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Old 09-27-2007, 11:37 AM
sjefke's Avatar
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Location: Atlanta, GA
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Pop rivets take shear, especially if the steel rod for "popping" is still in it, but the problem is when you have a 3D force, bending and stress situation. You can pull/push poprivets pretty easy out of holes, and bend them too. Hull plate rivets would blow into old WW1 submarines if they went to deep. Water pressure would press rivet straight through hole because the head would deform and squeeze itself. That's why submarines had welded hulls already early on. It is actually one of the historically inaccuracies in the WWII movie "Das Boat (The Boat)". You hear and see rivets popping into the submarine while under depth charge attack whereas they all had welded plates already in those days. Director thought it was such a dramatic effect (boat coming apart with gunshot kind of noise) that he wanted that in the movie.

'70 111 280SE/c 3.5 (4 spd manual) - sold
'63 MGB
'73 MGBGT V8
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Old 09-27-2007, 11:42 AM
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Location: Dublin, Ireland
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Originally Posted by MunichTaxi View Post
Rust repair= 40+ hours

First time I did a job like this. It became easier after I started using paper templates. I fiber-glassed all sheet metal pieces and seams. messy O/H job
All 4 corners needed treatment, about 12 different-shaped 20 gauge metal pieces: cut, bent and riveted. The largest pieces were the 2 front ends of the rockers, 18" & 26" long. The jacking supports are 'covered', so I will have to carry a different jack in the trunk.

I'll probly use truck bed liner next, with some POR-15 for other areas.

Please tell me you're keeping this car for yourself and not selling it !
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Old 09-27-2007, 11:59 AM
Jordan G's Avatar
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Location: Lancaster, PA
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I agree sjefke.....any kind of torsion or twisting would cause failure on a pop rivet. I guess I'm just having trouble visualizing the load path on a rocker. I guess it also depends if we are talking about a collision impact or normal stresses induced by wear and tear thru driving. A mechanical engineer would answer this much better than I.

Either way....rivets ARE better than rust
1981 240d - 135k - Arlene
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Old 09-27-2007, 01:14 PM
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Rivets would tend to concentrate the loads rather than distribute them over a continuous weld, that's why welds are used in some applications. I'd predict that if a failure occured it would not be of the rivet itself, but of the 20GA sheet metal (which, IIRC is 1/32") it was riveted to.

Depending on how close the rivet was to the edge it could shear out or, from repeated flexure elongate the hole which the rivet passed through. Assuming the steel had a shear strength on the order of 30,000 PSI and the rivets were 1/8" diameter the hole would shear out at only about 120 lbs of force. That's not that much. Of course, that's 120# per rivet, so if you used 4 of them you'd be OK to about 500#.

The stresses in the rockers consist of torsion and tension/compression but are complex and can't really be accurately analyzed by hand. Welding them would probaby be preferred to any mechanical fastener, but having said that what you did is probably still better than what most shops would do (just apply some bondo and paint over it) so I would not lose sleep over it - just look in on the rivets from time to time and see if they look like they are still tight and haven't torn out at all.

And yes, I am a mechanical engineer.
Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

Last edited by nhdoc; 09-27-2007 at 01:22 PM.
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Old 09-27-2007, 03:28 PM
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Join Date: Aug 2004
Location: Western Washington
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It's a hobby

"Please tell me you're keeping this car for yourself and not selling it"

Yes, I am. Unfortunately, my daughter has a firm grip on "owning" this 1977 280S Euro vehicle, since it is much nicer that the 1970 W108. The 1977 is a 'sweet' looking car, not a single dent in the body, and the interior looks 10 years old.
I suppose she'll drive it, since the W108 stays in the garage, when it's raining.

The engine compression is from 143 to 155 cold. The Weber carb installion was another challange, with the linkage being the toughest part.
1970 280S M130 engine- good runner
1971 250 M130 engine- #2 rod bearing, gone
1971 280SE (blown engine,parts car)
1977 German 280S W116-only 33 years old
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Old 09-27-2007, 04:54 PM
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I'm sorry to jump in with a stupid question but... the rocker panels are structural?
1979 240D w/4 Speed Manual, Light Blue Estimated 225-275K Miles - "Lil' Chugs"
Sold but fondly remembered: 1981 300TD Turbo Tan 235K miles, 1983 300SD Astral Silver 224K miles

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Old 09-27-2007, 09:10 PM
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Join Date: Apr 2005
Location: Lafayette Indiana
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In a unibody all parts contribute to torsional stiffness. That is resistance to twisting.

Tom W
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual. It still needs upholstery redone...I also have a 427 Cobra replica with an aluminum chassis.
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Old 09-28-2007, 01:14 PM
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Join Date: Jun 2007
Location: Seattle, WA
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Originally Posted by Dee8go View Post
Ever looked out the window of an airplane at the wing tips? They go up and down all the time.
You'd be pleasantly surprised to know that when the Boeing Company tests a new development wing section for new airliner programs, an exact working prototype of the wing is placed in a massive jig with which hydraulic rams apply simulated wing loads. This is done until the wing fails entirely and catastrophically - and with a tremendous bang. When the 777 wing was put through the paces, its wing tip was deflected close to thirty feet before it was no longer 'flying' and broke apart. If you can find a copy of the PBS documentary of the making of the triple seven, a segment of the film shows this very event.
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