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Ok, so I drained the block to change coolant over to the Pentafrost and ran some distilled water through it then torqued the drain plugs back to 33 ft-lbs. However when I got to the passenger side there was a click before reaching the required torque. Looking at the bung I saw 2 cracks in the flange area. With the help of Dr Bob i was able to regain my composure. and he offered some repair suggestions. I contacted JB weld and they said that I should use the original JB Weld. I did and sanded the best I could around the bung and added the epoxy. After 2 hours I added another coat. I purchased 2 flange bolts from Bel-Metric https://www.belmetric.com/m12x15-fin...k-p-14302.html. which is a 12x1.5 flange bolt 25mm long. After the epoxy hardened a couple of days I chased the threads as deep as I dared and screwed the flange bolt in. It did not seat and I noticed that the flange was to big for the flat. So I ground the flange down till it fit and screwed al the way in. I removed the bolt and added some pipe sealant to the threads and reinstalled it then torqued it to 15 ft-lbs. I think that the added threads that were deeper in the block added much more strength. I was going to put a F109SX: New Generation Fumoto Valve in but decided not to press my luck til I got an adapter for more thread depth. I reinstalled the coolant, brought the engine to operating temp and pressure, and checked for leak's. All was good. Thank you Dr. Bob
Last edited by Geo55; 05-05-2021 at 07:27 AM.
Reason: Wrong bolt length
The torque spec for the plugs is 33NM or 26 ft lbs sad to say. I cannot help but feel even the official number is way more than is really needed to seal 15 psig of pressure or whatever number it rises to when the pump is spinning ***** out at 6.5k rpms engine speed. This failure seems to happen quite a lot.
Glad you managed an effective fix. As Fred's comment reiterates the 33ft lb is a longstanding error in the WSM. When I replace the block drains (hate it - always get soaked and swallow some coolant), I leave it at 20Nm, so nervous am I of cracking the aluminium. Always check it later and if I found it was leaking I'd snug it some more, but it's never lost a drop at 20Nm with new crush rings.
This saga started with a PM thread, and thankfully ended in success.
There has been some discussion over the years about the suspected WSM "mistake" in the torque specs for these drain bolts. Some have managed to crack the threaded boss try to get one out after a lot of electrolysis/corrosion. I think this may be the only failed-on-tightening incident I remember, but that may speak more to my memory than anything else. Long-time member Dave C shared guidance in this forum thread: https://rennlist.com/forums/928-foru...-is-wrong.html and that ended up with significant discussion added.
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
This saga started with a PM thread, and thankfully ended in success.
There has been some discussion over the years about the suspected WSM "mistake" in the torque specs for these drain bolts. Some have managed to crack the threaded boss try to get one out after a lot of electrolysis/corrosion. I think this may be the only failed-on-tightening incident I remember, but that may speak more to my memory than anything else. Long-time member Dave C shared guidance in this forum thread: https://rennlist.com/forums/928-foru...-is-wrong.html and that ended up with significant discussion added.
The threads should strip before the casting goes **** up and Porsche would [should?] know this. I suspect that the damage would have been [unwittingly] done during removal [as most are] and tightening simply delivered the "Coup de gras" as it were.
When installing my water jacket plugs I use a 12 point 13mm longish ring spanner, tighten it until the threads bite and then give it a short sharp tug to finish off. I reckon that will impart something in the region of 15 ft lbs. As someone who did most of his wrenching work on British motorcycles I must have tightened a zillion bolts around that size in my poverty stricken student days when I could not afford a torque wrench. The only bolts I have ever screwed up were in fact when I was using torque wrenches- set to the wrong torque value of course!!!
I suggest that you never use a torque wrench on these drain bolts.
use a calibrated hand and a short wrench and some common sense to not over-tighten the plug.
NOTE a good guide is screw the plug in till it is seated by finger, then turn 30 to 45 degrees,
the plug will offer resistance and you should feel the sealing washer seating,
NOTE a torque wrench will not offer the same feel as a short wrench will.
Yup, Now I know the problem. Was toooo careful and thought that the book knew best. Been turning wrenches 50+ years and one would think that I would know better... I do now! Went with Dr. Bobs plumbers putty and 15 ft-lb. Thank you everyone for your thoughts and comments.
Nice work! I suspect you will be good for a long time. Yes, the sealing washer will typically distort before thread or block damage. I agree with using the calibrated arm approach, and get a good feel for the sealing washer.
05-04-2021, 05:50 PM
Cracked coolant drain bung on block
