How do you remove the spot welds from the motor mount supports?

[Rotmilky]

I need to replace the rear cross member on my '68 that I'm restoring and replace with a donor part. To get the rear cross member off, I need to remove the motor mount supports that are spot welded on. The problem is I can't get my drill into such a tight space. Since I need the rear crossmember support to be intact, I can't just cut off the top of the crossmember (the piece where the stickers go) to get access to the spot welds.

I see motor mount supports for sale often for people to use in converting a 912 to a 911. Can anyone describe how they got the spot welds drilled out to get those off?

[kodioneill]

Maybe a die grinder.

[James Brown]

you can use a spot weld cutter, looks like a wood plug cutter, they work good.

[mreid]

That doesn't address the drill angle. A die grinder or thick cut off wheel is the way to go. Wear safety equipment!

[Daves911L]

Von,
A good spot weld cutter is the way to go. With the emphasis on GOOD (no Chinese crap)! You can use it in a small right-angle air-drill motor and likely solve your clearance problems.

Alternately, you might want to source extra donor metal. Harvest the crossmember from one car, the mounts from another. So you can sacrifice what you need to by grinding one side away ("peeling" the spots) and wind up with a complete crossmember, and two complete mounts, which can then be nicely re-attached to your car.

DG

[Rotmilky]

I have loads of spot welder cutters but couldn't figure out how to get them in the tight space. All are about the same length, maybe 3" long give or take. Do they make shorties? With a short stubby one and a right angle die grinder, I might be able to get in there. Hmm...I suppose I could cut the back part of the shaft of the cutter down a bit.

I do have two donor parts. I guess worst case I can grind them out like you suggested, Dave.

[Iciclehead]

I have run into a couple of cases where things were tight, I just used two drill bits of the appropriate diameter. One was a normal bit that I cut down to start the drilling to establish the circumference of the cut, then I took the same size bit and cut it square (no conical point) and then used it to drill the remainder of the spot out....

Works fine and you can cut the drill bits to any length, I just used my grinder to do the cuts...

Dennis

[roblav]

Take the crossbar off without removing the engine from the car. Why are you trying to drill out the spot welds? Why not simply replace the entire piece? There's 4 fasteners at the engine and two on the chassis. It'd be easier if you take the muffler off.

[Rotmilky]

Not sure we're talking about the same thing, roblav. There is nothing left on the car to take off. Unfortunately, the car was hit in the rear and the rear crossmember is bent up. The only way to get the crossmember off is to remove the spot welds. There are maybe 10-20 along both the left and right. Those can only be removed after cutting off the fenders. Then the motor mounts have to be removed. There's a good 30-40 spot welds per mount, plus there are also solid stitch welds along both the front and back of the motor mounts.

I think this will be a one-time repair. I'll do it once and then never again. Next car I'm going to restore I'll look at the rear crossmember. If it's damage, I'll pass on it. What a pain in the rear.

[timmy2]

Plasma cutter or a small tip on an oxy acetylene torch if you can get it in there will work. Remove what you need to save with a little more from what isn't saved and then grind it smooth when out.
Pictures of what you are up against may help.

[roblav]

Ha Ha! Yes, I thought you meant something else. Now I see what you're doing.

[Fleming]

Have you been following Johns posts?

Long hood project


On the #3 post are a group of photos including the engine mount corner supports as they have been drilled out. That's what your trying to remove without destroying...right?

If I remember correctly the lid latch panel (where the decal indents are) is a two piece affair. Inside sheet is spot welded to the surface just inboard from the top lip - from side to side. The bottoms of both pieces are a spot welded fold down flange. That inside panel has a "c" channel shape that the engine mount is welded to.





That ledge just below the decal/latch panel is the one that is hard to get to - correct?

[HawgRyder]

Will a right angle drill not fit into the area?
Bob

[Rotmilky]

Thanks for the suggestions guys.

As Fleming mentioned, the area that's tough to get to is below the latch panel in the corners. Here are a couple of photos from the donor part that I'm trying to get off. Notice the 5 small black spots that I used to mark the spot welds along the back . They're a bit hard to see, but they're on the surface opposite of the three welds I've already drilled out.



I used a black marker to try to mark the row of spot welds along the back. Here's the same photo with a ruler showing the clearance. At best, it's maybe 2.5".



There are 5 spot weld along that surface that are kinda tight. I need that entire cross member and the upper latch panel. Maybe this is a crazy idea, but could I leave the mounts connected to the rear cross member and remove the cross member/motor mounts as a single piece. Then mount that onto the '68? There seems to be a flair in the longitudinal tubes that probably means the motor mounts have to be attached and slid into place separately from the rear cross member.

