Wildgoose Chase Moto Guzzi

General Category => General Discussion => Topic started by: Big Block Jon on October 01, 2012, 12:16:37 PM

Title: Sraightening a bent aluminum part.
Post by: Big Block Jon on October 01, 2012, 12:16:37 PM
Any advice on bending (or unbending) cast aluminum?   The bracket that holds the foot pegs and rear of the exhaust on my 1000s has been bent inwards.  I am unable to find a replacement (part 284435601) at any of the usual suspects, or reboot Guzzi spares in France, which was kind've my last hope.

So I'm going to have to try and straighten the bracket out.  I'm finding conflicting info on whether aluminum should/can be heated in order to straighten the part, and if so, how much.  This is complicated by the fact that it may be an alloy or it may be the straight stuff.   Intuitively it seems that heating it a bit with a torch or over a stove (oven?) might make it more malleable, but some sources suggest that this is (a) hard to do without catastrophic failure or (b) simply won't lead to it being more malleable.   Anybody have knowledge?
(http://s11.postimage.org/ykmgdyhvj/bracket284435601.jpg) (http://postimage.org/image/ykmgdyhvj/)



(http://s18.postimage.org/k0l006oqt/Bent_284435601.jpg) (http://postimage.org/image/k0l006oqt/)
Title: Re: Sraightening a bent aluminum part.
Post by: LeRoy on October 01, 2012, 01:09:17 PM
Consider widening your search to include the silver/gray version of the part: 28443560. The extra digit "1" at the end of the part number you quote seems to indicate the color black.

If you'd consider a silver part, have you called Harper's? The part number 28354460 shows up on their site in a Google search.

http://www.harpermoto.com/index.php?dispatch=products.search&features_hash=P1&variant_id=1&page=356
Title: Re: Sraightening a bent aluminum part.
Post by: Andrew Thomas Evans on October 01, 2012, 01:26:25 PM
Aluminum melts at or around 1200f, and doesn't show heat up until it melts it also doesn’t self anneal as it sits which is why is cracks easier and doesn’t last as long in some applications as steel.

How I did it back in college for an art class, is that Flux starts to melt at around 1000'ish so I covered the aluminum in flux and took the heat off once it started to get clear. From there it was pretty easy to get the metal to do what I wanted, and a person could raise a bowl or something pretty fast with aluminum if they wanted, it gets really soft and moves around a bit.
I didn't have to heat treat anything or make sure it was hardened as my application didn't call for that - but it wouldn't be too hard to work harden it piece after it was straightened.  I’d just pound on it a bit, not hard enough to move anything, but enough to put some pressure on it.


But then again maybe it’s an alloy that doesn’t like to bend or heat up and you’d just end up cracking it or something…
Title: Re: Sraightening a bent aluminum part.
Post by: grebmrof on October 01, 2012, 01:56:55 PM
Could there also be the same piece or similar from another Tonti bike - SP, Mille, T-3, T-5, etc that may be easier to source and be a suitable replacement for you 1000S piece?  Just a thought. 
Title: Re: Sraightening a bent aluminum part.
Post by: LeRoy on October 01, 2012, 02:08:44 PM
Could there also be the same piece or similar from another Tonti bike - SP, Mille, T-3, T-5, etc that may be easier to source and be a suitable replacement for you 1000S piece?  Just a thought. 

As a matter of fact, I think the Le Mans IV and V used the same, or very similar, parts.
Title: Re: Sraightening a bent aluminum part.
Post by: Tom on October 01, 2012, 02:24:15 PM
I have the 1000S sitting next to the LM IV.  I let you know in a few minutes.  That's next to the T3.  The SP1000 NT is 3 thousand miles away.
Title: Re: Sraightening a bent aluminum part.
Post by: Tom on October 01, 2012, 02:45:46 PM
Okay.....Just went downstairs.  LM V, LM IV, Strada and !000S have the same crisscross/honeycomb style mounts for the foot-pegs.  T3 has different style more of a straight rod but mount to the same holes.  Probably anything else that has is a Tonti frame and no floorboards would fit.  Hope that helps.
Title: Re: Sraightening a bent aluminum part.
Post by: gearman on October 01, 2012, 03:55:10 PM
I would say you can cold bend it back. I would not heat it because it doesn't act like steel.I remember once heating al with a torch when all of a sudden it broke in half. :o
Title: Re: Sraightening a bent aluminum part.
Post by: guzziownr on October 01, 2012, 06:11:57 PM
1991 Lemans


