MOT Failed. Welding needed!

[keynsham]

Today my 350i failed it's MOT on a cracked weld in the chassis. Having had a good look, I don't think it is as bad as it could be. There are two cracks coming from one of the front diff mounting bolt tube welds. Access would be reasonable to weld them up if I remove the diff and carrier, which I have done recently and was a pain but not difficult.

The yellow arrow shows the location of the crack in the top picture and the bottom picture shows the two cracks in detail. I cannot really see how far the crack on the left runs for as access is difficult. I think the large gap between the weld and the tube on the lower left crack top is just from TVR crappy welding!

So the big question is does anyone know a good mobile welder in the Bristol area who might be able to help out?

[KKson]

Looks like a fatigue crack rather than corrosion so I agree, you should clean it up and get it welded. Amore Autos near Thornbury have a resident mechanical so wonder he he could sort? Amore also have a 4 post lift which would make life easy.

[Shedding]

It does look like fatigue cracking, initiated at a weld toe. In a welded structure, this is where fatigue cracks generally initiate, partly due to the stress concentration at the geometrical discontinuity. The cracks have then grown into the parent material. When you are repairing, beware that the cracks may extend further into the parent material than first appears. Also, if access is good, it may be worth some weld toe grinding on the remaining weld and on the similar detail on the other side. This will improve fatigue life. It's hard to tell from the photo whether the weld toe crack has also continued around the circumference to the left.

[keynsham]

So who knew! The little classic car and service garage just within walking distance of me can do the weld repair. On top of that it turns out they have restored two wedges in the past including a body off job! The only downside is that they cannot do it until 4th January so I will need to pay for another MOT test, being over two weeks away.

As they do MOT's there, I asked him if they could MOT it too when it was in to be repaired. I don't normally go there. He smiled and said that it was of course possible that if they do the MOT then they might find other things that my usual MOT garage didn't, as they are more familiar with TVR's. I took the hint and booked it back into the original place for 10th January!!

So, my challenge now is to get a new MOT with no advisories. All I had was slightly faded number plates and slight play in the front wheel bearings, so it is definitely a possibility!!

[sixor8]

I wonder how many other cars with separate chassis (not just TVRs) have such issues. A heavy coat of underseal would have likely covered that up, possibly by accident.

[BlueWedgy]

Play in front wheel bearings, that old chestnut.
If it was driven and still relatively cold then there will likely be some play. The fronts have to have a bit to allow for expansion when hot. Stops them binding up and spinning the bearings.

[keynsham]

I get the slight play advisory every year but if you correctly tighten the bearings then there is always slight play. What I have never understood is that if the slight play is to allow for expansion of the bearings due to heat, then why is the pinion nut on the diff done up so tight to clamp the taper roller bearings in place and crush the collapsible sleeve? Surely they get hot too?

[Adrian@]

Back in the day the repair was to create a half box section that had two holes in and fitted/over sleeved the complete round tube/bosses by two joints along the top and bottom, (crescents at each end) which gave you a flat surface that you fillet welded into the edges of the original boss edges AND your new half box that is dressed down to the original boss heights. A@