MGB Register Forum

Has anyone had experience of fibreglass bonnets ?

My steel bonnet had some rust bubbles to the front corners and leading edge which I wanted to tackle. Its just about the only panel which wasnt replaced by the previous owner and is the only panel with any corrosion. I removed the bonnet and took an angle grinder to it cutting away the top metal skin in both corners and some of the front edge. Though I have modicum of metalwork repair experience and access to a mig welder im looking at this now wondering how im going to make and weld in small repair panels with the right curve to match the bonnet plus sharp bends for the front and underlip.

In short im trying to decide whether its worth repairing this or investing in a fibreglass bonnet which would also have the advantage of being rather lighter.

The bonnet is tricky to repair, mainly due to the double skin construction. But if you have it detached on a trestle and take your time it is quite feasible. Admittedly I used filler to get the final shape after cutting out all the rust, but definitely worth it I think
Ian F

You could do the repair using several pieces. One for the curved top. Then one for the front edge, and one for the underlip.

Alternatively, aluminium bonnets are always coming up in Ebay and were standard until 1970/71.

But learn from my mistakes and do NOT get a cheap modern repro. Whatever tooling they are using at the factory in Taiwan does not have the correct curve to meet the grille properly. Mine has gaps at either end because the curve is too flat.

As Tom says, use several small pieces to build up the repair. Easy to do with a MIG welder. I did start with a basically sound bonnet of course, with just a few holes and rust in the corners. If it had been significantly worse I might have taken a different course.
Aluminium bonnets in good condition would be an excellent choice, but if needing repair that could be tricky.
GRP panels also often require quite a bit of work to get a good fit, but I have no experience of MGB bonnets in GRP. Maybe someone here has fitted one?

Ian F

You really need access to an English Wheel to get the double curvature right, and the raised part in the centre that lines up with the MG badge on the grille will still be a problem. Now the show season looks like it will go ahead this year, find a bonnet that is in good condition and use that. Aluminium bonnets have their own problem as only the skin is aluminium and it reacts with the steel framework. They also dent very easily.

You might consider using your bonnet frame (if possible) and buying a fiberglass MGC racing bonnet (the one without internal frame) - then grafting the bulges to your bonnet. I am considering doing this.

If that's your kind of thing of course....I think MGC bonnets do really look great and it's the only way to get a decent one without breaking the bank. The fiberglass braced bonnets still don't have the strength of steel.

Thanks for all the advice. I found some galvanised sheet of the right thickness and made repair sections for each side for the top, front edge and underlip as suggested. An angle grinder took care of removing the galvanised coating from the top surface and I formed the curves with a panel beating hammer and a curved dolly. After welding the 6 pieces in place i dressed down the welds and cleaned the metal and then applied a couple of thin layers of P40 glassfibre filler to bring the front edge back to the right shape. Im now rubbing down the surrounding area to blend in the repair and will trial fit the bonnet when its in primer.

The fact its gone so well is a bit of a conundrum though as I was thinking this could be the opportunity to go for a fibreglass MGC bonnet - I have to admit i do just like the shape.
I spoke to RPS whose front and rear bumper/ valances I have and they recommended the ones from Anglia Composites which they themselves use in builds. At £ 150 plus VAT and delivery the Anglia Composites bonnets are not much more expensive than the ones from Generation Glassfibre or Honeybourne Mouldings but the fit and finish is apparently much better.


Still pondering what to do.

Glad the repair went well. Quite fiddly I bet.

Peter Cresswell wrote: ↑Sun Apr 11, 2021 11:35 am You really need access to an English Wheel to get the double curvature right, and the raised part in the centre that lines up with the MG badge on the grille will still be a problem. Now the show season looks like it will go ahead this year, find a bonnet that is in good condition and use that. Aluminium bonnets have their own problem as only the skin is aluminium and it reacts with the steel framework. They also dent very easily.

I have an aluminium bonnet. It is light and doesn't have a steel frame. It came with the car and does have a very slight dent, but you can hardly see it.
I like it for it's lightness, but am a bit paranoid about dents. I always drop the bonnet to shut it. Never push down.

Mine wouldn't close by dropping. The rule is never press in the centre above the grille badge. Use both hands and push evenly on both sides of the front edge.