I just came into free ownership of a pretty decent Super Tigre 3000. One problem........It looks like it had a stripped glow thread at one time and someone drilled and tapped it to 1/8 npt and put in an insert with glow plug threads in the middle. There is also a small socket head screw next to it to keep it from turning out (I think). I found the threads of the insert bubbling after-run oil and removed it. The threads seemed a little sloppy meshing. They had a little play in them until it locked down. I cleaned the threads and smeared some blue thread locker on it and reinstalled it. It still leaked a few days later.

What should I use on the insert to seal it permanently? I have some RTV silicone I was going to try next. Would pipe joint compound or teflon tape be better?

The RTV may seal if you use the copper high heat, but how long? I use Copper high heat to seal my mufflers. Loctite has a 660 retaining compound called quick metal. it is for sloppy bearing races, etc. I used it to glue a timing belt pulley on my sisters 1991 Mazda crankshaft and it is still running 6 months later. We found it at an Industrial Hardware Parts house. Hope this helps, Gary

PRODUCT DESCRIPTION
LOCTITE® Product 660 is a single component, anaerobic paste consistency retaining adhesive for cylindrical joints. This product cures when confined in the absence of air between metal surfaces. This product possesses excellent gap cure characteristics.
TYPICAL APPLICATIONS
Used to bond cylindrical fitting parts, particularly where bond gaps can approach 0.50mm. Typical applications include restoring correct fits on worn shafts, spun bearings, and damaged keyways.

Have the hole welded shut and redrilled for a turbo plug!!! [8D]

Send it to Clarence Lee and have him put a helicoil in it. He has an ad in the classified ads in the back of the model magazines. He does fantastic work.

Hello; I can't picture where the set screw comes in there, but the high temp copper, silicone sealer that loctite sells is what I would recommend. I have used Lostite's 660 but never on a sealing situation. It is designed to lock (for example) loose bushings to a shaft, and not to seal compression pressure in a high heat situation. If the oil is leaking from the set screw threads, a high heat thread locker will seal it.
I have seen many Irvine diesel heads leak oil from the set screw that locks the compression adjuster.

I would be tempted to pull the plug out and do a 1/3 turn clean up of the thread in the head and then do the same on the plug. Make sure that the threads are clean. Now use a good Hi Temp thread lock and screw it down really tight.

Question, is the 1/8 pipe material steel or aluminum. You may have a rough time getting a seal to last with all of the thrermal cycling an engine goes through, especially if the two materials have a different thermal expansion. You may be better served getting a new head. It may be the least expensive option after trying different compounds and possibly getting some of them in on top of the piston.



Don

weld it , drill it, turbo plug it.

Hi!
Easiest would be to just get a new head. Second a heli-coil.
Third send it to Dave Shadel at Performance specialties and let him put in a Nelson glow plug.

The NPT insert has a shallow flange on the top of it There is a notch cut into it. The set screw I mentioned is screwed into the head next to the insert and keeps the insert from unscrewing by it's presence in the notch in the flange. I believe, without the setscrew, the insert may unscrew if you unscrew a tight glow plug. Both the set screw and insert are steel. Mentioning that they are dissimilar metals wouldn't matter since glow plugs and head bolts are steel also and are screwed into the aluminum head.

I'm going to try the hi-temp silicone just because I have some left over from making glow gaskets in the past. I have never seen that stuff fail using it for back plate, exhaust or carby gaskets. What do I have to lose at this point?

If the high temp sealant doesn't work you can get a new head for $24.99
http://www3.towerhobbies.com/cgi-bin...&I=LXFX34&P=SM

You could have it welded, drilled, and tapped. But, if you can't do it all yourself, it would probably cost more than a new head.

I second sending it to Clarence Lee . I've read of many people with stripped glow holes, and they were very satisfied with his work, the price, and the turn around time. That's what I would do.

If the insert is not blowing out, I wouldn't worry about it. Revolvers work pretty good with a barrel/cylinder gap.

There is a big difference though. The steel glow plug doesn't seal against the threads in the head, but with the copper washer. If the plug expands at a different rate than the head, the linear expansion isnt much, so the gasket takes up the difference. The head bolts are slightly stretched when tightened, so the difference is accomindated with the elasticity of the bolts.

You mentioned that the NPT adaptor had a flange on top. Have you tried a copper washer under it? That probably is all you need.

Don

Hey Don, I hear ya about the washer. I have one the right size washer laying around but with that notch cut out of the flange and the set screw I'd have to notch the washer too and that would cause it to leak at that point. It's a no win thinking I'd seal it that wayl.

BTW the Hi Temp silicone seems to be sealing...there's no bubbles or leak but I haven't started it yet either.

I looked up your tower website and found out the ST head comes with a threaded insert installed as original equipment. Whoda known?

I suspect there is a big difference in a "Press-Fit Threaded Brass Insert" that was installed in a factory and a steel pipe plug that was screwed into a tapped hole where this insert used to be.

Can you post a photo of the head? I think that the copper washer might do the trick, even with the notch. If you can get the insert screwed down tight, you may not need the setscrew. My guess is that it was added as an afterthought because the flange was leaking and they thought it may be from teh insert unscrewing. A tapered thread has tremendous holding power, so the flange must have been interfering with the threads from locking fully. A gasket will further prevent the thread from locking, but it will provide a better seal. If you have one in hand that fits, give it a try before the silicone or other adheasives. Once the silicone goes on, there is no backing out from there.

Don

Remove the insert, goop it up with jb weld on the threads and reinstall. This is what CH ignitions does when they bush a 14mm plug down to a 10mm plug, it doesn't leak and gas engines normally run hotter.

It may be a spark plug ignition/conversion attempt gone horribly wrong.......