dbgrubbs
dbgrubbs Reader
7/23/17 7:55 a.m.

My son is about to get his e30 painted but before he does he wants to have his sunroof welded up......deleted. It was an aftermarket sunroof and is close to inoperable. He has a stock sunroof panel that can be used for a plug. He's looking for a competent welder to tackle this. He's talked to several people so far and while they all "say" they can do it, they have all also warned about warping the sheet metal. Doesn't give me a warm fuzzy. Anyone have any recommendations? Or better ideas?

SVreX
SVreX MegaDork
7/23/17 8:34 a.m.

I don't think they are telling you they are incompetent.

They are telling you that welding a plug into a roof panel has a high likelihood of warpage.

You're gonna get the same warning from any competent welder, because it's true. The guys you need to watch out for are the ones who DON'T tell you there is a risk.

SVreX
SVreX MegaDork
7/23/17 8:36 a.m.

The better idea is an entire roof skin, welded at the pillar corners where there is better reinforcing, and less total welding, which will equate to less risk of warpage. A junkyard roof cut is cheap.

But there is nothing wrong with considering the plug- just understand the risk.

Streetwiseguy
Streetwiseguy UltimaDork
7/23/17 9:53 a.m.

Maybe the question is, "Is your son planning on painting his E30 with a roller, or is it to be perfect?"

Welding a big, flat panel into an even bigger, flat panel is trusting to Mother Nature to be kind. The more patient and experienced the welder, the more likely it is that she will smile.

The entire roof panel isnt the worst idea...you would potentially get the headliner too. There again you need a skilled pro for the panel removal and prep. The welding is the simplest part of that job.

cdygrubbs
cdygrubbs New Reader
7/23/17 10:09 a.m.

Hey guys. It's actually my e30 (dbgrubbs is my father). I'm getting the car professionally resprayed. The car will not be perfect but I'd like to make it as nice as possible. There are very few people that want to deal with the roof but I've only contacted body shops so far. That's why I'm looking for a professional welder. Yes, the slicktop (non-sunroof) roof panel is still available from BMW, so that is an option as well.

SVreX
SVreX MegaDork
7/23/17 10:25 a.m.

In reply to cdygrubbs:

I've gotten complete junkyard roof cuts for $20. A battery powered sawzall, whack the A and B pillars, and pay the man at the gate. Less than 30 minutes.

Carry it to a body shop and they will know what to do.

You've got an original slick top car that didn't have the proper reinforcing for a sunroof, and someone whacked a hole in it. Now you're gonna do about 7 LF of welding- sheet metal to sheet metal on a large flat surface which is highly visible directly at eye level when it's done.

That's a really hard job.

The full roof is easier.

Are you gonna remove the glass for the paint job? Even easier to do the entire roof.

cdygrubbs
cdygrubbs New Reader
7/23/17 10:44 a.m.

Is it really that much easier to put on a new roof and make everything line up right again? I do plan on pulling out all of the glass and trim anyway.

As much as I'd love to go to the junkyard and cut off a roof, slicktops just don't exist in the yards anymore. I saw one back in 2014 but that was long before I had intentions of doing this. The only slicktop e30s were 1991 318i/is cars if ordered that way. Maybe I'll ask around on the BMW pages to see if anyone has a junked slicktop.

LopRacer
LopRacer Dork
7/23/17 11:17 a.m.

There is a huge (for a specialty) BMW junk/parts yard down the road from Road Atlanta, no I don't know the name but there are likely people here that DO.... I would try there first for a roof cut. Think this is the place.

BrokenYugo
BrokenYugo MegaDork
7/23/17 1:06 p.m.

With the E30 being a small car that gets caged pretty often I'd be surprised if the roof skin removal/replacement hasn't been documented at least a few times.

SVreX
SVreX MegaDork
7/23/17 3:12 p.m.
cdygrubbs wrote: Is it really that much easier to put on a new roof and make everything line up right again?

Yes.

TurboFocus
TurboFocus Reader
7/24/17 5:47 a.m.

I buy the idea that a whole roof is easier, and the better way to do it especially since this seems like a full restoration.

I'm also dumb enough to try and weld it in myself.

NOHOME
NOHOME UltimaDork
7/24/17 6:40 a.m.

Body shop wont want to do this. Takes skill and takes time.

If you do it yourself, here is what you are up against:

You have heard the old saw about when welding bodywork: "go slow, jump around and let the weld cool so you dont warp anything".

It is only partially true. What happens when you weld is that you are laying a puddle of molten metal across a joint between two panels. The molten steel will adhere to the tin on each side of the weld line. That is all good.

But what happens as the metal that came out of the MIG gun cools down? It shrinks. Think of a single bead of weld that straddles the two panels. As it shrinks, it pulls the metal together just like pulling the string on a purse. And the effect is the same; you get the wrinkled perimeter same as a drawn purse.

