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Bad main bolt Heli-coil

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Banjo40:
Years ago I had to have a heli-coil installed in an outer main bolt location on a 4 bolt 427 Chevy. The machinist drilled and tapped the hole at such an angle that the main bolt is canted enough that it rubs against the top of the main cap.  It's actually difficult to install that main cap without lifting the cap and inserting that bolt first.  I would like to use the block now to make considerably more horsepower for a FED and I would like to install main studs. Is there anything I can do to correct the helicoil repair and salvage the block? I used the block for many years after the faulty repair, but only in a street car.
Thanks,
Mike

ricardo1967:
Mike,

I'd suggest leaving as-is, or trying to grind off the interference points. Redoing all threads is quite a bit of work and may get expensive. Hopefully you're not going to be assembling/disassembling the main caps too often. When I bought my SBC 400 block (race prepped, but quite tired), some of the outer main cap threads (angled) were stripped or close to. I Heli-Coilled them at home, with a hand drill :-[. I'm sure the torque reading is off (different friction coefficients between cast iron vs Helicoil inserts), but at least that part of the block is holding up OK (despites of previous marks of cap fretting).

Now let's hear the Pro's.

LZ:
Hi Mike;
Taking in to consideration not seeing it and having one in front of me for reference,  hears a couple thoughts

* You might be able to do a twinsert helicoil to correct hole but this requires a special pricey kit, if using an insert type repair such as Keensert - timesert etc. you have to take into consideration the depth of hole available and either way you have to take into account the block web and how much your compromising that.
* Maybe just keep using headed fastener at outer spotsI am assuming the bad hole is just off location ?? or is it angled wrong??   
This sucks to say dollar wise but if your really uping the horsepower is the rest of block up to task. Theres so many aftermarket blocks available now and decent used if you look carefully. It would be  worthwhile insurance for all the benefits you get. My stupid opinion.
Good luck bud.
Luke

Frontenginedragsters:
 Good answers above and let me insert another thought:
Is the engine coming apart to do machine work? Then it can go in a vertical mill and bore the hole straight and install a repair insert.
Any correction to the threaded hole will require making the hole bigger for a repair insert of some kind.
Machining should be done CAREFULLY if the outer bolt is on the left/drivers side. The main oil galley is just under that bolt.
Drill to deep and you just created another problem.

Matt Shaff
Pro-Formance Specialties
Rochester, NY

dreracecar:
Heli coils are fine for carburator studs,  Time certs are the best and not that expensive if you look at the big picture.  Repaired a Alu block at the rear trans mount flange with a time cert and lasted for 12 years, finally it gave up and pulled, No problem, they have a kit that repairs previously repaired threads, something a heli-coil cant do. So if the hole has to be redone, an oversize time cert maybe your only option because of the size hole that had to be drilled for the heli-coil.

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