Ken asks, in regards to blowby:
> What is it? Why do I have it? And how do I get rid of it?
Ken, don't yank that head until you do a compression check.
Unless your gasket is really toast, it'll still be a useful test.
Oil blowby usually happens because of excessive pressure in
the crankcase, and that comes from leaking rings. The best
'shade tree mechanic' way to check is with a compression
gauge. For those new to the process, here's a rundown:
BTW, accurate readings require that the valves are properly
adjusted, and things are in good repair. Stretched timing chain,
bad cam lobe, bent valve, lots of other things can throw off a
diagnosis...
Warm up the engine (not too warm; you're gonna stick your
hands in there). Ideally, use a compressor and blow the crud
away from around the plugs. Loosen them a half turn or so and
start the engine again for just a few moments (this clears any
loose flakes of carbon that got knocked loose from the plugs).
Now, pull the plugs, disconnect the coil (just to be sure), block
the throttle OPEN (to allow better airflow), and make sure you're
in neutral :-). Screw the gauge into a cylinder, and crank the engine
about 4 or 5 power strokes (you'll see it on the gauge and hear
it from the starter). Record the top pressure. Repeat for the other
3 cylinders. [this is the dry test]
Now, time to get a tad messy! Squirt about a tablespoon of motor oil
into a cylinder (aim for the walls, not the top of the piston). Then do
another pressure test. Repeat for all cylinders. [this is the wet test]
DON'T FORGET to unblock the throttle before you put things back
together!
What did you learn?
1) Too much oil and you'll get a faceful of oil mist when you crank
2) The pressure should be even between all cylinders - within 10%
or thereabouts. Low cylinders don't put out as much power and
cause rough running. Near zero pressure probably means a hole in the
piston... Two adjacent low cylinders could indicate a bad head gasket
between the two. A single low cylinder could be bad valve adjustment,
a burned valve, or fried rings.
3) If the pressure was raised significantly by adding oil, you've
probably got leaking rings. Otherwise, low pressure points to
the valves.
Now, when you yank the head at least you have a starting point for
what to look at...
Second BTW: If you scrape the carbon off the pistons, leave a
ridge near the edge. Can't say authoritatively why to leave it, but
I've read that warning in several places.
For those of you still awake, sorry for the length...
If I'm being too noisy for the list let me know (privately, please)
and I'll quiet down..
-- John
John F Sandhoff sandhoff@csus.edu Sacramento, CA
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