The crankcases, cylinder heads, and pistons were all of aluminium alloy. Cylinder blocks and crankcases are often cast made of aluminium alloys. The 998R and non US 998S models had different crankcases with a deep oil sump. Radical when introduced, the design featured horizontally split crankcases and Heron heads. This put additional strain on the main bearings and crankcases, leading to reliability problems. Tunnel crankcases appeared in the 1930s with the first high-speed diesel engines. This plant is equipped to produce aluminum crankcases. The crankcases and crank were also redesigned for use with the Injectolube system. The standard 998 had crankcases which were very similar to the previous Desmoquattro. The restored bike has reverted to the older-style "HRD"-labelled crankcases. They sent some prototype crankcases for Seeley to work from. Early in the model run the crankcases were strengthened, after some cracking in racing use.