O-360 sticking valve update

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?

nrp wrote:
: 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.

I'll check that. Remember though, that it has done this in the summer as well
as now in the "winter." Not like the forecast high of 63 degrees today could really
be called "winter," but it was about 40 the last time it acted up. I'm pretty sure
when I left Milwaukee at New Year's time it acted up on takeoff too... probably 35
degree late-morning after a cold-soak overnight at 25 (with preheaters on).

: 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?

Well, due to liability concerns, they've killed all the student-accessible
machine shops. I basically had to beg the shop to chuck up the aluminum stock into
the lathe and ream out the 0.496" hole. The rest of it I built with a spoon and my
teeth (i.e. drillpress and hacksaw). It was a crude approximation of the tool
outlined in the SB388, but it worked to extend the valve's stem. As far as
measurement part, I used a dial indicator with magnetic base and manipulated it to hit
the rod vertically at 2.5" from the valve guide as per the SB. I didn't build the
holder doodad that goes on the rocker arm pivot rod. Not very elegant, but
it did work... just more of a pain to set up and move from jug to jug.

The biggest problem that I had was how much to open the valve. When it was
well-seated (i.e. fully closed) the clearance was very small. One it was opened a
bit, it opened up to about the limits. The SB doesn't describe how much the valve
should be open. I suspect the magic Lycoming tool compresses the valve spring enough
to deseat the valve, but it never says how much.

-Cory


--

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

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

wrote:
: 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.

That's more or less what we were doing for awhile.... hammer handle on the
rod with the greased pig of parts trying to line up. I didn't want to damage the rod
cap pushing too hard with misaligned rockers. We had additional hands, so the hammer
handle was used to depress the valve springs (as my sternum bruises can attest).

I was thinking maybe if one had an undersized rod to get everything started
and rotate the crank to put pressure on the lifters. Haven't tried it but given how
the lifters deflated nicely it seemed like it could work.

-Cory

--

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