Engine Crankcases
About Engine Crankcases
The crankcase is the main housing of the engine. It holds the crankshaft and bearings, and the cylinders bolt to it. A case is replaced when the original is cracked or damaged, or when a performance build needs a case made for a larger bore or stroke.
The cases listed here are for Harley-Davidson engines and are named by engine family, such as Evolution Big Twin, Dyna and M8 Touring, along with a bore size such as 3.500, 3.625, 3.937 or 4.125 inch. The bore has to suit the cylinders you plan to use. Some are Super Stock or big-bore cases for larger displacements, and some state generator style or alternator style, which should match the charging setup of your engine. Read each listing for what is included before you order.
The brand in this category is S&S Cycle. A new case is normally installed during a full rebuild, so you may also need Crankshafts, Engine Bearings and Gaskets, Seals & Kits. Our guide why a part didn't fit helps with checking compatibility first.
FAQs on engine crankcases
What does bore size mean in an engine case listing?
It is the diameter of the cylinder opening the case is machined to accept. A 4.125 inch bore case suits cylinders made for that bore. Match it to the cylinders and pistons in your build.
What else is replaced when I install a new crankcase?
A new case means a full engine rebuild. The crankshaft, rods, bearings, seals and gaskets are normally moved over or renewed, and the service manual lists the clearances to check as you assemble. Plan the whole parts list before you start the job.
Can I reuse my crankshaft and bearings in a new case?
Possibly, if they measure within the limits in the service manual. Bearings are normally replaced during a rebuild, and the crank should be inspected and trued if needed before it goes into the new case.
Why do some cases list generator or alternator style?
Older Big Twin engines used a generator and later ones use an alternator, and the cases are machined differently for each. Choose the style that matches your engine's charging system and year, and check the listing notes if you are unsure.
