Oil Drain Plug

One of the things on the 'to do' list was to fix my oil drain plug.  At some point, a previous owner had high centered the car, breaking several fins on the sump cover and causing one or more cracks.  From the evidence of the welding, one crack went through the drain hole area at the rear of the cover.

The drain plug had been replaced with a 1/2" standard pipe plug.  This was probably due to the welding and the lack of a 16mm x 1.0mm tap that would have been needed to use the original plug.  So I suspect that it was tapped to size where a standard US pipe plug would fit.

My original plan was to remove the sump cover, get some aluminum rod, thread the outside to the 1/2" pipe thread, screw a chunk in and weld it in place.  Then machine the surface smooth, drill and tap a new 16mm hole.  In discussing this with Lowell Brown's machinist friend, he was worried that welding in the plug would anneal the casting and make it too soft.  As it had already been welded on, whatever damage could be done probably had already occurred.  However, he did have a simpler solution that didn't require removing the sump cover.  Just get a brass 1/2" pipe plug, drill and tap that for the 16mm plug.  This leaves an adapter with 1/2" pipe thread on the outside and 16mm on the inside.  Then Loctite the adapter in place, leaving the 16mm hole for draining the oil.  There is some difference between the expansion characteristics between aluminum and brass, but for the temperature range and size involved, it can be ignored (Lowell is a physicist and looked all of this stuff up).  In looking for a brass pipe plug, I found that the current ones are hollow where the inside threads would need to be.  However, I did find an 1/4" to 1/2" adapter which was solid beyond the 1/4" threads so there would be enough material for the 16mm threaded hole.  Further this had a six sided head which fits well into the normal three jawed chuck on a lathe.  So Lowell chucked it into the lathe, bored the proper inside hole, tapped it using a 16mm x 1.0mm tap and then cut off the head.

I first drained the oil overnight and then cleaned the threads in the sump cover with brake cleaner so the Loctite would set up properly.  I had to use a cut off wheel on a Dremel to cut back the welds by the hole and at the top so the head of the new drain plug would clear.  Then I installed the adapter by putting a couple of washers on the 16mm drain plug, screwed that into the adapter and then using the drain plug, screwed the whole thing into the sump cover after putting Loctite on the outside.  After letting it set overnight, I removed the drain plug.  The adapter was purposely left a little higher than that face of the sump cover.  The 1/2" tapped hole wasn't quite square with the face on the sump.  I was originally going to use a cut off wheel on a die grinder to make everything flush, but there's too much difference to deal with that way.  So right now, I hope that the copper washer will seal properly against the adapter.  If not, I'll probably have to take the sump cover off and have a machine shop use a milling machine to true the face up with the threads.

The last item was to drill a hole in the drain plug for the safety wire.  Since this was a new plug, evidently Ferrari no longer makes them with the safety wire hole.

A few minutes on the drill press gave me a 5/64" hole that I chamfered so the safety wire wouldn't catch and break on the sharp edge.

Here's the final installation, safety wire and all.

A month later and no drips at all.  So I'm quite happy with the final result.