I just needed anOIL CHANGE
By Wes Fleming #87301 A multi-part saga
Part Three: Crossing TDC
AS I REPLACED THE ALTERNATOR BELT ON MY 2005 R 1200 GS (see Part Two), I discovered a disconcerting problem: I couldn’t turn the engine past a certain point. It stuck tight at some point in the rotation, whether I turned the engine for- wards or backwards and no matter how fast or slow I turned it via the crankshaft pulley. My boss, George Mangicaro of Beemers Uber Alles, quipped,
“Well, that’s not good.” He strikes me as a master of under- statement at times. After turning the
engine back and forth several times, we fig- ured out that the sticking point was at top dead center (TDC) or rather, nearly TDC. Some- thing prevented one of the pistons from moving through TDC and through the rest of the cycle. (Note: both pistons are at TDC at the same time, one in the compres- sion stroke and one in the exhaust stroke.) There are several
easy, it’s not fast, and I’d never done it before, so I wasn’t looking forward to this being the problem. George put a leak-down tester on both cylinders. The left cylinder tested nice and (air) tight. The right cylinder whistled like a construction worker trying to get a pretty girl’s attention. “OK, you’ve got to pull the cylinder head,” George said, looking
longingly at the R 1150 RT he still needed to put a clutch in to help pay the rent. “Let’s do it.”
The iconic BMW
things that could pre- vent the engine from turning through TDC, and most of them are bad. The worst-case scenario here was that in all my stall- ing and starting from the fuel pump controller issue (see Part One), a valve stem bent. If a valve stem bends enough, it could prevent the valve from seating properly, leaving it protruding into the combustion chamber. When the piston got close to the end of its stroke, the top of the piston would contact the pro- truding valve and stop. If this happens while the engine is run- ning, we refer to it as “piston-assisted valve closure,” and the valve could easily damage the piston, requiring a whole lot of work. Replacing a valve is a straightforward process, but it’s not
52 BMW OWNERS NEWS May 2016 Performing a leak-down test on the left cylinder.
boxer engine is a marvel of modern technology. A lot of the rotating action takes place inside the case—the part under the fuel tank. The exploding work that gets done to turn the crank- shaft and make the bike go happens in those cyl- inders that stick out the sides of the engine. The outermost part is the cylinder head cover; this is what comes off to check and adjust the valve clearances. One of the cylinder head covers is also where you add oil to the engine. Whether
it’s the left or right cover depends on what generation motorcycle you have. Inboard from the cylinder head cover is the cylinder head. This
is where the valves are, as well as the springs and mechanisms that keep the valves pointed and moving where and when they’re sup- posed to. The fuel-air mixture comes in from the throttle body at the rear of the cylinder head, and the exhaust gasses exit out the front. With the cylinder head off you can see the piston, and the piston
is inside the cylinder. Gaskets separate each major component from the next, and if you’re this far into the engine, chances are you’re smarter than I am and already have all the gaskets you’ll need to
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