Stripped thread oil sump
 

I have had an annoying oil leak from my sump for some time. I decided to bite yet another bullet and sort it out. I assumed it just needed new sealant. However, when reassembling it to the engine I discovered the front long bolt had stripped the thread on the engine block. There are two strange things about this, first of all by some extraordinary chance it was the last bolt I refitted and it had come out of the same hole that I was re-inserting it into. What a fluke!! The second thing is why was the bolt hole stripped in the first place. I hadn't noticed anything untoward when I was removing it.
The problem now is do I drill the hole out and fit a larger bolt which costs me nothing (virtually) or do I buy a helicoil kit at a cost of £40 approximately and repair it so preserving originality. If I drill out and tap, it would probably be 3/8" BSF as these are slightly smaller in diameter than 10mm.
What would others do

Could have been over tightened when it was put in some time in the past.
If you fit a BSF bolt, you will need to make sure in future you remember that bolt hole is 3/8.
I would not worry about originality

macafee2

Use a ‘nutsert’ rather than a helicoil, far easier to fit and much stronger.

If you have the tap and new bolt to hand and need the car back on the road then do it, if you can wait for hellicoil kit and want originally wait, me I would drill and tap couse chances are you won't be having the sump off again :}

I have examined the bolt which had come out of the "stripped" hole. It had ahelical coil wound on the threads so it appears that the hole had been repaired before. I attach picture of the coil. It may have been that locktight was used on re-assembly and this caused the coil to stick to the bolt and so the whole lot screwed out when I was removing the bolt.I may try a new coil otherwise 3/8" BSF tap and bolt.