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Starting Data Collection on Sticking Valves - Participants needed

Triumph1974

Well Known Member
In the interest of trying to understand what commonalities may exist in situation of airplane engines having sticking valves, and perhaps potentially help avoiding the occurrence in the future, (I had it happen many years ago in a Cessna 152 when going to meet the examiner for the FAA private check ride...which made for a long day to say the least) I am starting to create a central repository of data from those that have the 1st hand experience of a stuck valve....unless someone knows of any such database that already exist...and this project will be called off.

For now it will be an excel spreadsheet, with the following fields (feel free to comment if other data points should be added for collection purposes).

"Required" Requested Fields: Engine Type, Cylinder Manufacture, Brand of Oil, Weight/type of Oil, Any Engine Additives Used, If so what type of oil additive, and frequency of use, Frequency of normal oil change interval, Oil burn per every 20 hrs. Fuel Type, Any fuel additives used (MMO) etc., Hours since last Overhaul, Hours on Cylinder with the sticking valve, Estimated annual hours flown last 12 months on engine, estimated hrs. flown prior 24 months, State of flight when the valve stuck - Climb, Cruise, decent or taxi, Date of sticking valve occurrence.

Optional Fields: Normal CHT temps in Climb, Cruise, Decent, Normal EGT temps, Cruise at ROP, or LOP, Description of typical engine shut down procedure (Ex: Run engine to 1200 RMP for 20 secs to ensure cylinders are at 300 degrees prior to shut down, or no specific shut down procedure), Description of any prior notice of odd behavior of the engine prior to the sticking valve, "Other" info field, airplane type, N number.

Pilots can submit their info on their 1st hand experience on the sticky valve to the following email address@ valvedata@protonmail dotcom (the dot is a . for typical email formatting). The email will be monitored monthly, so please don't except a quick reply, but I will respond to each pilot submitting data to the database to confirm your receipt, or desire to submit data. I will likely send pilots wishing to contribute data to the project a fillable form of some type....just haven't figured out the best way to do that yet.

Thanks for spreading the word about the data collection project - it doesn't have to be only RV limited. Once there is a reasonable amount of data submissions I can report back out and share the info. :)


Thanks,
Paul

RV7A, O360
 
I would also be interested in knowing if they have ever performed Lycoming SB 388 C wobble test and if so how many hours since that was done before occurrence of stuck valve.

T Lockard
RV-10
 
...unless someone knows of any such database that already exist...
Hi Paul, I guess Mike Busch and the SavvyAviation.com team have data about the sticking valve event. You may want to see if you can collaborate with them. I think the value of their info would be enhanced greatly if they captured the additional information you requested, particularly oil data. They could also capture FI system, ignition, plugs, etc.
 
I wish you luck in this endeavor, but fear several variables will still be unknown. Kind of like those medical studies that observe eating behavior and heart attacks and then deduce that certain foods cause heart attacks, missing hundreds of genetic, lifestyle and environmental factors that weren't measured. I always refer to Jim Fixx in these cases. Some will remember that he was a public figure during the health movement in the 70's and a model of good eating and exercise practices, yet died of a heart attack in his 40's.

One item of interest is the valve stem and guide clearance, as well as parallelism of the guide to stem at full seating. Without knowing those details, it would seem that other variables could mistakenly allow you to draw inappropriate conclusions.

Larry
 
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Have a common link

I wish you luck in this endeavor, but fear several variables will still be unknown. Kind of like those medical studies that observe eating behavior and heart attacks and then deduce that certain foods cause heart attacks, missing hundreds of genetic, lifestyle and environmental factors that weren't measured. I always refer to Jim Fixx in these cases. Some will remember that he was a public figure during the health movement in the 70's and a model of good eating and exercise practices, yet died of a heart attack in his 40's.

One item of interest is the valve stem and guide clearance, as well as parallelism of the guide to stem at full seating. Without knowing those details, it would seem that other variables could mistakenly allow you to draw inappropriate conclusions.

Larry

Yes, your right Larry, correlation doesn't mean causation. But it may be a starting point for more detailed research. The only common data link I think we have right now is that all airplanes with the sticky valve had the engines running!
 
I just had valve train issues this summer. Send me a copy of the spreadsheet and I will try and fill it in.
 
