Engine Specifications

The basic engine measurements, such as bore, stroke, and corresponding installation tolerances, determine the displacement of a Harley-Davidson. Anyone overhauling engines, comparing components, or selecting aftermarket parts cannot do without these fundamental values. All measurements are listed in inches and are intended as a guide - they do not replace a service manual. Technical work should only be carried out by experienced mechanics.

This table allows you to quickly and conveniently read the resulting displacement of a Harley-Davidson engine based on the flywheel stroke and cylinder bore. For better clarity, the data is sorted in ascending order by bore and stroke.

Since the end of 2010 the bioethanol content of Premium gasoline was raised gradually from five (E5) to ten percent (E10) and sold on specially labeled pumps. This was due to an EC guideline for climate protection. Many owners of a Harley-Davidson motorcycle, in particular those of older models, feel insecure if their engines will tolerate the raised ethanol proportion. The good news are: for all current models and for most older H-D motorbikes it is no problem to change to E10 bioethanol fuel.
All stock Harley engines from model year 1980 onwards tolerate a ten percent proportion of ethanol and therefore allow for a trouble-free operation with E10 Premium gas (RON 95). For owners of Harley-Davidson motorcycles built before 1980, the manufacturer recommends to switch to „Premium Plus“ (RON 98), which will continue to be offered with a maximum of five percent Ethanol. For modified peformance Harley engines and for all Buell models the Motor Company recommends „Premium Plus“ (RON 98).
S&S engines: all types can be run with E10 Premium gasoline (RON 95).

All S&S flywheels have been stamped with serial numbers by means the technical specs can be easily determined. If installed in the crankcases the number on the left side flywheel (sprocket side) can be viewed through the timing hole. This is a very helpful feature when ordering replacement pistons. Code numbers on left and right side flywheel must be identical.