Triumph GT6 Bonnet Repair

With the weather turning a fraction warmer and the main body cockpit almost finished (just some sealing to apply before I remove it and roll it over), I thought I'd have a butchers at the bonnet and see what needs cropping - and, more importantly, how it should be cropped.

Below are three photos with the bonnet up-ended. The outer n/s and both the insides, which shows the extent of the rot around the wheel arches.

The lower section of the bonnet, as you can see, is a separate panel that's spot welded to the upper panel, but there's a plethora of spot welds around the headlamp panel and wheel arch. Unfortunately, some of the inner wheel arch (which is essentially a mudguard) has also suffered from rot, so I'm going to have to have to fabricate some repair sections, as the majority of it is sound and I don't really want the expense of new inner arches, despite new inner arches making the whole job a lot easier.

I made a start.

Removal of the offending lower panel was not as straightforward as I thought it would be, so I thought I'd just cut into it within the lines of the spot welds, remove the bulk of the old section, and then attack the spot welds with more room to manoeuvre with a grinder and air chisel.

It's a shame that the majority of the metal I removed is quite sound. The tricky bit was not removing metal than needs to stay and isn't on the replacement repair panel. The other tricky things was that removing the metal makes the bonnet inherently unstable in the vertical position, so I had to put it on a horizontal support I designed especially for the purpose (aka what we experts call an old chair).

Removing the rotted n/s lower wing section meant the inner arch (mudguard) dropped, being suspended at the front by small, horizontal panel that forms the headlamp recess. The inner arch then needed to be parted from the headlamp recess panel, but that panel was too far gone to be worth rescuing anyway, so separation was quite easy. Looking at the o/s, I ordered new headlamp recess plates for both sides at £150. Hideous price for such small panels.

Separating the inner arch from the remains of the lower panel was bloody difficult due to the myriad spot welds and filler. When I got it off, it looked hideous - lots of rust around the outer edge of the arch, with only a little of the original metal left.

Can't help thinking I'm looking at needing a new outer mudguard (the arch is split into two halves - the inner and outer) at £102 - twice, one of each side - but I thought I'd attempt a repair first. 

I could have simply cut out the rot around the wheel arches and used the new lower wing panel wheel arches, rather than the entire new panel, but that would have been rather fiddly, as well as wasting the cost of complete new panels. Also, the mudguard would still require fettling. The chance of something going wrong would be quite high, whereas spot welding a totally new panel into position is much easier, cleaner (not involving filler) and would last a lot longer.

The rot on the outer mudguard arch is mainly isolated to the lip, leaving enough metal to correctly gauge where the bend to form the lip that attaches to the outer panel should be.

I made a provisional repair section by slicing some mild steel into the right width with my nibbler, hammering down one edge on a vice to form the lip (I couldn't use my sheet metal bender, as the section was too long), and using my metal shrinker/stretcher to stretch the other edge to create the right arc (you can see the striations where the stretcher bit into the metal to pull it apart slightly - it's a brilliant tool).

Below is the part finished section roughly positioned against the arch. 

It will need cutting to exactly the right length and some additional bending is required on the non-lip side to cater for an angle on the arch in order to get it flush. That will be attempted with a hammer, but I ideally need to create a U shape, which is difficult on a curved section, and one side of the U is not homogenous along the entire length - it's fat in the middle and thinner at the ends, a bit like a dinosaur.

I will probably need to make another, as I think the non-lip side needs to be slightly wider and I went a bit overboard with the stretching (the curve is a little too tight). With the next one I'll use the curve of the outer wing to modify the arc I put into the repair panel, rather than just doing it by eye.

Had I cut the repair section to nearer the right length in the first place, it would probably have fitted in my metal bender. The photo above shows the repair section on top of the arch but, because the outer wing has to fit over the top, I think I'd be better putting the repair section on the underside of the wheel arch so as not to interfere with the fit between the wheel arch and the outer wing.

If it all goes tits-up, I'll simply order a couple of new outer wheel arch halves, which would be really simple to fit.

Sod it - I'm going to get half arches from Rimmer's. It's not worth spoiling the ship for several hundred quid.