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.
Sudden excessive blow is usually caused by
piston detonation. In other words a hole has been burned in piston top
or side. See Detonation
Is it
Valve Guides or Seals?
NO.
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.
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?
You would be surprised at how many people try to eliminate blow by, by
installing injectors, injector pumps etc. To no avail. Also almost everyone
that calls for pistons purchases almost everyone has "Perfect Cylinders'".
Makes me wonder why I am the only one that has to rebore or sleeve engine
blocks.
Keep
checking back These is MORE TO COME
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