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Classic Velocity Blog

Runs Great, Needs Pistons

Classic Velocity


Classic Velocity Rule #43: Whether you pamper and store your vintage vehicle, or use it regularly, you will spend the same amount of time and money maintaining it.

Sometimes we forget that vintage iron was mostly designed to be used regularly. Perhaps even in anger on the Autobahn or on sparsely populated country roads. The irony of our current usage is that they are often restored to better than factory specifications, and then used seldom and leisurely. Perhaps that is one of the reasons that we spend a good bit of time wrenching. We have violated the spirit and ethos of the machine. Said wrenching is not always convenient. Take for example a certain BMW R60 motorcycle circa 1958. It is equipped with a system of slingers which use centrifugal forces to separate contaminants and heavier items in general from your oil. A brilliant idea (or so it seemed at the time) which was used in lieu of various other oil filtration systems. These slingers are attached to the crankshaft, and are inaccessible without taking the engine apart. I don't know about you, but I find routine engine disassembly highly inconvenient.

But therein lies the rub. The slinger system needed attention every 50,000km (35,000 miles). In the 1950s, that was a more significant number of miles than it is today. Particularly for a motorcycle. In addition, it was a time when labor was cheap and parts were reasonable. Now neither is true, so any system which is labor intensive is viewed as a poor design. Thirdly, skilled labor was readily available. Fourthly, a large percentage of the population was not afraid of tools and work. Certainly, motorcycle owners were in that camp. The end result was that this system was really not the impediment to sales or ownership that it would probably be today. If it had been, the successful BMW /2 series would have failed.


The bad thing about the design was that there was (and is) no real way to inspect the slingers to see whether they needed attention. And if the slingers were full, oil passages for the main bearings closed up, and your engine seized. Highly inconvenient, and very expensive. There is also no real warning of what is to come. The bike may run perfectly right up until it does not. Which brings me back to the R60. It is not often that a story usually reserved for the garage section of this site jumps to the front page of the blog, but this one has earned it.

It was running better than ever on this late spring day, and I was reveling in how well it performed. Truly the best performing R60 I had ever owned or ridden, including /2s and a couple of /5 machines. As a reward I decided to treat it to an oil change, even though it had been relatively few miles, and not much time. This is the part in the movie when the more dramatic music begins, the clouds roll in, and the dark mysterious figure appears. First, the oil was pretty dark and mysterious for the milleage. Second, the magnetic drain plug had pieces of metal attached to it. Not good. Let me pause here to recommend Dimple magnetic drain plugs. It probably saved this engine by dragging metal down to one end of the sump, and not allowing it to circulate. I immediately dropped the sump, and there were more little bits clustered around the drain plug. A couple of the pieces looked like ring lands. Very not good.

In contrast to the slingers, the beautiful thing about the BMW R engine is that you can have a piston in your hand in 20 minutes. You don't even have to remove the heads. Just unbolt the entire head and cylinder from the case. The right side revealed that the piston's skirt had failed and broken off in pieces in the crankcase. A few more larger pieces were lying around at the bottom of said crankcase. I removed them and trolled around with a magnet to see if I could find anything else. I looked at the bores and fortunately they look great. The connecting rods, wrist pins and rings all looked good as well. No loose wristpin bushings, no discernible tolerances out of whack. The piston even looked good other than the indignity of losing its skirt. The left side was perfect with no damage of any kind. Hhhmmmm. I went to the Internet to see what that fountain of wisdom would reveal. It did not take long to discover noted restorer Duane Ausherman's article on this very phenomenon afflicting pre /2 machines like mine. Piston design changes followed by the time they got to the /2 machines in 1960.


How could this motorcycle have been running so well? How could a failure like that happen without me noticing? The collective wisdom is that pistons, particularly on a twin, and even more particularly on a horizontally opposed twin, need to be matched and balanced. Weight differences of a few grams or unmatched pistons have been blamed for rough idling and other performance maladies. My pistons might as well have been from two different make/model machines. However, my motorcycle started on the first or second kick, idled perfectly, and ran like a scalded rump dog! Could it be that I have unwittingly unlocked some performance secret?

Just like some of my previous garage adventures (see the $800 CV boot or Getting the shaft and other Blessings ), the experience imparts wisdom. The moral of this story of course, is to change your oil and examine it critically whether you have a newly rebuilt motor with few miles, or a much used workhorse. Thanks also to the Duane Aushermans of the world who take the time to document and explain phenomenon from long ago that would otherwise have us scratching heads, interpreting dried chicken bones, and wondering what we did wrong. However, you can look out for the Classic Velocity performance kit for pre /2 machines. Don't be alarmed when you see two completely different pistons in the kit. It's the secret sauce.