Technical Major Pitting 31 Frame Motor Mount Area

Got the 31 frame back from the blaster today and the pitting at the motor mount looks pretty bad. Not going to box the frame, I'm running stock mounts, and I want to avoid plating the outside of the frame at all cost. Thoughts are trying to fill pits with weld and grind down, add 1/8" plate on the inside of the frame, or a combination of the two.

What's the consensus for addressing this issue if it is really an issue?

-EDIT- Decided to patch the frame based on suggestions.

 

looks like your blaster did a really nice job, good and clean. thats quite common on A frames where the rubber mounts held moisture. to fix it right i would cut out the area and weld in new. or, if you are not running the banger motor again just fill the outside

 

Plate the inside for strength, and use body filler on the outside for looks.

 

I’d just plate the inside, well past the pitting. Then adapt new, narrower mounts to keep things inline.
I’d rather do that than two butt welds and section in a piece.

 

I would not trust that frame and you need to haul it to my house and drop it off so I can get it to the recycler immediately.

That would be the best and when you grind the welds do the inside also and it will never be a visible repair.

 

Ditto on the plate. Should be fine.

 

Yeah, plate on the inside and filler on the outside...

 

That is the spot on the A frames that sags with time... check very carefully... if it had sagged the grill, hood and cowl seams would never line up...
if sagged and pitted think about selling it to a high boy guy... no hood, no problem...

 

Yep. And make sure the frame is not sagged at the same time.

 

If you intend to use the stock mounts you can't add a plate to the inside because the frame would then need to be spread to compensate for the added thickness when using the stock mounts and also the stock flywheel housing. Alternatives; plate the inside and carefully narrow the stock motor mounts, make an accurate pattern of the area and replace the entire section with new metal - just do it below
the radius of the upper and lower rails. If originality is not too high on your list, just add a complete
structural brace to the inside of the rail but extend it several inches fore and aft of the original
motor mounts. Again, you'll need to narrow the mounts accordingly to the thickness of your added
section, but this type of repair will strengthen this portion of the frame that is usually the main
area for sagging. Many ways to accomplish this but your initial question left a few things out which can't be accounted for in offering suggestions to solve the problem . Waiting to hear more!

 

Based on responses, I’ll be replacing the pitted section between the radius of the rails. I don’t believe there’s sagging although I should check again. As of now, The car doesn’t have a body so plans are a bit open. The goal is to get a running rolling chassis together as I sort out a body for the car. The vision is a traditional fenderless roadster with a mild drop on wire wheels. This is my first go at this sort of thing, lots to learn! Picture of the starting point and the ideal end result...

 

What about adding a bunch of brazing mat’t to the surfaces? It surely would be a quick and easy way to at least get the surfaces in better shape, and increase the strength as well. Hard to tell from the pics, but if you have 2.5 mm - 3 mm of material thickness left, I think you would be fine from a strength perspective. Just look at truck frames these days, I saw one the other day that was riddled with hundreds of “accessory” holes.

 

most model A's have a sag in that area, its a weak point. too many holes especially if it had side mount spare brackets. pull a string line and check it out.

 

Checked the old gal and she ain't saggy! Hoping to get to this tomorrow or Friday, I'll post up pics when I do. Thanks for all the suggestions gents.

 

Fixed. Just need to ream the holes out a bit larger. Buggered the first hole when the hole saw decided to go wonky. Had to weld it up and re-drill with a drill bits.

 

Whats the backside look like? There is a TON of stress at that area, I would still be inclined to back it up.

 

Not as pretty but strong enough I believe.

 

On my phone it looks like the inside of your patch protrudes beyond the rail?

 

The welds look like you got good penetration but I would still be worried about cracking around the perimeter if the patch

 

way mo better

 

Couldn’t get the grinder in there to smooth it out all the way. You’re seeing the edge of a weld. Material is about .020 over thickness of the frame.

 

Good deal. Damned old eyes and phones.

 

As sloppy points out, the 19" area from the motor mount to the middle crossmember is a weak area on the Model A frame, especially on the drivers side. It's only a "C" channel with no bracing. The battery box is located in that spot, combine it with the drivers weight and bad roads from the 1930's can cause it to sag. I just trued a 1929 frame with a body shop Car-O-Liner, chains and 20 ton bottle jack that had about 3/8" sag. Do it now and you won't have issues with door and hood alignment.

 

There is no sag in the chassis.

 

Nice repair job. Reinforcing that frame in that area is a great idea. This is a product I developed a few years ago before I retired. For years people would go to the bottom of a can and scoop out the pigment to fill in pitting and pinholes . It's in a paste form , you can squeegee it on like body filler or you can brush it. It can be reduced and sprayed . This would be a good filler for non-stress areas on a chassis and on sheet metal

 

Not to be critical of your efforts. It looks to me like there is not
total weld penetration on the verticals shown on the inside of the chassis. It may just be the photos or my old eyes. If it is not completely welded through a small burr on an end grinder
could give a shallow trough that I would weld from the inside and then grind flush to insure adequate strength. I do think you chose a proper repair method.

 

While it may be possible to add a fishplate to the inside of the rail (only a complete mock up would tell that tale), you've taken steps to make that repair as strong and long lasting as possible: RADIUSED CORNERS on the patch! It makes my skin crawl (and makes me dubious of some of the structural repairs I see) when someone cuts square cornered holes in a panel (frame or body) and lays in the weld, grinds smooth, and calls it good. Square corners are stress risers, and no amount of welding changes that... take a look at any high stress fabrication and you'll see radiused corners.

 

An old English machinist once told me that square corners on anything are no good. Case in point, the de Havilland DH 106 Comet. Metal fatigue at square windows caused in flight structural failures.

Them suckers should be good. Made sure to get good weld penetration all the way around. Time will tell.

 

Something you may have picked up on, when drilling holes, the bits often don't make round holes when drilling thru thin metal. By that, I mean probably less than 1/4 thick or more. The problem is that the point protrudes thru into the air and no longer locates the center of the bit. You can get better results if you slowly increase the size of the holes with multiple drillings. Also, slower is usually better than fast with drill speeds as you increase hole size......although as you begin to break thru to the other side, a quick burst of speed can help keep from grabbing. Best is if you have some reamers (adjustable ?) but most people don't. Anyway, its kind of a touchy feely thing and you might want to drill a couple holes in some scrap and just take notice of what happens when you break thru each time. The thinner the metal you are drilling, the less likely the hole will be round. Drill a thin .030-.060 piece of sheetmetal with a 1/2" drill bit and look at the hole it made. Anyway, just a tip for drilling holes in the future............

One other thing, I would weld/reweld the inside portion of the patch. It looks like it could start cracking later because it appears to have an unfilled area around it. This is where most frames sag so you don't want any low groove looking area to serve as a starting point for a crack. To use airplanes as an example, cracks often start where the surface has an imperfection. Good luck with your project.

 

I am no one to comment, you are doing a good job but take note of the advice of others will only improve your endeavors.