Main Motorcycle: T140 cafe NRE900cc
Join Date: Jan 2012
Other Motorcycle: Yes
Extra Motorcycle: Of course
It could be as Stuart advises, a damaged gasket.
There are 3 studs coming down from the rocker box, the middle one is the only one that has a blind hole, the outer two have holes drilled all the way through the rocker box. This immediately gives a problem as studs were not meant to be used in through holes.
I cannot see a way around having the rocker boxes off to solve this if the oil is seeping down the studs.
With the rocker box off the bike:
The middle stud should be tightened in itís hole until it bottoms out, the resulting pressure pushes up against the whole length of the thread locking the stud in place using the entire length of the thread in the rocker box. When correctly fitted there should be 1/2 to 1 turn of thread showing above the rocker box face.
If you can tighten the stud until all of the threads disappear then the stud will jamb only at one point, where the thread runs out. This puts the entire load concentrated at this point which is close to the rocker box gasket face. There is a likelihood that this concentrated pressure close to the surface will pull the metal up causing a distorted gasket face.
If you double nut the stud(s) and remove it, you can check the gasket face for flatness, and reface it if necessary.
Because it is difficult to tap a blind hole all of the way to the botdtom, there is a chance that the stud will jamb Where the tapped thread in the rocker box runs out above the bottom of the hole. While not as bad as jamming at the top, it still makes for a weak fixing as the forces are concentrated at the jamming point in the bottom of the hole, the rest of the length of thread is effectively Ďlooseí.
To overcome the chance of this happening I remove the first turn of thread at the end of the stud. The stud will then press against the bottom of the hole, loading the entire length of thread evenly, making a strong and secure fixing.
The outer two holes have a real problem, there is no bottom of the hole for them to push against as they are drilled right through. The stud will definitely jamb near the gasket surface when the thread runs out, the rest of the thread is then effectively loose, perfect for allowing oil to work itís way down.
The solution to this is to fit the outer two studs with Loctite 270 studlock.
Clean the head and stud of all oil, coat the stud with loctite 270 and screw the stud in gently until it just starts to tighten, do not pull it down hard. In reality you have glued the stud in place rather than locked it in place. The resulting installation should not allow oil down the threads as loctite 270 is a very effective sealant.
If you ever need to remove the stud again, you will need to heat the stud to release the loctites grip. Trying to remove the stud without heating is likely to rip the threads out of the rockerbox.
+1 on the talcum powder trick (someone also has posted that powdered aerosol foot spray was easier to apply).
Here are some photos showing the poorly designed stud holes drilled all of the way through the rocker box:
Quick fixes are named after how long they stay fixed, not how long it takes to make them.