Spark plug thread inserts

I've been doing alum. cyl. head repair for 24+ years and see Heli-Coils as a fine way to go. The stuff I work on is strictly high performance and Heli-Coils hold up fine in these heads, so a Honda head would should work out fine too......

That's reassuring, but I have heard of Helicoils pulling out and blowing out from guys I talk to. I wouldn't think of using one normally (with plugs) and am fairly certain that Helicoil recommends againt it. Thanks for the reply.

Toyota MDT in MO

Ask if he used an oversized helicoil:

Be reassured again. I have been using them for 40 years with great success. I have also seen a number of botched installations that did blow out. And as your machinist said, it's the only insert that will fit. I don't know why he characterized it as other than a first rate repair. Heli-coils are used commonly on aircraft engines and can also be found in Porsche engines. Why would you not use one? And where in the world did you get the idea Heli-coil recommends against? The fact is they sell kits specifically for spark plug thread repairs.

Actually, they make a kit for spark plug threads. I've used them on outboard motors. Never had the occasion with cars.

Yes they do. I HAVE one of these very kits. The machinist installed a STANDARD Helicoil, the kind that is made of 2mm thick stainless wire. A real spark plug repair insert is solid, eliminating most of the compression blowby and erosion faults inherent in a standard Helicoil. In fact, the solid insert is to be installed with high temp sealer around it as a precautionary measure.

As previously stated, I felt uncomfortable trying to install my Helicoil brand plug insert due to the space limitations. The machinist said he could put one in over the phone, and he has more experience (good or bad) than I do, so I brought it to him. If he had told me that he was just going to thread a simple Helicoil in it even though I had asked for a plug insert specifically, I would have tried another shop.

Toyota MDT in MO

Yup, but the machinist installed a regular wire type Helicoil when I specifically asked for (any brand) of spark plug insert made soley for that purpose.

Toyota MDT in MO

just to make you feel better next time you have to have one of these repaired...

nate

Thanks for that tip. I've heard good things about Timecert, esp. in respect to the Ford V8s and V10 that throw plugs like a roman candle. Lisle has another system; when I asked the machinist he said that Lisle has a .020" larger outer diameter than the Helicoil brand but he mentioned nothing of Timecert.

Toyota MDT in MO

Sure, some Heli-Coil inserts come loose, but not because they aren't suited for the job. The ones that come out have been incorrectly installed. When the hole is machined correctly, and the insert is installed correctly, there is NO inherent blow-by and erosion. The spiral wire Heli-Coils have been the most reliable I've known in over thirty years of using them. And the "real" solid inserts you're on about are some of the most likely to come right back out with the spark plug next time it gets changed.

OK, thanks for the input.

Toyota MDT in MO

Did you go to school with Mittlestaedt?

I used one a Datsun B210 head and got about 200,000 more miles on the engine afterward. If the transmission hadn't exploded in a cloud of gear fragments on rt. 95, I might have been driving it years longer.

--scott

I bought a used BMW M10 engine that had helicoils in two of the holes. One galled to the spark plug and backed out when I pulled the plug, one seemed OK. I replace the one with a solid type insert. I strongly suspect that the one that failed did so because this engine had been sitting outside for quite a long time, and was basically toast. For me, if you do the job properly, use antisieze on the plugs and don't leave your engine where rain water will fill the spark plug holes for years at a time, helicoils are OK.

Brian