Best way to deal with this rust?

Best way to deal with this rust?

Author
Discussion

CrutyRammers

Original Poster:

13,735 posts

197 months

Monday 3rd August 2015
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Hey all,

currently engaged in a rebuild of a '77 MGB Roadster. The engine, gearbox, and the rest of the mechanicals all need total rebuilds, but the body seemed pretty sound. Or so I thought...this evening I found that the dreaded metal moth had paid a visit to the NS front chassis rail:
From outside:


From below:


From inside the engine bay:


Peering inside the holes and having a good bash with a screwdriver, it looks generally ok in there, no other holes, and the floor above is sound. (Looks like a new section in fact which has been welded in).

The question is, what's the best way to deal with it? Seam weld big plates over? Cut out and fabricate a whole new section and weld that in (which would end up being made of plates welded together anyway because of the curve)? Cut out pieces one at a time and patch it?

Currently I'm thinking of cutting out the bottom, welding a new piece in, then cutting out the side and replacing, leaving the rounded edge. Not sure if this will cause the body to sag while I'm doing it?

Expatloon

215 posts

156 months

Wednesday 5th August 2015
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A little confused at what I'm seeing, there are no seams or joins there nor does it look like previous patching and in fact it suggests to me that the forward chassis legs have been replaced at some time.

Patching should be OK but the welding should be to a good standard, I wouldn't worry about sagging.


Geordie MGmike

134 posts

138 months

Sunday 9th August 2015
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It looks me like the rear half of the leg has been replaced when the new floors were fitted.
Cutting out all the rot and patching is an acceptable repair but please use a suitable gauge steel! The legs are/should be quite thick and a good quality weld is essential to maintain strength. However, sagging shouldn't be a problem if the rest of the shell is okay e.g. castles, sill etc.


CrutyRammers

Original Poster:

13,735 posts

197 months

Sunday 9th August 2015
quotequote all
Cheers guys. Yes one bit of it's been replace but I'm not sure which. The passenger floor panel at the front has been replaced but I can't see anything else obvious. Time to break out the grinder then.