Big Bore Kit 1070cc "S"

Plug & Play Kit

Siebenrock Big Bore Kit – The Original: Powerful, uncompromising, and time-tested.
Back in 2004, Siebenrock presented its groundbreaking 1070 cc Big Bore Kit to the public for the first time at the Intermot trade show. The innovative design – featuring a short, weight-optimized piston paired with a forged H-beam connecting rod measuring approximately 151 mm in length – was a technical highlight. The extended rod geometry ensures that the piston remains entirely within the cylinder bore, eliminating intrusion into the crankcase. This clever engineering concept received immediate acclaim and has since inspired numerous imitators.
More than two decades later, the Siebenrock BBK 1070, now equipped with the renowned asymmetric camshaft, continues to rank among the most powerful, reliable, and refined plug & play upgrade solutions for classic BMW 2-valve boxer engines.

“Piston capacity can only be replaced by even more piston capacity” – this was the adopted motto during the company-internal development of the Siebenrock Big Bore Kit. The goal of this construction was to enhance the motor characteristics which were already outstanding thanks to the Power and Replacement Kits. We didn’t just say this, we went out and did it and the result for all BMW 1000 cc models from 1981 onwards was the 1070 cc Big Bore Kit, which turned out to be the ultimate solution for sporty touring riders. After modification, an amazing 80 hp is available at an engine maximum torque up to 116 Nm. That’s what we call a convincing result.

This performance boost was achieved using 151 millimetre long, high-stability connecting rods which, when weight-optimized and fitted with ARP screws, only put 420 grams on the scales. In addition, 98 mm pistons are used, which — thanks to their new optimization — weigh only 347 grams. Including rings, piston pins, and retaining clips, the total additional weight is approximately 97 grams.
A true plug-and-play kit.

Thanks to the well-designed piston form, it is not necessary to adapt the cylinder head to the big bore.

Top quality.
Small production runs.
Engineered in Germany.
Made in Italy.

Siebenrock product.
Each original Siebenrock product bears this seal that guarantees the highest quality possible, consistently optimized down to the last detail.

Scope of delivery
All components required for installation of the kit are included:

2 cylinders (98.0 mm), Nikasil-coated
2 forged pistons with DLC-coated piston pins and C-clips
1 cylinder gasket set including 2 cylinder head gaskets, 2 valve cover gaskets, 4 pushrod tube seals, 4 small O-rings at the cylinder base
2 H-beam connecting rods (151,0 mm) with ARP bolts L 19
1 ARP socket for connecting rod bolts
1 asymmetric camshaft including complete camshaft gasket set with 1 large and 2 small timing cover gaskets, 1 crankshaft seal, 1 O-ring


TIP
The matching connecting rod bearing shells
Part no. 1124460 standard size
Part no. 1124461 standard size +0.02 mm
Part no. 1124419 1st oversize +0.25 mm
Part no. 1124420 2nd oversize +0.50 mm
must be ordered separately.

With MOT/TÜV approval and installation instruction.
Price for the set.

For the classic BMW 2-valve Boxer models
R 100, R 100CS, R 100RS, R 100RT
Monolever models R 100RS (x), R 100RT (x)
Paralever models R 100GS (x), R 100R (x).

(x) = only permitted for vehicles up to 31.3.1994.

TIP
The use of dual ignition is strongly recommended.
Ready-to-install camshaft including camshaft gear and front camshaft bearing on request.

Information on product safety