Rockers

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The rockers on K motors are of cast iron 1.5 ratio solid-type design. They pivot on a central shaft, held in place by springs which press on the rocker posts. There is a nut-and-screw lash adjustment.


Improvement

Research by David Vizard has shown that lightening rockers gives little performance gain and greatly decreases strength and reliability of rockers. The tosco manual says you can lighten the valve train by grinding off the excess thread of the adjustment screws that you aren't using.

Apparently when you rev solid rockers very hard (ie: in a race motor) they have a tendancy to walk sideways, a common method of solving this problem is to replace the springs with solid sleeves. Close fitting pipe would be ideal.


Rocker Posts

There are two different types of rocker posts, alloy and cast iron. The alloy posts are longer than the iron ones, but the shaft for the rocker arm is in the same position, so you could mix and match if you wanted to. The better ones to use are the cast iron posts, usually found on 4K and later engines, the change was made as alloy expands at a greater rate than iron, and causes dimensional changes between when the engine is cold and warm


Higher Lift Camshafts

Understand that as the rocker pushes down on the valve, it's not going to stay in the same spot on the tip of the valve. In effect, it "wipes" across the valve. When running a higher lift camshaft, the valve wipe is increased such that it pushes the valve to the side, this is called "sideloading". Under extreme conditions, you may bend a valve, but you'll probably just wear out your valve guides quicker. When running a high lift cam, assemble the engine and turn it over with correct valve lash. Observe where the greatest valve wipe occurs, and shave the rocker posts to change that position of wipe to as low lift as possible. Even a fairly high lift street cam will only want about .060" (1.5mm) shaved off the posts maximum.


Service Specs

Valve lash for stock camshaft

COLD

Inlet 0.13mm (.005")
Exhaust 0.23mm (.009")

HOT

Inlet 0.20mm (.008")
Exhaust 0.30mm (.012")


Beyond Solids

So how about increased ratio rockers, or roller rockers? Unfortunately, there's not much available. People adapt K rockers to go onto Mini motors (as they come with stock 1.2 ratio rockers), so it goes to say you could adapt some Mini gear back onto a K if you tried. A set of Mini roller rockers will set you back about $600-$800.


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