Helicoils in block.

[jonblob33]

Hi all, i’m Looking for a bit of advice please. Just found water in no 3 cylinder. Took head off to find stud between no2&no3 cylinder pulling out of block. Re helicoiled with 2d 5/16 bsf helicoil fitted with thread sealant. No water coming up stud now but unable to torque to 20 ft/lbs. I think the helicoil is pulling out again. My question is I am thinking about re helicoiling to 3/8 bsf but not sure if there is enough area round the stud for the head gasket to seal ok. Has anyone done this mod? Any suggestions or advice much appreciated. 
Thanks. Kevin.

[Zetomagneto]

Helicoil  to 3/8 means a 7/16 hole, then a 3/8 stepped stud. In this situation you are better off making an insert 7/16 BSF od, 5/16BSF id. Drill and tap a 7/16 bolt in the lathe.
If you do this , loctite the insert, leave it slightly proud so that you can dress it with a file so that it is flush with the top surface of the block.If you use a helicoil you cannot do that.
By now you may be losing the true centre of the stud hole.
If possible redrill and tap on a mill.