O-360 sticking valve update

Hello all. I know it's been awhile since I updated, but progress has been
slow. Here's where we're at:

Last weekend:
- Pulled valve covers, rockers, pushrods, exhaust.
- Pushed on valves and were unable to feel any sticking like there was the last time
we definately had sticking valves. Decided to get the tool to compress the valve
springs and build a jig to do the "wobble test." (SB388C)

This weekend:
- Did "wobble test" after using tool to remove valve springs. Front guides (#1, #2)
in the middle of the "wobble range." Rear guides (#3, #4) at the top end of
acceptable (0.030 wiggle measured 2.5" away from guide). When the valve were almost
completely closed, the wobble test showed wobble towards the *tight* end of the range.
All valve seats, stems looked and felt good when spun in-place.
- Noticed some buildup of lead on exhaust valve stem as viewed from inside the exhaust
port. Nothing that seemed unusual.
- Could feel extremely subtle resistance to sliding of a valve or two in specific
orientations (both rotation and excursion). Stress the "extremely subtle" part...
couldn't feel it unless you were very careful and methodical to find it.
- For comparison, removed intake valve springs and intake runners. Noticed some
buildup of carbon on intake. Enough to change the tone of the *ding* when manually
closing the valve.
- Wobble on exhaust valve was a bit more than intake, but nothing too out of line.
- Pushing the valve almost out of the guide and examining with a light revealed very
clean-looking guides. No detectible wear or buildups.

Notes of possibly interest:
- Some of the valve spring end caps showed little indication of valve rotation
compared to others. Some had nice, shiny marks all the way around, and some had brown
oilgunk stains on them showing where the springs lived.
- All the crank rotation we did while checking stuff inflated the lifters so getting
the rockers on was a @#$^!!#$@@ PITA!


Conclusions:
- After my partner, mechanic, and I debated on everything for a good long while, we
had a tough time concluding that there was anything heinously wrong with the valve
train. We cleaned all valve stems and guides with generation applications of MEK,
Scotch-brite, and scraping for the lead salts and started putting it back together.
Thoughts are basically that marginal sloppy guides do not *inherently* cause sticking
valves, but they do promote additional buildup that can. We removed a lot of the
buildup. Short of pulling all the jugs off and having new guides put in, it seemed
like a sane choice.

- Operation procedure could be inducing the valve sticking at takeoff. I generally do
not like to get the CHT's over 250 before taking off since I don't want things to cook
too much on the ground. I usually want at least 200 before taking off, however.
Within a minute of takeoff, they're usually reading 350. Perhaps the shock heating
heats the low-mass exhaust valves so fast that they expand in the
still-heating-and-expanding guides and causes a slight sticking. Once everything is
up to temperature a minute or so after takeoff, everything slides as it's supposed to.


Thoughts? Comments?
-Cory


--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

Some Lycomings (earlier ones?) have different rocker arms for the
intake and exhaust valves. I assume you observed that (or they were
identical?)

Does this fade-off happen with only cold (cool) oil?

Anyone ever heard of Lycoming lifters pumping up?

nrp wrote:
: Some Lycomings (earlier ones?) have different rocker arms for the
: intake and exhaust valves. I assume you observed that (or they were
: identical?)

Oil squirter holes on the exhaust rockers.

: Does this fade-off happen with only cold (cool) oil?

As in my previous pose (almost 2 weeks ago initially), it seems to only do it
on the first takeoff of the day. Oil's off the peg, but not warmed up as in flight.

: Anyone ever heard of Lycoming lifters pumping up?

It took us awhile to realize that's what it was. Every other time I've put
them on, I had the lifters out, cleaned, and drained as well. This time we didn't
take the tubes out and had to compress the valve spring a bit to get the rod in. After
sitting for a minute or so, you could then move the rod with your fingers. It wasn't
just on one jug either (and yes, we were on TDC to make sure the cam was in the right
place).

-Cory

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

Another straw to grasp - Might it be an anomaly in your intake manifold
that is changing the fuel distribution as the oil warms up? Something
like a gasket protrusion ever so slightly affecting liquid-vapor fuel
flow along the manifold walls (like the gasket between the carb & the
oil sump). A possible confirming symptom would be if the problem is
sensitive to fuel source & possibly if the power output "switchover" is
abrupt (then it would be someting else) or gradual over several
minutes.

