The International Cessna^® 170 Association

Any thoughts about a little BOLD STAKING on the exhaust valve stem?

A minute particle of stubborn carbon clinging between valve and seat may the culprit and could possibly be transformed into a harmless powder. This has been known to work a few times.


I still wish we had 80 octane. Still puzzled with the LL label. 100LL . What is low about 4X the lead? I may be going off topic so I will stop


Regards

Staking a valve is a legitimate thing to try if excessive leakage is found at the exhaust valve. Continental still wants you to use the bore scope to visually ensure the valve or seat is not out of round and all is well in the cylinder.

The LL designation and the levels of lead it allows at one time where probably considered low. Today though it might be the highest leaded fuel you can buy. That is my thoughts without any research to back it up.

What is Staking a valve?

Robert Eilers wrote:What is Staking a valve?

The objective is to try and break up a piece of carbon lodged under the valve head, that may be causing a low compression reading on that cylinder. You remove the valve cover and, using a brass drift and hammer, you "stake," or hit, the rocker arm to make the valve suddenly open and then slam shut (from the valve spring tension). It's believed this may crush a carbon particle and sometimes it does.

TCM believes use of the borescope is the more effective procedure. That is, if compression is above that noted when comparing the compression tester against the master orifice tool (may be in the 40's) AND the borescope exam doesn't show any burning of valve heads, loose seats or cylinder scoring, the cylinder is OK to return to service. Of course, SB 03-3 says to first fly the airplane for 0:45 minutes if the compression is below the acceptable limit and then reperform the compression test.

Staking is an "old school" solution that sometimes works if something is partially holding the valve open. Often flying the airplane will do the same thing. If no burning, loose seats, etc. are noted with the borescope, it means the higher compression of a running engine is fully closing the valve, and you're "good to go."

100 LL fuel got the name when they reduced the hell out of the amount of lead that was in 100/130 fuel.

When I went through training back in the olden days (1942 to 1945), we had a plethora of various fuels for our various types of flying machines.

Primary trainers ( PT13, PT17, PT18, PT19,PT23,) etc.,all used the mighty 73 octane.(Clear ,uncolored) The next higher grade,80/87, could be used in an emergency.

Basic and Advanced trainers (BT9, BT13, BT14, BT15,AT6, AT7, AT8, AT9,
AT10, AT11, AT12,AT17,)etc. all used 80/87.(Bronze colored, if I remember ) As did many utility transport types such UC43, C45, C64 and similarly powered types.

Operational training in combat type aircraft and transports (A20, A26,B17, B18, B23, B24, B25, B26,C46, C47,C53, C60) etc., used 91/98 (Blue) and used reduced maximum power manifold pressure accodringlyfor take off or as needed.

When I got to B29 school, I finally got to use 100/130. The Wright R3350 engine was just too finicky to digest anything but the best. The refining of 100/130 octane fuel was really developed and expanded during WWII and was in relative short supply. Until very late in the war, all of it was going to combat. As a matter of fact, the very fortunate arrival of a tanker load of the "new" Shell developed 100/130 fuel to England was very instrumental to the outcome of the "Battle of Brittain". It gave the RAF the necessary edge to make a difference. British fuel was about 87 octane.

Late in WWII they developed a grade 108/132 fuel, but I don't believe it was ever produced in very great amounts.

From the early 1950s until the military forces phased out all their reciprocating engines, they used 115/145 (Purple) fuel almost exclusively.

There was a relatively significant advantage using this very high octane fuel. For example, a Douglas DC6 is powered with four
P&W R2800-CB16/17 engines. When using 100/130 fuel the engines are CB16 engines of 2200 max.H.P. @ 2800 RPM and 56 in.MAP. When using
115/145 fuel the engines are CB17 engines of 2400 max.H.P. @2800 RPM and 61 in.MAP. Both powers "wet", that is, with water injection. This extra 800 H.P. available for take off allows the gross weght to increase from 103,000 lbs. to 107,000 lbs. That's an additional two tons of revenue cargo.

Can you immagine the spark plug cleaning chores we'd have if we had to use 115/145 in our Continental C-145/O-300 engines?

Just doing my annual and I have a leaking intake valve. Last annual I had the same valve leaking and I gave it the tap treatment and it sealed. This time I boro'd the cylinder due to what are the odds it would be the same problem 10 months later. This is on a lycoming cylinder with aprox 200 hours smoh and 100 hours since re and re. When in doubt a boroscope can pinpoint the problem, I'll have to pull the cylinder to find out why about .750 of the valve face is not seating. More to follow.

