Philes’ Forum – Fall 2017
by NJ BMW CCA
By Vic Lucariello, Sr.
Hello, bimmerphiles! Here we are ending the 31st year of Philes’ Forum! The first, introductory column appeared in the January, 1987 Bulletin, and the first regular column ran the following month. In that column I addressed questions about valve adjustment and oil-filter replacement by colleague and then-coworker Paul Kujawski’s E21 320i. I also had a tech tip regarding small stainless-steel-wire brushes that are useful in cleaning off the grunge on a drum-brake backing plate. [They also work very well for cleaning disc-brake-caliper slides.] Fast-forwarding to the present, this time out I have an item pertaining to valvecover replacement on driver-school padrone Jeff White’s E39 touring. This car has provided a veritable cornucopia of Philes’ Forum fodder, so I hope Jeff and spouse Tricia keep it for a long time!
Jeff contacted me in a panic. He had been replacing the valvecover gasket on the 2000 528it and he had been provided with the wrong torque spec for the 6-mm diameter valve-cover holddown studs. Jeff had been given 18.5 lb-ft [about 25 newtonmeters (n-m)], but this is the common spec for tightening an 8- mm stud or bolt, not a 6-mm [6 mm is about ¼ inch]. The usual spec for an M6 fastener is more like 8 lb-ft [about 11 n-m], so you might predict what happened: one of the hold-down studs broke off.
Jeff was worried that the cylinder head would need to be removed in order for the failed stud to be replaced, but luckily these particular studs not only screw into the head, but they have a nice hex-head boss right where the upper-stud portion meets the boss. Jeff was able to unscrew the broken stud and replace it with a new one from Bridgewater BMW. In replacing the stud, I suggested that Jeff clean out the threaded hole in the head and install the new stud with a bit of Loctite thread locker. This will minimize the possibility of the stud unscrewing the next time the valve-cover gasket is replaced.
I also suggested to Jeff that he replace all the “rubber” grommets under the valve-cover hold-down nuts, but as a regular reader of Philes’ he already had done this.
While Jeff had things apart, he decided to replace the spark plugs, and he also had a question, this one posed ahead of time, about the recommended torque spec for the spark plugs and whether I recommended that anti-seize compound be put on the threads of the new plugs.
The torque-spec question was easy as all I had to do was consult BMW’s service information to see that the recommended tightening torque for Jeff’s application [14-mm-dia plugs] is 15- 21 lb-ft [20-28 n-m]. I have been using 18 lb-ft [24 n-m] on unlubricated threads on new plugs for a long time, with nary a one loosening on its own or being particularly difficult to remove provided it was not left in place for an extended period.
The question about using anti-seize compound is difficult to answer unequivocally. Most modern spark plugs have platedsteel casings, while any BMW I have worked on over the last 40 years has had an aluminum-alloy head. While these differing metals in close contact under heat and pressure might present the classic case for the use of anti-seize compound, things are not quite so simple.
First of all, the major spark-plug manufacturers universally agree that they do not want anything put on the threads of their new spark plugs. Some manufacturers claim that their spark plugs are treated with a “special compound” that prevents seizure of the spark plug in the cylinder head. Others claim that the plating on their spark-plug casings obviates the need for any lubrication. Of these two claims, the second one seems more plausible to me.
Secondly, some professional technicians claim that if you use anti-seize compound on the plug threads, you will need to reduce the tightening torque in order not to over-tighten the plug. This makes perfect sense from an engineering point of view, but by how much do you reduce the torque spec? This can actually be calculated, but really…
Thirdly, some claim that using anti-seize compound on sparkplug threads has an effect on the effective heat-range of the plug. I am not sure about this one.
Finally, we have thus far been talking about the installation of new spark plugs. Suppose you remove your plugs for whatever reason, is the “special compound” still there for reinstallation?
This subject has been frequently debated on iATN [International Automobile Technicians’ Network] and there are many differing opinions. Moreover, former Motor Magazine columnist Mike Dale, an electrical engineer, wrote a column on the subject. At the end of the column, Mike conceded that using a bit of anti-seize probably wouldn’t hurt anything, and I tend to agree.
My advice is: In most cases, do not leave your spark plugs in for the interval recommended by BMW. For example, I had great success changing 100,000-mile-recommended plugs at around 70,000 miles. With this approach I did not put anything on the new plugs’ threads and I had no problem removing them after 70k. Removing plugs after 100,000 miles or more is sometimes a different story.
That’s all for now, bimmerphiles. See you next year.
Anyone wishing to contribute to Philes’ Forum can contact me at email@example.com. I’m interested in tech tips, repair / maintenance questions, repair horror stories, emissionsinspection sagas, product evaluations, etc.
© 2017; V.M. Lucariello, P.E.