So the continuing saga of fitting the SS heat exchangers continue. I somehow pulled out the heli coil repair on the exhaust stud. The coil measures 9.5mm OD.
I suppose I need to re-tap the hole with a step stud.

So what size step stud should I use ?? M8 to (M10 or M11) ?
Where would I find such a stud ?
Is it do-able, drilling and tapping from under the engine ?
How the heck am I going to keep the bit and tap straight and not F/up ?

Man it never ends with old cars......
Thanks in advance for everyones help !!!! I really appreciate it.


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Its not that same area, however, i just had the threads on an intake stud strip out and i used a timesert, extremely simple, a little on the expensive side because you buy a whole kit when you use one but it worked really well. These might work better than a helicoil.

You need a time-sert. Search ebay. Way better than helicoils.

Your best bet now will be to get a M10x1.5 Time-Sert or Heli-Coil kit. This will allow for the installation of a M10x M8 step stud. The O.D. of the Time-Sert/Heli-Coil will be ~12mm. This is required now that you have pulled out a M8 Heli-Coil which, as you can see, has a ~10mm O.D.

Attempts to tap for a M10 stud only (no insert) will fail as the hole is already to large for this. A M10 tap requires a .325-.340 tap.

Keep in mind that drilling to deep will punch into the cylinder itself and the head will have to come off if this happens.

Also keep in mind that the repair you are about to make is pushing the limits of material that the stud boss will support. This is the end of the road as far as repairs that don't require welding. I would be hesitant to hit the road with a repair of this sort. This may be a stop gap that buys you time, but head work is likely in your future.

This sucks for you! And it's the reason I do not install inserts in T4 heads I reman. All repairs are weld repairs with M8 threads tapped. That way if a field repair is ever required there's something to work with.

Good luck.

i went through this, i fixed it with a very stout ezloc, i doubt i will ever have a problem
with it, plus there inexpensive and easy to install, and removable.....

http://www.ezlok.com/InsertsMetal/index.html

http://www.ezlok.com/InsertsMetal/threads-uncExternal.html

Be careful with the step-stud. You need to make sure that the angle of the new hole + tap = the angle of the original. Or, it will not seat properly on the header.

Ask me how I know.....

ouch, Hoffman laid that one out nicely.

Not trying to 1-up Len. Just trying to add to the conversation. I certainly don't have the expertise to contradict Len.

I use a fixture t ensure the holes and tap threads are on the correct angle
PS. heli coils are evil

The picture looks like a time cert. It has a shoulder.

dam that time sert pic from ebay looks like exactly what was pulled out. I guess I dont know what I actually had. It wasnt an heli-coil after all. Might look into that ez lock.

dam that time sert pic from ebay looks like exactly what was pulled out. I guess I dont know what I actually had. It wasnt an heli-coil after all. Might look into that ez lock.

You won't like this, but read it anyway. Remove the head and have it welded, machined, drilled, and tapped. There's a REALLY good chance the threads and inserts are going away because the head is cracked. Be sure they fix ALL the cracks. Plan on spending a lot of money.

BTW, there's NOTHING wrong with Helicoils if they're used as intended. They WON"T fix weakened or cracked base material, nor will any other brand/type of insert.

The Cap'n

Dam it. I dont think I have the minimum 9/16 depth for the ez loc. I have to crawl back under the car and check. This really sucks !!!!!!!!!!!

I did this a couple of years ago with the engine in the car. Go slow, get the angle right and measure the depth ahead of time so you don't go too deep.

One of the hardest parts of the job for me was finding a correct step stud. I had to mail order from Canada. No one had 'em or if they did the threads were cut incorrectly.

Good luck!

Everything The Cap'n said is correct. I've seen a gazillion of the cracks he describes. That said, I examined the photo and it appears that you may just have a stripped boss. Hard to be 100% sure, but that is my hunch.
And there is nothing wrong with Heli-coils if they are installed correctly. The biggest mistake is poor threading, regardless of the insert type. It's a touch task laying on your back to get it right. An unsteady hand will make a larger thread.
The biggest drawback to the heli-coil is that it can be difficult to install in certain situations, like this one.