(http://s13.postimage.org/wuueazpgj/lemans_1000.jpg) (http://postimage.org/image/wuueazpgj/)
Title: Re: Sraightening a bent aluminum part.
Post by: Tobit on October 01, 2012, 07:25:15 PM
Curious that Lafranconi's of the era that were said to fit 1000s were not the same part for the LMIV.  The footpeg brackets were different.  That's what I remember anyway.  Good to hear otherwise now from side-by-side comparisons. 

Anyway, if that were my part and I wanted to bend it back, I'd strip the finish off to reveal any cracks, then put it in a hydraulic press and work if very slowly.  It may be more pot metal than alloy.  I bent one on the LMIV and it snapped off when trying to bend it back with a rubber dead blow hammer.

 ;D
Title: Re: Sraightening a bent aluminum part.
Post by: Atavar on October 01, 2012, 10:53:14 PM
I have always been told that once a cast aluminum part is bent it will never be as strong again.  I am in no way a metallurgist so I do not understand the why's and wherefore's.  the other bit I was told (might be urban legand) is that aluminum has virtually no plastic stage when heating.  That is the stage with iron where if you heat it enough it gets softer and bends easier.  Apparently with aluminum there are just a few degrees of temperature between solid and liquid.

If there are any metallurgists out there i would greatly appreciated getting educated on this with the real story.
Title: Re: Sraightening a bent aluminum part.
Post by: Big Block Jon on October 01, 2012, 11:59:24 PM
Thanks for all the help, everybody!

Quote
Apparently with aluminum there are just a few degrees of temperature between solid and liquid.
   This fits in with the warnings that some sources are giving about the dangers of heating, although Andrew Thomas Evans is telling us that, at least with the pure metal, the temperature range between phase changes is much greater than that.

I was aware that the the Le mans (le manses?) from about 86 onward have the same part with a different finish, so I've been looking for that as well, without success.  I didnt realize the part number was different. Thanks LeRoy.
Title: Re: Sraightening a bent aluminum part.
Post by: averb on October 02, 2012, 12:08:53 AM
One, the part is definitely an alloy, nothing is made from straight Aluminium, can't remember if it is too stiff and brittle or soft and squiggy. Two, if you google "bending aluminium alloy" there are a few conflicting methods posted around the place. My reading lead me to think that you may want to gently heat the part to anneal it but no way do you want to try and heat it enough soften it. The other thing noted is that the part may well break and even if it doesn't it will be significantly weakened.
Sorry I can't bring any more positive comments

Steve
Title: Re: Sraightening a bent aluminum part.
Post by: mtiberio on October 02, 2012, 06:22:36 AM
aluminum can definitely be straightened. it takes a deft hand with the heat. I personally never go past a 95% repair.
Title: Re: Sraightening a bent aluminum part.
Post by: Mike Tashjian on October 02, 2012, 07:25:18 AM
I have had good luck bending it back the same way it got bent.  Hitting it with a mallet and or protecting the piece with a block of wood to save the finish.  No luck with the hydraulic press.  And there are some things that will just not respond to any method and just fail as soon as they are bent.  Locate a replacement first and things seem to work out. Try bending it first and be out of commission when it snaps.  Murphy's Law.  Mike
Title: Re: Sraightening a bent aluminum part.
Post by: Antietam Classic Cycle on May 27, 2015, 09:42:56 AM
I find myself in the same situation as Big Block Jon - the right peg carrier is not only bent inward but is also twisted slightly. Any sage advice (in addition to the above) on how to straighten mine?

