Keeping cool.

The missionary work to insulate and air condition the garage is paying off mightily.

As the riding season here in Scottsdale runs from September to April that leaves the furnace months of May through August to catch up on annual maintenance tasks on the motorcycles. And as it’s many years and miles since I attended to the sealing of the top end on my 1975 BMW R90/6 it was high time to see who is who and what is what.

Aficionados of the breed will tell you that, unlike British bikes, BMWs do not leak. Uh huh. The reality is that those large horizontally opposed cylinders contain connecting rods which move merrily up and down with every stroke, causing vertical vibration of the barrel against the engine case. Eventually that leads to oil seepage, as this image discloses:

Oil seepage past the base gasket of one of the cylinders.

The problem is compounded by the hardening of the rubber pushrod tube seals below the cylinders. These serve to connect the pushrod tubes to the engine block and with age these seals lose their pliability and can even crack. The airhead will not cease running, but the resulting mess eventually manifests itself as oil on your boots.

So the cylinder barrels have to come off to permit cleaning of the engine block and replacement of the base gasket and pushrod tube seals. Mercifully, the design of the horizontally opposed airhead twin makes this a relatively simple task.

The cylinder comes off just far enough disclose the wrist pin bushings and circlips.
Three nuts to remove the valve cover and four to release the barrel.

Once one of the circlips is popped out the wrist pin can be extracted using a puller and the head with the attached valve assembly comes off, disclosing the mess underneath:

The cam followers – the two black circles – confer force from the camshaft to the pushrods.
Oil deposits everywhere.

A throughly trashed pushrod tube seal. This fits into the orifices for the cam followers.

Clean-up commences.

After applying a thin layer of non-hardening silicone to a new base gasket and
installing new pushrod tube seals, the barrel is reattached to the block.

One of the new pushrod tube seals in place. These must be fresh and pliable,
and are also sealed with a thin film of non-hardening silicone.

And that’s about it.

Aaah! Alles in ordnung. The exhaust goes back on next.

Yes, it hit 117F outside yesterday while I was doing the work, luxuriating in 80F comfort in the air conditioned garage.

iPhone 12Pro Max images.