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The other day the gyro had a shake/ shudder develop. Sort of like a stuffed rotor head bearing but I knew it wasnt that as the day before I had had the rotors off & had checked the head bearing !! Next day during the pre flight I grabbed the back of the engine to see if there was any movement in the mounting rubbers , nother there but I could actually move the whole engine up & down about 1/2 inch or less
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Thats a bit scarey.... what is the engine mount/stand made of? I ask because if it is hollow tube steel or something that could be collapsing where the bolt passes thru? Might need a crush tube if that were the case?
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Carefull you don"t over tighten them.They only need to be snug.Use a heavy spring washer under the bolt and check every thousand hours or so.Without the washer it"s only 2 hard surfaces samwitched, with high HZ vibes, so even only a poofteenth movement will start it off.Don"t locktite, no nylocks or lock nuts, and a safety wire will only stop it go,n through the prop, not stop it from Moven.
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The bolt passes through angle , looks like steel chrome moly but its not hollow. Its not the bolt through the rubber bushes !I havent taken the bolts out yet to check them but I have 2 new ones to replace them in case the old ones have a mark on them etc etc, best to replace anyways !Thanks for the advice Birdy, I probably have overtightened them......didnt see any washers but I will put a spring washer under it anyway.
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Loktite would probably do the job, they are pretty tricky with sum of that stuff, but a heavy spring washer will take up the slack if there was any movement, and it won"t hurt.Over tighten them and pull the thread your in **** deeper n space.
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I have a lot of trouble convincing some people not to over tighten bolts. Recently had a machine in here with mast and top cheek plates distorted through over tightening. Lots of common sense required. If lacking use a torque wrench.
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When I mentioned that I have possibly overtightened the bolts, I never pulled them up any more than I would a similiar sized bolt, I try to be mindful of the size of the bolt & use spanners appropiate.I will check the rotax manual for torque before installing the new bolts so I get it correct.
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but a heavy spring washer will take up the slack if there was any movement, and it won"t hurt.Ok now its my turn to
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Chop, it"s not so much the size of the bolt in this case, but the material it"s screwn into.Stress that stuff n it"ll come out with the bolt next time you pull it out.I don"t know the rated torque ona bolt that size, but I"d never torque it that high.Rito Bones, you asked for it,
Firstly, if you don"t want to loose the tension wen your compressing two hard materials where there"s serious vibrations, you must have sum sorta compressible/stretchable material in the sandwich.Coz mild steel and the 912 don"t do it, and coz you can"t put 3 foot leaverage on the bolt, it won"t stretch, so you need sumthn in there that will take up the slack when the inevertable movement happens. And it"s only got to move a poofteenth a few times ( which it will in this situation), and every time it moves, a little tension is lost. It"s not long before it"s loose.And wen I say a heavy spring washer, I mean heavy.( 24" comet mill
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just look out side the square a bit with the lock-tite. they also make a gasket sealant. can"t remember the number right now [ maybe 513 or 518 ?? ]. but it will solve some of your problems
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When re-checking a nut tension with a tension wrench it pays to back it off first before rechecking. I used to think it was beloney and used to wonder why I blew so many EA81 head gaskets. The day I adhered to that practice I have never blown another gasket. (Unless you are playing with spring washers which may be another ball game) I worked in the A/C trade for 2.5 yrs, and the only spring washers I saw was in the VW combi which used to take us to work.
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Maybe I should point out that I"m just a SCG, I"v got no qualifications, no tickets, never even seen a university and failed grade 2.I"v just built lots of different ****, including aircraft, modified everything I"v ever bort coz nuthns made proper, and Nuthn I"v built or modified has ever failed, cept the machines I"v crashed, (but you know how"s responcable for that), so take everything I say with this in mind.
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You"re ok Birdy. You are a graduate from the university of life. When I was an apprentice auto. sparky they hired a bloke who had a batchelor of science degree and he was sacked because he was useless with anything practical. Could not overhaul a simple C39 generator without stuffing it up.
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