How likely this to be a serious issue?

[Colonel Sanders]

I'd love to know what proportion of engines that fly fewer than (say) 10 hours a year do actually suffer from corrosion

It depends. How much salt in the air? How much
humidity? Lycoming or Continental?

If it's a Lycoming, in a salty humid environment.
I would suspect that more than 99% of those
low utilization engines would suffer from internal
corrosion which will prevent getting to flight time
TBO.

If it's a Continental, in a salt-free, dry environment,
I would suspect that less than 1% of those low
utilization engines would suffer from internal corrosion.

[photofly]

Also, pull the spark plugs and use a borescope to look
at the cylinder walls. Fast and cheap.

Since there exists some doubt about the run-in procedure, would looking at the cylinder walls answer questions about this too?

[photofly]

If it's a Lycoming, in a salty humid environment.
I would suspect that more than 99% of those
low utilization engines would suffer from internal
corrosion which will prevent getting to flight time
TBO.

If it's a Continental, in a salt-free, dry environment,
I would suspect that less than 1% of those low
utilization engines would suffer from internal corrosion.

I respect your experience and suspicions, but some hard data would be lovely, too.

[Colonel Sanders]

great! Will use this going forward. Thanks CS!

The cheap tests - pulling a rocker cover,
borescoping the cylinder walls, etc - allow
you to quickly and inexpensively reject the
obviously badly internally corroded engines.

Of course, they are no guarantee of no
internal corrosion. Only a complete teardown
of the engine will give you that knowledge,
and that's obviously not an economical choice.

[Colonel Sanders]

would looking at the cylinder walls answer questions

Sure. You should see the cross-hatch from
the honing. If you don't, that's a problem -
that's called a "glazed" cylinder wall.

[Colonel Sanders]

but some hard data would be lovely

Ok. My buddy Fred Cabanas flew for decades out of
Key West. Worst corrosion environment I can think
of - hot, humid and salt everywhere. Even with daily
flights, he simply could not make TBO on a Lycoming,
and he was a fanatic about maintenance. He was an
A&P as well as an ATP.

Always the cam and lifters would go. Hell, he corroded
out his ailerons on his S-2C in only a few years and
had to replace them.

At the other extreme, I flew an airplane with an original
Lycoming from 1978 to Canada for an import. It lived
in the dry southwest. Just under 1300TT, and 35 years
since new. I was nervous as sh1t about it, because it
was a Lycoming and had not been flown much lately -
the owner died - but after 13 hrs flight time home, the
AMO cut open the filter and didn't see any metal.

You simply cannot disregard the conditions the engine
is exposed to, and you cannot disregard the metallurgy
of the engine (Lycoming vs Continental) when you consider
internal corrosion. Projecting that n-dimensional space to
a single vector - hours flown - loses a lot of essential
information.

Over the decades, I have seen Continentals parked for
extreme lengths of time - that would have killed a Lycoming -
and came back to life with only a stuck valve to fix. Incredible.

[iflyforpie]

I've brought four Continentals back to life over the last two years.... three O-300s and one IO-520 which had not flown for over three years... two of which I personally flew during their first ferry flights. I can echo CS's statement that Continental engines don't have the same corrosion problems as Lycomings do.

The worst was the O-300 with about 1500 hours where the insides of the cylinders corroded beyond service limits.... no big deal unless you have to pull a jug. The best was an IO-520 with 300 hours that had not even turned a blade for eight years and there was no detectable corrosion at all during internal inspection. BC interior for all of these planes.

[akoch]

Speaking of the sticky valves... I just got back from the airport, had to cancel my flying. The exhaust valve on the cylinder #2 clicked when I turned the prop during preflight. I located the source of the click, and pulled the covers on the #2 cylinder and can see the valve sticking - not moving, and then suddenly jumping up with a loud click.

So I figure this is exactly the problem CS described a few times in the past, and just in the post above? Now, actual question - how do I deal with it? This is Continental IO-240.

[Colonel Sanders]

how do I deal with it?

AME's here don't like to talk about sticking valves,
for some reason.

Anyways, there are several things you can do.
Some people will whack the valve with a rubber
hammer, to try to free it up. This is called "staking"
the valve. Temporary fix, at best.

Or, you could add some Avblend. Problem is, it
will only soften the carbon on the exhaust valve
stem. It will not touch the lead accumulated on
the top, inner portion of the guide.

Your AME will probably tell you to pull the jug,
which is total overkill. Like hunting flies with
a shotgun.

However, there is a far easier way to fix it -
called the "rope trick". You use rope (or
compressed air) to hold the exhaust valve
in place, while you compress the spring and
remove it. You get rid of the rope, rotate
the cylinder to BDC then push the exhaust
valve into the cylinder. You drop the exhaust
valve out a spark plug hole and clean the stem
as best you can. You also mechanically remove
the lead from the guide. I would strongly
recommend carefully measuring the guide
diameter and comparing it to the table of limits.
You may be surprised.

