Fancy pistons? Those pistons have been used for decades as standard equipment in pre-Evolution Big Twins with great reliability. Even S&S supplied them with the 80 cu In and 84 cu in "road special" stroker kits when longevity was the main criteria and sane break in tactics would be employed. I believe the steel strut was cast in. I had a set of them in my 86 cu in Panhead for over 30 years.
How do those engines compare to a Commando in RPM and piston speed?Fancy pistons? Those pistons have been used for decades as standard equipment in pre-Evolution Big Twins with great reliability. Even S&S supplied them with the 80 cu In and 84 cu in "road special" stroker kits when longevity was the main criteria and sane break in tactics would be employed. I believe the steel strut was cast in. I had a set of them in my 86 cu in Panhead for over 30 years.
With a 4.520" stroke at 5500 RPM and a rod ratio of 1.645:1, I would say piston speed in the Harley Big Twin is higher than an 850 Commando engine (3.50" stroke with a rod ratio of 1.679:1) at 7000 RPM.
Perhaps I should have qualified the HD as having "slightly" higher piston speed, but yes similar.
If you want tight piston to cylinder clearance then go for the line2line graphite coating. A .0015" coating on each skirt gives you a clearance of a thou or two. Since the graphite is a lubricant - any tight spots will burnish off without scuffing. The metal to metal clearance must remain the same as suggested by the manufacturer. I've been doing this for years and it works great. Pistons remain tight and rocking is reduced to a minimum. Piston life is extended up to double.
For a few bucks more you can dot the piston and still be able to measure the metal to metal clearance on installation.
But the piston speed will be slightly higher with the HD even at 5500 RPM. Rod angle is also slightly more in the HD putting more side thrust on the piston. As long as the piston does not expand to the point of seizure, the closer skirt clearance will put less stress on the piston.