Yes, your right Larry, correlation doesn't mean causation. But it may be a starting point for more detailed research. The only common data link I think we have right now is that all airplanes with the sticky valve had the engines running!

Unfortunately very true. I applaud you for trying to collect some info though, as it is an interesting issue with nothing more than opinions floating around as to cause. I will say that Lycomings path of using various different exotic materials in the exhaust valve certainly points to them thinking that hot exhaust valves WERE causing a problem and the most likely problem they were addressing was sticking exhaust valves. Unfortunately also speculation, but backed by data.

I did post on a similar topic a few months ago. I have 850 hours and the wobble test recently showed loose, not tight guides. I listed quite a few details about how I operate the engine in that post. You will need a contrarian group (those without sicking valves) with similar variables if you hope to find a smoking gun.

Larry
 
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Larry makes a good point. Just looking at failures might not help. I know that Lycoming wants us to do SB388 with some frequency. Do people actually do this on a schedule?

I had valve sticky issues a while back - search for my posts. At the time, SB388 seemed very invasive and maybe unnecessary / excessive. I performed SI1425 on the offending cylinder and moved on.

If folks actually do SB388 without symptoms, would collecting data from SB288 be helpful in addition to engine parameters like CHT? Seems to me that correlating those datasets would maybe lead to an “ah ha” moment.
 
Larry makes a good point. Just looking at failures might not help. I know that Lycoming wants us to do SB388 with some frequency. Do people actually do this on a schedule?

I had valve sticky issues a while back - search for my posts. At the time, SB388 seemed very invasive and maybe unnecessary / excessive. I performed SI1425 on the offending cylinder and moved on.

If folks actually do SB388 without symptoms, would collecting data from SB288 be helpful in addition to engine parameters like CHT? Seems to me that correlating those datasets would maybe lead to an “ah ha” moment.

I did the wobble test (SB 388). That is the method for determining approximate guide clearance; Covers both excessive guide clearance due to wear AND minimal clearance due to deposits. It is not invasive at all, just remove the valve keepers and spring, though it took me some time to build the testing tool. SI 1425 is not testing, but remediation once tight guides are found via SB 388 or actual symptoms like morning sickness.

Lycoming states some of the rationale for the problem in SI 1425:

Field experience has shown that engine oil contamination increases the possibility of sticking and/or
stuck valves. This situation occurs when the
contaminants in the engine lubrication oil become
deposited on the valve stems, restricting the valve
movement, and resulting in intermittent engine
hesitation or miss. If corrective action is not taken to
remove the deposits, a valve could become stuck
causing engine damage.
Since the rate of oil contaminant accumulation is
increased by high ambient temperatures
, slow flight
with reduced cooling, and high lead content of fuel,
owners and operators experiencing these conditions
are encouraged to consider the following suggestions
for operation and maintenance if they have experienced valve sticking.

The prime cause of valve sticking is the accumulation of harmful contaminants in the oil and oil filter

Investigations have shown that exhaust valve
sticking occurs more frequently during hot ambient
conditions. The lead salts that accumulate in the
lubricating oil from the use of leaded fuels contribute
to the deposit build up in the valve guides.
They are
mostly eliminated each time the oil and filter are
changed

It would seem clear from this that lycoming believes that a combination of heat and excessive lead salt deposits in the oil are the primary factors involved in Exh valve deposits. This doc states that the heat allows the deposits to accumulate in the guide faster and this is consistent with their efforts to keep the exh valves cooler over the years. They are clear though that it is a combination of heat and lead salt deposit accumulation causes the problem

Larry
 
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The conclusion from Lycoming doesn't seem supported by the user who reported stuck valves on a diet of unleaded fuel.

It's more likely that the oil is coking on the guides, stems or both.
 
On my engine it was no. 2 cylinder 350 hours from new normally runs around 330 cht never above 400 superior IO360 180hp
Shell multi grade 1 quart every 8-10 hours.
Valve only stuck momentarily once, but when checked was tight. Reemed it and no further problems.
Engine always warmed until 75c on oil before taxi. (100 before takeoff) Cruise descents only and cool down before shutting down.


One observation I’ve made reading all these posts that it’s nearly always no2 cylinder. I wonder how much is caused by our baffle arrangement and uneven cooling. On my -10 build I’ve made a DanH suggested duct to allow air to get to the lower front fins. Not flying yet but it’ll be interesting to see if it makes a difference.

