Did I just screw up my carb by trying to add my carb temp sensor?

[ArVeeNiner]

Well, I may have made another expensive mistake. I had a lead plug in the spot on my carb that accepts the carb temp sensor which I got with my Dynon. Following the directions, I carefully drilled out the lead plug without enlarging the hole. So far, so good. The directions said to tap the hole to 1/4-28. I tried but it wasn't taking the threads because the hole was too small. So, I drilled the hole out to 1/4". I think this is where I made my mistake. Then I tapped it to 1/4-28. You know where I'm going with this. Now the hole is too large for the sensor. What do I do now?

Do I try to figure out a way to plug the hole back up and forget the sensor? Can I bond in the sensor? Do I add a Heli Coil? I hope I didn't make a huge mistake!!

[osxuser]

My inclination would be to first find out what the correct size/pitch is, then try to find a helicoil that may work and see what the size/pitch of the tap is for it. If it's too close to 1/4 to make it work nicely, I'd find a 1/4-28 plug, screw and stake it in, and leave the carb inlet temp to those who really need it (cessnas).

[kiwipete]

Kelly

You have indeed drilled the hole out to the wrong size. The correct size is always smaller because you have to allow for the thread depth.

It seems you now have two options:
1) Get a helicoil fitted
2) Drill and tap it for a larger plug.

Personally I'd take it to someone and get the helicoil fitted. Then you can still have you temp gauge. As someone who's experienced carb icing before I think it's a good idea to have the gauge.

Peter

[Chappyd]

Heli coil would be my choice. You can buy a kit with the proper drill , tap, and helicoil inserts and tool i to insert fairly inexpensively

http://www1.mscdirect.com/CGI/NNSRIT...MT4NO=60863234

Something like this. A little searching and you may find cheaper

[carguy614]

I used to own an auto repair and machine shop, and found the best thread repair system to be the ones manufactured by Time-Sert. These have a flange at the top, are solid sleeves, and install flush in a counterbored groove that is cut in the part with a tool that is supplied in the installation kit. I have installed thousands of these. most high mile Cadillac Northstars have the cylinder head bolts retained in the block with this system. I have installed them in several positions in Lycoming case halves in the past. They are air and fluid tight, totally structural, absolutely permanent, and there is no way the threaded repair can unwind from the back and end up in the venturi and get swallowed by your engine. The kits are very expensive, and the inserts can run about 3 bucks each, so it is probably best to contact your local well equipped automotive machine shop and have one installed. I would expect this to be a 30 buck repair. Yes, a Helicoil will work, but if you want the very best repair that is airtight and secure, this is the way to do it.

Hope this helps,
Chris

[chaskuss]

Originally Posted by ArVeeNiner

Well, I may have made another expensive mistake. I had a lead plug in the spot on my carb that accepts the carb temp sensor which I got with my Dynon. snipped So, I drilled the hole out to 1/4". I think this is where I made my mistake. Then I tapped it to 1/4-28. You know where I'm going with this. Now the hole is too large for the sensor. What do I do now?
snipped

Kelly,
The correct size to drill for a 1/4"-28 tpi (NF) is a #3. For 1/4"-20 tpi (NC) is a #7. You can find a tap drill guide here. See

http://www.newmantools.com/tapdrill.htm

Chris' suggestion above sounds like the best solution to me. Second choice is to install a HeliCoil. I don't know if there is enough "meat" around the hole to install a Time-Sert. If you have never installed HeliCoils or Time-Serts, your new carb is NOT the place to learn. In that case, take it to someone with experience doing this. A machinist would be my first choice.
Charlie Kuss

[ArVeeNiner]

Originally Posted by carguy614

there is no way the threaded repair can unwind from the back and end up in the venturi and get swallowed by your engine.

Chris

That's exactly what I was worried about. I'll check around and have an expert do it.

I would guess that I don't want the repair to protrude beyond the carb wall on the inside downstream from the butterfly right?

Lesson learned: If you feel a bit rushed, just stop and come back tomorrow. I was aware at sometime in the past that you had to drill a hole a bit smaller than what you're tapping but that information flew right out of my brain. I hadn't worked on the project too much this week and I wanted to get a quick job done last night. Now it's a bit longer job but fortunatly, not something that cannot be fixed.

Thanks for all the help.

[rzbill]

As suggested, a 1/4-28 timesert is the way to go. These are the "good stuff".

http://www.timesert.com/

For those that are not familiar with this product, it is a particular type of solid thread insert. It is much thinner wall than a Jergens, Carr Lane or Eze-Lock because the Timesert uses a custom outside thread design that "nests" with the desired internal thread. Most compact solid insert repair possible.

Per Charlies comment, there may be limited meat for a standard Eze-lock type, but there is gobs of room for a Timesert. The second advantage is the top flange for the reasons that Chris mentioned.

I don't find these to be common knowledge. Make SURE the machinist knows what you want.

[Mike S]

I will add my aye vote for the time sert, but I suggest a couple of things when using it.

1. Machine a spot face on the casting----this is a smooth area for the time sert flange to sit on. A decent machinist will know what to do.

2. Use a sealant to prevent leaks. Locktite 567 should do well.

Good luck.

[trib]

I would first check and see if there is a temperature probe with a 5/16 or 3/8 thread. Dynon and JPI would be a good source. These are fairly simple probes and hopefully there will be different sizes available. You can then drill and tap for the larger size and avoid having to use a thread insert, which gives you two possible leakage paths instead of the one. In any event, make sure you determine the correct drill size for the tap. The metal on the carb is also very soft, so if you are unfamiliar with tapping a hole, it would be a good idea to first take a piece of 1/4" aluminum (any, not necessarily your good airplane stuff) and practice drilling and tapping, using a bolt to check your fit. Getting a cohort who is familiar to give some advice might be a good idea also. Bottom line is you want to dry run your technique before possibly buggering up your carb.

I know this is probably a bitter pill to swallow, but this is a learning experience!