Another Thread Chaser
By Charles McCullough
My son needed a solution when working on a car with a cross threaded blind hole in the engine block.
I made a thread chaser very similar to the tool made by David Hawkins in his tip Blind Hole Thread Chaser (click here to view this tip). On my thread chaser, I drilled a hole lengthwise through the center of the bolt, of a diameter slightly larger than the width of the slot sawn down the bolt (I used two hacksaw blades ganged together to make the slot).
Then, after squeezing the bolt tip to insert the bolt threads past the damaged threads, a piece of drill rod (with a rounded end for ease of insertion) was poked down the hole to force the split bolt open again. Backing the bolt out of the hole then formed the damaged threads back into place. By using the rod down the center of the bolt to expand we could insert the bolt deep into the hole without having to keep the slot exposed.
It was easier to insert the split bolt into the hole if we ground the remaining bolt threads “flat” across the slot in the bolt. We also made sure the result was not sharp so the bolt would form the smashed threads back into position, rather than cut them.
In the figure you can see where the remaining bolt threads were ground off for ease of insertion and the dulled edges that prevent the slot from cutting into the old threads.