What About No Loctite?

[Bruce Tuncks]

Yesterday when doing a service, I thought about how the spark plugs and head-bolts and tappet-nuts don't come loose even though they have oil or anti-sieze, the opposite of loctite.

 

Then there is the check of the flywheel screws.. But these are loctited so unless they are broken you won't be able to see if they have lost some tension.

 

Has anybody been brave enough to not use loctite? I understand how the factory wanted to "weld" things like the flywheel on so it was there for good, but this may have been too hopeful, as the flywheel saga shows.

 

Would the flywheel or head bolts come loose ?

 

When you consider split pins on nuts which are tightened down, it is obvious that they don't stop the nut from coming loose, they only stop it winding right off. That first small turn which the split pin allows will cause loss of tension in the bolt. So loctite is better than split-pins, but still not needed if the nut doesn't come loose to begin with.

 

Please don't think this is a Jabiru knocking post. My engine has gone just great for 13 years now and I would buy another tomorrow.

 

 

[Downunder]

Excuse my ignorance, but are jabiru requesting loctited bolts to be re-torqued? That doesn't make sense to me.

 

 

[Bruce Tuncks]

They are asking you to check that the bolt has not broken, by putting a torque onto it. You could have a broken bolt stuck there and seeming ok with your fingers.

 

I wonder how long before the first bolt failing and then the rest going. There would have to be quite a long time on average for this check to be effective before the flywheel departed.

 

I reckon the security of the propellor is the most important thing for these bolts, and these days I use a nail-varnish trace between the prop and driver flange to see if there is any movement there.

 

 

[Doug Evans]

Why not just replace all the bolts with new ones and that way u know they are fine ?

 

 

[facthunter]

I wouldn't do that in situ unless one at a time carefully. I have a bit of difficulty with things like Loctite. You can't run a spanner (and tension wrench) over an engine. Just removing the bolt later can be difficult. (You might say that is what the Loctite is for). IF the bolt (s) are coming loose something is wrong. Retightening them may help if done at the right time. Nev

 

 

[Bruce Tuncks]

Doug, if they have been put in with the recommended loctite you can't "just" replace them. It's a big job, and there is a danger that you might break one trying to get it out.

 

 

[Doug Evans]

Bruce

 

I understand that, but whats I would do is if there is any doubt of that component may fail because of a broken bolt would be to replace , if u re tighten the bolts u would be breaking the lock tight bond anyway so for my peace of mine it would be a safer path to redo and replace . Just my two cents worth , hope it helps

 

Doug

 

 

[fly_tornado]

Wouldn't this backyard butchery qualify as Jabiru's dreaded poor maintenance?

 

 

[dlegg]

Jabiru is the only engine manufacturer that uses loctite so lavishly that I know of. Cat, Cummins and other mainstream diesel engine engineers would have a fit if they knew the extent of loctite glued in bolts on crankshafts to flywheels etc. If these bolts break they are extremely hard to remove and replace.

 

Cat gear for example only use flat washers under the heads and say that if a bolt is tensioned correctly nothing else is required. Loctite should not be applied IMHO and a regular torque check should be maintained to check for irregularities.

 

 

[fly_tornado]

loctite is cheap

 

 

[RKW]

So is torque!

 

 

[old man emu]

Jabiru is the only engine manufacturer that uses loctite so lavishly that I know of. Cat, Cummins and other mainstream diesel engine engineers would have a fit if they knew the extent of loctite glued in bolts on crankshafts to flywheels etc. .

As I have said here: http://www.recreationalflying.com/threads/casa-draft-proposal-for-jabiru-aircraft.126874/page-3 , Jabiru has shown that it does not have clue about the correct procedures for assembling an engine. One could add to your list of engine manufacturers, Lycoming, Continental, Poll Royce (Merlin) General Motors (Allison), Ford etc, etc. Rotax probably wouldn't do it either.

 

OME

 

 

[Chird65]

Doug, if they have been put in with the recommended loctite you can't "just" replace them. It's a big job, and there is a danger that you might break one trying to get it out.

What type of Loctite are they using. Are the proper tools being used to undo the Loctite'd bolts?

