Helicoil or Timesert (thread insert) a Stripped headbolt block hole?

[62cutlassconvert]

So one and possibly 2 of the head bolt holes in the block that also hold down the rocker arm assembly are stripped out. Engine is fully assembled in the car. Head, valve train, and intake are removed. The hole that is completely stripped previously had a crack and the crack on the valley side that was welded up when the engine was rebuilt about 3000 miles ago. There was no thread repair done in that hole as far as I can tell.

Both the Helicoil and the Timesert drill out the hole for the 7/16″ bolt to 29/64″ and tap it with a special STI tap with a outside thread diameter of 0.534″. Since these holes are on the inside edge of the block deck at the lifter valley, the hole wall is getting kinda thin and I am concerned about the pressure the thead insert type will exert with it’s expanding “binding” threads.

Wondering if anyone has had experience repairing these holes specifically or other head bolt holes in general?
Have you used the Helicoil or a thread insert like Timesert?
How did it work out when you torqued down the head?

(I would attach a pictured but the allowed size is 0Mb. Don't understand that one)

Thanks

[keithg]

Tape it up to protect the rest of the engine from debris and carefully drill and tap it for the helicoil. I am pretty sure that all the head bolt holes on my 215 are helicoiled. Take a drill bit and put it in the existing hole to get the depth and drill to the same depth with the larger bit. Carefully tap (it is really soft aluminum, IMO) and make sure to get all shavings out of the engine place the helicoil. If the 'spring' comes slightly above deck, you will have to take a grinder and grind off the bit and may have to dress it up to make sure the head bolt goes in. Good luck. Head bolt torque should be 'by the book', IMO.

[62cutlassconvert]

Thanks for the feedback.

Yeah, machine shop that did the engine says all the holes should have been done that way and that they will frequently do that. So why not, not known.

So you use Helicoil rather than the Timesert style of insert?

[keithg]

Yes. I have only used Helicoils or Helicoil copies. Key retained inserts usually require larger diameter holes and there is many times not enough wall to get them in. I'd prefer to retain as much wall as possible.

[62cutlassconvert]

Yeah, that’s my concern too. Not much wall in that location.

The Timesert insert threads into the same size hole and tap size as the helicoil but then with the installer it “spreads” the bottom of the insert into the native metal of the hole. In other words applies pressure to the hole wall to lock it in.

Don’t know how much pressure or the effect so concerned in that location.

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