If you have been living right and you do a perfect insert installation the unit may just stay put. If it doesn't you are facing removing the head.

I can sell you a M10 x 8 step stud. My supply of the damn things is dwindling but I can spare one for a forum member in distress.
It will be M10-1.5 x M8-1.25

I may be wrong about this, but I believe the EZloc requires a larger hole than the time-sert or heli-coil. If that is the case I would not consider it for this job as you are about out of boss material.

A bit of advice that may sound counter intuitive, but trust me on this. Before you install whatever insert you decide to use slather both sides of that baby with copious amounts of copper anti-seize. Copper because it will stay put at higher temps without turning to paste like the silver kind. This will help keep the threads from corroding and increase the odds that the insert won't pull out over time.

The Time-Sert will be much easier to install in this situation than the heli-coil.

I don't drill too straight let alone run a tap straight while on my back.

Do you reccomend removing the head in the car or out of the car ?

What is more feasible, taking the head to machinist to weld and check for cracks around the stud bosses OR
get another used head. But then what is needed to mate the used head to my block ?

Which route is most feasible would you guys reccomend ??

Because of the proximity of the ex seat to the stud boss simply welding the boss and remachining (which needs to be done on a mill on a fixture for accuracy) is not a good idea. The welding causes distortion to the seat counterbore and can/likely will lead to a dropped valve seat.

The right way (and the only way I approach this situation) is a total remanufacturing of the heads. Anything short of that is patch work. Doing a little work here (welding) and a little work there (replacing one valve seat) but not doing a complete job will have you revisiting other issues at some point in the future.

Once you make the decision to pull the head, my advise is to pull both. Have them properly gone through, put the thing back together and don't worry about head issues for a very long time.

There are shortcuts and many people have tried them. Some have gotten lucky, many have not. You have to ask yourself, "Do I feel lucky?"

I have never used E-Z LOK inserts so I can't recommend or warn against them but I was looked at their site and found the drill/tap sizes.
If I was looking at pulling heads and having them rebuilt or trying to save 1 while on the car? I would look close at how bit the hole in the head is. An 8mm thread repair requires a 10.4mm drill and a 12mm tap, you might be able to get away with that and avoid the step stud.

Just a thought.

Jim

For 8mm x 1.25mm thread repair:
E-Z LOK Part No. 453-8
Internal Thread M8-1.25
External Thread M12-1.75
Length mm 12.5mm
Tap Drill Size 10.4mm
Tap Size M12-1.75
Minimum Full
Thread Depth 14.5mm
Drive Tool
Catalog No. 500-4

For 10mm x 1,5mm thread repair:
E-Z LOK Part No. 453-10
Internal Thread M10-1.5
External Thread M16-2.0
Length mm 17.0mm
Tap Drill Size 14.0mm
Tap Size M16-2.0
Minimum Full
Thread Depth 19.0mm
Drive Tool
Catalog No. 500-5

The M8 EZ lock O.D. is ~ the same size as the M10 Time-Sert and Heli-Coil.

Since the EZ lock uses a std 1/2 tap it looks like for this specific situation it would be the way to go. No pricey kit to purchase. Just the tap and an insert. When finished you can use a typical M8 stud.
I'd be inclined to give it a try before I pulled the head off. It might just hold up fine. If it doesn't work at least you won't have much invested.

ok, so I checked it again, appears the depth of hole is deep enough for the following ez lok. I think I will go with the standard external threads thinking easier to get the drill bit. I put the 27/64 drill bit in my hole and it looks like it barely have enough meat for it to clean up, but it will not go in the hole without drilling. Is this a good indicator I have enough meat for the ez lok ?

The next important part is drilling/tapping straight. I know it is VERY important, can I rent or borrow anyones jig or fixture they have made. I promise not to damage or will pay you for it. If the tap is crooked, am I all lost, is it still possible to tap the stud straight with mallet or something. Of course I am going to eye ball the best as possible. Any reccomendations and experiences to share ?

Once I buy a good quality 27/64 bit from Home Depot or whatever, I'm kinda scared of the HF one. HSS is good right no need for cobalt I think. I am going to turned it down in my friends shop so I can chuck it in my 3/8 drill and not have to man a heavy 1/2" drill under the car.

