Visual Representation of Structural "Frame"

[lespaul]

Does anyone have a reference to a good source or pictures or diagrams that show a visual representation of the structural frame of a longhood? This will help me distinguish between rust holes that are simply cosmetic and can be patched and those that may impact the integrity of the car.

Thanks.

Brad

[304065]

Well, the factory workshop manual has a couple good photos for crash repair purposes.

However, I would fix ALL the rust.

[lespaul]

Thanks John. I do plan to fix all the rust. However, if the rust consists soley of a quarter sized hole in the side of a fender or rocker panel, my inclination is to simply grind down to bare metal and fill with body putty.

On the other hand, if a structural member has a quarter size hole in it, I would be looking to cut and weld.

I am looking for something to help me know which solution is proper for each individual situation.

[Ron.G]

I think that any rusted area should be cleaned up and welded.
Filling a rust hole with putty is a clear sign of a hack job IMHO.

Bondo it ment to fill / smoothen small imperfections not fill holes.
Again just my opinion, to each his own.

[lespaul]

You might embarass me into buying a small welder.

Any recommendations?

[Zeke]

Originally posted by lespaul
Thanks John. I do plan to fix all the rust. However, if the rust consists soley of a quarter sized hole in the side of a fender or rocker panel, my inclination is to simply grind down to bare metal and fill with body putty.

On the other hand, if a structural member has a quarter size hole in it, I would be looking to cut and weld.

I am looking for something to help me know which solution is proper for each individual situation.

What would you use for a "bridge" in order to fill the hole? I mean people have done some really cheesy things of this nature, like steel wool pushed into the hole and covered with bondo.

I have done something similar to what I think you are thinking. I have used fiberglass mat and POR 15 as the "resin." I've also used epoxy liquid. Both work and do as much to keep the rust from returning as POR alone. The other thing is, there aren't many areas that aren't considered structural, especially as they mate up to other pieces (where rust is quite likely).

Except for some minor repairs, welding in new metal is best and more accepted by your peers.

[lespaul]

Well I was going to use the POR filler in a tube and fiberglass, but now I am thinking of going down to Home Depot and buying a welding unit. Any recommendations?

[Rich Lambert]

Like these?

http://www.pelicanparts.com/911/911_Parts/1969/body_big.htm

http://www.pelicanparts.com/911/911_Parts/1969/body3_big.htm

[lespaul]

THanks Rich. Those are very helpful.

[EarlyPorsche]

I should stop in my tracks with this whole remaking my chassis out of POR15 putty? It says strong as steel on it.

[Zeke]

I don't think you'll ever be sorry that you bought a welder if you buy a decent one. There are always things around the house they are handy for. You can also rent welders by the day to see if you like them. I'd recommend the MIG (with the gas).

Learning how to weld out of position (anything but flat) can be tricky. I've found copious material on the web, but the best thing I did was go to school. Working with the smaller, cheaper units poses some control problems when welding thin materials.

[scottbooth]

Hi Brad,

I have finally completed the rust hunt on my 78 911SC. It turns out that there are issues with the torsion bar tube, and even without diagrams I can tell that is serious stuff. So the welder is definitely going to be necessary. Unless I want to start tracking a different car. Or buy a tub.

Until this point I was on the same fence as you are, thinking that I had only a few fender rust issues to deal with, and maybe just filling the holes would be fast and easy even if the purists don't like the idea.

But if I am going to buy a welder then I will weld.

What I have learned so far is that the Lincoln MIG units sold at Home Depot and Lowe's are somewhat dumbed-down versions of the similar units you can get at welding shops for more money. The cheaper version has a stepped current output (a rotary switch with 5 positions) while the better version has a fully adjustable power supply, so you aren't restricted to 5 settings. The Home Depot unit is called the SP-175HD while the continuously variable unit is the SP-175+. Note that the model numbers are *very* similar. I have yet to weld anything, so I am worse than a novice, but the added adjustability seems like a good idea to me. This seems to be backed up by what I have read on the web. And personally I think the model number thing is a bit shady. Apparently the cheaper versions are available only at Home Depot and Lowe's, and were designed to meet a price point.

