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Posted by: Porschef Apr 10 2013, 07:05 PM

Well, it seems that the constant reoccurrence of an exhaust leak stemmed from a pulling exhaust stud. I'd tighten it, the noise would go away, come back, rinse, repeat.

A couple of weeks ago I took her out for a spin, heard that sound, and got under after cooling to see what the deal was.

A quarter turn later, the stud dropped right out.

So I'm gonna do an EZLOK insert, and pray.

Pics to follow, along with any tips, snags, or bonifide cuss sessions.

The fun never ends

Right Joe?

Posted by: Rand Apr 10 2013, 07:14 PM

A step stud is a solid solution, no prayers needed. I'll take new real threads over an an insert any time I can. Exhaust stud is one of those times. They were cheap at my local VW shop. I think I even have extras.

Posted by: 76-914 Apr 10 2013, 07:17 PM

drill it in 3 steps i.e. use 3 different sizes working up to the final required tap size. this acts almost like a guide and you can't miss. be ready for the drill bit to want to pull into the soft aluminum. mark your bit depth with some blue painters tape. you won't be able to see blk elec tape in that recess and duct tape is the shiots to get off.

Posted by: Rand Apr 10 2013, 07:28 PM

Depends on the size of the step stud I guess. I just tapped mine once and done. I don't see a reason to redrill three times. If you have to drill at all, just drill the right size. Yes it needs to be straight, but you knew that.

Posted by: Porschef Apr 10 2013, 07:49 PM

Rand,

Thanks for the offer. After getting twisted up about stepped stud availability, I realized that there was already a stepped unit in there. So I'm gonna go with an EZLOK to get me back to using an 8mm stud.

I love a repair that could lead to a partial teardown if done improperly...

Posted by: Rand Apr 10 2013, 08:05 PM

Hope it goes well.

Posted by: ThePaintedMan Apr 10 2013, 08:45 PM

Don't let anyone fool you, it's not that hard. I did three at once. Mark the bit depth, and drill at the exact same angle the original stud was at. If you can, use some kind of drilling lubricant - Harbor Freight sells a good foaming kind that won't drip out.

I know that others here have far more experience than I do, but personally, I wouldn't worry about the step stud. If THAT one pulls out, you won't have enough aluminum left to tap the hole for a Time-Sert/EZ Lok. If you install a Time-Sert (which I would recommend) the first time correctly, with red Locktite, you won't have to do this job again later.

Sounds intuitive, but some may not know this - you must remove the heat exchanger first so you can see what you're doing.

Posted by: Rand Apr 10 2013, 10:13 PM

Wait, what? About the step stud? You prefer an insert? With Loctite? Did I hear that right? Oof. Really? That's why I'm not painted.

Posted by: Porschef Apr 11 2013, 04:35 AM

Yes, heat exchanger is off..

I don't want to use the stepped stud as the hole for an 8 mm stud insert Is obviously smaller. So I'll track one down, and go with the EZLOK as a hopeful solution.

Looks like Saturdays project...

Posted by: ThePaintedMan Apr 11 2013, 07:32 AM

Sarcasm aside (and I did say that you guys know more than I do ), a Time Insert is a stronger and more reliable option. If I remember correctly, several engine builders here have recommended that when heads are rebuilt that Time Serts be installed to avoid future headaches. They are along the same lines as "case savers" for Type 1s, which are installed to prevent case studs from pulling in high HP applications.

Aluminum gets brittle as it is heat cycled over and over. If you drill out a stud, re-tap the aluminum and install a step stud, is it not just a matter of time before the step stud pulls out from the same forces that pulled out the initial stud?

Finally, if a Time Sert pulls out (which I have not heard of), another can be reinstalled. If a step stud pulls out, the hole will then be large enough that it is doubtful you'll find another step stud large enough at the base, but still small enough at the stem to fit our heat exchangers.

Anyway, the point of my original post was to reassure Porschef that if he goes slow and takes the right precautions, it's not as risky as one might think. Drill straight and do NOT drill too deep. You'll be fine.

Posted by: worn Apr 11 2013, 09:56 AM

I am afraid that Time Certs aren't magic and can pull out. At least that is what I read in the 911 books. Also, if a time cert actually pulls out, that leaves a pretty big hole. I don't think you are going to get it back in. With that said, I like time certs. They move the stud interface from steel to aluminum to steel-steel. Then when the electrolysis corrosion fairy comes calling, it will lock the time cert in place, not the stud. And hopefully the loctite will even prevent that.

Posted by: ThePaintedMan Apr 11 2013, 10:02 AM

Sorry, I guess I meant loosen, as in the Time Sert unscrews with the stud. I imagine it is possible for the Sert to pull out of the aluminum, but I personally have not witnessed it.

