Type 276, Type 247, and Type 248 engines

[Steve]

What is the difference between the Type 276 (through 1973), Type 247 (post-1973 other than R45s and R65s) and Type 248 (R45s and R65s) engines? The 247s and 248s look the same from the outside.

[Barry]

Where to start- some major and too many detail differences to mention. Few parts are interchangeable between the two.

The type 248 engines are physically the same outer crankcase dimensions but have a shorter stroke making them narrower across the cylinders. The crankcases though are not the same item due to internal differences such as the lack of a oil drain back hole on the 248. There are other differences such as smaller diameter clutch. Gearboxes are the same as the 247's.

The 248 frame and forks are different and the wheel base shorter. in 81 the 248 wheelbase got a little longer due to a change in the swinging arm length but still shorter than a 247. Front wheel size on a 248 is 18" rather than 19". 248's always had conventional dual piston brake calipers and handlebar mounted master cylinders.  Instruments are quite different and the 248 headlamp is smaller in diameter. Exhaust pipe diameter is smaller at 36mm.

[Bob_Roller]

Here's a reference you should save .
It is the most comprehensive source for technical info for older BMW airhead motorcycles .
If you can't find it there chances are good you're  going to find it difficult source the info .

https://bmwmotorcycletech.info/

[Steve]

So there are differences not just in the engine but throughout the motorcycle. But there are always differences from year to year and from model to model. Is the R65 so different from the other years and models to warrant calling them a different type?

[Barry]

So there are differences not just in the engine but throughout the motorcycle. But there are always differences from year to year and from model to model. Is the R65 so different from the other years and models to warrant calling them a different type?

Absolutely yes, because the differences are more than the detail changes from year to year as will become evident when sourcing spare parts for a type 248.  There are a few major assemblies that are common between the types - gearbox, final drive, rear wheel and mudguard. Pretty much everything else is different.

[Steve]

I had a theory for a while that the main reason the 1979 R65 got its own "Type" was that its bore-to-stroke ratio was much higher (very over-square). But then I found out that the 1979 R100 had the same high bore-to-stroke ratio as the R65! Disproves that theory.