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.

More on Rockers

Finished them today...

Rockers

Two different sizes for Port and Starboard, this is to compensate for the 9mm stagger on the cylinder alignment and to ensure that the Port and Starboard valves operate with equal geometry. Two 3mm dia. holes have been drilled in each Rocker, the centre is for the fulcrum and the other is for lightening. To manufacture the Rockers, I've made a fixture to machine the lightening necking and to drill and tap the M2.0 threaded hole for the Tappet adjustment screw. All this will become apparent when you see the finished items in a future blog. In the mean time, here's some pix of what I've done today:-

Blanks cut from the material they're sat on. (5mm Gauge plate)

The fixture for cutting the necking.

Ready to start machining...

I learned today the results of my AGM proposal to pit on the North side of the runway when the wind is from the South. A resounding failure in the voting, 5 for, 19 against. The reasons given were due to a motor cycle training school setting up on the Southern perimeter and the main road being nearby. In fact, setting up on the South side means you are a runways' width closer to both. Oh! well, I guess I'll not be going flying when the wind is from the South in future as I don't feel safe in the pits when others are taking off towards the South side. I wonder if someone decides to set up a business near the North side of the runway or on the Hammer head, if we'll get kicked off the site due to health and safety reasons. It could so easily happen.