Last updated: January 13, 2010
The Type 247 engine is a horizontally opposed twin, often referred to as a flat-twin or "boxer" engine. Boxer engines provide excellent primary balance, and do not require balance shafts or crankshaft counterweights like some V-twin and in-line engine configurations. There is a slight second order vibration because the cylinders are not the same vertical plane -- an airhead's left cylinder is offset slightly forward of the right cylinder. The boxer configuration allows a lower center of gravity than most other motorcycle engine configurations, but is significantly wider.
During the years 1969 to 1995, models ranging from 450 cc to 1000 cc were produced. The corresponding motorcylce model numbers use the displacement divided by 10. A R65 has a 650 cc engine, a R80 has an 800 cc engine, etc.
The R80 had a bore/stroke of 84.8/70.6 mm, while the R65 had a bore/stroke of 82.0/61.5 mm. The compression ratio of the 1985 US versions (nikasil cylinders) was 8.2:1 and 8.7:1 respectively. Albert Lindberg reports that pistons for 9.2:1 are available for the "plain" steel barrel R80's and that R80/7s were produced for the Egyptian police force with R100 heads, 40 mm carbs, and lower compression ratios to cope with lower octane/RON gasoline.
Most R80 and R65 engines use Bing 32mm carbs.
Return to Rovero's: BMW R80RT Page Home Page
