Removing small dent in primary cover

I would like to remove a small dent in an aluminum primary cover.
It looks like a brake pedal slid up the cover, making a shallow dent 1/16 deep, 1/4 wide, and 1 inch long. Sorry, pictures don't really capture this.
I could leave it.
But I would like to try tapping it out.
Probably using a wooden hammer on flat metal surface.

I think it might be worth heating the dented area enough to anneal. Then let it cool, and bump it when it is cold.

Anybody have any luck doing something like this?
Or am I just going to crack the casting, making it worse than it is right now??

Stephen Hill
Victoria, BC

Use a piece of CLEAN plywood to set it on, that being laid on the concrete floor, find a bar, rod or the like 1"D. x 6-12" long, (aluminum preferred) with a flat face, use a 2 lb. steel hammer to hit it from inside. Start easy, slow, keep checking, work up with intensity, but you'll probably not need much. Annealing not required for shallow movement. :mrgreen:

I had a small gouge that I ground, sanded and polished out, but it wasn't dented enough to planish. You have to be very careful with heat and alloy because right after it gets hot enough to get soft, it gets weak enough to collapse. use the flat face of a large ball peen hammer with the cover laid on a chunk of hardwood for a dolly.

I haven't tried to remove dents from a primary cover, but I was told some years ago that if you heat alloy to the point that solder melts when held against it is hot enough to allow some movement without being overly hot. Not scientific I know, but but pretty much everyone has some solder in their shed and it works really well as a measure. I've done it quite a few times on heads with bent fins (as well as on alloy barrels). Obviously in such cases it really only helps on the very top ot bottom fins where you can apply heat carefully/directly.

When annealing aluminum, the temp indicator I use is a stripe of bar soap on the side not heated. When the soap stripe turns black you're hot enough. Obviously the heat must be applied gradually in an area, not in a spot & a relatively gentle heat source such as propane or MAP gas is appropriate, not acetylene. After heating you can let it air cool or quench...makes no difference with non-heat hardening metals such as aluminum & copper.

A nice big arbor press might do it safely. If hammering make sure whatever you're hitting conforms to the shape you have on the inside cover, then hit that with the big ball pein hammer.

The bar soap trick works - you can just rub it over the side you are heating, when it starts to go black - stop with the heating already.
Another method, in case you don't use hard soap, is to keep rubbing a piece of wooden stick across the area you are heating , once that scorches, you're done. Don't heat too big an area, but don't be afraid to re-anneal after hitting it for awhile - it will work harden.
I guess you could buy temp crayons and use those - if you know the annealing temp of the particular grade of alloy you are working with.

Most people hit too hard when trying to knock out dents. The excess force stretches the metal making it a relatively skilled job to shrink it back. Start from the outside and work in. Be patient, it won't "pop" back unfortunately.

I would use a metal workers sandbag. Mine are stout leather full of sand. I have no idea how much they cast and if it would be worth getting a proper one. You could easily make one with a strong sack and some sieved sand - you don't want to impress rock shapes in there, or any other textured surface.
The striking tool would be a bossing mallet - pear shaped hardwood head on a stick. The nice round shape won't put moon shapes in your cover.

Good Luck.

I did a google search on bending/shaping cast aluminum, and the general advice seems to anneal it first. Then, after you anneal it, the advice divides on whether you should bend it hot, or cold. Bending it cold after annealing seems to be the best answer I could find. And re-anneal between bending efforts if needed.

I didn't anneal the cover first as I was afraid of warping it. I laid the cover over plywood resting on an anvil, hollow up, and used the rounded end of a ball pein to bump the worst of the dent out. Then I sanded down the remaining depression, fairing out the removal to retain the shape.

Clearly this is a game of chicken: the more you bump it, the smaller the dent, but the greater the chance of cracking. The less you bump it, the move you have to sand off.

I ended up with no dent and a very small groove which I can live with. I think if I tried to pick this out the aluminum would have cracked. Or if I sanded it out the cover would be eggshell thin in that spot.

Stephen Hill