Stuck valve - future prevention

[flyboy0681]

After a few episodes of morning sickness, our engine was examined and found the #4 exhaust valve was sticking. Time since overhaul is 620 hours.

Now that it's been cleared, what's the best way to prevent the buildup of gunk going forward? My partners and I are aggressive when it comes to leaning, but that didn't seem to help the situation.

[EricJ]

Lycoming says regular oil changes help, i.e., keeping the oil clean.    The lead in the fuel contributes to the sticking, but there isn't much we can do about that yet.

Lycoming SI 1425A addresses valve sticking:

https://www.lycoming.com/sites/default/files/attachments/Suggested%20Maintenance%20Procedures%20to%20Reduce%20the%20Possibility%20of%20Valve%20Sticking.pdf

 

[ArtVandelay]

I use MMO before each oil change.

[flyboy0681]

35 minutes ago, EricJ said:

Lycoming says regular oil changes help, i.e., keeping the oil clean.    The lead in the fuel contributes to the sticking, but there isn't much we can do about that yet.

Lycoming SI 1425A addresses valve sticking:

https://www.lycoming.com/sites/default/files/attachments/Suggested%20Maintenance%20Procedures%20to%20Reduce%20the%20Possibility%20of%20Valve%20Sticking.pdf

 

We've been pretty religious about 25 hour oil changes, but no more than 30.

[Andy95W]

Supposedly Lenkite has evidence- possibly apocryphal- that their AvBlend product helps prevent valve sticking. It has other properties similar to CamGuard. Aviation Consumer magazine had some positive things to say about Lenkite AvBlend, but didn’t specifically mention valve sticking.

[PT20J]

I had one stick on a factory rebuilt engine at around 400 hours. I don't think there is much you can do about it. It's a function of the Lycoming valve design. I change the oil frequently and use Camguard. Here's Ed Kollin's take on it, FWIW.

Camguard-Parts-1-to-3.pdf

[Utah20Gflyer]

The best thing you can do is brutally lean the engine during ground operations.   I lean until right before the engine will quit.  

[philiplane]

Camguard oil treatment is well known for reducing internal engine deposits. That will help keep the valve stems clean, which will prevent them from sticking.

[PT20J]

22 minutes ago, philiplane said:

Camguard oil treatment is well known for reducing internal engine deposits. That will help keep the valve stems clean, which will prevent them from sticking.

Maybe, but it didn't work for me . I've not seen any data from controlled tests that prove that anything reduces valve sticking in Lycomings. Everything is anecdotal. BTW, 30 years ago in another airplane I dropped a can of MMO in at every oil change. It stuck a valve, too. But maybe I'll try AvBlend. Who knows?

[philiplane]

exhaust valve sticking is caused by two factors: valve to guide clearance being set too tight, at the minimum end of the acceptable range, and by deposits from leaded fuels. If the guide clearance is too tight, nothing will fix that short of reaming the guides in place. Which is not that hard to do. 

[EricJ]

Keeping temps up, especially at idle, to keep the lead vaporized might help.

[flyboy0681]

21 minutes ago, EricJ said:

Keeping temps up, especially at idle

How is that accomplished?

[EricJ]

31 minutes ago, flyboy0681 said:

How is that accomplished?

During cruise or normal operation by monitoring CHT that it doesn't get too low.    On the ground keeping idle not below about 1000 rpm helps.

[flyboy0681]

2 minutes ago, EricJ said:

 On the ground keeping idle not below about 1000 rpm helps.

Well that ain't going to work. I always conduct ground operations above 1,000 rpm and the temps are usually on the cool side.

[EricJ]

5 minutes ago, flyboy0681 said:

Well that ain't going to work. I always conduct ground operations above 1,000 rpm and the temps are usually on the cool side.

Keeping the idle rpms up keeps the combustion temps high enough to minimize lead fouling, but the power produced isn't enough to keep CHT very high.    

[flyboy0681]

2 minutes ago, EricJ said:

Keeping the idle rpms up keeps the combustion temps high enough to minimize lead fouling, but the power produced isn't enough to keep CHT very high.    

In that case, I'm doing everything correctly. But as others have said here, valve sticking is just an inherit condition of the Lycoming design, so the best we can do is follow all of these recommendations and hope for the best.

[dzeleski]

45 minutes ago, flyboy0681 said:

In that case, I'm doing everything correctly. But as others have said here, valve sticking is just an inherit condition of the Lycoming design, so the best we can do is follow all of these recommendations and hope for the best.

Close the cowl flaps on the ground. I find that helps increase the temps by a good amount. I have even started taking off with them closed in cooler temps and only opening them as temps build.

I've also decided that occasionally riding the brakes with a higher idle is cheaper then reaming a valve guide. But im sure that might trigger a few people. I have had several stuck valves on a 400 hour engine. I stopped using camguard as well. In fact I dont use any additives anymore just Phillips XC and regular changes.

I have had less issues since doing these things. Could be luck, could be the fact that the valves guides are the "right" size now. Who knows, its an annoying problem though.

[Yetti]

On 10/12/2023 at 10:54 AM, EricJ said:

Keeping the idle rpms up keeps the combustion temps high enough to minimize lead fouling, but the power produced isn't enough to keep CHT very high.    

don't think it is a lead fouling issue.   Rather a coking of the oil in the valve guide.   There were some really great articles that talking about the design of the A1A and how it contributed to the coking.    MMO seems to work.   50 year old product on a 50 year old design.

[EricJ]

19 minutes ago, Yetti said:

don't think it is a lead fouling issue.   Rather a coking of the oil in the valve guide.   There were some really great articles that talking about the design of the A1A and how it contributed to the coking.    MMO seems to work.   50 year old product on a 50 year old design.

The Lycoming document cites contamination of the oil with lead salts from the leaded fuel as a source of the problem.  

[Yetti]

On 10/13/2023 at 2:59 PM, EricJ said:

The Lycoming document cites contamination of the oil with lead salts from the leaded fuel as a source of the problem.  

of course they could not accept the blame for bad design.