How can I harden my aluminum bonnet where it was annealed by a fuel fire in the engine bay?

An area as big as a 17inch pc monitor (looking around for a comparison) at the front end of the bonnet is now as soft as plasticene.

I only wish I'd been able to anneal the rear panel to this standard when I needed it..


tia
Dave

From my experience with annealing ali, you might have to Solution heat treat it to get it age hardened. With annealing you typically have to work harden it, so unless you can find someone with a large oven to stick it in you could be buggered. Mind you if you stick it in an oven it might not come out the way it went in though.

There could be a way of SHTing the area affected with a blow torch or something like that. How you do it though, I don't know. Could be worth looking into though.

Chris

Thanks Chris,

I'd never heard of that. So armed with a little knowledge (a dangerous thing) I then found this..

http://www.aluminium-components.hydro.com/alloytemper.htm

Artificial ageing (if that's what is needed) does seem to be very difficult. Is that what you described but by another name? Baking for 4-10 hours at a temp between 160 and 190 then slow cooling?

Look like SHT is different.

As they describe it SHT is almost exactly what happened to my bonnet. High temp, rapid cooling resulting in the soft area.

Fire ignited in an air filter, burned under the bonnet for a while, then big cold wet cloths were thrown over the bonnet until a CO2 extinguisher was found, bonnet removed and the fire was extinguished (SHT happens!?)


Anyhow, either way I'd have to fold it pretty small to fit in my oven.

I guess I'll just live with it until I make another.. the car's back on the road anyway


Dave



[Edited on 14/6/03 by Dave Ashurst]

Hi,
Couldn't you get one of those gas powered space heaters and use it to heat the bonnet up uniformly to a fairly high temperature by placing it right in front of the heater. Then use localised heat from a propane torch played over the affected area in circular motion to heat that area up to the "magic" temperature. Then slow cool by moving the bonnet farther from the space heater over a period of time.

Fairly non-scientific but worth a try if the only alternative is to make another bonnet.

HTH,
Craig.

Hi Craig,
Good plan, worth considering.
I'll see how expensive it would be compared to the cost of a new bonnet since I don't have free access to a space heater. Also it would difficult to maintain the 4 to 10 hours at that temp at home. Couldn't do it in the garage. Perhaps make a temporary oven in the back yard from loose bricks.

Alternatively our old iron (as in ironing board) gets quite hot. Perhaps I can apply enough heat locally if I leave that on... might try that first.

New bonnet might not be too difficult.

cheers
Dave

sht requires heating to around 500 odd degree's for around 30 minutes then quenching it in water, after an hour the metal returns to it's origonal makeup and should be hard again. Like you say though, you need a rather big oven to do it. You could try and find a ali workshop around you (aircraft one's are great, I have westlands just down the road and a mate work's in the sheet metal bay, lets me cook things in his oven) but they might charge you an arm and a leg to do it.

I think you would be better off just making a new bonnet -

chris

Hi Chris
I think I'd be better off with a new bonnet too - already started it
cheers
Dave

Hiya,

What are you doing with the old bonnet??? Having just stuck my carb on the engine, I've discovered that the filter will stick up above the bonnet line and having a soft bit of ali around that point would make it easy for me to form a bonnet vent!

So, to get to point, do you want to sell it????

Cheers
Chris

Chris,

Later yes (if it will fit your setup) but not yet, sorry. I'm still using it. Also it might not be to your taste - I won't be offended! -
I'd already modified it a bit with a louvred patch over the old downdraft opening. I was just too tired to make a new bonnet when I changed the carbs.

It looked like this before the fire. (Spot the homebase alloy louvre!):




And last year it looked a bit like this:




Anyway I have to get the new grp nosecone made before I can finish the new bonnet and Triton tell me it will take one or two weeks from order. They offered to make a close colour match to the old one and I need to get myself over there with a sample before they can start. I have to find a quiet afternoon and slip away from work early and we're very busy these days. So might be some time.

I'll drop you a line in due course. Could be up to a month or six weeks from now. Then if you're interested we can arrange a pick up.

(But please don't ask me to post it!!)

Dave

nice one mate, a month to six weeks will suit me fine! In wimbledon for the next two weeks so won't be able to do anything to the car (gutted!) Give me a shout when your ready, and how much you want for it.

Just remembered. Is your's a book locost? If so it should fit fine, might need a bit of adjustment but nothing a small hammer won't fix!


Cheers
Chris

[Edited on 21/6/03 by flyingkiwi]

It's a book locost. Note that the fit of the bonnet also depends on the scuttle and nosecone. They are what tend tend to differ, so you might want to compare measurements.

I'll measure the rise and the length of the front and back bonnet edges for you.....

Cheers
Dave

[Edited on 22/6/03 by Dave Ashurst]