Join Date: Apr 2002
Location: Dandridge (Near Knoxville), TN, USA
A compression test is one of the first things to do if a problem is suspected, because it is easy to do. If the compression test does show too much variation between cylinders or too low readings, then the best next step is to perform a "leak down test". This is harder to do, and requires a leak down tester, which is a manifold with two pressure gauges, with a valve to control the flow into the manifold from an air compressor, a 0.040" orifice between the gauges, and a hose with adapter to screw into a spark plug hole. This is attached to a cylinder, the engine blocked at top dead center on the compression stroke for that cylinder, then the engineheld so it cannot turn. (I positioned my cylinders just past TDC then in 5th gear strapped the rear brake down).
Then the valve on the manifold is slowly opened until 100 PSI registers on the inlet gauge. The reading of the cylinder side then shows "percentage" of air held, the difference being the leakage. If the output gauge reads 85 PSI, then you have a 15% leakage (of course this is a relative number, but very useful). The greatest advantage to this type of test is that you can tell where the leakage is by listening/feeling. Air out the exhaust is signs of exhaust valve leakage, out of the intake is signs of an intake valve leaking, air out of the oil filler shows piston ring leakage.
I don't want to achieve immortality through my work...I want to achieve it through not dying.
EX: '01 Black LT, BAT BYKE (Totaled at 110,000 miles)
IBA SS, BB, BBG, 10/10ths.
No bike now, but maybe in the future.