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Author Topic: Drat - crack in door post.  (Read 3600 times)
ceieio
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« on: April 11, 2006, 10:52:07 PM »

While rooting around in the old warhorse (taking out interior parts for an update) I came across a crack in the top of the aft door post just below where it meets the roof.  On the MC-7, this is a narrow post between the triangle window and the door.  It appears to be made out of a light gauge stainless steel (non magnetic metal anyway), with an external "skin" plate held on by a single vertical row of rivets.

Sitting outside looking at the bus, you would think that this thing might be structural, perhaps in tension.  Looking at the material on the inside you might think it is from Wrigley’s.  There is no sign of corrosion, so I would guess it work hardened and cracked just outboard of the original weld area.  This is no deformation or misalignment that I would expect if the crack was due to an impact.

At any rate, I could use your thoughts and opinions on the best way to address this.  I think that stainless can be wire fed, brazed, or tig welded.  I would think that a wire feed would put less heat into the part than brazing, and a tig setup would be awkward in that location.

So the questions are:

1) Braze it, wire feed, or tig? (or mechanical fastners, liquid nails, chewing gum...)
2) Is there any special consideration like a jig, blocking, or anything of the like that should be done before the repair?
3) Should a gusset plate be fabricated for this?  If so, should it be stainless, or some other alloy?

Many thanks for any advice, experience, or opinions!

Craig

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Craig MC7 - Oregon USA
Greg Roberts
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« Reply #1 on: April 12, 2006, 02:53:12 AM »

From your description it sounds like you have a cycle fatigue crack. I won't go into a deep recitation on metallurgical failure modes but will focus rather on repair methods.

Cycle fatigue changes grainular structure of the metal in the failure zone. Typically these grainular changes are not favorable for weld repair alone. Also, the failure mechanism can be assumed to be still present going forward unless you are able to identify the primary cause of the fatigue in the structure. So, I would recommend that you tig weld the crack and then overlay a gusset to stiffen the area and make it more fatigue resistant. If you will take pictures of the failure area and include I wide shot, I will tell you the best size for the gusset.
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gumpy
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« Reply #2 on: April 12, 2006, 04:24:18 AM »

This is a common break in MCI buses. I've seen it in several, if not all I've had the opportunity to view the framing in this area. My 9 had the same issues in the same area.

I concur with welding the crack, grinding, and gussetting.

craig
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Craig Shepard
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ceieio
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« Reply #3 on: April 12, 2006, 08:18:45 PM »

Thanks gents.  I'll get a picture of it and post it, as soon as I get home from fishing... the salmon season closes on the Columbia tomorrow!

Craig
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Craig MC7 - Oregon USA
gumpy
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« Reply #4 on: April 13, 2006, 04:35:43 AM »

Thanks gents.  I'll get a picture of it and post it, as soon as I get home from fishing... the salmon season closes on the Columbia tomorrow!

Craig

Not a problem. In lieu of us sending you a bill for the free advice, you can just send us a frozen fish, preferably pre-smoked.  Cheesy

craig
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Craig Shepard
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roadrunnertex
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« Reply #5 on: April 13, 2006, 07:39:51 AM »

Before you repair the crack that you speak of on your MCI.
Make sure that you stop drill the crack.
To do this this you use a #10  or a 3/16" drill bit.You drill the hole at the end of the crack.This will keep the crack from getting any longer.
You can then plate over the affected area with a doubler.
jlv
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gumpy
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« Reply #6 on: April 13, 2006, 09:55:27 AM »

If he welds it, as suggested, he won't need to stop drill it.
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Craig Shepard
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« Reply #7 on: April 13, 2006, 10:03:01 AM »

If he welds it, as suggested, he won't need to stop drill it.

Craig,
I thought you were always suppose to do a drill and fill with a work crack.
Maybe I've been misled?
Dallas
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kyle4501
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« Reply #8 on: April 13, 2006, 10:07:16 AM »

Stop drilling won't hurt. The last crack I welded (with out drilling first) continued to run ahead of the weld puddle. So I stopped welding, drilled it, then it behaved.

