Topics

Old & new 3/8 throughbolts


Mick O'Connor
 


Ron Milan
 

Mick:  A picture is worth a 1000 words, THANK YOU!

Is that a Viton "O" ring in the very middle of the "new" case stud?

Ron M


-----Original Message-----
From: Mick O'Connor via groups.io <mickoconnor909@...>
To: JabCamit <main@jabcamit.groups.io>
Sent: Sat, Feb 13, 2021 10:16 am
Subject: [JabCamit] Old & new 3/8 throughbolts










Mick O'Connor
 

RON,

Don’t think so, it is black and looks like rubber. It i square section, not circular.  Jab description includes ‘with damper’.

 

Mick

 

From: main@JabCamit.groups.io [mailto:main@JabCamit.groups.io] On Behalf Of Ron Milan via groups.io
Sent: 13 February 2021 16:07
To: main@JabCamit.groups.io
Subject: Re: [JabCamit] Old & new 3/8 throughbolts

 

Mick:  A picture is worth a 1000 words, THANK YOU!

 

Is that a Viton "O" ring in the very middle of the "new" case stud?

 

Ron M

-----Original Message-----
From: Mick O'Connor via groups.io <mickoconnor909@...>
To: JabCamit <main@jabcamit.groups.io>
Sent: Sat, Feb 13, 2021 10:16 am
Subject: [JabCamit] Old & new 3/8 throughbolts

 

 

 

 

 

 

 

 


Clive James
 

Bob, the bolt failures were in training aircraft in the main that did lots of circuits. 
I had to agree with that failure mode as when I embarked on teaching my son and son in law to fly my Jab a bolt snapped. 
A section of bolt with the nut parted company. So unless you plan loads of circuits it shouldn't be a worry. 
I agree with David though, if you are splitting the cases why not upgrade to the fatter bolts and be done with it. 
I did this on my 3300 years ago mainly to improve the clamping forces on a very leaky engine but it was simple enough to do and the look and feel of the thicker bolts made me think it was the correct decision. 
It's amazing to think you have no hours on that engine Bob, I assume the plane isn't quite finished.....?
Regards, Clive


jabcamit@...
 

Hi Clive,
Here are 3 views of your sheared bolt. 
First view shows the failure location - in the body of the threads
Second view shows sheared face with beach marks (perhaps one per WOT take off?)
Third view shows the transition from threaded to waisted section of the bolt. It looks pretty  graunchy in there, but  despite those stress risers, the bolt failed in the smooth even section of the thread -  I'm guessing where the nut applies tension to the bolt.

I'm not expert in bolt failure analysis  but my gut feel if that the failure was caused by a levering effect on one side on the nut due to contact with the cylinder wall/ flange. The nuts you sent Clive have a small underside (filed?) radius. Don't know about the nut that was on  the failed bolt (I' guessing the same.

Last pic is  from an ARP catalog. Note how ARP  emphasise IN CAPITALS the need to use a specialist  thread lubricant when torquing bolts.  I just can't understand  why Jabiru  don't  follow basic engineering common sense. 


Clive James
 

Ah yes, I should have remembered we've had all these discussions before, there is a large amount of Deja-vu on this forum as there is little that's not been discussed before. 
Just as a forgetful old fart I'm reliving some of it for a second time.....
CJ


Lyle Passfield
 

There’s a lot to be said for Old Timer’s Disease: you learn new stuff and meet new people every day!

On Tue, 16 Feb 2021 at 08:14, Clive James via groups.io <zcrj90=yahoo.co.uk@groups.io> wrote:
Ah yes, I should have remembered we've had all these discussions before, there is a large amount of Deja-vu on this forum as there is little that's not been discussed before. 
Just as a forgetful old fart I'm reliving some of it for a second time.....
CJ


jabcamit@...
 

Hi Clive,
"there is little that's not been discussed before. "  Thats because jabiru consistently fail to understand/follow/adopt  the basic  engineering principals identified (and repeated ad-infinitum) on this site in response to multiple jabiru engine design problems. 

My Jabiru 90% complete,  90% to do (exactly as reported 5 years ago).


BobP