My friend says a 1/4" x 20 set-screw will work for the small plugs...
The feller then went on to describe his difficulties locating 1/8"-NPT internal-wrenching pipe plugs, suitable reamers and so on.
----------------------------------------------------------------
Yeah, it'll 'work.' But that don't mean it's a good idea.
I know what you're running into and as I mentioned in the original article, I usta use set screws back when I was young & foolish and had lotsa hair. But if you absolutely HAVE to use a set screw, go find a
5/16" and tap for that. Herez why:
Nominal drill-size for a tight quarter-twenty is a #7 drill bit, about
0.201" in diameter. Go mike the plug you pulled outta the hole -- or mike the hole itself -- and tell me what you got. Should be around
0.240. (...or 6mm)
See the problem? Start out with a big hole, the threads are going to be shallow; they won't provide much strength. On a cold day, your oil pump can put out as much as 300psi. That'll actuate the oil pressure control valve and open up the by-pass port but take a look at the size of that port... not even a quarter of an inch. Now lookit the outlet of your pump. Damn near half an inch. That means that even with the pressure relief activated, if the oil is thick enough, you're going to see one hell of a lot of pressure in the oil galleries -- over a 100psi in most cases, until the oil warms up.
Now, you gotta ask yourself: Are you feeling lucky? :-)
...because luck has a lot to do with it when you tap a .24 hole with a .25 tap and expect the thing to withstand 100psi. If you live in a warm climate (like I did, back then) you may get away with it, at least long enough to learn how to do it right.
----------------------------------------------
Don't take this as a kick in the ass. You're doing good, pulling the plugs soz you can clean things up. But a quarter-twenty in an M6 hole is too risky.
If you can't find the right size pipe plugs & tools, then step up to a
5/16" set-screw and drill the case out for at least a 75% thread engagement. I can't remember remember the drill... letter-size bit, about a 'G' I think. (Lookit up on the internet. I can't remember s*it nowadays :-) And be sure to strake it good. Steel set screw will loosen up when the case heats up, which is why you want to start with a tight thread to begin with.
-Bob Hoover