Having never had the need to remove cylinder studs, I'm not sure I can give you an authoritative answer to your question from a BMW repair standpoint. However, I feel competent to answer your Loctite question.

There are numerous grades and types of Loctite. While only one or two are sold at the local hardware store, there may be as many as 15 commercial grade Loctite products you might want to consider to resolve your particular issue. These other products are generally more common in the industrial setting, and so once identified, you'll need to procure them through McMaster-Carr, Grainger, and those type resources.

As far as "thread lockers" go, Loctite has generally color-coded these for ease of identification. As any standard thread gets larger, there is more free space between the male and female thread. So naturally, you'll need to use a more viscous thread locking compound on a large thread like the BMW head stud. So what you want is a Red or Yellow thread locker, which will be labeled as "stud and bearing mount", "stud retaining" or some such similar label. This indicates large diameters with large gaps to fill in a more permanent, fixed position. Something not likely to be disassembled next week. These type products will stop oil flow, but are primarily (85%) aimed at "retention".

There are also Loctite "gasket makers" (#510, #515, etc) which have some retention capability (10%), but who's main job is filling gaps and stopping oil flow. These can fill up to 0.015" gaps and are useful when gaskets can't be used.

Here is a brief users manual which will cover the latest product line..... http://loctite.ph/php/content_data/LT4680.pdf

Further Notes
• The previously mentioned "color coding" was strictly adhered to up to about year 2000, but their newest products seem to violate this standard somewhat. The only way to really know if the product is correct is to read their literature.
• The hardware store grades of "thread lockers" are generally Blue in color and their viscosity is most effective on 2 to 6mm threads. This is why they are not optimal for your 10mm stud repair.
• All the series of "thread lockers" rely upon thorough cleaning of both threaded parts for maximum effectiveness. This can be achieved with lacquer thinner or acetone, but aerosols (such as carb cleaner) generally are more handy in a motor repair setting. Be sure and blow both parts clean and dry with lots of compressed air.
• Hardware stores have recently taken to stocking lots of "me too" products from China. This is not the time or place to experiment with low-grade products.

Hope this helps.

Thank you for your help.

After I walked away from the problem and then came back to it. The issue became very clear. I noticed that the very front of the stud holes on the right rear were extremely smooth. The six others were normal. Yet the stud would hold securely once I threaded deeply enough into the space. I took a closer look at the studs and noticed that the two of the studs that went into the right rear cylinder were about 3/4" longer than the rest. I ran a camera down there and it confirmed my suspicions. A PO had drilled out the hole and inserted a helicoil way in the back. The rear studs were so loose because there was nothing at the front of the hole to support the sides of the stud. Now that I know the issue I believe once I use the red loctite on the studs, they will be securely in place.

I've attached some pictures to show my dilemma. I'm not happy with the endoscope camera focus or resolution but I believe you can see that there is an insert at the end of the hole. There is a significant difference in color at the end and what appears to be the top edge of an insert. Also, you can see how smooth the front of the holes are and the difference in the stud length.

One more question, if I may. Does using a thread locker on the top studs inhibit the oil flow to the head? I'm not familiar with the path except that it passes through the top cylinder stud area.

Thank you again for all your support.

Ken

Thank you for the suggestion about initially running the engine with the valve covers off the double check the oil flow. This will go a long way to assuaging my paranoia. It turns out the the discrepancy is due to a bit of BMW engineering. They recessed the two right rear cylinder studs to mitigate stress, according to Tom Cutter. Here is his reply to a posting from a friend discussing the issue.

"This was done to move the tensile strain of the cylinders from the outer cylinder wall, and put it to the thick casting above and below the rear main bearing. The other 6 studs are not positioned for that to be possible, or they would have done it to all.

When we built racing bikes, we saw the occasional split crankcase from this issue."

Again thank you for all your help.

Ken

Of all the parts of an engine, the valve gear takes the least amount of lubrication. So the presence of ANY oil coming to the rocker arms is going to be a very good sign.