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Posted by: ctc911ctc Feb 23 2020, 09:17 AM

I finally got the car in the air to investigate an exhaust leak. Thank you for all of the lift advice, the QuickJack seems to be working great!

Looks like i am missing a bolt. Nothing to attach the nut to, so my question is what to do next? Looking at this picture, does this look like a broken part? perhaps there are threads in there?

Assistance please.

Posted by: 76-914 Feb 23 2020, 09:44 AM

Looks like it twisted off. Remove the header then drill and remove it. May require that you tapping it to a larger bolt size if the threads are messed up.

Posted by: Mark Henry Feb 23 2020, 10:56 AM

Looks like you have SSI heat exchangers, the ears are a weak area and a PO has cranked it down in a futile attempt to seal the leak and broke the bolt. The exhaust mount ears can bend and break, the sealing surface gets out of square, this has to be repaired.

You have to get the exhaust off to get a better look at the stud repair. Level of expertise and tools needed for the job, I do broken studs and it's one job I hate.

Posted by: brant Feb 23 2020, 11:06 AM

The lnida job you want to be careful on

You don’t want to destroy the head and make the problem worse

Posted by: ctc911ctc Feb 23 2020, 01:38 PM

********UPDATE********


Took the manifold off - cannot believe how easy things are with the QuickJack!

Seems that the hole has threads - cannot figure out of those are inserts or the original threads??????? Seems that there are 7 good threads, dirty but solid.

How deep are these holes supposed to be?

Also, how damaged is the valve from running hot?

Where do i order the studs?



Long shot of the hole and valve



Angle shot to show threads



Straight shot - does the hole for the stud go into the exhaust gas chamber? Clean out the hole?

Posted by: rjames Feb 23 2020, 04:50 PM

I was thinking that it looked like maybe someone already put a timecert in there and maybe drilled too far. Either way, there shouldn’t be a hole through to the chamber.

Posted by: ClayPerrine Feb 23 2020, 05:15 PM

Been there, done that. You now have a hole straight into the combustion chamber on the head.

The bad news is... the only way to fix it properly is to pull the motor, remove the cylinder head. Then take it to a machinist to have it welded up and a new stud properly installed.

Posted by: Superhawk996 Feb 23 2020, 05:16 PM

Which heads and which hole are we looking at? The hole as shown on the side with the valve guide side doesn't go directly into the combustion chamber.

On my 2.0L heads all holes are much deeper than 7 threads and none go into the combustion chamber. Appears to me that you have corrosion or dirt that has bridged the hole and that is what you're seeing a hole through the blockage.

Quick check would be pull spark plug, and use air nozzle to blow air into the exhuast stud (with that cylinder exhaust valve closed). You shouldn't be hearing any air in the combustion chamber. Could also pick at the hole with a needle pick and see if it simply crumbles away like dirt or corrosion 1st.

Posted by: cuddy_k Feb 23 2020, 05:59 PM

Posted by: rjames Feb 23 2020, 09:04 PM

Come to think of it, when I retapped the exhaust stud threads where one stud was stripped on my 2 liter it was deeper than it looks in the picture here. Interested to see how this plays out.

Posted by: HAM Inc Feb 23 2020, 09:37 PM

That's just crust where the bottom of the stud used to be. If you drill that particular stud to deep you hit the valve guide. Too deep on the other row of studs and you go into the combustion chamber.

Posted by: porschetub Feb 23 2020, 10:54 PM

You need to run a 8mm tap into it and see what thread is left,not looking good in that pic,I have used a stepped stud before which is 10mm into the head then 8mm on the other end,there is enough material in the thread boss to hold them.
You will need to get this stud made unless you have your own lathe or someone you know has one,or go for a thread insert ,I prefer the stepped stud as it holds on really well due to the larger thread (10x1.5mm) and is a permanant repair.
Thread inserts/heli-coils are great but I don't like them used on an exhaust stud repairs.

Posted by: rjames Feb 24 2020, 12:38 PM

I had to use a stepped stud when repairing mine. I had a hard time finding the stud. The Type IV store used to carry them at one time.

Posted by: porschetub Feb 24 2020, 03:33 PM

Yes totally agree about drilling too deep...there is no need to besides,when I fit stepped studs I under cut the thread with the tap so the stud backs up tight before passing through the threaded hole ...if that makes sense.

Posted by: Superhawk996 Feb 24 2020, 06:18 PM

You lost me but I'm interested in what you meant.

Posted by: HAM Inc Feb 24 2020, 08:08 PM

There's nothing wrong with a properly installed Heli-Coil in the exhaust boss. Use a genuine Heli-Coil tap and genuine Heli-Coil inserts. Knock off inserts are crap and don't fit properly. Properly installed you will not have a problem with them.

Good tapping technique is critical. We do it on one of our milling machines all the time. We installed nearly 400 M8 Heli-Coils last year in exhausts from air-cooled 911's to 9A1's.

Heli-Coils are great inserts. Porsche used them in all 356/912 heads in the spark plug threads and after more than a half century of use I have never seen one unwind all the way out even on the most carboned up heads. VW installed them in cases for the drain plug. I have never seen an issue with those either.

Not sure why they get a bum rap other than people poorly installing them and then having issues or using knock-off inserts.

As always, YMMV.

Posted by: brian minson Jul 8 2020, 01:14 PM

I am curious if anyone has an opinion on the condition of that exhaust valve?

Brian

Posted by: 914_7T3 Jul 8 2020, 01:38 PM

Just went throught this with my car. The Studs for a 2.0 Liter are 8x56mm and the 1.8 Liter motor uses a step thread with 9mm on 1 side and 8mm on the other.

I believe that either are availalbe from European Motorworks in Hawthorne, CA

http://www.europeanmotorworks.com/

Here is a pic of the M8s I picked up there




However, the M9 step studs can also be purchased from AASE Sales,

https://www.aasesales.com/collections/porsche-914-fuel-exhaust/products/noloc-b52-35i-116916ds

Posted by: aharder Jul 8 2020, 02:29 PM

When I repaired my 1.8 heads, I went with a M10 x M8 Step Stud and got them from
Belmetric.