[Walt Fricke]

Bummer. How could someone cross thread these threads?

A bit hard to imagine you can fix this without taking the motor out and apart.

But first I think I'd screw the fitting in without a sealing washer, and see if it will hold torque (don't know spec off top of head, and maybe with red Loctite (or even green sleeve retainer Loctite) you don't need full torque). That would give you some hope. Then you could machine the sealing base of the fitting (because you can take that to a machine shop) at least the thickness of the washer so it could go in deeper to grab better threads, and might not have to mill the case.

I'd do some measuring to see just how far in the threads extend (the case I have apart has the fitting screwed into it, or I'd have taken this measurement).

You can make the hex of the fitting fairly thin (allowing the threads to go in deeper), as you can torque it with a socket, though I'd like to leave it at least thick enough for a thin wrench, so you can counterhold it when next you need to remove the pipe fitting (or, in this case, not to overtorque the case threads when tightening the hose part on - normally you don't have to worry about counterholding except when unscrewing, when you don't want the fitting rotating).

If there are some good threads in deep which you can't get the fitting to reach, you might have a machinist make the threaded part of your fitting longer. Might involve welding and cutting new threads, but I'd expect a machinist to be up to something like that. Anything to avoid pulling the motor apart.

You can figure out the thread specs, and look on the Helicoil website to see if they make something for that. Or one of the other, similar, devices, but all call for drilling and tapping. But it is going to call for a pretty hefty drill size, and a quite expensive big tap, and you may not be able to handle one or both with the motor installed. If the Helicoil is too deep for the space available, you can shorten it.

And see how that does with a new seal ring.

But perhaps Henry has concluded this won't work without milling down the boss some? Although with a bare case half in hand, and a milling machine, that wouldn't be hard to do. Doing something with the engine in the car might call (if even possible) for a different approach.

You need enough mechanical strength so you can compress the seal ring enough to keep oil from escaping. And you need enough mechanical strength so that the normal jostling and vibrations of the engine and driving don't allow the rest of the fairly long oil line to the right side of the engine and the oil tank from trying to come loose. But perhaps the normal attachments over by the oil cooler are sufficient?

An engineer friend once told me you got a surprising amount of strength - maybe 80% - out of just two full threads engaged on a standard fastener. Though that was steel on steel, not steel on magnesium, though.

Another possibility is to drill and tap for the next larger thread diameter. You could even see if there is an SAE which is larger, but not as large as the next DIN. Then drill if needed, and tap, and have a special fitting made up. But that faces the same problems of doing anything this big in the close confines of an in place motor. It is not for nothing that taps, for instance, have handles sticking out both sides, and the larger the tap family, the longer the handles.

The passage way extends quite a long way into the case before it reaches anything (like the O ring seal). Perhaps it could be drilled and tapped to allow a much longer special threaded piece to grab onto it (i.e., stock thread extended inward)? But this faces the same issues with the engine in place.

All drilling/threading the case approaches involve metal chips, although that can be solved with a greased plug stuck down deep, with a means of extracting it when done incorporated into its design.

The oil tank drain plug is, for some reason, susceptible to cross threading. A shop owner once said he used some kind of basically self tapping SAE plug to deal with this. It cut its way through the buggered threads, which was enough to allow it to compress the seal ring. I tried this, but results were not perfect, and got worse with each draining of the oil. But it never fell out or allowed an unmanageable oil leak. Something like that, with the other side of the fitting welded on, might work at least once. But that sounds pretty crude, and I'm not sure I would try it.

Henry's approach, or a variant which achieves the goal of getting stock threads down deeper in the stock case, is at least proven. This disaster is nothing compared to the fitting being spit out on the highway.