The lifter pump-up on disassembly is certainly normal as you probably
now know.

nrp wrote:
: Another straw to grasp - Might it be an anomaly in your intake manifold
: that is changing the fuel distribution as the oil warms up? Something
: like a gasket protrusion ever so slightly affecting liquid-vapor fuel
: flow along the manifold walls (like the gasket between the carb & the
: oil sump). A possible confirming symptom would be if the problem is
: sensitive to fuel source & possibly if the power output "switchover" is
: abrupt (then it would be someting else) or gradual over several
: minutes.

Interesting theory, but I have a hard time believing that the oil warms up
appreciably in 60 seconds. I've had the power come back abruptly, and gradually. The
gradual one is the worst because the problem is already so subtle and intermittent so
it's tough to know it happened if it comes back slowly. The time it was "abrupt" it
was quite noticable.... similar to a second mag coming online (although I'd done a mag
drop during that particular problem takeoff, so it wasn't that).

: The lifter pump-up on disassembly is certainly normal as you probably
: now know.

Erg. There's gotta be a better way than having three people (one compressing
valve springs, one pushing the rod, and the other wiggling the rocker arm) futzing
with it. Given that we were going to really *do* anything to the lifters even if we
removed them, I didn't figure it was worth taking the tubes out and having to get new
seals.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

Interesting theory, but I have a hard time believing that the oil warms up
appreciably in 60 seconds.

My thoughts:

The application of full power on an aircooled engine causes things to
heat up very rapidly since there is little thermal inertia. On startup
& taxi, the oil bypasses at the relief valve & doesn't get much access
to the heat of the engine until you get to a certain point, where it
really begins to remove heat, quits bypassing and then warms up
quickly. The specific heat of oil isn't very high yet the heat input
once things get to spraying around the crankcase are probably pretty
substantial.

Somewhere the intake manifold might be changing from a mixed
liquid/vapor flow to an all vapor flow at a corner or an obstruction.
Look up the manifold and on the carb gasket when you do the throttle
plate bit. Check for loose clamps etc on the manifold tubes - but it
sounds like your mechanic etc (I. e. you) are pretty well on top of
things and have done that already.

Q - How well did the Lycoming clearance measurement thing work? I
built one but have not used it yet. Was your's per their plans?

On Sun, 29 Jan 2006 20:46:17 +0000 (UTC),
wrote:


Erg. There's gotta be a better way than having three people (one compressing
valve springs, one pushing the rod, and the other wiggling the rocker arm) futzing
with it. Given that we were going to really *do* anything to the lifters even if we
removed them, I didn't figure it was worth taking the tubes out and having to get new
seals.

I've got a 6 # sledge with an 18" handle, labelled E-18 only (sort of
an inside joke). The butt end of the handle is beat to crap from it's
application to waaaay more rocker arms than I care to think about.

The drill is to make sure the p-rod, rocker & pin + rotator cap is
liberally coated w/assembly lube, start the pin in the boss, poke it
the p-rod. make sure the rotator is in place.

Put the rocker in place, place the butt of the handle directly over
the rocker tip, place the sledge head in the middle of your sternum,
apply adequate pressure by leaning inward and poke in the pin.

Wait 'til you have to do a set of splayed valves, they've got a thrust
washer to line up also...

TC

writes:

nrp wrote:
: Anyone ever heard of Lycoming lifters pumping up?

It took us awhile to realize that's what it was.

A engineeering school classmate told me he accidently put his Fury
III with a big block into low gear, at highway speeds.

A) It went in..
B) It stalled at once..
C) They sat at the side of the road for an hour+ waiting for the
lifters to bleed down so the valves would close.....

--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

comment and question...
First questions, did you look at the cam lifts? to see if they were in
the ball park? And how did the throttle plate look?
Comment, since you have checked the valves for binding it is time for
AVBLEND + MMO Cory... Then if it still acts doggy on takeoff it is fuel
or spark....

denny

Denny wrote:
: comment and question...
: First questions, did you look at the cam lifts? to see if they were in
: the ball park?

We haven't done that, but in any event it wouldn't cause intermittent power
loss.

And how did the throttle plate look?

That's on the agenda before buttoning it back up. We're actually waiting on a
starter repair and alternator overhaul at the moment as well. Probably won't be
putting anything back together until later this week or next weekend.

: Comment, since you have checked the valves for binding it is time for
: AVBLEND + MMO Cory... Then if it still acts doggy on takeoff it is fuel
: or spark....

In general I'm skeptical of MMO and other snakeoil treatments. Seems like
more than circumstantial evidence for a lot of aviation folk on this one, though.
Between that, the increased CHT warmup, and the cleanout of gunk on the guides, it
wouldn't surprise me if the problem doesn't come back... for awhile.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************