When we are doing oil consumption calculus, timing the occurence of visible exhaust smoke in order to figure
out the source of the unwanted oil injection is an approximation at best. Let's take your acceleration test
as an example.
Immediately prior to the acceleration test the intake manifold (& thereby the 8 intake valve guides/stems/seals)
was under a vacuum, so there was oil pulled into the intake port. You accelerate, burning this oil charge off,
following by a long pull where the intake manifold is near atmospheric pressure (ie: no net pressure differential
across the valve stem seal) and the smoke clears up.
Compare that to the same acceleration test where there's no smoke at the start, but the blue smoke starts
to increase the longer we perform the pull. This is due to the blowby from the weak rings pressurizing the
crankcase, and then this blowby is plumbed back to the intake (instead of the old road draft tube) and the
blue smoke starts to roll.
Given the above, your description favors the former vs the latter. So this tends to steer us more towards
the intake valve vs valve guide clearances. And of course the intake valve seals on top of all this. But before
I declare replacing the seals is a guaranteed fix, I'd like you to watch exactly 3 seconds of a video where a
tired 327 small block is being disassembled. More specifically, watch the valve being checked for excess
side-to-side valve guide clearance. (Should be ~.003"-.004" total service limit)
Just watch from 0:32 to 0:34 near the beginning of this video:
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Wow, that looks more like 1/16-1/8" (0.0625"-0.125") of clearance? Needless to say, throwing a fresh set
of valve stem seals on those heads isn't going to last any time at all before the intake valve stems gyrating
wildly inside the worn out guides doesn't beat up the new seal into submission. (!)
But from my remote vantage point I don't know if *your heads* have proper guide to valve stem clearances
or not. And since you can apply compressed air via the spark plug hole & replace these seals without major
engine disassembly, then maybe you take a gamble, swap the seals out (maybe only on the cylinders showing
excess oil on the spark plugs) ...and see if you can't make a measurable difference in the blue cloud.
There's a lot of debate about replacing vs eliminating these o-rings during the refreshing of a set of
SBC heads. Personally, I default to whatever guidance is in the relevant FSM, (Factory Shop Manual)
and if I decide to deviate, it's because of a specific reason that's been adopted since the original manuals
were written/printed. In English, I am not necessarily stuck in the mid-'90s, but at the same time I
don't discount those manuals 100%. But I use them as a starting point. So here's the relevant page
out of the '95 GM service manual regarding the o-rings:
You must be registered for see images attach
NOTE: I found it interesting that they actually have the technician check the replaced o-ring for leakage with
a hand vacuum pump & attachment. (!)
Now having pointed this out, your lack of blue smoke puffing at start up tends to contra-indicate oil getting
past the intake seal package you currently have in place on the first startup of the morning? Pulling this all
together, do your symptoms indicate a good seal when the valve is stationary, but at the same time the
same seal can't keep up with a valve stem with unwanted side-to-side dancing in addition to the desired
up-and-down motion? (I'm not trying to overthink this; instead, I am trying to brainstorm how to best
explain the real-world symptoms you are seeing.)
****
Changing my troubleshooting vector for a moment, in my last reply I generalized high compression test readings
= good rings. Not so fast, for as Schurkey correctly pointed out, compression testing is primarily focused on
the compression rings. It's possible to have good compression rings having their job *aided* by excessive
oil not being properly scraped off the cylinder bores. (!) And if you & I were neighbors & we decided to pull off
the heads and then saw the following, then all bets are off, ring-wise:
You must be registered for see images attach
(credit: Google search for scored cylinder bores)
If we were to discover these vertical scratches in the bore(s), this would tell me that the PO wasn't too
particular about keeping the air filter in his airbox in place. Or if in place, intact. Or worse, insufficient
cleaning post machining if this is a reman. And we can think of these vertical scratches as engine oil
bypass paths. :-(
So what to do with all this? If you think that the cylinder heads are still in pretty good condition
(ie: the valve stem to guide clearances are still good) then you could decide to read all 8 spark plugs,
and only renew the intake valve seals on those cylinders where the plugs are oil fouled. And maybe
even add the o-rings back in just to eliminate a variable. Think of this approach as a measured response.
Or you pull the heads and verify that the cylinder walls are still in good condition. (No scratches, hone
marks still visible, no excess ridge, etc.) If so, then either bring these heads back to new clearances
-or- use it as an excuse to install a set of quality remanufactured (or even new) heads?
****
I'm usually all over the O2 sensors and ensuring a robust feedback loop. But in my humble opinion, we
need to find/fix where the excess oil is coming from upstream of these sensors. Otherwise, we're just
going to pollute the new ones into acting like the replaced ones all too soon.
****
I know that this might read as if I'm trying to play both sides of the fence, but in reality I just want to
highlight the highest probabilites of the various possibilities when it comes to excess oil consumption.
I am comfortable in this area only due to the sheer number of old soldiers I've been asked to
diagnose over the years. And the silver lining in all this is that I learned some from engines in good
condition, but I learned a whole lot more from the oil burners I crossed paths with. :0)
Hope this helps. And please be sure to watch at least the 3 seconds of that video I linked to.
Clearances are key when it comes to parts like intake valves cycling anywhere from 5 to almost 50
times per second.
Food for troubleshooting thought.
Cheers --
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