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Straightening a cast aluminium cover ? #724040 02/02/18 2:55 pm
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ferretjuggler Offline OP
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I seem to have an ever growing collection of dented primary covers.
The perceived wisdom seems to be that due to "work hardening " none of the damage can be bent back into shape.
Any attempt to simply knock out the dent will quickly result in breakage or even a shattered casting.

But I did read somewhere that it's possible to anneal cast aluminium and work it to a point.
Allegedly quite a difficult thing to do but not necessarily impossible.
I really don't have the expertise to know if this is practical or just theoretical.
Does anyone know the exact details of how to do this ?
I think I can remember a temperature of 300°C mentioned, but I can't remember if it was slow cooled or quenched.

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Re: Straightening a cast aluminium cover ? [Re: ferretjuggler] #724063 02/02/18 6:29 pm
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Blown Income Offline
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This is the procedure I use for annealing aluminum which works really well.

1) Oxy-Acteylene torch outfit
2) Fire up torch with only the acteylene, soot the area to be annealed with the smoke from the flame.
3) Re-adjust torch with Oxygen to correct burn flame and wave flame over the sooted area until the soot is gone.
4) Once soot is gone the aluminum is now upto annealing temps and can be worked w/o a high chance of cracking.
5) Repeat as needed.


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Re: Straightening a cast aluminium cover ? [Re: Blown Income] #724066 02/02/18 6:52 pm
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Originally Posted by Blown Income
4) Once soot is gone the aluminum is now upto annealing temps and can be worked w/o a high chance of cracking.
No! Aluminum is a material that is "hot short," which means that it has a high tendency to crack if bent when it's hot. If you're lucky the casting has a composition that allows it to be annealed, but it has to be back at room temperature to bend it or it very likely will crack.

Re: Straightening a cast aluminium cover ? [Re: ferretjuggler] #724073 02/02/18 7:48 pm
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Andy Higham Offline
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Some grades of aluminium stay relatively soft, others are always brittle even after annealing, it all depends what went in the melting pot.
My metalwork teacher st school showed me an indicator for annealing aluminium, soap. Rub soap on the metal and heat it, when the soap turns brown the temperature is correct


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Re: Straightening a cast aluminium cover ? [Re: ferretjuggler] #724085 02/02/18 9:08 pm
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gavin eisler Offline
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I straightened out my 71 air box , it was cracked and bent, similar to the soot /acetylene method , I used soap, rub ordinary washroom soap bar ( I used Cussons Imperial leather, I like the smell) , around the area to be heated, i used a propane torch and heated till the soap turns brown/black ( annealing temp), when cooled I used two clamps and a block of steel under the crack to apply pressure and bend to straight, Rinse and repeat till satisfied ,I found a little overbend was needed to allow for spring back. After strightening , the crack was ground out and welded, after clean up it was dead true with no sign of the repair.
Should work on primary cases the same way. Handy for straightening or bending Alloy levers as well. I have also used this technique to straighten clutch levers and bend brake pedals . Dont expect it to straighten all the way in one go, the alloy work hardens quickly, little and often is best.

Last edited by gavin eisler; 02/02/18 9:10 pm.

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Re: Straightening a cast aluminium cover ? [Re: ferretjuggler] #724099 02/02/18 11:49 pm
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ferretjuggler Offline OP
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Thank you all.
So there's no quenching required.
Any idea what sort of temperature we are talking about?

The "hot short " thing sort of ties into my experience.
Point taken about work hardening and having to re-anneal several times

Re: Straightening a cast aluminium cover ? [Re: ferretjuggler] #724114 02/03/18 2:58 am
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Jerry Roy Offline
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Just to add fuel, go to BING or Goggle and enter annealing cast aluminum, or a variation thereof. Spend an hour and get more info than you really want. T.M. Technologies is a good source, although he mostly talks about aircraft grade aluminum . <http://www.croucher.us/water-quenching> has a chart at the bottom that covers the various alloys of cast aluminum, so you are stuck with making a WAG as to what kind of alloy your cover is.
Personally, I use the soot and torch on cast primary covers, with a cold water quench, which seems to soften the aluminum. I don't heat the whole thing, just around the affected area. Placed on a sand bag or thick rubber sheet, (think tire tread), some gentle rapping with a plastic or rawhide mallet can move the metal, and if it seems to resist, try another round of soot and heat. Too much, as MM says, will leave you with some pieces on the floor.

JR

Re: Straightening a cast aluminium cover ? [Re: ferretjuggler] #724128 02/03/18 12:50 pm
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gavin eisler Offline
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Quenching might help on a big piece just for handling sake. , i let my bits air cool , I dont think there is a Critical Cooling Rate for Al, unlike some steels.
10 secs with google.
https://www.thermtech.net/full-annealing-1


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Re: Straightening a cast aluminium cover ? [Re: gavin eisler] #724628 02/07/18 12:07 pm
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jaycee Offline
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several years ago i was perusing a goodson catalog. they sell a variety of engine reworking tools. on the cylinder head section they had a fixture for straightening warped aluminum cylinder heads. the idea was to heat the head in an oven (i think 500 degrees ,but dont quote me) with the head clamped up in the fixture for "x" period of time repeat as required. seems like a fella could do the same thing at home with some steel plate

Re: Straightening a cast aluminium cover ? [Re: ferretjuggler] #725055 02/10/18 6:53 pm
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ferretjuggler Offline OP
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I pulled a heavily repaired set of A7 crankcases straight using a thick drilled steel plate and lengths of all thread.
Took about five sessions in the gas oven IIRC.

Maybe that is the answer.
I need to find some thick plate from somewhere.
Spacer block under primary cover then pre-tension the all thread ?
Repeatedly roast in the oven re-tensioning as it yields ?

Well that's the theory anyway.

Re: Straightening a cast aluminium cover ? [Re: ferretjuggler] #725081 02/10/18 9:40 pm
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Irish Swede Offline
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Scrap yards in industrial districts often get pieces of thick steel plate.
They usually sell it by weight. Try to find a piece about the size and thickness you need.

Re: Straightening a cast aluminium cover ? [Re: ferretjuggler] #725147 02/11/18 7:32 am
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jaycee Offline
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ive never done it but you know there might be some "youtubes" inre to the cylinder head straightening that might give you some ideas. but that gradual approach seems like a prudent go. how much is it out? and how the devil did it get that way?


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