I need to put Helli coils for the fuel bowl screws of a holly dbbl pump.
I have the kit but it doesn't come with the drill and doesn't say what size to use?
Does anyone know this important information?
Thanks T.C.

Are you sure it doesn't say on the tap to use drill # xxx

Duhh, I didnt think to check.
But I will.
Thanks T.C.

Nope not there, I remember they usually do say but this one was made in some third world country (not China) and all it has is the size and country, and they are just printed onto the tap.
T.C.

What size is the tap?

TC,
You might not feel comfortable with this but ..... I have NEVER used a drill when repairing the bowl screw holes on a Holley using the Holley HeliCoil kit. I just give it a shot of thread tapping lube and push the tap into the hole pretty hard while turning it. It will dig right in and cut the threads no problem. I bet I have done a hundred of them this way. You need to have a good tap handle and just be carefull to keep it straight, but it works just fine.

From my experience its usually always drill a 1/64" over the thread size you want. So if it was a 3/8 bolt you'd drill a 1/64" over that and tap.

Quote:From my experience its usually always drill a 1/64" over the thread size you want. So if it was a 3/8 bolt you'd drill a 1/64" over that and tap.Unquote

??????????

Tap drill sizes can be found on the web:

http://www.efunda.com/designstandards/screws/tapdrill.cfm

I strongly advise you use the size drill for the "loose" threads. In steel, any thread depth greater than 50% does not add any strength to what you are screwing together, and a 50-60% thread depth will result in fewer broken taps and longer tap life. And, as in engines, any oil is better than no oil when tapping.

Thanks for the replies:
The thread is 12-24 and the main body is not alum. or steel, it's some kind of alloy?
I think I will try BillK's way as I have done this on other projects and it worked just fine.
Thanks again T.C.

"From my experience its usually always drill a 1/64" over the thread size"

Just remember this is a Helicoil tap which cuts a larger thread so if you are going to drill you need to use the correct size drill for this tap. I am pretty sure it is on the tap.

By the way, this is probably the only time that I dont use a drill when tapping something. I think I was fixing a carb many years ago and could not find a drill and tried it without. Worked so good I never used a drill again. Must be the soft Holley material :)