1850 subframe rear mounting hole repair

[GaryR22]

Having removed my 1850 subframe and had it grit blasted I’m concerned about the rear mounting holes for the main fixing bolts. These have corroded around the edges of the hole as per the first photo attached. The steel is quite thin at the edges of the hole. Although the lower rubber bush and associated conical washer plate appear to bear into the shoulders of the recess and are therefore unlikely to pull through, I presume a repair would be prudent while it’s off the car. Does anyone know what diameter the hole should be? I was thinking of having a washer plate welded onto the top face as per the second photo, having first ensured the inner hole in the washer is opened out to the correct diameter. The run of weld would be onto the shoulders of the mounting point so would give a robust arrangement. However will the thickness of the washer plate (4.5mm) cause any issue with alignment (it will obviously push the rear of the subframe down). Also will the overall area of washer cause any issues (the ones I’m looking to use are 65mm diameter). This will bear against the rubber bush that sits sandwiched between the sub frame and body. Any thoughts would be appreciated!

[xvivalve]

It is a common repair!

Often used are the same washers that sit beneath the subframe mounting bolt heads in the engine bay. (obviously you don't use your actual existing washers, they are still needed; you need to source additional ones!)

[GaryR22]

Many thanks for the prompt reply. Those are the very washers I’ve sourced to do the job. Any idea what diameter I should widen the holes to?

[TrustNo1]

last time I done that I used thick washers welded on.

[xvivalve]

When I did this repair, I didn't widen the hole, I just made sure it was positioned centrally

[GaryR22]

Many thanks to you all - much appreciated!