If you look up old parts manuals, you won't find oversize pistons for the IOE models. Replacing a piston wasn't an easy thing then as Harley-Davidson from 1914 on equipped all pocket-valve engines with conically bored and honed cylinders and cylindric pistons. Of course, oversized pistons were available to dealers, but boring a cylinder was a task that one would maybe like to leave to the factory — and of course the factory offered this service. <br />The then used piston types nowadays not being readily available nor the friendly factory service being offered any more, our range comprises modern oval shaped high strength and highly heat-resistant pistons that are forged from 2618 aluminum and heat treated to T61. <strong>As with all modern pistons the cylinders must be cylindrically bored.</strong> The 30° piston dome will give you about 6:1 compression ratio but may be machined to lower compression to 4.5:1 stock compression rate. .003” clearance — as indicated on the piston packaging — is a good starting point for engines that are low compression, subject to moderate loads and that are broken in carefully. Heavily working higher compression engines may nevertheless require up to .008”.

If you look up old parts manuals, you won't find oversize pistons for the IOE models. Replacing a piston wasn't an easy thing then as Harley-Davidson from 1914 on equipped all pocket-valve engines with conically bored and honed cylinders and cylindric pistons. Of course, oversized pistons were available to dealers, but boring a cylinder was a task that one would maybe like to leave to the factory — and of course the factory offered this service. <br />The then used piston types nowadays not being readily available nor the friendly factory service being offered any more, our range comprises modern oval shaped high strength and highly heat-resistant pistons that are forged from 2618 aluminum and heat treated to T61. <strong>As with all modern pistons the cylinders must be cylindrically bored.</strong> The 30° piston dome will give you about 6:1 compression ratio but may be machined to lower compression to 4.5:1 stock compression rate. .003” clearance — as indicated on the piston packaging — is a good starting point for engines that are low compression, subject to moderate loads and that are broken in carefully. Heavily working higher compression engines may nevertheless require up to .008”.

All OEM and identical aftermarket pistons for 45”/750 cc models 1929→ (except WR) have the same compression height. Different compression ratios are achived solely with different cylinder heads for the respective model group like D, R, W, WL, WLD, WLA etc. These range from 4.3:1 to 6.0:1.