Search for a replacement has proved fruitless thus far. Stein-Dinse has the left-side, but not the right.  :(
Title: Re: Sraightening a bent aluminum part.
Post by: Chuck in Indiana on May 27, 2015, 10:13:08 AM
Is that a cast part, Charlie? I'm assuming it is, which makes it tough. Aluminum age hardens.
Here's what I would try. You'll have to anneal it, which takes 800 degrees. Fire up your acetylene torch, no oxygen, and make your part black with it.
(http://i29.photobucket.com/albums/c294/elwood59/Lario/08-009_zpss6qpguvr.jpg) (http://s29.photobucket.com/user/elwood59/media/Lario/08-009_zpss6qpguvr.jpg.html)
Then, adjust to a neutral flame, and *carefully* burn the carbon off.
(http://i29.photobucket.com/albums/c294/elwood59/Lario/09-010_zpsrmdr7uou.jpg) (http://s29.photobucket.com/user/elwood59/media/Lario/09-010_zpsrmdr7uou.jpg.html)
What you are trying to do is have the whole part of what you are trying to form at 800, so keep the heat moving constantly. When it's hot enough, quench it in water. Just drop it in a bucket.  :o I know, you don't do that with steel, but this isn't steel.  ;D
If that doesn't do it, you gave it your best shot...
For instance, this hard aluminum piece would just break if you tried to bend it without annealing..
(http://i29.photobucket.com/albums/c294/elwood59/Lario/11-012_zpspogyrwsd.jpg) (http://s29.photobucket.com/user/elwood59/media/Lario/11-012_zpspogyrwsd.jpg.html)
Good luck!
Title: Re: Sraightening a bent aluminum part.
Post by: leafman60 on May 27, 2015, 10:22:42 AM
If it's bent beyond comfortable use, why not try to straighten it?

I've straightened cast aluminum successfully. 

An entire industry has developed around straightening cast aluminum auto wheels with a bent rim.  Don't try to heat. Hydraulic pressure or a judicious rap with a wooden mallet is what I'd try.
Title: Re: Sraightening a bent aluminum part.
Post by: Triple Jim on May 27, 2015, 11:02:52 AM
That's a very minor bend, so I wouldn't hesitate to put it in the press and carefully bend it straight.  The argument against annealing it first is that it would then probably need to be heat treated to prevent much easier bending in the future.  Just my opinion though, as they say, YMMV.
Title: Re: Sraightening a bent aluminum part.
Post by: canuguzzi on May 27, 2015, 12:38:00 PM
If it's bent beyond comfortable use, why not try to straighten it?

I've straightened cast aluminum successfully. 

An entire industry has developed around straightening cast aluminum auto wheels with a bent rim.  Don't try to heat. Hydraulic pressure or a judicious rap with a wooden mallet is what I'd try.

 :+1

Trying to slowly bend cast aluminum is generally a bad idea. The fast manipulation of the part is the way to try it.

Don't heat it. First, you need to have a good and accurate way to measure the heat of the aluminum. It is far more hassle than it is worth and is unlikely to work. If you can risk breaking it, go for it.

For the typical home shop, access to hydraulic presses isn't usually an option. You likely have a vise, a hammer of various kinds and so on. Don't make it a 9 day bicycle race. If it can go into the vise, secure it and then as stated above rap it nice and good to bend it. Be prepared for it too crack.

For thinner aluminum parts, you don't need heat either. A quick bending effort is what works really good. Aluminum work hardens very quick so you get one, maybe two chances with thin stuff.
Title: Re: Sraightening a bent aluminum part.
Post by: Sasquatch Jim on May 27, 2015, 12:42:15 PM
 Some aluminum alloys can be annealed by heating to 800 to 1,000 degrees and quenching in water.  That hardens steel but anneals aluminum or copper.
 If it breaks , you are no worse off than you were when you started.
Title: Re: Sraightening a bent aluminum part.
Post by: kirb on May 27, 2015, 02:49:56 PM
For something completely different...would it be possible to refab the part out of a laser cut piece? CNC piece, or fab/weld some things together to replicate the part?