 

 

[old man emu]

I wonder if anyone at Jabiru has read something like this

 

http://www.mechanicsupport.com/torque_loss.html

 

and http://mechanicsupport.blogspot.com.au/2012/02/tightening-rubber-gaskets.html

 

You need to look at this, too.

 

http://en.wikipedia.org/wiki/Poisson's_ratio#Poisson.27s_ratio_values_for_different_materials

 

OME

 

 

[Bruce Tuncks]

Chird, it is loctite 620 which is very strong and high temperature stuff. You need heat to soften it but you can't apply this heat direct to the socket-bolt heads in case you soften the bolt.

 

 

[Bruce Tuncks]

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.

 

I don't think Jabiru use loctite on the big end nuts, does anybody know?

 

 

[AVOCET]

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.I don't think Jabiru use loctite on the big end nuts, does anybody know?

[Oscar]

To remove Loctite'd flange bolts, the recommended technique is softening the Loctite with a heat gun to remove them and cleaning out the thread with a (bottoming) tap followed by a blast of air. Re-attach the flange with NEW bolts, torqued up in one hit.

 

The flange/shaft mating surface MUST be cleaned scrupulously before the flange is replaced: any paint etc. removed and use Loctite 7471 primer to clean the bolt holes, the bolts, the flange and the shaft before assembly.

 

 

[AVOCET]

I would add , that when applying the 620 Loc. that its used sparingly , and that TO MUCH in this case , will probably squeeze out onto the flange face ,

 

That face has to have No residue between the mating surfaces after tourqing .

 

Just imagine one bolt squeezed loctite it the join and not the other ,

 

After tourqing i do a run out test with a dial indicator .

 

A heat gun will not soften a cap screw ,

 

Engine rebuilt at jab have loctite 620 on big end caps .

 

Mike

 

 

[Bruce Tuncks]

If I were to remove the old cap screws, clean the threads with a bottomingt tap, and replace them with NO loctite then I will be the first to do so huh?

 

One problem I can see though is just what torque to use and whether to use anti-sieze.

 

I wouldn't be brave enough to do this on a client's engine, but I am considering it for mine.

 

 

[AVOCET]

If I were to remove the old cap screws, clean the threads with a bottomingt tap, and replace them with NO loctite then I will be the first to do so huh?One problem I can see though is just what torque to use and whether to use anti-sieze.

I wouldn't be brave enough to do this on a client's engine, but I am considering it for mine.

Ho Bruce , once the screws are out and cleaned up , i would screw them in by hand and feel how much " slop" between the screw and thread .

 

There will be some slop , if you feel that it's excessive , i would get a second opinion .

 

The loctite will take up that small amount of slop .

 

I would not recomend assembly of jab flywheel to crank without it .

 

These procedures are the way i do it and have removed& replaced at least 8

 

units over the years and have had no issues .

 

This procedure is most critical and needs to be perfect , otherwise , trouble .

 

Mike

 

 

[Guest Andys@coffs]

Bruce

 

What problem are you trying to solve???? If yours haven't broken, and you do as you say and they continue to not break and stay then is that good or bad or merely a continuation of status quo?

 

It seems to me that in your case the only possible outcome of significance,you can have, is that it wasn't as good, or am I missing something? Hard to end up with statistically relevant outcome on a sample size of 1

 

Andy

 

 

[Bruce Tuncks]

Thanks Mike and Andy, sensible advice.

 

There actually isn't a problem, I guess I have been influenced by all the stories about failures that you read on this site.

 

 

[Downunder]

If the bolts are not too expensive, it may be wise to replace with new ones everytime they are removed?

 

Anti seize will INCREASE the actual torque above your setting because of the reduced thread and bolt head friction.

 

 

[AVOCET]

Thanks Mike and Andy, sensible advice.There actually isn't a problem, I guess I have been influenced by all the stories about failures that you read on this site.

If you like Bruce , i can come down and pullit off for you and check it out ,

You'll have to order some new screws

 

Any exuse to come down

 

and have some aviation fellowship , and of course , your wine cellar !!

 

Mike .