Thursday, July 3, 2008, 12:30 PM ( 5558 views )  - Posted by Administrator
The first year saw a series of performance developments. The old exhaust fell apart (the worst parts of this period BMW are usually the seat hinges and the exhaust) and I soon replaced it with a Luftmeister 2-into-1 set.

The Mikunis were rather oversize- 32mm on a 600 twin is a bit much by conventional thinking, and I was warned it wouldn't work. Quite to the contrary, it worked very well. The little R60/5 had become a screamer, with characteristic neck-snapping Mikuni acceleration.

But soon it became evident that the two carbs had enough differences- in wear if nothing else- that a new pair was in order. I went through a series of jetting experiments and finally came up with a workable combination. Velocity stacks added a nice finished touch to the carbs. No air filter, that's right- fortunately the Northwest is rainy but rarely dusty, or I wouldn't risk it.

In this form I proceeded to ride the hell out of it, and had much, much fun. The front end was superb- although there was only about three inches of travel remaining in the front end, it was enough, it never bottomed out, and it was always reliable and well-mannered. Well, almost. It did suffer the classic 'rubber cow' head shake going around a fast curve with no banking- like certain highway ramps I know. A steering damper would help. But overall it was quite tractable, and fun.

As far as speed, the oversized carbs seemed to balance the oversized exhaust, and it was extremely quick, it would outrun most any airhead up to about 75 mph, and there it hit a brick wall and would go no faster. Clearly the stock valves and detuned cam were holding it back.

In this form I rode it to the National BMW rally in Spokane (conveniently held in 104 degree heat). It performed admirably all the way there and back again, although I wilted quickly in the heat. I made a steel bracket that mounted under the seat to hold soft luggage out of the wheel, and away I went- cafe touring bike.

It was then that vintage racer Charlie Baker kindly offered a set of R60 race heads with oversized valves. This removed the 75mph limit entirely- now it went well over 100mph with room to spare.

But I made a mistake with these heads- I tested them by installing them, and rotating the crank to see if there was interference between piston and valves. There seemed to be none, so I went racing. However, this is not the right way to do it- the right way is to check clearances everywhere, there should be 2mm of room to compensate for everything flying around at high speeds. I hadn't- and after a few months of thrashing, it developed a bottom end knock. Disassembly showed that not always, but during high speed operation the valves contacted the piston, hammering the main bearings which were now toast.

So back to the garage it went, to be torn down and rebuilt anew.

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