Your point about the steel-steel interface is a good one, and exactly what the designers had in mind, from what I understand. If I ever rebuild a set of heads, I am strongly considering installing Serts in each exhaust stud hole from the get-go; I trust them that much.

Posted by: stugray Apr 11 2013, 03:57 PM

FWIW - in my business (aerospace) threads directly into Al, is absolutely Verboten!! Inserts ONLY (they can be replaced).

That said - when I got my first 914 (I was ~20yrs old), it was not assembled when I bought it, so I did not know what the exhaust SHOULD look like. I didnt know what the "funny shaped steel thingy" under the trunk carpet was for....

I drove the car for a year or two with no rear exhaust support for the exhaust and all the weight (and torque) was being applied directly to the exhaust studs.

No wonder that I had to replace exhaust studs every few months.

By the time I figured it out (and installed the exhaust support bracket) I had:
Drilled stripped stud, tapped, insert new step-stud
Drilled out stripped step stud and replaced with insert + stock stud
Drilled out stripped insert and replaced with New Insert + Step stud

Learned that exhaust is supposed to be supported from the back with bracket

Lesson learned is: Make sure the rear is suported.
The heads can be drilled & redrilled with the heads in the car and inserts installed more than once, but requires the skill of a Anal-retentive person that has drilled thousands of holes in Al.

I do NOT condone such stupidity that requires you to do this repeatedly ;-)

Stu

Posted by: yeahmag Apr 11 2013, 04:15 PM

Time Sert is the way to go. I think Aircooled.net sells the inserts and rents the tools.

Posted by: yeahmag Apr 11 2013, 04:26 PM

http://vwparts.aircooled.net/Time-Sert-Thread-Insert-8-x-1-25-x-11-7mm-18121-p/18121.htm

Posted by: ThePaintedMan Apr 11 2013, 04:49 PM

Hmm... see, I may be painted, but I'm not crazy.

Posted by: Porschef May 2 2013, 07:56 PM

Lazy man finally posts pics...

Here's the hole from which the stud pulled out...



The tools required. Pretty basic- a drill index, a 27/64ths drill bit, ultimately, a 1/2"x13 tap, the same size sawn off to create a bottoming tap, and the EZ Loc.



The EZ Loc. Cost about four bucks at Fastenal.



Drilled it out, and tapped it. Then I ran the flat bottomed tap in a bit to make sure there was enough thread to grab...



The EZ Loc screwed right in



I forgot to take a pic of the stud in the insert. I picked it up at the local Ace hardware. An 8mmx8mm exhaust stud. Cost just over 2 bucks. It had a flat, that would bottom out in the insert, without hitting the head. It was a little longer than the others, but the nut would tighten without any problem. After, reattaching the exchanger went fine.



All went well, the leak is gone.

Posted by: Chris H. May 3 2013, 07:52 AM

You sir are a stud (repair guy).

Posted by: r_towle May 3 2013, 08:06 AM

Very nice.

Is there red locktight on that insert to keep it in place as you tighten or loosen the nut?

Just curious how things stay put.

rich

Posted by: stugray May 3 2013, 10:24 AM

I replaced the three exhaust studs that came out during disassembly (two were 9/8mm step studs). Went to put the exhaust stubs on last night and the rest of the studs are all jacked up and need to be replaced as well. They all have rusted threads and sections of threads missing right where the stock nut took a bite and then rusted in place over 40 years.

So tonight will be fun removing 5 more studs from the assembled engine.
At least it is still on the engine stand so I can turn it upside down to work (not quite so much fun with the engine in the car ;-)

Can I get enough heat into the heads with a propane torch, or will I need Mapp gas like some of the other threads on exhaust stud removal?

Stu

Posted by: saigon71 May 3 2013, 05:01 PM

Looks like a fine repair!

Posted by: Porschef May 3 2013, 10:37 PM

Rich, yes, there's a loctite type material on the insert. Once it heats it's supposed to stay put. I tapped out the hole just deep enough to accept the inserts depth, then tightened it a bit more..

Stu, I'm not sure; do you mean to remove the existing installed studs? I don't know about heating them; others surely know better. Could be as simple as a vice grip, or at least double nutting.

Thanks Bob.

Posted by: stugray May 4 2013, 02:05 PM

Thanks for the tip! I posted a thread about where to find exhaust studs just a week or so ago.

I searched at Ace better and found them! 8X1.25 X 62 mm.

Just a tad long but that is fine.
I also found two different types of stud extractors just like the pic posted at Sears.
Well see how it goes tonight.

Stu