Anyways, you put it all back together, and off
you go. Hopefully you didn't bend a pushrod!

PS Lycoming talks about this in SB 388C and
SI 1425A. I am sure TCM has equivalent
references for disinterested AME's, because
TCM have exactly the same problem.

Good luck! I spend 'way too much time doing
this sort of thing.

[akoch]

aha! Thanks! I'll talk to my AME on Tuesday about this then.

[Colonel Sanders]

Two words: dental floss.

If your AME doesn't know about dental floss,
well, I guess you're going to have to spend
the big bucks to unnecessarily pull the jug.

PS I designed and built this fixture to rapidly
reinstall the rocker arm. Cost about $5, took
5 minutes to make. Makes the job a breeze.



Biggest hassle about the rope trick is pulling
the exhaust. If the nuts are corroded badly
and seized on the studs, well, order some
new studs.

IMHO, do all the cylinders - not just the
one that's sticking right now. They all
have the same problem to varying degrees.

Your AME will likely tell you to pull all
the cylinders and do a top overhaul, for
many thousands of dollars. You can do
that, I suppose. Or, spend a day and
clean the valve guides

[supercub7]

CS, what is your opinion of Mystery Marvel Oil being added to the engine oil and fuel of small Lycoming and Continentals? I have been using it for about 150 hours in a Lycoming 320 with great results so far. Some AME's seem to swear by this stuff, and yet others have not even heard of the product.

[Colonel Sanders]

IIRC Mystery Marvel Oil simply contains varsol
and light oil - google it. It is not approved for
certified engines - you can use it in homebuilts
only - but like Avblend (an FAA-approved solvent)
it will help dissolve the carbon on the exhaust
valve stem, which is half of the problem of the
stem-to-guide clearance disappearing. The
other half of the stem-to-guide clearance
problem is the lead deposits on the inside of
the exhaust valve guide. No chemical (solvent)
that I am aware of, is effective at removing
that lead. It must be mechanically removed.

Lyc SI 1425A talks about reamers. You can
spend a lot of money buying a lot of weird
sized reamers, but in my experience they
are not good at removing lead from the inside
of the guide - merely measuring the inside
diameter of the guide, which is certainly
nice to know, but not exactly the whole story.

[PilotDAR]

Akock,

Lots of good advice for you there, and I agree with just about all of it! I own a Lycoming and a Continental, and the information you have here agrees with my observations over a long time. I do use Marvel Mystery Oil.

An internal inspection with any chance of being conclusive will be two cylinders removed, certainly $1000+. What CS tells of exhaust valve fixes works and I have done it. However, it it not for the maintenance faint of heart, and there are some risks of damaging things more. That said, the resulting "fix" is likely temporary. I have always ended up taking off the cylinders and having them overhauled anyway.

If the cost of proper engine maintenance is a put off, you might rethink your purchase. Interim maintenance might work, but it is just that, you're going to have to pay at some point....

From what you describe, I would suspect that the engine was not properly broken it. That can be it's own problem, and you'll be pulling all four cylinders. However, if you build that into your expected purchase price, it might still be worthwhile, and then you'll know exactly what you have, for some long time to come. Your only risk is getting the four cylinders off, and finding that is does need a cam. That's the chance you'll have to take. Checking for metal in the filter (a MUST prepurchase anyway) is good insurance against this risk.

[akoch]

PilotDar, thank you for the advice!

The one I'm looking to (maybe) purchase is the 52h Lycoming one. And this is the one I was curios about regarding possible corrosion.

The Continental one I got the sticky valve on at 585h is my current airplane. And this is the one I'm looking for fix now. Sorry for the confusion.

[Colonel Sanders]

The Continental one I got the sticky valve on at 585h

SB 388C (admittedly for Lyc, not TCM) says to check
the exhaust valve-to-guide clearance every 400 hrs,
so I don't think there is any mystery here.

If you were at my airport, in around 4 hrs, we could:

- remove cowl
- remove rocker cover
- remove exhaust
- remove rocker arm
- remove valve spring
- clean and measure valve stem and guide
- reinstall valve
- reinstall spring
- reinstall rocker arm
- reinstall rocker cover
- reinstall exhaust
- reinstall cowl

Biggest hassle is the exhaust. If it's in
good shape, all you need is a new gasket
and washers.

Find an older AME with some gray hair,
that moves a little slower and knows what's
not in SI 1425A. You really don't need a top
overhaul. You really don't need four new
cylinders. You just need to clean the lead
deposits from your frikken engine.

[nameme]

I currently maintain 2 R44 since they are new. Robinson ask for 300hrs valves check. For the first check at 300hrs, no problem . Second check at 600hrs, both needed a valve stem and valve guide cleaning, the valve on the left rear cylinder where not sticking but dragging a bit too much. Did not pull the cylinder, just used CS way. So far , next two inspection, nothing.
P.S. Both are on AvBlend since new. The check need to be done, even with it.