I am not a welder, nor have I played one on T.V. But I did stay at a Holiday Inn once. Smiley

kyle4501
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ceieio
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« Reply #9 on: April 13, 2006, 09:53:05 PM »

Well, fishing was a bust.  I was able to study the inside of my eyelids for a while though.  Napping on a boat trumps being at work.  We stayed later than we had planned, certian that the big one would jump in the boat any minute, so by the time we yanked the boat out of the water and got home it was too dark to take pictures.  I'll take a run at it tomorrow or Saturday!

Craig - MC7 Oregon
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Craig MC7 - Oregon USA
gumpy
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« Reply #10 on: April 14, 2006, 04:33:32 AM »

If he welds it, as suggested, he won't need to stop drill it.

Craig,
I thought you were always suppose to do a drill and fill with a work crack.
Maybe I've been misled?
Dallas


Probably won't hurt to drill it. I guess if there's tension on the member, it could continue to crack ahead of the arc, as it did on Kyle.

I suspect in this case, it's a moot point, as I'm sure the member is completely cracked through, so there's probably no place to drill. That's the way this particular place in the bus typically breaks.
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Craig Shepard
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ceieio
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« Reply #11 on: April 14, 2006, 10:27:03 PM »

gumpy-craig

I think you are right, it is probably all the way through.  I will need to pull the window out and some of the door jam as well to be sure, but I think I will find it is all the way through.

I included two shots, one from the outside with the trim off.  In this shot, I believe that the discoloration at the top of the post is from the crack working.  It reminds me of what you look for on an airframe inspection.

On the inside shot, the tip of that fantastically drawn arrow just touches the crack.  Looking above the crack it looks like the bus was attacked by birds. :-)  I am hoping that it is a failed repair from days of old, as they could not have turned that kind of work out of the factory (I hope!!).

some-other-craig MC7 Oregon
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Craig MC7 - Oregon USA
gumpy
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« Reply #12 on: April 15, 2006, 05:47:14 AM »

On the inside shot, the tip of that fantastically drawn arrow just touches the crack.  Looking above the crack it looks like the bus was attacked by birds. :-)  I am hoping that it is a failed repair from days of old, as they could not have turned that kind of work out of the factory (I hope!!).

Don't bet on it. I saw some pretty crappy welds in my bus (saw some after I worked on it, too  Wink

This is a typical place for cracks. Either in this member,or in the horizontal member directly above this area.

Weld it. Grind it. Plate it.  Another option is to remove the D window and double up the vertical member. More work that way, though.
« Last Edit: April 15, 2006, 05:49:22 AM by gumpy » Logged

Craig Shepard
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Dallas
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« Reply #13 on: April 15, 2006, 08:32:33 AM »

On the inside shot, the tip of that fantastically drawn arrow just touches the crack.  Looking above the crack it looks like the bus was attacked by birds. :-)  I am hoping that it is a failed repair from days of old, as they could not have turned that kind of work out of the factory (I hope!!).

Don't bet on it. I saw some pretty crappy welds in my bus (saw some after I worked on it, too  Wink

This is a typical place for cracks. Either in this member,or in the horizontal member directly above this area.

Weld it. Grind it. Plate it.  Another option is to remove the D window and double up the vertical member. More work that way, though.


As one guy told me when I hired him as a finish carpenter:
"A job worth doing, is worth screwing up!"
'nuffsaid
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ceieio
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« Reply #14 on: April 15, 2006, 09:35:23 AM »


Weld it. Grind it. Plate it.  Another option is to remove the D window and double up the vertical member. More work that way, though.


It is tempting to pull the D window; they date the styling and I can't see a practical use for it.  I am thinking of pulling the windows and skinning them over.  I may fix it as is and do the window project after the summer season.  Here at short-attention-span central, it is good to get the bus out and remind oneself (OK, my wife) that this is FUN, and that is why having a 40 foot long beast in her driveway is a good idea.

Hmm, looking out the window, maybe I should just skin the window now and forget putting in new windows; that way I will just hear the rain.

Thanks for all the good advice!

Craig

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Craig MC7 - Oregon USA
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