GlenL

First off... I used the 3/8" bending beam torque wrench and always have. I'll take them to 25 Nm as that's where the sealing rings stop yielding.

Stripped out a spark plug on the 1987 944 N/A which has the 2V head. Seems like a simple enough job to use a rethread kit to fix...but which kit?

The Heli-Coil kit looks good enough. It doesn't have the coils but has the tube that the other kits have. I like the self-aligning reamer/tap. The sleeve's are "straight" with knurling at the top that get's expanded using a driver. My concern is the sealing approach with high-temp RTV. Is there a better product to use between the sleeve and the head?

There's a kit from NAPA that seems good enough. The reamer/tap isn't self-aligning, though. The sleeve has a lip around the top to seal with the head but it doesn't get inset into the surface. The sealing ring for the plug won't add to the sealing between the head and sleeve. The kits comes with some special sealant and the instructions say the engine is "ready for service" immediately after installation. RTV take 24 hours. I don't know what's in the tube.

The best-looking kit is the Time-sert. Of course, it's over $200 and the others are sub-$40. This has the self-aligning reamer/tap. The sleeves have a lip at the top and the kit includes a tool to ream out a groove in the head surface so it's inset. It'd take some skill to get that just right but it'd seal to the block and then let the sealing ring on the plug seal it all up.

Time-sert looks like "the best" but also the most money and not readily available. The Heli-Coil and NAPA kits are available at nearby parts stores.

Any advice or experience? I'm especially interested in how to seal/lock the sleeves into the block.

fasteddie313

You want the sleeve style, a coil style will leak compression..

Set that piston just after BDC on the exhaust stroke so the piston is down and the exhaust valve is open, put your shop vac on the end of the exhaust pipe and blow through the exhaust pipe all the way through the spark plug hole so your chips from tapping blow out straight away and don't stay in your cylinder.. Take the top and filter off your shop vac so it just gets clean air from the room..

That's what I have done before..

The inserts may seal/lock by expansion from putting the spark plug in, but I don't know..

Van

If it were me, I'd change the head... They are plentiful, and there's plenty of while-you're-in-there type of stuff to make it worthwhile. Including water pump, belts, rollers, front seals and head gasket.

The car will thank you for freshening all those up.

FRporscheman

A spark plug blew out on my dad's 4.6L F-150. I bought the timesert kit, because I wanted to fix it once and have it last forever. Also, I never want to take the heads off of that engine, and even if I did, a used head is not a good option, because spark plug blow-outs are very common on those.

For you and your 944, stripped spark plug threads is uncommon so a used head is a good route. Especially if you were ever planning to do engine work. If not, I say don't invest money in the timesert kit and just go with a helicoil or something. It will work fine. Even if it doesn't, then you can take the head off and get a good one.

A friend of mine has a helicoil-ed spark plug hole in his 968 - it's held up for at least 30-40k miles and going.

GlenL

Thanks, Guys. I've settled on the Heli-coil kit with high-temp red threadlocker to hold it in.

I'll post how it goes.

GlenL

Well, that could have gone better.

I got the Heli-Coil kit and set to it. I tucked a few paper towel pieces into the cylinder to help catch chunks and fluids and then tapped the hole. The reamer/tap is nice as it starts with a 14mm tap to guide/pull the reamer section and then there's a 15mm (?) tap section. Still had to push on it to get it straight but the tapping sent well.

Cleaning out the hole was a challenge. I thought to use the shop vac to suction them out all out. I got the crank aligned on the exhaust stroke to let air in and sucked out the shards. The paper towel suck in the hole and I pulled those out with pliers. Still, when I went at it with compressed air and a long-nosed blower attachment there were many chunks flying out. Finally got it clean and could proceed with the sleeve.

The sleeve has these knurls at the top and I was concerned about test-fitting it as that might be the final fit. Using an old plug as a tool, it went in part-way well so I gloobed it up with the high-temp red threadlocker (Permatex) and ran it in. I smoothed the threadlocker off with a bit of paper towel so it covered the threads and there wasn't a lot of obvious excess.

After running it in to tighness I could see the last tiny bit of sleeve was proud of the surface. Maybe 0.2mm or so. Easy! I'll tighten it a bit harder. No progress. So maybe it's supposed to be like that and the driver thing with the kit rolls it down. Hit it strongly but no movement. After all that and the threadlocker setting it wasn't coming out nor did I try. The hole looked tapped right an the tap was deep but maybe it needed a few more turns. The answer, as is so often is, was more tools.

I got a few small grinding bits at the hardware store. Not Dremel as those looked to be too light. One cone, one ball and one barrel that has a flat top. The seat is about 3/4" across so need small tools. Using the ball on the drill quickly took most of the exposed lip off. Then using the end of the barrel made it all flush. Looked and felt good and didn't eat into the aluminum head much.

So it's ready? No!

When I went for the spark plug it had a hard time getting down into the sleeve much. Worked slick on the bench. I got the 14mm thread chaser out and it refused to even start. That left the 14mm tap as the option. It was a bit of a challenge to start but it found the threads well and cleaned them out. Some resistance along the way so the sleeve had become distorted. Probably from using the driver thing on the exposed lip.

Now the plug went in fine and snugged up tight. Done.

Lessons: Prepare to blow out the cylinder. A compressor and long-nosed blower tool are required. Make sure the hole is tapped fully.

V2Rocket

if you ever do take the heads off, the post-03 2v heads have more threads in the spark plug holes so they don't strip (as easily)

fasteddie313

If you blow through the exhaust out the spark plug hole while/during/the whole time you are doing your tapping operation the chips blow straight out and don't go into your cylinder in the first place.. Shop vac that has the blow attachment, or an electric leaf blower on the exhaust pipe..

FRporscheman

^Nice trick!

Sorry you had a hard time of it. Maybe you used too much thread locker? You only need a little bit, and it should stay on the outside of the insert. I did have a similar problem one time putting in a helicoil - I couldn't get it to go in all the way before the tang would break off. It was because I was using a metric tap (I think m14, for an m12 insert). I bought the special Heli-Coil brand tap for m12 inserts, and it was a TINY bit larger than the one I was using. Insert went in like silk.

I'll keep that in mind, thanks!
But having already dropped $450 on the Timesert kit, I might just put inserts into the rest of the holes instead of buying 2 heads.

GlenL

I did apply the threadlocker more like antisieze than a typical drop. I wanted it to seal the threads and not just hold. It's not that thick. Maybe it set-up on me during the operation but I doubt that. The insert is a sleeve and not a coil like the typical Heli-coil used for thread repairs. No tang and it's a tube. I'm not certain why it stuck but it could be that the hole wasn't tapped well enough or that the knurling in the top 2-3 threads jammed.

In any case, it's fired up and I'm back to fixing driveability problems.