Works BMW Flat Twin

The book Classic Motorcycle Engines has a chapter on the 1955 works BMW flat twin. I've uploaded it to:

https://drive.google.com/open?id=1gLaaD_xzHFQNXzSrnkPifBdrWnM_IWkg

The book was published 1986 and had detailed technical descriptions with historical context on 20 outstanding engines. In the case of the BMW chapter the engine under discussion dates from 1954, so the drawing and original discussion 1955, and the historical discussion dates 1980s. 

The technical description of the engines is incredibly dense, packing an almost unbelievable amount of information into each paragraph. I dipped into it tonight and I'm sure there was information that wasn't there yesterday. However, if you don't read it attentively you might miss things like the reference to the 500cc flat twin with desmodromic valve gear, unfortunately abandoned because of lack of funds. 

Full citation is "Classic Motor Cycle Engines: a new perspective on 20 outstanding designs", Vic Willoughby, 1986, Motor Racing Publications Ltd, Great Britain. 

Enjoy!

Carburettor Rebuild

After what I imagine is 35 years without disassembly I took the carburettors off the bike and rebuilt them. I replaced:

• All the O-rings. 
• The diaphragms. Both were inflexible. 
• Cap screws. These had corroded somewhat. 
• Vacuum Blanking screws. These were damaged from repeated removal. 
• Throttle shafts and screws. The peening of the original screws meant that they damaged the brass threads on removal. 
• Gaskets on cold start and float chamber. 
• Main jet washer. These were a bit corroded. 
• Throttle and cold start return springs. 

A few pics of this:

Before: 35 years of gunk. Note the carburettor on the left has the cold start spring replaced with a pair of other springs.

Before: The carurettor on the left, with the darkened piston, is the one with the damaged diaphragm.

Diaphragms. The one on the right is so badly damaged I'm surprised I was able to tune the bike at all. 

After: all clean, ready for reattachment. 

A few comments: 

• One of the main jet holders was difficult to remove, there was so much gunk in it that it wore the threads down as I removed it. It reassembled okay, despite this. 
• I couldn't adjust the idle down on the LHS carburettor far enough to be able to set the idle mixture. I removed it from the bike and reseated the throttle butterfly, being more careful this time to ensure a good seal against the throat. 
• I had no device to remove the peening on the throttle butterfly retaining screws, and damaged the threads on the shaft when I removed them. I replaced the shafts and screws and used lock thread on reassembly. 
• I crimped the fuel hose attached to the LHS carb on reassembly and it got no fuel. Replacing that section of hose fixed the problem. 
• I don't have a compressor so I used a can of compressed air and a can of carburettor cleaner. 
• I found this youtube clip from "Boxer2Valve" immensely useful: ·         https://www.youtube.com/watch?v=MpBA6wimjLc&list=PLXo0yJ7WoKfvSNxo1uZU3qupxkkf9xU4w&index=5 

•  Probably I should've done this 20 years ago. 

The bike is running much better, it pulls better and I think that the range has increased 20%. 

Hand Guards

It's winter in Oz so I've gone looking for a way to stop my fingers from freezing. These handguards are black versions of ones fitted to R80GS models. I sourced them from Munich Motorcycles.

Part number is 71609062160. The white equivalent is BMW: 71 60 2 303 496. I'm not aware of any bike for which these guards are standard equipment. 

Installing the guards was straightforward but fiddly: I needed to loosen the handlebar retaining bolts and cut a couple of cable ties before I could wiggle the RHS one into place. 

They help considerably on cold mornings.  :-)

Nearly-There Sportster

In the dusty archives is this road test of the LS from 1983. The scan is from the yellowed pages of "Two Wheels Road Tests: Full tests of the year's top bikes" and includes other bikes like the Kawasaki Z750GT and Honda CBX550.

The LS was new at the time and wasn’t necessarily seen as an improvement on the recent BMW models or the R75/5 from 10 years previously. It wasn’t seen as a cost effective way to purchase a motorcycle: it carried the premium associated with BMW but didn’t have the robustness of its pedigree nor the performance of its peers.

It’s been a while since I’ve seen a Z750GT or CBX550 on the road, though…

Access it here (file is 20MB). 

My Bikes

I rode a Honda CB400T in 1985, and at the end of the year swapped it for a 1983 BMW R65LS. This I rode for more than 2 years before swapping it for a Ducati SD900 Darmah. After this I had various BMWs: a R80G/S, a 1985 R65 Mono, and a R100TIC (the police special R100RT). After selling this I went without a bike for a year or so, and when in 1996 the itch again rose I found another LS, identical to the one that I had sold in 1988.

In 2019 I found a 1984 LS in good condition at reasonable price and purchased it. It took 6 months to sort out the teething issues, particularly with the carburetion, but it now provides the advantages of identical historic bikes: I can ride one while I work on the other; I can troubleshoot problems by transferring components; the restriction to 60 ride days per year is now two rides per week; and their performance can be routinely compared.

The two bikes are in everyday use. The 1983 model has just over 185,000 km on the clock and the 1984 model 140,000.