[Robin Craig]

Chris,

I apologise for the delay in replying.

I would always suggest pre heating the area and using a high nickel content electrode or wire. Preparing the end of the fastener with a bevel and spacing it off the hull by making up a small magnetic fixture or a mechanical one will aid in both alignment and being able to achieve a full penetration weld and then do some post heating to slow the cooling down.

The concept of buffing of the old fastener and drilling the hull and putting the new one through using a tapped hole and setting it just below the inside surface to allow a small weld on the inside, then buff the inside weld flush.

I would not do the drilled hole method myself as I am confident I could do the exterior full penetration weld.

As far as the cracks around the exhaust holes, how long are the cracks? Honestly I don't think they represent anything that is worth being concerned about. The flanges of the exhaust components that pass through the hull should have a proprietary heat rated type gasket made up on either side and the bolts exert a clamping pressure sufficient to seal the assembly. The cracks are not going to propagate and cause the side of the hull to fall apart in service in the next 50 years I would bet.

To deal with a crack, the first step is always to prove where the end of the crack is and drill a holes right through the end. It is only then that one can consider vee groooving out the crack and welding it and grinding flush again. Honestly I have seen these small cracks on several other Ferrets and have left them. Drilling armour steel isn't fun and I don't see the area as having any structural loading such as a wheel station attachment point or a lifting point that is used where safety would be jeopardised.

I think being pragmatic about those ones will save you a world of hurt and work and effort.

If you measure the length of the crack and divide it by the number of years since the vehicle was made what is the mm per year ratio? The area suffers from thermal cycling and the further away from the passage for the exhaust gases one gets the less it will cycle and therefore the less the crack will propagate.

If the cracks have made it past the flange area I might have some concerns, can you show us a photo to illustrate your concern?

These are my own opinions, based on a pragmatic approach.