Those damn heat exchanger studs!

[Paul914]

Ok, I'm sure everyone knows what a pain in the ass the heat exchanger studs (in the head) can be - well I've got another stripped one! The normal studs are 8mm on both ends (with a 12/13 mm nut). In the past, I've simply re-tapped the hole to 9mm and used a 9-8 step down stud (9mm on the head side, 8 on the other end). I'm out of 9-8's and can't locate anymore - does anyone know where I can get some? I have a 10-8, but that's for "the next time" it strips. If I use it now, then the next time (assuming it'll happen again sooner or later) I've made a bigger project out of it than need be (I don't think there are 11-8's, and even if there are, they may not fit/work)! Help! If anyone has any or knows who carries these, let me know .. thanks!

-Paul

Paul

I just purchased the studs your looking for at Riddle Machine (RIMCO) in Costa Mesa, CA. They were $1.25 ea. They're phnoe # is (714) 549-0357 (Whew, that was easy). Anyone seen any benifit to "time-serting" these over tapping out one size bigger ea. time they come out. I've really only seen mine strip out when I installed exhaust systems with poor or no rear trans. support brackets (!)

[Paul914]

Well, I just got off the phone with them and the guy told me "sorry, we don't carry them". Maybe the guy on the phone was just a little slow - do you have a part number on the receipt from your order? If you could get me a part# (from RIMCO) for the 9mm-to-8mm 125 pitch studs, I'd really apprec it! You know the studs/application I'm talking about, so I'll trust you over some guy working the phones over there - thanx!

[Tim Polzin]

I had a couple of studs strip and reinstalled them using the spring type insert. I bought the kit to do the 8mm stud repair which included about 8 inserts, a drill bit, a tap and a funny little tool to insert them. The only problem I had was that the insert was shorter than the hole, so I ended up using two in tandem. They have been in for over two years with no trouble.

I'd be interested to know if using the oversize stud is a better approach.

[Wayne 962]

Hmmm, I don't think that using the oversized stud is the best idea if you can put the inserts in. Our machine shop does this as a regular procedure for repairing the head studs. The inserts are steel and won't strip...

-Wayne

[Paul914]

I have used the oversized studs in the past with much success! Besides, there is another advatnge to them - you are only increasing the size of the hole by 1mm. So if it were to ever go bad again, you could then go to a 10-8, and if that were to go bad (what are the odds?), you could then go to an insert. No sense in rushing into making the hole bigger than necessary to stick an insert in ..

Two other nice things about the step down studs - (1) its fast and easy, and can be done withthe engine in the car (2) it's basically the same as the original stud setup, except since the base is slightly larger, it should now be even stronger (in case of over torqing, you have less of a mechanical advatage on the nut side).

To each his own - I've had good luck with the studs, so considering there ease of installation, cheap cost, and good reliability, I'll stick with them for now!

BTW: It appears that Porsche still sells the studs - part#N.014.684.1 .. they go for $2.40ea, but most dealers will have to order them (week or so wait).

-Paul

[Wayne 962]

You're right. I was thinking that you would want to put the inserts in when you are rebuilding your heads...

-Wayne

[JP Noonan]

The inserts, brand named "Helicoil", are used at the NAPA machine shop I used to work at. According to the manufarcture they are indeed stronger than a normal threaded hole in alum. The reason is that the Helicoil distributes the stress over a wider cross section, true this means that the hole is bigger, but the helicoil and the stud are steel (actually stainless in the helicoils case) so the threads don't seize to the stud causeing strip out. Personally I don't like the step down studs because the ones I've seen are 9mm at the shaft and then stepped down to 8mm. This caused a fit problem (read: "time for the the hammer")with my after market SS heat exchanges, this problem didn't exist with stock studs.

[Paul914]

Ok, I'll buy the explanation about why the helicoil is stronger .. but I don't see why you'd have any problems with the fit of the 9-8stud. The "9mm side" of the stud is threaded into the head - it doesn't stickout/show itself at all. The only thing coming out of the head (i.e. that the heat exchanger goes over) is the 8mm side of the stud (which is the same as the original stud).

Whatever the case - as I said before, I've always had pretty good luck withthe 9-8's (knock on wood), so I like to us them. Plus you only have to increase the size of the hole in the head by 1mm for the step down (as opposed to the rather large hole needed for the helicoil) .. my philosophy: if the 9-8 strips, you can always go to a 10-8, then a as a last resort a helicoil .. 3 chances to screw it up!

-Paul

[John Rogers]

We have a 914 now and this problem will probably visit us too. Years ago we had a 73 VW van and had trouble with leaky exhaust and stripped studs in the head. To fix it I removed the headers, drilled and inserted 10mm studs(no step down), drilled the headers to fit the studs and NEVER had another leak. There is more tightening torque available with the larger studs and there will be a much better seal. The inserts in the head are the way to go.

[Dave at Pelican Parts]

I think there is a little bit of confusion over which option is which.

One option is the step-down stud. Pretty obvious.

The next option is the HeliCoil. This job looks like a steel spring. With the HeliCoil, you drill the hole just *slightly* (<1mm usually) oversize, tap the hole for the oversize threads, then run the coil in to bring it back down to the original size. As an example, the M6 HeliCoil kit I have uses a 1/4" drill bit, which is less than 1mm over 6mm.

The "insert" (one brand is TimeSert) is more like a nut that gets put into the head. In the case of this insert, you have to drill a hole somewhat larger than the original stripped hole to put the insert in. The inserts are either steel or stainless steel. There's more area for the head and insert to grab onto each other, so these inserts tend to be stronger than HeliCoils. However, they take more work to install, and are more expensive.

One exhaust stud hole on my car was repaired with an insert--badly. There wasn't enough material left to put another M8 insert in the same location, so my mechanic used an M9 or M10 insert, and a step-down stud. No problems so far. He did the work with the engine in the car, as well.

--DD

[Bruce Allert]

I need to replace a stud. The one I tried to use would almost tighten to the 16# torque rate then, it became loose & wouldn't tighten. Do I need to re-thread the hole at the next size up or can I just try a stud that is the next size up? My way of thinking is I need to re-thread.

..........b

[Biggy72]

Right now I"m the head mechanic at our saw shop and I'm constantly fixing magnesium saw cases. The only thing I will use is the timesert inserts simply because they really aren't that hard to put in, they are really strong, and if they do come back out they don't strip the surrounding area. All that needs to be done is a new insert needs to be put in. I won't go back to helicoils ever again.

[Dave at Pelican Parts]

Bruce, you can't just screw in a new stud. You'll need to somehow get new thread into the head for the stud to grab onto. Which means either drilling the hole oversize and tapping the threads in, or going with a Helicoil or a threaded insert.

--DD

[Bruce Allert]

That's the kind of answer I was waiting for.... someone to draw me a picture. Thanks Dave

.........b

[Otto]

Are you using the muffler hangar?

[Bruce Allert]

Yup, got the original. my muffler is only a couple years old so should do the trick. I went & got a helicoil kit ($31) with about 10 coils a tap & little tool to insert the coil. Drilled the old stud hole, stuck in the helicoil. Then put some locktite on the stud & screwed it in. Will know tonight if I can unscrew just the nut off the stud!

.........b

[BigD9146gt]

helicoils work great, as well as the bigger studs. You could go to the bigger studs untill you strip them out, then helicoil those. If your ever in a pinch (on a trip and a head stud pulls out and have 200 miles to go and no machine shop open, you can even put fast drying JB weld in the hole and on the thread and screw it it, wait 30 minutes, and drive... yes, i did this on my old motor. worked great till the day i rebuilt it....50K miles later.