Frame mounting bolts

[Hugo]

That's got to be unusual, hasn't it? If they all do this, it suggests a design weakness.

[Series1 Stu]

It sounds like Geoff's IRS mounts were missing the packing shims between the mounts and the chassis. They are there to fill the gaps between the chassis rails and the mounts and prevent fretting and shear loads on the bolts.

The thread damage could equally have been caused by hammering the bolts through misaligned mounts when fitting the IRS.

If you fitted bolts with too long a plain section then you might not have got enough thread to fully tighten the bolts. I wonder if you used a different grade of bolt to standard because all bolts of a given standard usually have exactly the same length of threaded section. It's just the plain section that varies.

Like I said before, if the bolt gets any shear loads then the joint has failed or it had not been correctly assembled in the first place.

We can't really afford to be a bit sloppy about things like this. People's lives depend on it.

Regards

[Hugo]

We can't really afford to be a bit sloppy about things like this. People's lives depend on it.

Regards

Not like an aircraft they don't! I meant we don't need to be OCD about it - you'd have to be pretty unlucky to kill somebody because you've used a setscrew rather than a bolt somewhere.

[abowie]

Not worn through, just side pressure on the threads had flattened them a bit. Every bit as tight as they should have been.

Geoff

Probably thread damage from where they were hammered through the holes in the frames at the factory. Common finding.

[Gfhug]

Stu, the packing shims were there and maybe the damage was done on fitting (hammering) the bolts.

However, if you're fitting a 1/2 inch bolt into a 1/2 inch hole in two or three items to hold them together then the only part of the bolt that should be in contact with the hole is the plain shank. If you look at the bolts supplied by SNGB etc for, say, the IRS mounts where they fit the body then the threaded section is too long such that part of the holes the bolts go through has the thread not plain shank touching the holes in the mounts/body. In aviation, bolts come in 1/10th or 1/8th inch increments, always with the same amount of thread on them whatever the length of the bolt. Enough to take the nut, a washer and a bit of spare that would be seen beyond the done-up nut.

Just a difference of how standards are from one industry to another. And I've no wish for a long discussion. I put my original comment in as an observation, not intending to go way off topic. For which I apologise.

Geoff

[Hugo]

No, it's all interesting stuff - I've learned a bit from the discussion

[Series1 Stu]

However, if you're fitting a 1/2 inch bolt into a 1/2 inch hole in two or three items to hold them together then the only part of the bolt that should be in contact with the hole is the plain shank.

...... has the thread not plain shank touching the holes in the mounts/body. In aviation, bolts come in 1/10th or 1/8th inch increments, always with the same amount of thread on them whatever the length of the bolt. Enough to take the nut, a washer and a bit of spare that would be seen beyond the done-up nut.

Geoff

Sorry, Geoff. I disagree. What you are saying is just not practical. I guess we'll leave it at that?

Regards

[Hugo]

I dunno, it sounds right to me, even if it is a counsel of perfection.