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Popping or "Oil Canning" of the Hard Top

MarsChariot

Contributor
Planetary Offroader
Joined
Oct 12, 2004
Messages
2,301
Loc.
Albuquerque, New Mexico
Popping hardtop (oil canning)

The problem:
Sometimes when driving on the highway, particularly on a windy day, or when passing a big truck, the hard top makes a popping sound like sheet metal slapping back and forth or “oil canning”. The sound is more or less random, but it is pretty loud. The first time you hear it, you imagine that your hard top sheet metal is undergoing some sort of catastrophic failure, or is going to end up wavy and ruffled with ridges at the end of the drive.

Why it occurs:
No one has done the wind tunnel study, but a some people think it results from lifting of the sheet metal on the roof because of the low pressure that occurs by passage of air over the roof at high speed; kind of like an airfoil. On days when there are high wind gusts, or in the turbulence around a large truck, the flow of air over the top may suddenly change, and that allows the top to snap back to relaxed condition, or it may even be lifted more.
Whatever the ultimate cause, when it snaps back, it contacts support cross members or the oil canning sound of metal flexing is transmitted into the interior.

What to do to fix it:
The flexing of the sheet metal cannot be entirely eliminated, and it is probably not a good idea anyway since there is some need for expansion and contraction just to allow for expansion and contraction with temperature variations. The “fix” that works for most is to reduce the noise by adding some sort of sound suppression or insulation. Simple layers of sound deadening material (such as Dynamat) can reduce the ringing of the metal as it flexes. For those with cardboard headliners, either the sound deadening material or simple foam or interior type insulation glued to the underside of the sheet metal roof can help reduce the sound. Insulation is probably a good idea in sunny climates, since it can reduce the inwardly radiated heat from the metal roof on especially hot days; and it really helps in cold climates where the loss of heat through the roof can be high on clear nights when upward radiation is high.
 
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kntr

Bronco Guru
Joined
Oct 7, 2006
Messages
2,278
Tennis ball between the rollbar and top helps too.
 

white64

Jr. Member
Joined
Jun 29, 2010
Messages
104
Loc.
Pittston, Maine
I've been thinking about how to keep my half cab from oil canning... especially when it comes time to block sand it (it's like sanding a moving target!)

Was thinking... that if I made 5 or 6 ribs out of 1/2 thick x 1 inch wide styrofoam or notched plywood, glue those to the roof inside, spaced 6 inches apart, then cover the inside of the top with a few layers of fiberglass covering the "ribs", which then become fiberglass impregnated stiffeners....

I suppose one could always sand the fiberglass and paint it, or cover it with a headliner...

Anyone tried it? Foresee-able drawbacks? Dumb friggin idea?
 

redpony

Sr. Member
Joined
Aug 9, 2004
Messages
744
Hi, Try putting one or more headliner bowes in. This is in addition to the one that is there already on the wagons.
 

MikeCon

Full Member
Joined
Apr 7, 2019
Messages
255
Top is flexing between 2 braces. Don't over think it. I ran 2 wood braces fore and aft between existing braces using liquid nails. Added some liquid nails between old braces and roof. Not solid ,just here and there. Not worried about cosmetics since it will be covered by insulation and headliner. Solved problem.
No headliner? You can order a third brace.look at Hood.
 

iSense67

Contributor
Jr. Member
Joined
Feb 18, 2022
Messages
52
Loc.
Sarasota
Curious if this issue occurs more or less with the new metal tops as I need one? If I do get a new one should I have the shop add more ribs or otherwise to mitigate this problem? Also I’ve been going back forth on a fiberglass option and curious if that has the same issue? On the BC design I do like the idea of being able to remove the side windows to have a safari top. Thoughts?

My metal option: https://www.dennis-carpenter.com/br...p/c9tz-9850202-kit-tkcf75-bronco-hard-top-kit

Fiberglass option: https://broncodesign.com/product/hard-top/
 

Madgyver

Contributor
Bronco Madman
Joined
Jul 30, 2001
Messages
14,193
Glass top here.. metal sides and liftgate removed on this shot. Currently reinstalled now as it is being daily driven.
as for the thin canning affect on metal tops, I have salvage a bunch of support ribs from other tops that got trashed and will use them in the halfcab top and another full top that I plan to repair.
 

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iSense67

Contributor
Jr. Member
Joined
Feb 18, 2022
Messages
52
Loc.
Sarasota
Glass top here.. metal sides and liftgate removed on this shot. Currently reinstalled now as it is being daily driven.
as for the thin canning affect on metal tops, I have salvage a bunch of support ribs from other tops that got trashed and will use them in the halfcab top and another full top that I plan to repair.
Looks awesome. So you went with fiberglass top and metal sides? Is the fiberglass top quiet at higher speeds and over bumps?
 
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