I do think I can get my plasma torch into the space. Hadn't really thought about that for removing those spot welds. Might give that a try. The holes will be ugly since I can't hold it very steady, but I don't see why that wouldn't work. If not, my thought is to attach a small grinding wheel to a dremel and then see if I can't grind them off. Might take awhile but should work in theory.

[timmy2]

Easier to cut everything you need and more from donor car as a section, then trim to fit in new area.
(unless trying to save sections of donor car)

[Rotmilky]

Originally Posted by timmy2

Easier to cut everything you need and more from donor car as a section, then trim to fit in new area.
(unless trying to save sections of donor car)

I've thought more than once that this repair might be easier if I cut off the rear longitudinal just at the front of the motor mounts and then welded on a donor section that consisted of the rear longitudinal, motor mounts, rear crossmember and latch panel. Some days I think that might be the right approach for ease of replacement. But then I think all I need to fix is the dented crossmember/latch panel and I go back to trying to drill out the spot welds. I really worry that cutting the rear longitudinal *could* result in the whole rear part of the car being a bit out of whack. Plus, it's not easy to hold up the donor section to mark where the cut needs to be.

[Fleming]

Von before this gets to be a bigger project :-) look to your machine supply house for small end mills. 3/16" carbide mills, ball nose, four flute, double end (so you double the use) are about $15. Great to attack spot welds from an angle or use them in the drill press to drill out bolts, riviets, etc.

Dremel metal rotary rasp cutting bits are "burrs".

There is a range of Miniature Carbide Burrs with 1/8" shafts that will cut metal in a very controlled manner. Just remember sport welds have been localized heat treated and will be harder than the surrounding metal. SD-51 and SE-51 are about $10 each.

If your working with 1/4" air or electric die grinders you have a wide variety of Oval or Tree shapes to work with, single or double cut.

Better to drill out a few spots than have to align and butt weld a larger structural panel.

(Just an opinion).

[Rotmilky]

Ordered some ball end mills to try out from my 'local' machine supply. In remote nowhere New Mexico, that mean McMaster Carr. At least, that's the company I use to get raw metal stock, etc, for work-related experiments. Also picked up a set of 1/8 rotary burrs. Hope to be able to try them out over the weekend if they arrive.

[Rotmilky]

Thanks for the suggest of 1/8 rotary burrs. They worked wonders! Got all the difficult-to-reach spot welds using a ball end burr and my dremel with about as much ease as drilling the spot welds. Wow, those suckers can really chew through spot welds.

So, now I've drilled or ground out roughly 40 spot welds on ONE mount. That piece came from a '77. Wow, Porsche didn't want those coming off. (As an interesting point, there are far fewer spot welds on the early 70s donor piece. Somewhere between the long hoods and the short hoods, they cranked up the spot welding). Anyway, I also removed 4 stitch welds along both sides. However, I can't get the thing to budge. I went after it with a hammer and chisel and it's still on there good. In fact, I bent the rear cross member that I'm going to use! So, I decided to put the hammer down before I tear anything up and see if anyone has suggestions.

I've run into this before on other pieces, but they it was relatively easy to find the sticky spots. You could get one end loose and once it started to tighten, the next spot weld or two would be the suspect ones. This is the first time I've had 40 spot welds in a 6" space. There's such a high density that I can't figure out who is behaving badly. Any suggestions on how to find the sticky spots? I'm wondering if heating the drilled out spots with a torch might loosen up any remaining edges that weren't removed. The other thought would be to start widening all the holes with the burrs or a drill (I sorta hate to use a drill bit, with the holes so big I'll damage the cutting surface when drilling the hole out.

Anything suggestions would be appreciated.

Here's the way it currently looks. A bit swiss-cheesy, no?

[Fleming]

Von,

I have a center punch with a barb off to the side (exaggerated in the sketch) that could grab the side of the hole to push down on the behind panel to verify the spot had been removed. Strong light and a loupe helps to see what was going on.

Work around each hole. When it was loose the back panel edge would flex, if the spot still had gripe - both panels would take a dip. Tedious - but that's what it sometime takes. Stick in, tap, move on.

May work for you. (?).

A quick shot of a spray paint, let dry and sand off leaving any low spots to verify there aren't any "hiding in plain sight" spots welds remaining to be drilled.




If all else fails BA hammer and a offset chisel. (I've really like a 1/2" chisel, it cuts sheet metal in tight places - opens welds - cut's heads off bolts - all purpose. off set like this:


I hear a Lisle 51900 works well.