Regards Peter
 
The conclusion from Lycoming doesn't seem supported by the user who reported stuck valves on a diet of unleaded fuel.

It's more likely that the oil is coking on the guides, stems or both.

IIRC, they are saying it is the oil and the lead salts are also there and deposited. I certainly agree that the oil is the fundamental carrier and cause of the deposits, but unleaded fuel could simply extend the time before sticking, but quantifying unleaded fuels and full synthetic oil effects would be interesting.

If it were a scientific study I would guess that initial stem-guide clearance, operating temperatures, oil presence (and cleanliness) at the top of the guide, and hardness/wear rate of the guide would all be parameters for a design study of the condition. Guide wear could be allowed to out run accumulations, but may lead to premature overhaul.


I remember tests in the employing an internal annulus at the top of the valve with suction and the oil collected was correlated to temperatures, clearances and oiling methods from flooded to misted. This was in a number of SAE papers back in the '80s when the industry was working on emissions and wear of the guides, and oil consumption (catalyst contamination). All, of course, on liquid cooled engines, diesel and gasoline.

I have no challenge to the performance of this study, but can not assume a constant set of contributing variables to the occurrence. The study won't hurt and may uncover some interesting relationships.
 
IIRC, they are saying it is the oil and the lead salts are also there and deposited. I certainly agree that the oil is the fundamental carrier and cause of the deposits, but unleaded fuel could simply extend the time before sticking, but quantifying unleaded fuels and full synthetic oil effects would be interesting.

The fact that they attribute anything to lead deposits in this case doesn't make sense as we have a user saying he got sticking when leaded fuel was not used- many hundreds of hours down the road when some wear would be present, increasing stem to guide clearances.

Given what I've seen in turbocharger center sections over the years, most of this comes down to temperature and oil formulation. Bring the temps down and coke doesn't form. Bring the coking temperature of the oil formulation up (synthetic blends) and coke is reduced or eliminated. Coking used to be a big deal here 35 years ago. Not much any more with the advent of water cooled center sections and synthetic oils.

From Exxon, relating to fully synthetic formulations:

Coking occurs because the temperature and the oil residue time are higher than the oil stability limitations.
Coke formation increases dramatically as local metal contact temperatures exceed 300°C.
Operational factors can influence coke formation, such as hot shutdowns, which promote coke build up.
High post-shutdown temperatures due to conducted or convected heat increase deposition in low-drainage areas.
Unprotected reactive metals in the oil system, such as lead, cadmium or magnesium, can increase deposits (reaction between oil and metals).
Low-alloy iron and copper can stimulate coke formation by catalysis.
Positive washing of system surfaces by high liquid oil flow reduces residence time.

Aeroshell, which is 50% synthetic has a flash point of 460F. Other non-synthetic blends may have lower temperature limits.

Certainly exhaust valve stems are much hotter than this in a Lycoming opening the possibility of coke deposits forming. Guide material could be a factor here as well from a deposition standpoint. No idea what Lycoming uses here.

Stem to guide clearance at operating temps will not be the same as with a cold engine. The stem is hotter than the guide and made from different material with different coefficients of expansion. Hot exhaust gases may travel up the guide as well in the first part of the exhaust stroke when pressure differential is highest. It's a harsh environment for the oil. You need enough to prevent scuffing but you don't want too much which would result in higher oil consumption.
 
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The conclusion from Lycoming doesn't seem supported by the user who reported stuck valves on a diet of unleaded fuel.

It's more likely that the oil is coking on the guides, stems or both.

That has been my speculation all along. The lyc position made me think that the lead salts could make the oil coke more easily and why they see a correlation with the lead load in the oil. Not a chemist, so all foreign to me.

Larry
 
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good info from Lycombing

Thanks Larry for sharing the Lycoming info.

One interesting point to note so far is that one data contributor did the wobble test shortly before a sticking valve incidence. This may mean that perhaps getting the correct measurement during the wobble test is something that needs to carefully considered and there is a little more to getting a correct measurement....

I haven't done the wobble test myself yet as I have a low time engine (although some of our data contributors had sticking valves around 250-280 total hrs. on their engine). Perhaps if anyone does do the wobble test on a period basis could do a video of it (or maybe a good one already exist), it would be beneficial for those doing it for the first time so they are confident the measurements are taken correctly.

Thanks again to those sending in your data.

Paul
 
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