Replacing U/C bolts

[geoffreywh]

At 500 hrs the u/c bolts (6) have to be replaced. It's turning out to be a MAJOR problem. Firstly the nuts are extremely tight. So tight that the threads are ruined by the nut on its way off)... This is caused by the tops of the bolts ( the threaded part) being bent. This, in turn, is caused by the way the bolts come thru' from underneath. The inner part of the fuse behind the seats ( where the outer bolts come thru') is not flat or square to the bolt hole. The fuse floor is "squared up" by epoxy and a small alloy plate. This has all crushed and broken away when the "engineers" at Flogem & Fugit (sorry, Jabyru ) tightened the bolts. Obviously putting the alloy plates back on with glue to support them is just wrong. After getting the bolts out which I have not done yet ... ( Will have to have the heads cut off and be driven out upwards.) ANY IDEAS how to fix the fault??????? I believe that a hollow dowel partway into the u/c bolt hole and a TIGHT fit into the much thicker , tapered in section (now steel) nut plate might help....What a mess....

 

 

[Dieselten]

Which model of Jabiru is this, please? If possible, some photos of the damaged area would help. On my J160C the u/c bolts are AN6 in various lengths (different from the factory spec due to uneven thickness of the fuselage layup) and I have had no difficulties removing and installing them. I used the suggested torque value for AN6 bolts into fibreglass as laid out in AC43-13B, which was about 8ft-lbs if I recall. Sounds like your bolts were somewhat over-torqued.

 

 

[geoffreywh]

It's a 230, the bolts supplied by the factory were all different from those I have so far been able to get out. I estimate the torque to have been 60-80 ft.lb. ( LONG tube on a 3/8 sq dve. snap on socket , I thought it would break!) The outer two go through the fuse and around the u/c leg through a flat plate clamping the leg to the body. They don't screw into glass. I'm guessing 3/8 x 60. It's AN-6 -32...PS.................. I just checked the manual the 160 and all others are the same EXCEPT where the bolts are shown going through the fuse, They come out on the very edge of that plate shown.. not on the flat part. The factory manual does not give a torque value, just says do not overtighten. Too late mate !

 

 

[jetjr]

No problems on my j200, changed bolts once,bushes a few times. Should not be tight, inners only crushing rubber bushes and outers shouldnt be out of alignment as lower plate isnt fixed. Bolt lenghts are a problem, need special lengths or washers.

 

Sounds like somone forced yours, not sure how they bent the end, tough bolt.

 

 

[biggles]

At 500 hrs the u/c bolts (6) have to be replaced. It's turning out to be a MAJOR problem. Firstly the nuts are extremely tight. So tight that the threads are ruined by the nut on its way off)... This is caused by the tops of the bolts ( the threaded part) being bent. This, in turn, is caused by the way the bolts come thru' from underneath. The inner part of the fuse behind the seats ( where the outer bolts come thru') is not flat or square to the bolt hole. The fuse floor is "squared up" by epoxy and a small alloy plate. This has all crushed and broken away when the "engineers" at Flogem & Fugit (sorry, Jabyru ) tightened the bolts. Obviously putting the alloy plates back on with glue to support them is just wrong. After getting the bolts out which I have not done yet ... ( Will have to have the heads cut off and be driven out upwards.) ANY IDEAS how to fix the fault??????? I believe that a hollow dowel partway into the u/c bolt hole and a TIGHT fit into the much thicker , tapered in section (now steel) nut plate might help....What a mess....

Horrified by what I read Geoff . I assume that it is a factory built aircraft , and not been tampered with in any way since manufacture .They would normally be a part of the 100 hourly , could they have been over tightened then ? If not , I would certainly be making the problem known to someone in authority at Jabiru .

 

Bob

 

 

[geoffreywh]

Yup 24- rego. Bolts checked at every 100 hours, never tightened though ( always by me) No-one else ever put a spanner on it. The bolts have been SEVERELY overtightened to the extent that the last 15mm ( not all of them) has bent, the flock and epoxy has been crushed and the alloy plate has been deformed and forced into the threads of the bolt....To help matters the aircraft is going on a round Australia flight on Friday...CURE? ...I have turned up an alloy ring with the same I.D. as the floor reinforcement. I cut segments of the ring. milled a flat on the segment and drilled for 11mm..... made a top hat bush with 8mm sticking out below the segment. (towards the inside of the circle ).......... I'll enlarge the holes for the bolts into the floor 8mm and Araldite all. THis will stop the sideways loading of the bolt as I tighten .........Got to work......................Couldn't be any worse.

 

 

[Head in the clouds]

The bolts have been SEVERELY overtightened to the extent that the last 15mm ( not all of them) has bent, the flock and epoxy has been crushed and the alloy plate has been deformed and forced into the threads of the bolt....

Could this same effect be produced by a hard landing? Depending on the setup, which I haven't seen on the Jabiru, a hard landing - or the drag loading from running through a rut, or very hard braking - could load up the bolts in tension and cause the thread and compressional damage you describe. Just thoughts, and not casting any aspersions on your landings Geoff, would've been when you lent the plane to ...

 

Anyway hope you get it fixed quick for your trip.

 

 

[geoffreywh]

It's not my plane , I just work on it...Hard landings wont give the damage seen as that would be a compression / shear load. What I've got is tension damage...The threaded part of the bolts (inside the fuselage) are bent in opposite directions as would happen when you tighten a nut on a curved surface