I noticed that the factory oil pressure switch was leaking on my 914. I removed it but the previous owner put it in crooked and stripped the threads in the case that the switch threads into. Can this be repaired with engine in car? What size drill, tap and insert do I need or is there another way to fix it? Thanx L

It's rather risky, but this can be fixed in the car. The technique is to get the proper tap and coat the tap heavily with a thick, sticky grease. Then, turn in the tap until it starts to cut threads and go about 1/2 to 1 turn more, remove the tap, clean the chips and grease off, re-grease the tap and repeat until you go in deep enough to create sufficient new threads. Two full turns should be sufficient.

The idea is that the chips should stick to the grease on the tap and not fall into the engine. I've done it on horizontal holes and it worked okay. I haven't tried it on any vertical-down holes.

The risk is that metal chips can fall into your oil passages, which would be not good.

If it were me, I would be thinking about removing the engine, draining the oil, mounting it on an engine stand and rolling the engine upside-down. That way, any chips that don't stick to the grease should theoretically fall down out of the hole, instead of into the engine.

One other option, which is somewhat safer but potentially more difficult is to use a die to make the tapered thread on the switch deeper. I would actually recommend doing it to a brass fitting rather than the actual switch (and screw the switch into the fitting), just in case you mess it up. But, this only works if there are still good threads deeper in the hole in the block. If not, you'll have to re-tap the hole in the block.

I'd wait for McMark, Chris Foley, Brad Mayeur, or one of our respected engine builders to chime in.

Just guessing but I'd guess it will take tapping it for a different thread and using an adapter.

Don't drill with engine assembled, too much if a chip contamination risk.

Four or so wraps of teflon thread seal tape on the switch works, just be sure to keep the tape 2 threads away from the end of threads. You don't want tape fragments to enter the oiling system.

For info in general. The threads will be BSPT G-1/8" , the thread form and count is slightly different than NPT 1/8". BSPT in this size is slightly smaller than NPT but the two are close enough that, in this size, NPT in BSPT will " work " if needed.

Rather than type it app, go here for a chart. http://pipeandhose.com/?q=node%2F2

No teflon tape here. Switch grounds thru the threads.

Even with teflon tape there will usually be some metal to metal contact. If there isn't a hose clamp +a ground wire will fix things. Or put a short compression spring around the threads / under the switch.

The "right" way to fix this is to strip the motor bare and helicoil, but that gets to be $$$.

I googled it -- turns out you can use helicoils to fix NPT holes. Did not know that.
http://www.stanleyengineeredfastening.com/..._HC903-rev4.pdf
But, since it requires drilling and tapping, it's not something you can do with the engine in place.