Engine Cylinder Design and Function - Part 9

Weird and Wonderful
Unique cylinders

Honda NR500

Over the years there have been cylinders that have stood out because of the way in which they differ from the ‘normal’ hole in a block. Its worth mentioning them here as they show that cylinders can become of a component than just a feature.

First off, in the 1979 Honda went all out nuts and produced the NR500. This was a V4 engine with oval piston, below shows the pistons and rods.

Honda’s reasoning for detaching from the norm was due to the rules of the MotoGP at the time. The 2 strokes of the age were kicking arse and a 4 stroke didn’t have much chance. This pissed Honda off as they had made good progress with 4 stroke designs for their road fleet. To this end they wanted to increase the number of cylinders to create more power, unfortunately the rules at the time stated that engines can only contain 4 combustions chambers.

So back at Honda HQ they decided to make a V8 engine with only 4 cylinder, or be it an engine with 32 valves, giving the engine the flow capacity of a V8 with only 4 cylinders. This venture worked but there were some issues, like the strange piston ring arrangement and the high reciprocating masses involved by have 4 massive pistons.

Honda suffered from a lot of setbacks until they final sorted out all of the bugs and the bike ran pretty well. The V4 500cc engine developed 130 bhp at over 20,000 rpm, which is quite scary. Unfortunately the new bike didn’t win any silverware and they turned there backs on the engine and started developing the NS500 2 stroke which won the 1983 500cc World Championship.

One thing to consider in the realm of cylinders is how they cut the cylinders and more importantly how they achieved a honed surface. The point being is that not all cylinders are, well cylindrical.

RCV engine

The RCV or rotating cylinder valve engine uses the cylinder as a valve. The cylinder is ported like a 2 stroke engine but instead of relying on the piston alone the entire cylinder rotates to cover and uncover ports with the barrel.

 

This in effect is a 2/4 stroke hybrid. In reality it’s a 4 stroke with a valve system similar to a 2 stroke. The entire cylinder is free to rotate with another cylinder. The outer diameter of the cylinder is coupled to a gear that runs off a mitre gear from the crankshaft to keep the cylinder in time. As the cylinder rotates it uncovers ports then allow for induction and exhaust outgassing at the correct moment.

One of the challenges of the design as sealing the cylinder whilst maintaining free rotation. This engine is still under development in the Dorset in the UK, and some engines have been shipped to customers worldwide. The main market at present for these engines at present (2015) is as a UAV powerplant. 

The cylinder itself has become a moving component that controls port timing.