Anyone, anyone I can or borrow your jig/fixture to drill straight ?

http://www.ezlok.com/InsertsMetal/SSthreads-uncExternal.html
P/N 653-8
Internal thread M8-1.25
External thread 1/2-13
Length .484
Tap Drill 27/64
Tap size 1/2-13
Min Depth 9/16

Thanks All !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Hmm who sells the normal M8-1.25 exhaust stud ?

Both myself and Phoenix914 have used the EZLOC with success, i used the M8 1.25 x 1/2" 13 also, I have step studs and helicoils but the EZLOC looked like the beefiest solution that i doubt would ever pull out. I have had many failures with Helicoils pulling out. EZLOC's are easily removed which i liked over the Timecerts but can be also be locked in place.

I used a hand drill on mine very carefully and wrapped tape around the drill bit to set the depth. The existing hole was my guide.

Ace Hardware or Hardware Hanks sells metric exhaust studs.

I doubt hardware store grade studs meet the requirements. Porsche dealers can get the correct studs for you.

The Cap'n

I found this at http://www.mcmaster.com/#

93275A030

Seems to have the right dimensions.

Hello, did you buy the special tool or just used a big flat screwdriver ?

Big flat screw driver. Used a punch to lock the Ezloc after installation as described in the instructions.

Ace hardware does carry good grade exhaust fasteners in the specialty drawers. Step studs and all.

Remember to oil the tap and run it in and back it out removing the debris until you reach the final depth.

If you go slow, it should be fairly easy to drill stratight since you already have the existing hole as a guide.

It's a scary job, but one that I found to be very easy when I took my time.

This repair with the engine together requires surgical precision. It also requires a lot of luck.

I think more luck than precision ......................Repairing stud holes under a 911 using a drill guide is difficult enough. Doing the same on a 914, especially with a hogged out hole for a guide, is much harder, especially as the holes are at an angle to the rest of the head.

The Cap'n

I've done this same repair on my car and its been holding fine. I made do with what I had handy. I used an M10 time cert and then an M8 into the M10. I don't use studs, I use 993 pressure plate bolts with the tri-square head. It really helps if you have the car up on a lift so you are not working on your back. Go slow with the drill and match the other stud for the angle. Don't drill too deep. I also always use red locktite with to install time certs. Good luck. In my case, if it pulls out then I'll remove the head and have it welded but its been working great. Use a torque wrench.

Yup, this is what I used (from McMaster Carr) They make them in several body sizes for different pilot hole sizes.
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Fastenal carries them also.


I had to make an extension for my tap by using a 1/4 socket and extension with a
tee handle. My regular tap handle wasn't long enough to get in there and turn.

The only thing that I would add to that is to step drill it. If you can spread it out over 3 - 4 sizes it will be a snap w/ less chance of a goof up than if you drill it all out in one step.

I used these as well. You will need to grind the tap so it will thread deep enough. A bottoming tap may work. I have only plug taps so I cut mine down. These inserts may be bigger than timeserts. I have never used a timesert.

I am 1 lucky SOB. I was successful this weekend. Thanks to the help of all your support and suggestions. What helped was slowly drilling in steps to the desired 27/64 bit for the ez lock. Yeah I can see how a hand drill would have helped. My power handdrill lickily had a speed control so I turned it way down. Oh, for the EZ lok, FYI if you want a free sample. They will send it to for free. ezlok.com They are great and I would use it again in the future.

My new question is the replacement stud I screwed in. It tightens up too far deep in the hole. When I test fit my heat exchangers there are not enough threads to screw the nut. The desired depth I can rotate the stud to by hand. So would it be ok to add some blu loctite and screw the stud to desired depth which will give me enough threads for the nut or just not use any loctite at all and just tighten it down with the HE ????????

I even thought about using a CV bolt instead. Would this ok to use or was there a very good reason why there was a stud there originally instead of a bolt.

Man I dodged another bullet this weekend.

Thanks for all the help guys.

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One would think that the obvious answer, "use a longer stud", would have come to mind. Possibly even the "correct" stud!

The Cap'n