Whilst it is nearly always possible to rebuild the stock Evolution 4 1/4" stroke Big Twin flywheel assembly, there are situations where an alternative crankshaft is required. The most common application for this, is where a capacity increase is desirable by increasing the stoke. Even if the rest of the engine configuration is still close to stock (for example, stock heads, moderate compression, and mild cams), the benefits are very noticeble at lower and mid range rpm levels. If other performance modifications are also carried out at the same time, then a "Stroker motor" really comes alive. S&S stroker flywheels have been a foundation stone of their reputation for half a century, and we have been using them with great success for over 20 years.
This S&S 4 5/8 stroke crankshaft assembly forms the basis of our 89" Evolution Big Twin stroker conversions utilising the stock bore cylinders. We do this a number of ways, with different compression ratios, head work, and camshafts, to suit the intended application. The same stroke is also used with our 96" and 106" stroker/big bore conversions.
These crankshafts are of far stronger construction than the OEM ones, and are totally rebuildable here. We also supply and build different stroke crankshaft assemblies for custom builds and drag racing.
Please note that different pistons are required for stroker applications, and some minor crankcase clearancing and main bearing work is necessary for correct installation. All of this can be done here, including cylinder boring and honing to suit the new stroker pistons.
Starting in 1954, Harley-Davidson used a tapered pinion shaft and pinion gear, and the 1977 revision carried over into the Evolution era. In 1990, Harley changed this to a cheaper to manufacture, but weaker, parallel shaft that relied on the clamping load of the nut to transmit the drive to the valve train. S&S, sensibly, chose to maintain the use of the earlier, and far stronger, tapered arrangement. 1984-1989 engines can reuse the existing oil pump drive gear, pinion gear, spacer, and nut. However, 1990-1999 engines require the use of these earlier parts as they do not interchange between year groups. For simplicity, S&S offers this Pinion shaft conversion package to be used whenever their crankshafts are used in the later engines.