O-360 sticking valve update

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

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 *
************************************************** ***********************

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 *
************************************************** ***********************

Your observations were discussed at our coffee-shop klatch this morning
& a new possible theory came out. A local EAAer had a factory reman
Continental C-90-12F that would sag immediately post-takeoff. He
wrestled with the problem for about 300 hrs before he tore it down.

He found that there was insufficient ring gap and that the cylinder
bores had become glazed such that they looked like mirrors. He rehoned
them and reassembled & it fixed the problem completely.

I too find it hard to believe, but it might at least be worth a look
into the cylinders next time you have the plugs out.

nrp wrote:
: Your observations were discussed at our coffee-shop klatch this morning
: & a new possible theory came out. A local EAAer had a factory reman
: Continental C-90-12F that would sag immediately post-takeoff. He
: wrestled with the problem for about 300 hrs before he tore it down.

: He found that there was insufficient ring gap and that the cylinder
: bores had become glazed such that they looked like mirrors. He rehoned
: them and reassembled & it fixed the problem completely.

: I too find it hard to believe, but it might at least be worth a look
: into the cylinders next time you have the plugs out.

Interesting. How does that cause a power sag... just extra friction? Seems
unlikely in my situation since I've got chrome jugs (*already* mirror smooth except
for channels), excellent compression (78-80/80 on all four), and 8 hours/qt of oil
consumption.

Might try to get ahold of a borescope and have a looksee though.

-Cory

--

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

Supposedly the power sag was due to friction. I didn't witness it
myself.

You probably wouldn't need a borescope. Just lower a small bulb into
the cylinder in a dark room & look at the walls.

There might be a scenario where your excellent compression & low oil
consumption is a symptom.......!

nrp

nrp wrote:
: Supposedly the power sag was due to friction. I didn't witness it
: myself.

: You probably wouldn't need a borescope. Just lower a small bulb into
: the cylinder in a dark room & look at the walls.

: There might be a scenario where your excellent compression & low oil
: consumption is a symptom.......!

I have a hard time believing that friction could be the culprit. If I'm
losing 5% power, that 5% of ~150 hp (fixed-pitch prop at 2000'DA). If all of that
10kW is going into *friction*, something gonna fry and wear through pretty quickly.
I've never considered 8 hours/qt "low" oil consumption... Probably healthy since too
little can be worse than too much oil consumption.

Anyway, I'll try to take a look.

-Cory


--

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

This may be a shot in the dark, but many years ago we had a similar problem
(slight sag in power during initial climb) with the O-320 in a Cherokee-140.
After some troubleshooting we determined that most of the lost power could
be restored by significantly leaning the mixture. That led us to determine
that the cause was a partial obstruction of the intake air path between the
air filter and the carburetor, causing the mixture to be excessively rich.
I don't recall what the obstruction actually was (or how it got in there)
but it seems that it would be most pronounced at high power and high nose-up
attitude.

If you haven't done this already, next time the "sag" occurs, see if leaning
helps a bit. Sorry if you have previously reported that you've already
tried this.

--
-Elliott Drucker

wrote:
: This may be a shot in the dark, but many years ago we had a similar problem
: (slight sag in power during initial climb) with the O-320 in a Cherokee-140.
: After some troubleshooting we determined that most of the lost power could
: be restored by significantly leaning the mixture. That led us to determine
: that the cause was a partial obstruction of the intake air path between the
: air filter and the carburetor, causing the mixture to be excessively rich.
: I don't recall what the obstruction actually was (or how it got in there)
: but it seems that it would be most pronounced at high power and high nose-up
: attitude.

: If you haven't done this already, next time the "sag" occurs, see if leaning
: helps a bit. Sorry if you have previously reported that you've already
: tried this.

We're going to pull off the induction system and carb to just check for
oddities before putting it back together. We'll take a look.

As far as leaning goes, that's one of the first things I try when it acts up.
Field elevation here is 2100', so (especially in the summertime with DA over 4000')
some leaning is required for best power.

-Cory


--

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