The only way to fix this is to stretch the weld. You do that by first grinding it almost flush with the surface ( on both sides) and then hammer on the weld while holding a dolly behind. This in effect smooshes the weld and spreads the tin back into the proper relaxed state.

So, the game is you fit the panel, put a few tacks in to locate everything, grind back the welds and use a metal yardstick to lay across the bead and observe the dip, then beat on the tack until it comes up. Repeat for each tack. Now go do some more tacks and repeat over and over and over.

Of course you are going to screw up and over-stretch some of the welds, so go look up "shrinking disc" on youtube.

SVreX
SVreX MegaDork
7/24/17 6:55 a.m.

One other part...

You are using a sunroof panel. Let's assume the after-market sunroof was the exact same size as the factory sunroof (which may not be true)....

If that's true, the panel will be too small.

Sunroofs don't fit tightly in the openings. They have gaskets around the perimeter, which are usually about a half inch thick. If that's the case, your metal panel is a half inch too small in all 4 edges. That's too much to fill with a welding bead.

Are you confident the panel is bigger than the actual hole cut?

cdygrubbs
cdygrubbs New Reader
7/24/17 10:40 a.m.
SVreX wrote: One other part... You are using a sunroof panel. Let's assume the after-market sunroof was the exact same size as the factory sunroof (which may not be true).... If that's true, the panel will be too small. Sunroofs don't fit tightly in the openings. They have gaskets around the perimeter, which are usually about a half inch thick. If that's the case, your metal panel is a half inch too small in all 4 edges. That's too much to fill with a welding bead. Are you confident the panel is bigger than the actual hole cut?

The aftermarket sunroof is completely different than the factory panel. Basically, I went to the junkyard and pulled a factory sunroof panel to be used as a patch panel. The factory one is actually longer (side to side) and roughly the same from front to back. It's hard to tell without removing the frame that is attached to the roof but either way, it should be close enough to work if I went that route.

I'm really leaning towards replacing the entire roof skin now. I'm going to call around today and see what I can find. At this point, I'd even consider one with a factory sunroof if I can't find a slicktop.

cdygrubbs
cdygrubbs New Reader
8/3/17 5:59 p.m.

I found someone to weld in a new roof. He's done quite a few and says the e30 will be easy compared to newer cars. The only thing that I wonder about is the fact that he's cutting at the pillars. He says there will be 3 different cuts made to each one. Apparently there are 3 sections of metal at each pillar and cutting them at different spots will increase rigidity once welded back together. Does this sound right? I find it odd that he doesn't want to replace just the roof skin itself.

gumby
gumby New Reader
8/3/17 6:45 p.m.

As a welder, I would skip that altogether.

Cut a plug big enough to flange the edge all the way around and panel bond it to the current skin from the inside. Finish the outside and paint.

Wall-e
Wall-e MegaDork
8/3/17 6:54 p.m.

At the body shop we usually went at the pillars. Done right you will get the least warping and most durable repair. Doing just the skin or patching the opening gives you lots of chances to have problems and filler on a roof skin can crack pretty easily.

crankwalk
crankwalk Dork
8/3/17 7:22 p.m.
LopRacer wrote: There is a huge (for a specialty) BMW junk/parts yard down the road from Road Atlanta, no I don't know the name but there are likely people here that DO.... I would try there first for a roof cut. Think this is the place.

I'm not sure how Strictly German is still even open. He's pretty proud of his junk piles on front anyway. I'd look and the pull a parts or on CL for a wrecked one with a good roof OR embrace the sunroof and roll with it.

SVreX
SVreX MegaDork
8/3/17 7:56 p.m.
cdygrubbs wrote: I found someone to weld in a new roof. He's done quite a few and says the e30 will be easy compared to newer cars. The only thing that I wonder about is the fact that he's cutting at the pillars. He says there will be 3 different cuts made to each one. Apparently there are 3 sections of metal at each pillar and cutting them at different spots will increase rigidity once welded back together. Does this sound right? I find it odd that he doesn't want to replace just the roof skin itself.

With all due respect, didn't we cover this?

It's a lot easier to cut at the pillars than to skin it.

cdygrubbs
cdygrubbs New Reader
8/3/17 8:51 p.m.
SVreX wrote: With all due respect, didn't we cover this? It's a lot easier to cut at the pillars than to skin it.

You said "pillar corners" which made me think of cutting it at the factory welds where the pillars join the roof skin. This guy wants to chop the pillars where there is no factory seam. I hope that makes sense. I'm more of a diy mechanic and don't know much about body work but it worries me that he's just going to chop it in a random spot. It seems as if this would be much harder to get right.

SVreX
SVreX MegaDork
8/3/17 9:03 p.m.

Nah- I just meant the pillars are at the corners of the car.

Hack the pillars. It's easier.

SVreX
SVreX MegaDork
8/3/17 9:07 p.m.

NOHOME described how difficult it is to weld the skin without warping.

The pillars are rigid- they won't warp as much. Hack them, weld them, grind them smooth.

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