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bonnet stiffening?
02GF74 - 2/5/06 at 11:47 AM

I have notice that my bonnet can be flexed by pressing it down in the centre and wondering if it camn be stifferned up? As the ali gets warmed up from the engine below, the metal will expand so will be a loser fit so may flop about?

I am thinking of fitting a couple of right angle ali piece beneath using the existing bolt holes - goo idea or not?

(when I drove it up and down the garage, I seem to recall the top vibrating quite badly on take up of drive).

DIY Si - 2/5/06 at 09:03 PM

I'd suggest a couple of ribs running across the inside. It's what i'm planning to do if mine turns out a bit wobbly. Unsure as to bolt or araldite them in though.

Chippy - 2/5/06 at 10:40 PM

I have the same problem, have been thinking of putting in a couple of fibre glass ribs, but not sure if it will adhere to alloy. Will have to check with CFS. atb Chippy

DarrenW - 3/5/06 at 10:05 AM

Could you make / obtain some strips of ali (stiffening ribs) and bond these to the underneath in strategic locations? Im sure bond&seal or sikaflex will bond them securely.

Peteff - 3/5/06 at 10:53 AM

If you use 16g it should be thick enough not to need reinforcing when the bonnet clips have it under tension. Aluminium shouldn't expand due to engine heat, it is very good at dissipating heat.

02GF74 - 4/5/06 at 10:26 AM

quote:
Originally posted by Peteff
If you use 16g it should be thick enough not to need reinforcing when the bonnet clips have it under tension. Aluminium shouldn't expand due to engine heat, it is very good at dissipating heat.


hmmmm..... don;t know what temp bonnet gets to, but guess around 80 C; there have been posts sayingthat the exhaust near the block gets up to red heat ~600 C so that will heat up the bonnet quite a bit - and this is what worries me.

DIY Si - 4/5/06 at 07:26 PM

Go for belt and braces. Put strenghening ribs in and wrap the exhaust manifold. It keeps a huge amount of heat inside and away fom the engine bay.

Simon - 4/5/06 at 08:25 PM

That's not the prob I have. If I was about 3 stone lighter, I reckon I could stand on mine

ATB

Simon

[Edited on 4/5/06 by Simon]

MikeRJ - 8/5/06 at 03:39 PM

quote:
Originally posted by 02GF74
quote:
Originally posted by Peteff
If you use 16g it should be thick enough not to need reinforcing when the bonnet clips have it under tension. Aluminium shouldn't expand due to engine heat, it is very good at dissipating heat.


hmmmm..... don;t know what temp bonnet gets to, but guess around 80 C; there have been posts sayingthat the exhaust near the block gets up to red heat ~600 C so that will heat up the bonnet quite a bit - and this is what worries me.


I think you are worrying about nothing, the actual amount of expansion you will see will be very small. The coefficiant of expansion of aluminium is 23.86 x 10-6°C-1, most alloys will be simmilar. Not sure how wide the alloy in a standard F27 bonnet is but taking a guess of 150cm and assuming the bonnet fits correctly at 25C:

1500*23.86 x 10-6*(80-25) = ~2mm

If the bonnet really is getting much hotter than 80C then more ventilation is required! That high a temperature will kill wiring and electrical components (especialy batteries) very quickly.