Originally Posted by disston
Essentially doing a Heli Coil or other thread repair is two parts. First you drill the striped threads out with the correct oversize drill bit so the hole will be the needed size. Second the hole is threaded to accept the thread repair insert so the resultant threads are the original size. All this drilling and threading produces chips and debris that we don't want to be left in the transmission. The way to prevent the Aluminum debris form being left behind is to put heavy grease on the drill bit and the threading tap so the grease will catch the Aluminum bits. The bit or tap is used part way and cleaned off then more grease applied and used further.
The drain plug on a /5 four speed transmission is M14 x 1.5 Be careful when you buy the tools and parts for this because there is another thread often used that is different. It is m14 x 1.25 The one you want is M14 x 1.5
There are many brands of Heli Coil type repairs these days Some of these are a little cheaper and may come with the needed drill bit. If you buy the original Heli Coil brand the kit will not come with the drill bit. Get that extra. (this is what i usually do, I prefer the Heli Coil brand)
There are also other types of repairs. Some are called "Time Sert" or "Big Sert" These are also thread repairs and may have advantages sometimes but they are also extra work and not needed for this repair. Get the Heli Coil Kit for an M14 x 1.5 repair.
All my helicoil kits have the drill bits. They are boxed kits, from McMaster or MSC but I believe the pouched kits are the same.
A tricky aspect of the helicoil is breaking off the tank at the end. It must be done with needle noses and pulled out rather than punching it in per usual. A good method is to set the helicoil in red locktite (you do this anyway), let the locktite set up 24 hrs (at room temp, not in the cold garage) then you can twist on the tang without tearing out the coil.
The oversized plugs look like a much better repair. For one thing, you don't have to try to sell off the now unneeded helicoil kit. You do have a drill bit and tap left over tho'
I'm not a big fan of the grease method for this. You really want the hole square and the tap square. That takes a fair amount of skill to freehand. Doing multiple pecks at it just makes it harder.
I'm currently reworking an oil filter that has a similar issue, don't get any particles in side the filter when grinding away the exit hole. I'm thinking of setting up an air blast through it and grinding against the air flow.