One of the standard diagnostic tests for engine health is the compression test where a pressure gauge (compression tester) is inserted into the spark plug hole, the engine is turned over at high speed, and the resulting compression reading provides an indication into the condition of the combustion chamber. If the compression is too low you might have a leaking valve, worn piston rings, a scored cylinder wall, a leaking head gasket, or a cracked piston, any of which would result in low or no power from that cylinder.
However compression testers don’t work very well on small engines, or engines that are pull start such as lawn mowers, snow blowers, etc., engines I often find myself working on. They also don’t do much to help isolate the problem other than to tell you, “something’s wrong in there”. Enter the leak down tester which doesn’t require the engine to be turned over and which also helps identify the specific problem causing the compression loss.
You can buy a leak down tester for anywhere from $100 up, which was more than I could justify, so I went looking for options and found a whole series of YouTube and Instructables guides to building your own. And it turns out I had all the key components already and was missing only a few smaller pieces and connectors, solved by a quick trip to Canadian Tire and Home Depot. After a bit of light machining and assembly I now have my very own leak down tester for about $15 over and above the bits and pieces from my never-throw-anything-out bins.
As soon as the temperatures rise above the current –20s (brrrrrrr…) I have a couple of small engines I can’t wait to try it out on.