HELP! Stripped case
 

I am rebuilding my 73.5 911T original engine. I have had some oil leakage from around the oil pressure sender. When I removed the sender, it is apparent that the threads are partially stripped. It looks like the thread is M12 x1. Should I go with heli-coil or time-cert? Should I have this done at the machine shop? Thanks

to begin with, verify what the thread is by using the oil pressure sender you just removed...then, use a thread "chaser"...NOT a thread tap on the case threads you are concerned about...if you get stuck and/or want a second opinion, call mark burkit at Specialty Cars in Allentown, PA and tell him bob at design assoc said to call him...you can bring your case to him and he can inspect it for you and give you the best advise around...he is ~ 1 hr north west of philly...not sure how far from pittsburgh...good luck...bob

Timesert is better than helicoil. Clean, clean, and clean again after doing any tapping on the case.

The sender uses M10x1.00 thread. However, it screws into an adapter. The parts catalog shows an 18mm crush washer, so it certainly isn't an M12 thread. It has to be an 18. 1.5 is a likely pitch, but you just want to measure it.

Which threads are buggered? The ones in the middle of the adapter? If so, just get another adapter.

The ones in the mag case itself? That's trickier, but you have lots of options. Timecerts or Helicoils (plenty strong for the job) should work, but you may be better off having a shop do this - they will already have the special tools, and you may never need them again. I used a Helicoil on an aftermarket aluminum case oil sump drain plug, and it doesn't leak - the sealing is done by the crush washer, not the threads. Or a machine shop could easily make a larger adapter, and drill and tap your case for it.

As you must have guessed, the adapter is there because that oil passage is drilled/finished all the way from the top of the case down and out the bottom, but the senders use a smaller threaded section.

Turns out the bad threads are where the adaptor threads into the case. It actually is M12x1.0. Unfortunately, neither Helicoil or Timeserts come in that thread. My mechanic is suggesting making an adaptor from a 14mm screw drilled and tapped to fit 12x1.0. Anyone tried this?

Just saw M12x1.0 Helicoil kit on E-Bay? Maybe a typo? I think it is M12x1.5.
According to the Mfg. catalogue, you are correct, they don't exist.

Lots of technical info about Helicoils here:
http://www.helicoil.in/pdf/HeliCoil%20Catalogue.pdf

Helical Wire Insert Thread Repair Kit M12x1 0 12mm | eBay

I'd measure this again. 1.75 is normal, so fine usually is 1.5, maybe 1.25 at the smallest. Not 1.0. Maryland Metric's catalog lists a 1.0 for M12 bolts (and for M18), but I don't think that is anything Porsche used.

I also question 12mm. The sender is 10mm, so there would only be 1mm wall thickness. The crush washer in the parts catalog is 18mm, not 12mm.

What I'd do is check the plug on the other end of this hole - the one which holds the pressure setting spring and piston in place. That is an M18/1.5 bolt.I think this has the same thread. You could check that against the steel insert you removed.

If the bad threads are in the aluminum case (and that's what you have said), then an adapter would have to be made from an M14 bolt of appropriate pitch. You want a bolt because you have to screw this thing in (maybe that is what you mean by screw).

But maybe we are talking about the wrong hole in the case? I'm assuming it is on top of the right case half, to the flywheel end of things, and close to the oil temperature thermostat.

Well we are actually talking about the rear of the case, right side. My mechanic repaired it with a 14mm bolt. It is in fact 12x1.0. This is an adaptor which the oil pressure sender attaches to. Thank you all for your help. Hopefully, it won't leak when we get it back together.