I finally got my old Fuel Pressure Switch off, LHD5642AA. It was on there tight! Turns out I needed a 12mm crowsfoot, even though the new one needs an 11mm to put it back on.
When I finally broke it loose, the threads on the old sensor were messed up. I couldn’t thread the new sensor on, so I checked it out and it seems that I needed a 10mm-1.00 tap to fix the thread…
I may have taken it too far. When reinstalling the new sensor, I kept tightening until I snapped the head off of the new sensor, Basically the crowsfoot leveraged the head off while I was tightening the sensor back on.
I ended up removing the broken sensor and am prepared to order a new one, however, did I really botch this up? Did I clear out a tapered female thread in the engine? Does anyone know what the threads are supposed to be? I see 1/8-27 NPT on line, but that can’t be right, that’s not even close to a 10mm-1.00…right?
1/8 pipe thread is very close to 10mm and 27 tpi very close to 1mm pitch ( 25.4 mm per inch)
Might need replacement “spider”
Assume the “fuel” was a typo as it’s actually for oil pressure.
NPT (pipe threads) are tapered. When you tighten a pipe into a fitting the taper causes everything to become tighter(and leak-free) as you go. Add a little teflon tape-no leaks.
Your metric adapter has plain (parallel) threads, like a nut and bolt. The copper washer is where the sealing takes place. This is why teflon tape used on things like brake line fittings is a waste of time- the sealing takes place where the fittings join together. Hope that helps!
Please understand that a copper washer is basically a single use item. The copper washer is annealed ( softened)…by being soft, it conforms to the sealing faces. But once you apply pressure of tightening…it causes the copper to work harden. Once a copper washer is work hardened, it will not reseal without reannealing…hence why so many oil pan threads get striped out. People try to reuse an old copper washer…and while trying to get it to seal and eliminate that last drip…they keep trying to tighten until the threads are striped.
You can reuse a copper washer…but you must re anneal it. Use a propane torch and heat the washer to cherry red then let cool naturally…it is now soft again. Just remember, as soon as you apply clamping pressure to it…it will turn hard, then require re annealing.
No, no. M10 threads- no tape. Just the washer.
NPT need the tape!
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
12
Copper washers are great. What I like even better, though, are those metal washers with a rubber bead around the ID. Most auto parts stores sell them these days, and you can just pick the size you need.
I cheat, though, and find a thin (1/16" thick) nitrile O-ring that just fits the thread, and then I find a narrow copper sealing washer that just fits around the OD of the O-ring. It’s easy to assemble the two when screwing the item into place. It’ll tighten onto the O-ring first, then crush it until it hits the copper washer. Snug it up, never leaks! If you take it apart later, you’ll have to replace the O-ring but you can reuse the copper washer forever because it’s not really doing any sealing, it just keeps the O-ring from blowing out as you’re tightening it down.
So I ended up take my your advice Kirbert! I used a copper washer and a rubber washer that was 5/16”ID. The M10-1.0 adapter for the 1/8NPT worked great. I think it may prolong the life of the sensor as it no longer is snug up against the engine block, so it shouldn’t get as hot as it was getting before. Also, I’m not sure the rubber boot will get trashed as easily either.
Thanks for the advice guys! Unless I find a leak, consider this thread closed!
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
15
They are awesome. Not cheap, though. I seem to recall being charged more than $2 each for the things.
Obviously, if there’s a lot of heat involved, you might need to stick with copper washer seals. The applications we’re talking about don’t run that hot, though.