[xj-s] Oil consumption

["Richard F. Dixon" <rfdixon@chs.cummins.com>]

>When your engine is running, the pressure gradient between both ends
of the
exhaust valve stem is such that absolutely no oil can find its way
between
valve and guide. The only flow there can be is in the other direction,
namely blowby gases. The only time oil finds its way down the guide
is at a
stop. Given time, it will seep down onto the back of the valve and
--should
the latter be open-- thence into the combustion chamber. When you
start the
engine again, the oil in the cylinder will burn (blue smoke), that
on the
back of the valve will cake it up, part of what's between valve
stem and
guide will be blown back whence it came and the remainder will cook
and
produce a nice varnish coating on the valve stem. Varnish has no
known
cooling or lubricating property. I am confident that, in a not so
distant
future, Kirbert Palm will find a way to divert the flow of pressurized
oil
so it constantly cools and lubricates the guides without leaking
into the
cylinders(may I suggest we replace the cotters with some sort of
ball
bearing so the valve can be rotated via a ratcheting tappet, an
oil feed
hole half-way down the guide, a helical groove in the stem and a
flame
proof seal at the bottom of the guide?). In the meantime, if you
want to
lubricate your exhaust valve stems properly, you will have to stop
your
engine for a half hour for every few minutes of running.
If the exhaust side is not normally lubricated, why would you want
the
intake side to be, which is subject to much less stress and heat?
But
assume you would. It would stand to reason that you would want to
reduce
the oil flow progressively as the engine wears and the clearance
increases.
It appears that this is the exact opposite of what the original
seal
achieves, since it loses all effectiveness after a few thousand
miles!
Let's face it: the sole purpose of intake valve seals is to prevent
ANY oil
from being sucked down that way. <

Michel,

Do you work in the engine development field? Because most of this is BS. I do work in the field of oil consumption here at Cummins Engine Co. I believe you are working on theory and not real experience like we have here. The solutions you propose here are complex and answer a question no one is asking. The systems in place by most manufacturers work well and are a fine balance between wear, oil consumption, and cost. If you think you can do better, try. But bring money. Engine test cell time is around $200 US an hour plus fuel. One 100 hour engine test here at Cummins in Charleston, SC is about $15,000. And we are cheap!

Yes, heat and hot oil do degrade polymer seals over time. But time measured in years not a few thousand miles. Remember, most of the engines here we are talking about are older engines near or past what would be considered the normal life cycle of 10 years. Teflon would last somewhat longer but not by a lot. What material would you use?

Stop spreading misinformation based on theory and listen to people with real experience. Not me necessarily, but folks like Roger Bywater. After all, how many engines have you designed built and sold, like Jaguar?

Richard Dixon
Engineering Test Services,
Cummins Engine Co.

 
 

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