It looks fairly flat with the peg brackets on it. Would not be too hard to replicate it and have it laser cut or CNC or both.
Title: Re: Sraightening a bent aluminum part.
Post by: Antietam Classic Cycle on May 27, 2015, 03:43:29 PM
For something completely different...would it be possible to refab the part out of a laser cut piece? CNC piece, or fab/weld some things together to replicate the part?

It looks fairly flat with the peg brackets on it. Would not be too hard to replicate it and have it laser cut or CNC or both.

It's a fairly intricate part. Replicating it would be costly no matter how it was done.

(http://www.stein-dinse.biz/images/product_images/popup_images/28446060.jpg)
Title: Re: Sraightening a bent aluminum part.
Post by: malik on May 27, 2015, 04:00:59 PM
Bring on cheap 3D copiers! Perhaps in a few years there'll be one in every second garage - copy the part at home, send the file out to be made up.
Title: Re: Sraightening a bent aluminum part.
Post by: normzone on May 27, 2015, 04:08:26 PM
Mike is correct. If you buy an available replacement and then attempt to straighten the original, it will work flawlessly.

If you DON'T purchase a replacement, it's guaranteed to break during the attempt, and suddenly no replacement will be available.
Title: Re: Sraightening a bent aluminum part.
Post by: canuguzzi on May 27, 2015, 04:13:47 PM
Some aluminum alloys can be annealed by heating to 800 to 1,000 degrees and quenching in water.  That hardens steel but anneals aluminum or copper.
 If it breaks , you are no worse off than you were when you started.

If it breaks it is completely unusable. Pretty sure that qualifies as FUBAR.

Maybe space the part from the other side to account for the bend and at least gets things somewhat aligned? Might not be real pretty but might be functional until a better solution is at hand?
Title: Re: Sraightening a bent aluminum part.
Post by: Triple Jim on May 27, 2015, 04:27:40 PM
I don't know... if it breaks, it's still most likely weldable.
Title: Re: Sraightening a bent aluminum part.
Post by: atavar on May 27, 2015, 04:28:59 PM
Another old timers trick is to rub bar soap on the part before heating.  When the soap turns black the aluminum is the right temperature for working.  Don't do this with a critical part you don't have spares for, it is as likely to break as bend.  
Title: Re: Sraightening a bent aluminum part.
Post by: beetle on May 27, 2015, 07:35:12 PM
What leafman60 said. It bent quick, so straighten quick. No heat. I've had to straighten the cast brake lever on my Griso twice.
Title: Re: Sraightening a bent aluminum part.
Post by: boatdetective on May 28, 2015, 11:33:41 AM
Remember that the part is cast, not wrought. Totallyy different grain structure. A little research. With metals sites will givecrecommendation s on cold formability of cast aluminumvalloys.
Title: Re: Sraightening a bent aluminum part.
Post by: Muzz on May 28, 2015, 05:21:51 PM
I have had good luck bending it back the same way it got bent.  Hitting it with a mallet and or protecting the piece with a block of wood to save the finish.  No luck with the hydraulic press.  And there are some things that will just not respond to any method and just fail as soon as they are bent.  Locate a replacement first and things seem to work out. Try bending it first and be out of commission when it snaps.  Murphy's Law.  Mike

 :+1
Breva fell over in gravel and badly bent the gear change. In the middle of nowhere it was all or nothing; couldn't change gears either way.  Used a modified method of above and heaved a big sigh of relief when it worked. ;D

Used above system many times since and it has always worked. (subject of course as to what is actually mixed in with the aluminium.)
Title: Re: Sraightening a bent aluminum part.
Post by: jbell on May 28, 2015, 11:55:41 PM
Well, Big Block, this thread should clear it up for you.   :BEER:
Title: Re: Sraightening a bent aluminum part.
Post by: tris on May 29, 2015, 01:46:11 AM
Another old timers trick is to rub bar soap on the part before heating.  When the soap turns black the aluminum is the right temperature for working.  Don't do this with a critical part you don't have spares for, it is as likely to break as bend.  

 :+1  What I was going to write

IIRC if it goes yellow its too hot and you should desist from heating it immediately or risk a puddle of shiny metal on the floor  ;-T