>What is it? Why do I have it? And how do I get rid of it?
>
>I've got copious amounts of oil coming out the PCV tube. I've checked the
>caulking on the PCV baffle on the valve cover, per Ross's posting a while
>back where he thought a motor needed rebuilding but ended up just needing
>a new valve cover, but mine looks OK.
>
>Is this oil blowing by the valves? rings? Clue me in here... My valves
>are absolutely caked with carbon buildup. Last time I had the intake
>manifold off, I looked in there and could barely even see one of the
>valves there was so much crud. I'm pulling the head this weekend to
>change out a leaking head gasket (right rear corner) and was wondering if
>anyone had any experience with products that dissolve carbon buildup?
>
>Any tips are greatly appreciated!
Ken,
In addition to what John and Rick have already mentioned I want to add
that from your description of the crude (high tech term <G>) that you see
looking into the ports, much of the oil may be getting past the stem
seals (little rubber caps) and between the valve stem and the guide into
the combustion chamber. You may have excessive valve stem to guide
clearance, too. As a general rule of thumb, a valve should rotate
smoothly in its guide (without a seal) but not move side to side at all.
Measuring is best. Blowby is combustion pressure that bleeds past
(usually) worn rings and pressurizes the crankcase. If the rings/cylinder
walls are worn enough to allow enough pressure into the crankcase, it can
actually push oil out the dip stick tube.
I had this happen once on a Chrysler 318 V-8. When we moved back here
from Riverside, CA, my wife drove our Dodge S/W back first to start a job
while I wrapped up things in SoCal, and she didn't check the oil for a
couple of months. My father put over three quarts of oil (total was 5, I
think) in it after it started overheating and smelling. I'm surprised
that it didn't seize, but it did start pushing enough oil out the
dipstick to make a big mess.
On a motor as old as yours may be, replacing the valve guides and seals
and doing a valve job without re-ringing the motor probably would make
blowby worse since you're giving the top end of the combustion chamber a
new/tight seal. That just increase the pressure on the already tired
rings.
I know this may be news you'd rather not hear, but I'd rather you be
aware of all the possibilities rather than go through the head, think you
have the problem solved, only to have to tear into the motor again. In my
experience with L-series Datsun motors, the blocks tend not to wear
excessively as the castings are very hard and they used soft rings, so
most of the normal wear tends to be on a relatively inexpensive/easy part
to replace.
FWIW,
Ron
________________
Ronnie Day
rday@airmail.net
Dallas/Ft. Worth
'71 510 2-dr (Prepared class autocrosser)
'73 510 2-dr (Street Toy)
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