This is very relevant as it is fairly common repair procedure, on SOHC 4s and other bikes.
It come to my attention that.. coff ..coff, some on here are not grasping the finer points of, drill/tap/insert alignment..
So here goes:
You will need a tool, lets call it tap alignment or centering tool.
Easily made yourself if you have access to a lathe, or sweet talk someone who can do it for you. It can be done for a reasonable cost, if they tell you otherwise, they are not doing you any favors.
Basically you need one or more pieces of round bar, 3/8 works pretty good, a piece 1 inch long will work, but a second one out of 1/2 by 3 or 4 inches long is quite handy as well.
Insert work in lathe, and cut 60 degree point on one end (included angle), on the other end, centre drill, till you are about 1/4 inch or so wide on the hole. Small tip centre drill works best
Now you are ready.
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First off you have to locate your hole and be centered on it. (if you need more on that, will add later)
After you have drilled your hole to size, let work remain in place. It should be fastened so it does not move.* This step is crucial.*
Say you are tapping. Insert newly made tool onto the drill chuck & tighten. Which end is sticking out depends on whether the tap end is a point or a centre hole. Mount tap in tap wrench or holder. line up end of tap to the tool in the drill chuck. Start tap in hole Carefully. Start tapping with very light pressure on drill chuck, so it moves with the tap... after about 3-6 turns it will be running straight, finish tapping.
That is the key to tap alignment, works on drill, mill, and lathe. Works with taps, reamers & helicoils.
Any questions, I will try to help out.
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A few notes on helicoils.
Do youself a huge favor. Mahine or grind, a punch or rod to fit fairly snug in the installed helicoil.. 4-8 thou clearance is good, make sure end is squared up. Use this to snap off tang.. applying the pressure close to the breakoff point is needed to get good results, and eliminate coil unwinding.
If you have to remove one, try filling a notch in the first coil about 1/2 coil down. Then use a 3 corner file or scraper to back out coil . Dont apply too much pressure as it will wedge the coil and tighten, you may need more than 1 notch.
Hope this helps..
