Bruce Tuncks Posted November 13, 2014 Share Posted November 13, 2014 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. 1 Link to comment Share on other sites More sharing options...
Downunder Posted November 13, 2014 Share Posted November 13, 2014 Excuse my ignorance, but are jabiru requesting loctited bolts to be re-torqued? That doesn't make sense to me. 2 Link to comment Share on other sites More sharing options...
Bruce Tuncks Posted November 13, 2014 Author Share Posted November 13, 2014 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. 1 Link to comment Share on other sites More sharing options...
Doug Evans Posted November 13, 2014 Share Posted November 13, 2014 Why not just replace all the bolts with new ones and that way u know they are fine ? Link to comment Share on other sites More sharing options...
facthunter Posted November 13, 2014 Share Posted November 13, 2014 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 Link to comment Share on other sites More sharing options...
Bruce Tuncks Posted November 13, 2014 Author Share Posted November 13, 2014 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. Link to comment Share on other sites More sharing options...
Doug Evans Posted November 13, 2014 Share Posted November 13, 2014 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 Link to comment Share on other sites More sharing options...
fly_tornado Posted November 14, 2014 Share Posted November 14, 2014 Wouldn't this backyard butchery qualify as Jabiru's dreaded poor maintenance? Link to comment Share on other sites More sharing options...
dlegg Posted November 14, 2014 Share Posted November 14, 2014 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. 3 1 Link to comment Share on other sites More sharing options...
fly_tornado Posted November 14, 2014 Share Posted November 14, 2014 loctite is cheap Link to comment Share on other sites More sharing options...
RKW Posted November 14, 2014 Share Posted November 14, 2014 So is torque! 3 4 1 Link to comment Share on other sites More sharing options...
old man emu Posted November 14, 2014 Share Posted November 14, 2014 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 Link to comment Share on other sites More sharing options...
Chird65 Posted November 14, 2014 Share Posted November 14, 2014 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? Link to comment Share on other sites More sharing options...
old man emu Posted November 14, 2014 Share Posted November 14, 2014 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 Link to comment Share on other sites More sharing options...
Bruce Tuncks Posted November 14, 2014 Author Share Posted November 14, 2014 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. 1 Link to comment Share on other sites More sharing options...
Bruce Tuncks Posted November 14, 2014 Author Share Posted November 14, 2014 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? Link to comment Share on other sites More sharing options...
AVOCET Posted November 14, 2014 Share Posted November 14, 2014 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? Link to comment Share on other sites More sharing options...
Oscar Posted November 14, 2014 Share Posted November 14, 2014 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. Link to comment Share on other sites More sharing options...
AVOCET Posted November 14, 2014 Share Posted November 14, 2014 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 1 Link to comment Share on other sites More sharing options...
Bruce Tuncks Posted November 14, 2014 Author Share Posted November 14, 2014 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. Link to comment Share on other sites More sharing options...
AVOCET Posted November 14, 2014 Share Posted November 14, 2014 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 Link to comment Share on other sites More sharing options...
Guest Andys@coffs Posted November 14, 2014 Share Posted November 14, 2014 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 Link to comment Share on other sites More sharing options...
Bruce Tuncks Posted November 14, 2014 Author Share Posted November 14, 2014 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. Link to comment Share on other sites More sharing options...
Downunder Posted November 14, 2014 Share Posted November 14, 2014 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. 1 Link to comment Share on other sites More sharing options...
AVOCET Posted November 14, 2014 Share Posted November 14, 2014 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 . 1 Link to comment Share on other sites More sharing options...
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