Engine Blow By

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What is Engine BLOW-BY and How does it Effect Diesel Engine Operation?
The term BLOW-BY denotes the escape of compression and combustion gases past the pistons and piston rings into the crankcase. All engines have some blow-by. Excessive blow-by is usually found by higher oil consumption. If you are using a quart of oil in 1000 miles than you have a problem. Blow by is a time factor problem. Cranking speeds leave more 'time' for compression to pass the pistons and rings, resulting in harder starts on a cold engine. This is why many people use either to start even in warm weather. Once piston speeds pick up there is 'less' time for the compression to pass the pistons and rings and engine runs. This is why we get " it's hard to start but then it runs good" . There is no way to repair blow-by other than redoing cylinders and pistons. In other words remanufacture the engine.
Is it Valve Guides or Seals?
Probably Not. The fact that most diesels do not have any intake manifold vacuum makes it unlikely that oil is passing the valve guides as you need engine vacuum to pull it thru. Of course there are exceptions. I've seen valves and guides so worn that oil would pour passed them, but this will show up in a very bad idling and off idle engine performance.
	Looking at the diagram at left you see cylinder wear. The worst part is at "A". This is caused by the double rocking motion as the piston reaches Top Dead Center and starts down again. We have had some engines with as little as 90,000 miles that had one or more cylinders worn out by .060 of a inch. This situation left unattended to will cause the "tick" that people think is a lifter problem. To extreme it can lead to piston breakage and a worthless engine core. I always hear ' The cylinders look good'. How can a cylinder 'look good' with hundreds of thousands of miles on it I ask "have you checked it with a bore gage? The response is usually 'What's that?
	Keep checking back These is MORE TO COME

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