a toothless ring gear.

 

Old Man Emu

It's a fine thread OME. I recently installed a new (larger) prop flange for my new Jab Scimitar prop.

I followed old directions using primer and 620 on a cool day. Did the tension in three steps, very quickly and all seems to be good. If I were to do it again, I would be using the new procedure in that the screws are torqued straight up to 30'lb in one go.

 

Laurie

 

 

[Keenaviator]

Yes thats about it , and also ide be reluctant to go against jabs recommendations ( regarding loctite )Ive got the 620 , but no primer .

Give is a call when your ready .

 

Mike

Mike, have you done the 'dowel' mod on the flywheel attachment? I believe there is a drilling jig. Also if I were to do this I would fit the steel 'spider'. I have 620 and primer, a couple of weeks rec leave and a desire to visit some folks in SA.

Laurie

 

 

[AVOCET]

Mike, have you done the 'dowel' mod on the flywheel attachment? I believe there is a drilling jig. Also if I were to do this I would fit the steel 'spider'. I have 620 and primer, a couple of weeks rec leave and a desire to visit some folks in SA.Laurie

I havnt done the dowel mod on the jab , have done similar work though , i have the gear to make the jig up to suit , jab have the procedure to follow ,straight forward enough .

Again with this type of work you have to be able and confident .

 

Be happy to help

 

Mile .

 

 

[AVOCET]

I can't remember what the thread on these flywheel bolts looks like.If it is a coarse thread, then the metal the bolts are going into is "soft", like aluminium, cast iron or alloy. When the were initially fitted and torqued up, there would have been damage to the threads into which the screw was going. That is the way screws/bolts work. They get tight by distorting the material they are screwing into. This also happens to the bolts as they tighten. If you take the bolts out, you are left with a minutely "stripped" thread, so that the next time a bolt is screwed in, it is going into an over-sized thread. That's why it would be a good idea to at least replace the bolts each time they come out.

 

This all begs the further question: Why are the flywheels being taken off? The only reason I can see for removing a flywheel is to replace a toothless ring gear.

 

Old Man Emu

I think its recomended to check the torque every 200 hrs on older engines ( without looking it up )

 

During a visual check during a survive , i noticed at the back of the fly wheel a streak of oil radiating from the hub ,

 

It turned out to be one sheared bolt !

 

All the rest were ok , but just goes to show , if this sign was ignored , or worse , missed , would probably resulted in a flywheel failure ,

 

For the record , this early 2200 had been used in FTF and had a 44 in pitch prop . ( recomended 42 in pitch )

 

From memory engine hrs on rebuilt engine 480 hrs

 

Airframe 6750 hrs

 

LSA55 s/n 015 ( an early one )

 

Mike

 

 

[old man emu]

OME, that reference of yours agrees with the part in the Sky Ranch book where the story is told of how Continental or Lycoming tried every "safety" method on big end nuts, eventually using nothing.

The Mechanics Toolbox and the Sky Ranch are written/produced by the same person. Essential reference material for anyone doing aircraft maintenance, and very interesting for people keen on mechanical engineer.

 

It's a fine thread OME. Laurie

Now, that might be the key to the problem. What is the material that the bolt is going into? Also, have you ever seen fine threaded bolts used in association with high torque?

 

OME

 

 

[jetjr]

Pretty sure new manuals say Flywheel bolts to be REPLACED at 100hrs

 

I hate these cross the board changes, as it may mean making problems worse.

 

 

[skeptic36]

I can't remember what the thread on these flywheel bolts looks like.

It's over here :http://www.recreationalflying.com/threads/jabiru-flywheel-bolts.9116/

 

 

[old man emu]

Hmmmm.

 

Metric bolts. Bloody hard to get certification for Metric bolts compared to AN, MS and NAS imperial bolts. Sorry, I just don't trust the hardware used by Jabiru. They might sometimes get it from China via Bunnings.

 

I recommend that you click on skeptic36's link. This picture is from it:

 

 

These are Property Class 12.9, which is the highest class of metric bolt.

 

OME

 

 

[old man emu]

Here is a quote from the above post:

 

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 (New Zealand), 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.)

 

Here is a picture of some of the snapped bolts:

 

 

12.9 Class bolts are the top end of classification of Metric bolts. In other words, they are the duck's guts. However I have found that is is virtually impossible to obtain certification documentation for Metric hardware, whereas AN, MS and NAS hardware can be tracked right back to the furnace that smelted the ore.

 

There is also the argument to be had whether bolts should be lubricated or dry when fitted. I'd support dry fit in this situation as it is said to produce more distortion of the threads in the hole and the bolt. It is this distortion that makes the clamping pressure to hold the parts together. At least Jabiru recommends a situation that leads to higher applied torque. (24 Nm = 17.7 foot-pounds; 32 Nm = 23.6; 41 Nm = 30.42; 43 Nm = 31.7, and 56 Nm = 41.3)

 

Old Man Emu

 

 

[jetjr]

Pretty sure its listed somewhere they are from Unbrako

 

 

[old man emu]

This, from the Unbrake site, fills me with confidence ... not!

 

COATINGS:

 

1. We have largest capacity of cold forming for bolts in India. We can cold forge up to 36mm dia bolt.
    
   
   • We can do close tolerance in hot forming.
      
     

 

 

 

 

 

 

 

• We have in house CNC machines.
   
   
  

 

 

 

 

• We have in house Spherodize annealing plant for wire rod.
   
   
  

 

 

 

 

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[*]Xylan

 

• He have in house electro galvanizing of zinc & copper cadmium.
   
   
  

 

 

 

 

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• He have in house Kunz Decrotizing coating.
   
   
  

 

 

 

 

• He have in house PTFE coatiing
   
   
  

 

 

 

 

Spec for 12.9 class metric bolt:

 

12.9 M1.6-M100 alloy steel, quenched and tempered

 

OME

 

 

[AVOCET]

test, please ignore

 

 

[Downunder]

Obviously not aviation grade, but in the industrial world, unbrako are considered a reputable brand.

 

Rotax engines are metric. I'm wondering what they use?

 

 

[jetjr]

They are considered highly

 

They do have E code tracability??? something to do with markings on head

 

Theres a engineering guide pdf on the site

 

http://unbrako.com/docs/engguide.pdf

 

 

[facthunter]

Always considered benchmark in my day. Nev