Projects In Metal

1/4 Scale

Whats wrong with this photo you ask? Nothing, as long as you are looking at it through 1/4 scale eyes. We'll save the 1/4 scale tool box for last, as I'll bet you want to hear about the 1/4 scale Chevy small block V8 that actually runs. The specs on the engine are as follows, Displacement-36cc's with a 5/8th's bore and a 5/8th's stroke, developing 2 &1/2 hp at 12,000 rpm. The engine burns a mixture of alcohol and synthetic oil. Why the alcohol and synthetic oil mixture you ask? Good question, the reason being is that I built this V8 along the lines of a model airplane engine. What I mean is yes, it is a 4 stroke engine just like the full scale V8. What the problem is, when you scale the engine down, there are problems with the lubricating system and the ignition system in a model this size. I wanted the finished engine to run reliably and decided to build the engine along the lines of a glowplug engine. To do this, I built the engine with a pressurized crankcase, and I am running only 1 piston ring on the pistons, allowing for blow-by that allows for proper lubrication of the crucial parts of the engine. In this photo the distributor just visible at the rear of the engine, is the collector to drive the glowplugs via the sparkplug wires when starting the engine. Yes,the engine does have electric start in the shape of a electric motor that normally is used in a radio control model car. The electric start would normally be energized from a radio control transmitter. The interesting part of the electric start is how this is acomplished at the engine. I had to think outside the box on this one, but here is how it works. I am using cogged drive pulley on the electric motor, and a much larger cogged pulley mounted on the crankshaft that just fits inside the bell-housing of the engine. This cogged pulley has a torrington needle roller bearing mounted in the center of the pulley that slides in place over the crankshaft. This needle roller bearing has a very unique feature in that it free wheels when rotated in one direction and locks when rotated in the opposite direction. So here is what happens when you are ready to start the engine. Power from a on-board battery is supplied to the starting motor, with switching activated by the radio control transmitter. The starting motor turns the engine over because the torrington locking needle roller bearing that is mounted on the crank, within the cogged pulley locks on to the crankshaft allowing the motor to be turned over. When the engine starts, and as the rpm's of the engine increase, the needle roller bearing in the pulley unlocks as the engine is turning fast enough, to allow the cogged pulley to stop turning.. The power to the starting motor is shut down and the crankshaft turns freely in the needle rollor bearings, allowing the cogged pulley to sit still on the crank.

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