[GyvAir]

Once you have the offending valve stem protruding from the sparkplug hole, what tools and techniques do you use/recommend for removing deposits from the stem and from the guide? I would be concerned setting certain people loose on such a task, that as much damage as good could result if their approach was inappropriately aggressive.

[Colonel Sanders]

What accumulates on the exhaust valve stem is
merely carbon, which is easily removed with
mineral spirits and NO SANDPAPER. You can
use MEK for the full experience, if you wish.

The difficult thing is remove is the lead, on the upper
inner portion of the guide. In SI 1425A Lycoming
recommends reamers, which like the mechanical
fingers, don't work worth beans. Dental floss is
far superior to the mechanical fingers, and I will
let you figure out how to remove the lead, to
avoid having this thread deleted (like the others)
by a yammering avionics tech from out west.

No chemical will touch it, in my experience, and I
have tried just about every chemical there is,
with the exception of mercury which would
probably work if you left it for a long time. I
keep thinking that one of the commercial gun
barrel cleaners should work (safe substitute
for mercrury) but in my experience they didn't,
perhaps because the lead deposits inside the
exhaust valve guide are so much thicker than
what you find inside of a gun barrel. Maybe I
didn't have enough patience.

I have accumulated a special toolbox of parts
and tools just for this job, I do it so often. I
had two Lycoming engines (not mine) with
stuck valves just last week. Once you get the
hang of it, you can do it very rapidly. The worst
part is R&R'ing the exhaust.

Remember, you don't need to remove every
part from your airplane and send it to an AMO.

Do you remove spark plugs and send them to
an AMO for overhaul? Of course not.

Just clean the frikken carbon and lead, and it
will run much better.

[GyvAir]

I've never liked "cleaning" anything with a reamer, unless an oversized hole is what you want. Hence, my curiousity about alternative tooling to what the SI suggests.

[Colonel Sanders]

Agreed - the reamers are about as bright an
idea as the mechanical fingers. If you want
to scratch up the inside of the guide, a reamer
is a great way to do it.

I spent a lot of money on many different sizes
of reamers, only to discover that their only use
is as a gauge, to determine the inside diameter
of the guide.

As I said before, you can either chemically or
physically remove the lead. Gun barrel cleaning
technology is probably the most promising for
the chemical route - you are removing lead,
after all - but I never had much success with it.

So, I physically remove it, in about 15 seconds,
then the valve goes back into the perfectly shiny
and clean guide, using a piece of dental floss
through the guide, tied to the valve neck. Some
people use magnets, but they make me nervous
around the valvetrain.

Sorry I can't tell you more, but I'm tired of being
attacked by idiots here who threaten to report me
to Transport, for (e.g.) touching up fabric paint with
a hobby brush I would refer you to the ridiculous
thread, but a really weird avionics guy from out west
had the moderators delete it.

And then there was the time that the people here
on AvCan reported me to Enforcement for squirting
contact cleaner on the bendix drive of a Prestolite
starter on a 172 from Brampton.

In the immortal words of William Shatner on SNL
to the trekkies in the audience:

[GyvAir]

So, in the interest of thread drift... will the phasing out of 100LL spell the end of lead fouled plugs and sticking exhaust valves, putting junior AME apprentices out of work and engine shops out of business?

[akoch]

FADEC alone could have done 70% of that. Perhaps this is the reason it is not seeing wider adoption?

[PilotDAR]

FADEC has always had certification challenges associated with demonstrating continued operation following system or electrical failure.

Yes, less 100LL might mean less work changing fouled plugs, but there will still be lots of work repairing fuel systems which have noticed the change in fuel, to the unknown future fuel.

As for DIY or economy engine maintenance, yes, accomplished by a suitably trained and experienced person, with the required tools and resources, it can be beneficial, though more so, just in the short term. But, it is not for everyone, and I tread very lightly discussing maintenance tasks beyond elementary work, on a public forum.

Qualified maintainers are so, so there is the required resource for the maintenance on our aircraft. We will of course support them, so they are there when we need the work to be done in accordance with the requirements for the aircraft. Entering certified aircraft ownership, planning on DYI maintenance could be disappointing....

[Colonel Sanders]

will the phasing out of 100LL spell the end of lead fouled plugs and sticking exhaust valves

I sure hope so. Mike Busch seems to think so, too.

PS You can really reduce lead fouling by always
leaning the mixture on the ground, and if you have
to idle and wait, do it at 1100 - 1200 RPM. Most
people don't bother, though.

PPS A friend emailed me this link, this morning:

http://www.brushresearch.com/brush-types.php?c1=4#

A tool for quickly removing lead from a gun barrel.
Fascinating, eh?