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Cylinders, case stud threads, heads, top-end, intake spigots, break-in procedures

If you are installing a camshaft and/or followers, READ http://bmwmotorcycletech.info/cams.htm regarding assembly pre-lubrication.

You may think that pulling off a jug is major surgery & frightening to contemplate. Once you do it, perhaps at a TechDay; or, from the information in this article, you should no longer have much apprehension about doing it yourself.

CAUTION-1:  Every year comes questions about removing a head, perhaps for a simple de-coking (and not pushrod tube seals), & whether it is possible or not….to keep the cylinder sealed at the bottom. In order to do this, you would have to very securely wrap bungees …or via some other means, …around the cylinder fins, across the motor, & all-around the motor. Or some such. You would have to keep the cylinders from moving off the base area in the slightest. This method has been done when I only needed to work on the heads & was being done ‘in the field’, such as at a Rally, or a TechDay, & no O-rings and no piston ring compressor were on hand, etc.  But,  in order to do it, the bungees must be super-tight & evenly surrounding the cylinder, fore & aft. I recommend you not try it. Chances are high that you will not be fully successful & your cylinders will leak oil.

CAUTION-2:  Never reuse a head gasket unless it is a real emergency. While it is possible to leave the two head-to-barrel nuts in place (the ones located at 12:00 and 6:00), & to reuse the gasket by never separating the head from the barrel, this is a poor idea. It MIGHT result in distortion of the assembly. I have not seen that distortion, if the assembly is done fairly quickly, within minutes. Pure speculation anyway. These 2 head nuts (located at 12:00 & 6:00) are supposed to be the first to be loosened, the last to be tightened (in the usual cross-staging).  

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Airhead Cylinder Base Sealant

Everyone has things they swear by, and sealants for engines seems to be one of them. Back in my Norton days I gave up on Hylomar because I found it would only remain leak free for a few thousand miles. One of my buddies mentioned that his Yamaha dealer used some stuff called Yamabond to keep the oil in his two stroke dirt bike, and I figured if it could keep that motor dry it was worth a try for the Nortons. It was, and it worked very well. When I started working on Airhead BMWs it was only natural to continue using Yamabond (now a days called Three Bond 1209), and it continued to work well. Right up until the day I pulled a cylinder for a compression bump upgrade and found ThreeBond almost blocking the oil passages leading up to the valve gear. Clearly I’d used way too much of a good thing and almost caused me a bunch of trouble in the process. So when the Gurus on the Airheads mailing list recommended Hylomar because if too much was used the extra would float harmlessly away in the oil, it made sense and I started using it again. Of course my old tube from the 1980’s was dry, but since those days Permatex started carrying it and a quick trip down to Kragen’s and I was back in business. However, it seems Permatex is no longer distributing Hylomar, and while my tube should last me another ten years, there are other Gurus that contend, as I had found with the Nortons, that the Hylomar would not provide a good cylinder base seal over the long run. And these guys recommend the Permatex equivalent of ThreeBond 1209, a silicon based sealant.

One of these Gurus is Ted Porter, principal of The Beemer Shop in Scotts Valley, California. I visited Ted one misty January afternoon to drop off a transmission for a mainshaft circlip installation, and during the course of our conversation I mentioned the Airheads sealant thread. He offered to show me how he uses the silicon based sealants.

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