What's the best way to find a dead cylinder?
Okay guys. As promised, here's the data on my sick engine. The first six photos are the results of the leak down test on cylinders one through six. As you can see, several of the cylinders are way down from the 100 psi that was pumped in initially. The final photo is the compression values from cylinder six (top of the page) down to cylinder 1. Now I gotta decide what to do. Looks to me like a complete teardown. I do have a spare 225 engine from a 1974 Dart with only 83K miles on it. The dilemma is whether to rebuild the current engine (very expensive) of put the replacement engine in.
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OK, you performed a cylinder leakdown test. I notice the breather cap or oil fill cap are in place. I imagine the air filter was on and the throttle closed. When you perform a leakdown test, remove the breather or the oil fill cap and the air filter assembly and block the throttle open. This way when you find a low cylinder you can listen for hissing at the valve cover, carburetor and the tail pipe. This will indicate where the leakage is; rings, intake valve or exhaust valve.
When performing a compression test, again block the throttle open to allow full air in. 4 or 5 compression strokes are enough. After doing a "dry" compression test you can squirt a bit of oil in any low cylinders. A pump oil can works well and on a slant or Vee engine, a bit of hose on the end will let you get the oil to the high side of the cylinder wall. You need to fill the hose until oil just starts coming out to make certain you are getting oil delivered to the cylinder wall. Just 2 or 3 pumps is enough. If the compression pressure comes up, the problem lies in the rings.
If on the leakdown you hear no hissing, you could have a bad cam. Remove the rocker cover and use a dial indicator to measure how much the intake valves open to start with. Valves that open say 0.100" less indicate a cam lobe worn.
I recommend doing the leakdown again as I describe and then if notbing shows there, check valve lift. A bad exhaust will cause it to run rough but compression can still indicate good.
Nail the source of the problem before getting serious with the wrenches. If it turns out to be valves you just need to remove the head. You could think about larger valves and pocket porting while doing that. If it is the cam you can change it with the engine in the car. Radiator definately needs to come out. Pain in the butt getting the lifters out and degreeing a new cam, but then pulling the engine is a nusance also.