Written by Tim Huber.
As the old saying goes, ?practice makes perfect?, and with more than 30 one-off BMW builds to its name, the UK?s Side Rock Cycles, let? just say; knows a thing or two about churning out custom airheads. Based on the southern coast of England in Bournemouth, Side Rock is headed up by Pete Hodson, who?s career in the motorcycle and automotive world spans over four decades and includes a plethora of competition experience. 

?I know how a bike should work and that?s reflected in the design and execution of our builds,? Pete says bluntly. 
Though it has a trio of projects currently underway, one of Side Rock?s latest completed efforts is this street scrambler based on a 1982 BMW R45, which was the smallest boxer twin offered by the Bavarian brand. When Pete and the gang first got the Beemer up on the bench, it had already been converted to a 650, though the client who commissioned the bike was still yearning for more power. 
?So, the motor and transmission were torn down for refurbishment and upgrades and a Siebenrock 860cc power kit was installed with higher compression, lightweight, short skirt pistons, and new lightweight Nikasil-lined cylinders,? Pete tells us.

The stock Bing carbs were binned in favor of larger 34mm Mikuni’s paired with high-flow Ram-Air filters. To cope with roughly 30% boost in oomph, the clutch was beefed up via a heavy-duty spring and plate, the transmission was gifted with all new bearings and seals, and a higher ra...