Rust in Pan, How to explore properly
 

I have some pics of the visible rust on the car in this thread a while back. This is a '77 911 Coupe.

http://forums.pelicanparts.com/porsche-911-technical-forum/911797-rust-replacement-panels-fender-bottoms.html

What is the proper method to take the chip/undercoating off near those 2 holes in the pan? What tool? Grind wheel? Needle gun? Chemicals?

Mobile Dustless blasting is available in my area. Is this a better option?
Surface Preparation | Carencro, LA | Blastworks, LLC
Can the heater box tube be damaged by this kind of blasting?

I attained a perfect driver fender to replace the rotten bottom one in the picture from an '88 911. Any reason this wouldn't be a great fit on a '77 as opposed to buying a repop?

My plan is to take both fenders off and remove the oil lines so I can get in there and repair what is rotten. There is little to no rust anywhere else on this car (that I can see) and I think it's worth it to repair properly.

Suggestions on removing the fenders? Is there any easy way to get the seam sealer/bond to separate from the fender flange to the connection piece that is attached to the outer tub? Some of the bolts inside the fender are completely covered in that sealer/undercoating material.

I have found that using a 4 1/2 electric grinder with a knotted wire wheel works best for removing the schutz. you can also clean the rust pitted metal as well. be sure to wesar a face shield and good gloves.

once you have cleaned the area and cut out the bad metal, I would media blast the area. take care to protect the heater box tube.

The fender flare on the 88 may be different than the 77. The fender should bolt in place the same. However, the fit at the top of the door may be different.

I use a hole saw without the center bit to remove the schutz from around the bolts inside the fender. Once all the hardware is removed, use a heat gun to warm the flange and pry apart working from the front to the rear and the bottom up. There may be a tack weld at the back of the fender inside the door jamb.

Good Luck, Bob

I second the recommendation of a twisted wire wheel. All the other things I tried completely sucked.

Thanks for the great suggestions. Fantastic idea on the hole saw around the fender bolts.

Any advantage to a particular style of wire wheel on the schutz? Cup or wheel?

Wire Wheels

Do you have to apply pressure or this is one of those "let the tool do the work" kind of thing?

wheel works best with enough pressure to let the tool work. Be careful of the edges and around holes in the sheet metal. I call these the "wheel of death" because once you catch the edge of the metal the tool jumps. firmly hold the grinder with both hands.

I know this is a little late. But to minimize the mess use a heat gun and scrapper first to scrape off the heavy stuff, then go back with a wheel and clean off the residue. Using just a wheel will fling bits of paint, rust and shutz everywhere that you will then need to clean up.