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How to Fix Stripped Sump Stud Holes in the VW case…

Prevention is the key. All studs in any aluminum engine part are installed with an interference fit. This means the hole the stud screws into is just a teensy bit smaller than the diameter of the stud itself. They’re not meant to unscrew ever.

If you look at any air cooled VW engine, you’ll find there’s not a single bolt that screws into the engine, only studs. This is because aluminum is real soft and strips easily. It’s not meant to have bolts screwing in and out of it, particularly “bolts” that are often removed such as this one – a sump stud converted into a bolt by the cap nuts that came on this engine as new from the factory to prevent very minor dripping and perhaps give a finished look. Using this faux bolt will eventually strip the case and worst case scenario, this   loose stud falls out when driving and all the oil runs out of the engine at speed like on the highway at 60 mph  (I’ve seen these installed in worn threads where it’s more like a nail than a bolt). This will kill the engine quickly at that speed. By the time you notice the oil light or the noise from a loose rod, it’s too late. You say you have an oil pressure gauge? It’ll still be too late unless you stare at it all the time instead of keeping your eyes on the road … maybe. So don’t use cap nuts unless it’s it’s a museum piece. For practical purposes, use normal nuts. They won’t catch the end of the stud and as much, much  less  likely to turn into a faux bolt and you may never have to fix another stripped stud hole.




Screwing this faux bolt into the case repeatedly will eventually strip the case. The cap nut jams onto the end of the stud and turns it into a bolt. This one came off with 2 copper rings. Don’t use cap nuts – ever!! (Except for a museum piece). If a stock stud comes out like this, install it with red Loctite and use normal nuts. Make sure the threads are dry of oil for the Locktite to work.  See below to obtain the proper length sticking out of the case.


If you do strip the threads, you can’t put the metal back …


This stud stripped during the assembly of the engine.


You’ll need a stepped stud like this to fix it …


 The big end is 8X1.25 millimeters; the small end is 6X1.oo millimeters.


And a tap like this – 8X1.25 millimeters ….


Notice the taper on the tap. This taper is the key to bulletproof, permanent repair. And, as printed on the tap – you’ll need a 17/64 drill bit.



Drill the hole all the way through …jobessumpdilledPut some grease on the drill bit to capture the cuttings but don’t freak if you think you got some in the motor. A little won’t hurt – aluminum is soft and it won’t hurt anything. Small particles get captured by the softer  main bearings at worst and teensy particles of aluminum rubbing on the crank won’t hurt it – it’s much softer than forged steel. As a matter of fact, some new main bearings are all aluminum. Again, a little aluminum won’t hurt ANYTHING.


The key to doing a bulletproof  job is to NOT run the tap all the way through the hole – you want the hole to be tapered so the stud will jam into the taper. That makes it permanent. Careful trial fitting of the stepped stud will result in a tight, bulletproof fit …


 Don’t run the tap all the way through! Trial fit using two nuts locked onto the stud as shown in the pic below.



The stud, after jamming into the taper, should stick out of the case by the thickness of the two nuts jammed onto the stud like so …


The nuts are locked together with the end of the stud flush with the second nut.  Use red Loctite.

Tighten until the bottom nut contacts the case and the stud will stick out just the right amount …

jobessump2nutsthickRemove both nuts and you’re done. You may need to grind a 10mm open end wrench very thin to grab the bottom nut but you can probably hold it with needle nose pliers with effort. This is now better than it was new.




Now you’re done.  None of the studs stick out past the plate. Safer that way. And with proper installation of the stepped stud, it’ll never strip – it’s permanent and it’ll never turn into a faux bolt. You may think a helicoil is the way to go. But why add an extra part that can fail (the helicoil itself) when you don’t have to?


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