Even more on Rockers

This engine is all about design and development. Having learned a lot during the making of the KT54fs more thought has gone into the KT120fsT. I've decided to scrap the steel rockers and go for aluminium to reduce the mass/inertia problems that may occur at high speeds. Not that I'm expecting massive RPM figures, but every little helps, and it reduces the overall weight. The tips at the valve end are, of course hardened and tempered Silver Steel, and I've fitted Phosphor Bronze bushes at the fulcrum.

New design Rockers

I've also redesigned the cams, based on my original design but larger to prevent stress and wear to the gearbox housing. The radial holes are strategically placed for timing purposes when setting up the lobe separation angle. Here I have a choice, two of the holes in alignment will produce 106 degrees and the other two 110 degrees. The profiles were generated using a zig-zag of co-ordinates worked out on AutoCad and the resulting ridges dressed out with a file. The inlet cam is designed to open comparatively sooner and quicker than the exhaust, stay open longer and close later, thus allowing more mixture into the cylinder for combustion. Both cams have a 2mm lift.

New design cams, exhaust on the left

You should be able to take a closer look at the pictures by clicking on them. In the Rockers picture the cap head screws at the tappet end are M2.5 and the hardened steel tips are held on with M2.0 cap heads.