There is also a comparable Miller unit, the Millermatic 175, which is a bit more expensive. It has an auto-tracking feature that adjusts wire feed speed as you change the voltage. Some people on the forums have said that they like this, others hate it. It can be disabled. I get the impression that Miller welders are overall viewed a little more highly than Lincoln. Not sure if this is justified by performance.

Both of these are 220V units that require a dedicated outlet. The next step down are the 135 amp units that run on standard house current. In theory these are supposed to be strong enough for auto body work but I would rather have too much power, than too little.

Hopefully someone with some actual experience will chime in here and help us both out. But this is what I know.

Good luck
Scott

[unclebilly]

Rust is like iceburgs. The small amount you can see is just the tip of a much larger problem under thge paint around it.

I you have a rust hole, how thin is the metal around it? Unless you remove the rust and seal the steel, the rust keeps going.

[Zeke]

Scott, that is not quite the way it is. True, the 135 and 175 Plus models are continuous type current adjustment, while the T is "tapped," or steps. You can buy the T at many stores, not just the big box home stores.

The new models are 140 and 180 C and T, which is easier to understand. The smaller number is 120v and the bigger is 230v. While the 230v model will indeed weld heavier thicknesses, the 120v model is perfectly suited for light gauge sheet. The other advantage to spending more money is a longer duty cycle.

In fact, the lower the setting you can get the job done with is the best setting to use. Inexperienced welders usually weld too hot at first. AFA tapped machines go, one can vary the current through resistance with the amount of stickout of the wire.

[unclebilly]

I bought a miller 175 for where I work and I love this unit. I had the 135 at my previous employer and it was fine too.

The 175 is a great unit and I have welded structural sttel over 3/8" thick with it and it's been fine. If i didn't already have a unit at home (and access to the one at work anytime), I'd buy the 175 (as my buddy did on my reccomendation).

[NathanR]

Scottbooth wrote:

Both of these are 220V units that require a dedicated outlet. The next step down are the 135 amp units that run on standard house current. In theory these are supposed to be strong enough for auto body work but I would rather have too much power, than too little.

My whole home service is 100 amps. Most new homes have 200 amp service. If you wire a dedicated line, a 220v unit should take half as much current.

Food for thought.

n.

[unclebilly]

The Miller 175 draws 40 or 50 amps ony - not 175 amps. There is a transformer there. For autobody work, all you need is a small century unit like I have at home. The 135 or 175 are overkill if this is all you want to do. My Century runs off of a 15A 120 volt outlet but will overheat if I run it continuously for more than 10 minutes (welding subframes etc.).

[lespaul]

Thanks Scott and all. This is very helpful. Just as I was leaving work this morning, my wife said "what do you want for Father's day." Just guess what I said.

[scottbooth]

An update - I bought a Miller 180 MIG welder last week (early Fathers Day gift ), and have played with it a little so far (one afternoon only unfortunately - more to come). This is going to be tricky and fun...

This is a 230V unit that plugs into the same type of outlet used for electric clothes dryers. I am running mine on a 30A dedicated circuit that I added to the panel a few months ago when I was updating the wiring in the garage. You can buy or build a heavy-gauge extension cord if you don't have a dedicated outlet near your work area. I will need to put together a short one when I have screwed up enough scrap metal to be ready to weld on the car.

So far I have made a couple of good welds and a number of crappy ones. Now the trick is to figure out how to make the process more repeatable so I can improve my odds. But it is starting to make sense.

As I mentioned earlier, this is one of the units that has infinite adjustment of both voltage and wire speed. Now that I have used it, I can see that the infinite voltage adjustment is probably not strictly necessary - for any given voltage setting, there is a range of wire speeds that will produce a good weld. So having a tapped transformer with 5 settings (or whatever) does not look like a huge drawback.

Also, as a newbie, the added adjustability may make the process harder than it has to be. Sometimes it seems like the second adjustment just gives me a whole additional dimension in which to screw things up.

I am very happy with my purchase, and I expect that with more experience I will be glad to have the additional adjustability. But I figured that I would expand on my initial post now that I have a faint clue what I am talking about.

One feature of the Miller units that I *do* like is that the welding tip is not energized until you pull the trigger - so I can start the weld by resting the wire on the bead area. This is probably bad form, but it helps to get things started in the right place. I know some of the other units keep the wire electrically hot all of the time.

Cheers
Scott