In flight my number 4 cylinder exhaust valve stuck last Sunday. Returning from trip in Florida and had to stop in Tuscaloosa, Al. I think what attributed to it getting stuck was that I closed the throttle to decend through a hole in the clouds. I usually keep some power in when decending but this time I needed to dive into it a bit. Once I added power again it began to run very rough. I landed and left the plane in Tuscaloosa.
I use TCP and Marvel Mystery Oil. The machanic asked if I leaned aggressively and said the plugs had white deposits on them. I think that is the TCP at work. I lean to rough then richen some. I have a one probe EGT and it reads about 1150 ish when leaned. He said the O300 needs the lead to help lub the valve stems.
Thoughts anyone?

Curtis,

An EGT of 1150 (I'm assuming Fahrenheit) sounds on the low side . How far downstream of the cylinder is your probe? Do you have a self-powered EGT gauge, or is it electronic? A probe that is too far downstream, or has a longer than recommended wire between the probe and a self-powered gauge can cause a lower reading. Running at lower throttle settings will also cause lower EGT's even when leaned properly.

I have a 6-cylinder system with all the probes two inches downstream of the cylinder exhaust port, and an electronic gauge (pretty much immune to wire length). When leaned I usually see all EGT's in the 1300-1450 range. If your 1150 reading is real, and you're running at normal throttle settings (2400+ RPM) then I would suspect you're not leaning as much as you think.

FWIW, I know many folks use MMO and TCP and have good results with them, but my engine does just fine with straight 100LL. About 120 hours SMOH with new cylinders and the plugs have only been out once; at annual inspection.

Another thought: how much time do you have on your cylinders? Burning any oil? If a cylinder is burning oil, the stuck valve could be due to carbon fouling.

Miles

I suspect I have the probe too far downstream. But it is still useful as a guide to leaning. I run at 2500 RPM or more and use very little oil, about a quart every 10 or 12 hours. I have just over 500 hours on the overhaul with ECI cylinders. I started using the TCP and MMO about 250 hours ago because of a stuck valve.

The condition of the baffling can also be important, I would check the condition of the small baffle pieces just behind the valve covers.

Curtis Brown wrote:He said the O300 needs the lead to help lub the valve stems.

A complete myth that just won't go away. There is no data to support this old wives' tale.

Tetraethyl lead does NOT lubricate the valve stems.

It slows down the burning of the fuel and inhibits detonation by raising the octane rating of the base fuel. That's ALL it does.

Perhaps I should should qualify the above by saying that that's all it's supposed to do. It will also clog up your spark plugs on many installations.

I have a standing offer challenging anyone to show historical documentation where engine valves were in need of lubrication and TEL was added to fuel in order to meet that requirement.
Simply not true. It was added purely to increase octane numbers.
It did "cushion" valve seats/faces in old soft seats, but if your engine cylinders have been overhauled/replaced since the late 70's it almost certainly has hardened seats and so-called "100 octane" valves.
TEL is universally bad. It poisons the envirionment, it is abrasive to upper cylinder components, it fouls plugs, it sticks valves, and it contributes to sludge in engine crankcases and sumps. I will be so happy if/when 82UL is universally available to us.
As bad as TEL is, and as expensive as avgas is...it's still what I insist upon in my airplane, tho'. I use TCP in every tankful, and no other additives.

Right, George,
TEL was found to lube/cushion the valve face to seat surface. It is only bad for the stem/guide clearance. Additionally, even though TCP is used, the TEL is still coating the valve surfaces, etc. It just makes is soft and more easily scavenged.
When I was studying automotive engineering in college in the 50's, TCP was a big item. We ran a lot of engine tests (auto engines), and concluded the above.

bsdunek wrote:Right, George,
TEL was found to lube/cushion the valve face to seat surface. ...

I believe this is a chicken-and-egg argument....
I believe that engine mfr's began using cheaper components (such as inferior valve/seat mat'ls, and that when unleaded fuel became available it was found the cheap components did not hold up, so hardened valves/seats were re-introduced. My basis? Early flat-head Ford engines (introduced before TEL was universally included in fuels) had valves/seats that withstood/still withstand unleaded fuels without any modifications.
My 1939 Ford engine support group occasionally gets a newbie who asks about using MMO or some other snake oil to prevent valve problems using unleaded fuel (or the newbie will ask if he should use a "lead substitute" to protect his valves)....and he will be deluged with responses from the others that the early Ford engines ALL already "had hardened seats".
Of course, I believe that's the chicken/egg argument. They didn't create the engine in 1939 with valves/seats unnecessarily hard. They simply made subsequent engine models with cheaper/softer valves/seats when they found out that they could save money on those parts because fuels had changed to include TEL universally.
There was a short time period in the early '70's that phosphorus was introduced to cushion valve seats to prevent "valve seat recession" caused by unleaded fuel, but the phosphorus killed the newly-introduced catilytic converters which were coming onto the market, so EPA banned phosphorus in fuel. This lead to "re-inventing the wheel".... re-introducing what Ford had done in the early years.... valves/seats hardened and faced for unleaded fuels.
Trivia question: How did Phillips 66 get their brand name?