Crossthreaded?

I got a new screw in sensor that fits in the top of the engine block. When I unscrewed the old one I found the previous "mechanic" (no it wasn't me) had put the old one in crossthreaded. Now when I try to put the new one in, the threads lock up and I've started to strip the threads on the new one. I was fortunate to get the old one back in to plug the coolant from leaking (I hope it doesn't let go on me). Where do I go from here, besides to a garage. Is there a way to straighten up the threads in the engine block? The new sensor is brass. The engine block is iron or cast iron. anybody? (rec.autos.tech) eh?

Reply to
erness.wild
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Get a tap and thread it in. See how tight it is, then put in the new sensor.

If there isn't enough good metal to do that, you're going to need to use a helicoil.

Teflon tape may help get a good seal with poor threads.

--scott

Reply to
Scott Dorsey

Maybe, maybe not. I'm envisioning a pipe thread, in which case the fix would be to drill oversize and insert a pipe bushing. Probably a job the OP could handle, but it would require a drill with cojones grandes, a very large drill bit, and a very expensive large size pipe tap, so it might be best to take it to a mechanic. (presumably not the one that did the deed in the first place.) Even cleaning up the threads would involve having a pipe tap, and last time I checked a 1/2" NPT tap was over $30 from McMaster-Carr.

if I had a fairly comprehensive home machine shop at my disposal, this is what *I* would do. Get a pipe nipple one pipe size larger than the sensor, drill and tap the block for it (I assume actually the head, but never mind.) tighten the nipple as tight as possible with a pipe wrench. Cut off flush with the head, grind level with a 4" angle grinder. Drill and tap for sensor. Et voila. This is assuming a fairly small size where the next pipe size up will be small enough to be tapped for the correct pipe size.

If the head is aluminum, this may not be as good an approach, as the aluminum may expand enough when hot to loosen the "plug." I dunno, never tried it.

I would go ahead and post to RAT. some professional tech might be aware of a more elegant, purpose-made solution.

If you wanna try a cheapass solution, and you can confirm that the sensor is in fact NPT threaded, you *could* try getting a nipple already threaded in the appropriate size, cutting several slits partway through it in the threaded area with a cutoff wheel (making it look like a tap) and threading that into the hole, see if it cleans up the threads acceptably. It probably won't work, but it might be worth a try.

Also if this is a disposable car and you don't anticipate replacing the sensor again, you could simply put it in crossthreaded, crank it down, and keep on rollin.

good luck

nate

Reply to
Nate Nagel

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