Disaster! Pulled crankcase oil return fitting HELP!

[hasaramat]

We are replacing oil return tubes in a friends 1971 911T and got to the last tube and noticed that oil return line could move. Upon further inspection we noticed that the fitting in the crankcase would rock back and forth a little. YIKES! We got the hose off and the fitting unscrewed by hand and was covered in plumbers tape. The top two thirds of the threads are damaged and the fitting has chisel marks on the outside, as you can see in the pics. There is about 6 to 8 mm of thread in the bottom of the hole that are clean. Has anyone ever repaired this problem in the car? Do they make a longer fitting to grab the lower threads? Helicoil? Insert? Epoxy? Any ideas?

[KTL]

I have a few of those case fittings if you'd like a good used one.

I would try to put the fitting in place with a new sealing washer. Which makes me wonder, was there an aluminum sealing washer installed under the hex of the fitting? Maybe that's why they used teflon tape (that's a hack......... I hate that stupid tape) to install it.

When installed, the threads should be locked in place with high strength threadlocker. All the cases i've worked on have had the fitting threadlocked in place. So as long as you can get the fitting to grab some threads in the case, you should be able to get it to seal. The aluminum seal ring does the sealing, not the threads.

[Henry Schmidt]

We've seen this over the years. The way to fix it is to machine the boss on the case down a few threads and machine the hex portion of a new fitting where the sealing washer goes. It's only a small amount on both surfaces but it seems to make a sound repair.

[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.

[Lapkritis]

Probably over-tightened at one point which will clear the receiving threads away fairly quickly.

[hasaramat]

Here is my solution or at least my attempt at a sound repair. The fitting is from Patrick Motorsports and it had an 8mm collar above the threads. I machined 3.5mm off the collar to bite the deeper threads. It looks promising. Sorry for the bad phone pic.

[Gene Smith]

That looks good! You cannot expect to stop a leak with goop or tape on a straight thread. I found my adapter fitting loose compared to the hard line pipe and had a Hell of a time working a tool in there to counter-hold this adapter. Now I want to get a safe but sturdy torque value for re-assembly. DOES ANYONE HAVE A GOOD TORQUE VALUE FOR THE ORIGINAL FITTING INTO Mg CASE?

[KTL]

It's just tight enough to compress the aluminum sealing ring. The fitting is installed in the case with a threadlocking compound & therefore doesn't need to be super tight. I always find the threads have a green threadlocker on them.

[Flat6pac]

I wouldn't worry about torque values as just a snug fit.
I have seen cases broken from hitting the wrench
Bruce

[chris_seven]

Is this the fitting that has a long plain portion under the threaded region?

If it is you can tap it down a little deeper and use a fitting with a longer thread.

The plain portion in the bore is the correct diameter for tapping.

We have a bunch of these fittings that are made in Grade 5 Titanium.

[BoxsterGT]

hasaramat-

Should be a viable solution. I have had some of these extended fittings in the past, but mine are 22 x 30mm I am pretty sure.

For a 71 2.2 motor I assume you have the 22 x 26mm fitting. Please let us know how it works out.

Len at Autosportengineering dot com

[jdbunda]

I hope you can salvage this. Just know that it could be worse! I am in the midst of a complete rebuild due to a prior owner substituting a straight nipple for that oil line adapter. Then, at some point, someone tried to stop the resulting leaking by cranking down ever harder on it. Having no external flange, the nipple kept threading into the case until it hit an internal web, at which point it cracked the case all around the fitting, and of course, still leaked. I just know that somewhere at some time there was a guy patting himself on the back for using $2 worth of Home Depot plumbing parts and saving the $30 he would have had to cough up for the Porsche adapter...

[BoxsterGT]

For anyone interested-

I have ordered few more of the extended M22 x M30 Case fittings similar to one shown in Post #10 above but in steel. Expect to have them from Germany in another week.

I will have the same but in M22 x M26 for the early oil lines in another 30 days or so.

Just in case......

Len at Autosportengineering dot com

[wayne robson]

I agree with KTL and flat6pac,that Torque values are not such a problem,
but there is a product that i use alot in my professional work called Loxeal
it is used by plumbers engineers etc,especially here in Australia New Zealand,
What makes this so good is it is clear, will seal any metal,and can be ready to use
only after 30 minutes.Not saying that locktite is not good, just another great product to use.

[David Borden]

If there is room, another option is to cut an o-ring groove in the sealing surface of the fitting. I recently had an issue with getting a good seal on an oil pan drain plug that was tapped ever-so-slightly crooked to the sealing surface. A copper washer would not seal, but an o-ring worked perfectly with no leaks.

David

[BoxsterGT]

Thought I would bring this post up to date.

I keep in stock a few "Oil OUT" Case fittings (M22 x M30) that connect the "Cross Under" Pipe to the case and routes the oil to the Thermostat or Oil Tank....





The factory originals are somewhat short, and while swapping Exhaust and Oil Lines it is possible to strip out the threads of the engine case.

I offer fittings with additional length and thread depth that will still grab and be secure in the case.

If anyone has a need, please email me.

len.cummings at verizon.net

Thanks for looking.

Len

[rudedude]

Along these same thoughts is it advantageous to run the cross under pipe in an older motor that has the flexible hose going up and over the tranny?

[Mark Henry]

Originally Posted by rudedude

Along these same thoughts is it advantageous to run the cross under pipe in an older motor that has the flexible hose going up and over the tranny?

Some 914 guys do this, if braided hose make sure it doesn't touch the hot wire on the starter.

[BoxsterGT]

The type of Clutch and the release mech will determine how the Oil Lines or Hoses are routed.

When upgrading to a later Motor and/or Trans you may need a totally different clutch and Oil Line setup.

Not everything is interchangeable.

I have made up a number of different oil hose layouts over the years.

Here is a set for a 911SC with a Front Oil Cooler that needed "Up and Over" Hoses to clear fat rear tires...