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Stuck Exhaust Valves

Bowie

SPONSOR
West Milford, NJ
https://vimeo.com/287329436[URL] O...would like to avoid having this happen again.
 
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Look at top of pistons and make sure you didn’t hit piston with valve or bend valve. If a valve head breaks it will most likely smash through piston and the travel throughout engine ruining engine.


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I would lean aggressively on the ground at startup and after landing. Also would avoid prolonged warmup.
  1. Engine is warm enough for take-off when the throttle can be opened without the engine faltering.

    DENNY


 
Lou- I'll give leaner a try and see were my CHT land
AKtango58- I have a low rpm higher compression lycoming and must run straight 100ll
Steve- We are pushing valves in and reaming
Denny-I do lean aggressively on the ground I could shorten warmup
Thanks
 
Mike I've heard of e-gap but it's above my pay grade and need to find someone who speaks bendix mag. I have the bendix dual mag (one drive two mags) it's got about 220hrs on it since install. I'm assuming you can check in place but need to remove to adjust. Almost zero space between firewall and mag.
 
Mike I've heard of e-gap but it's above my pay grade and need to find someone who speaks bendix mag. I have the bendix dual mag (one drive two mags) it's got about 220hrs on it since install. I'm assuming you can check in place but need to remove to adjust. Almost zero space between firewall and mag.
This is a place to start. http://enstromhelicopter.com/wp-content/uploads/2016/11/Magneto-maintenance.pdf The dual mags can be a bit more troublesome if not done correctly.
 
This is what happens when the valve sticks and stays stuck. Next time it has morning sickness, leave it in bed until fixed.

Nashvile. landing.png
 

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Thanks Skywagon.
WiskeyMike I'll take that to heart, First and last time I'll fly when the bird's sick. It was the first time I've had that happen, I convinced myself that I had run some water through the carb and it had cleared, yes I did sump during preflight, bad call on my part.


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Bowie
It also helps if you do your run up leaned like you have it set when you taxi.
Good call on leaning aggressively while respecting no higher than 380 CHT. If anything you will have lower CHT’s when leaning greater then 50 ROP.
On another point I get better results using Lucas upper cylinder treatment to reduce carbon buildup then I ever did with MMO. Cheaper too. Mix 3-4 oz per 10 gals of gas. Best if done on a long cross country.

Lou
 
also look for bent push rods after a stuck valve..... they have been known to wear/break into 2 pieces inside push rod housing then...
 
Last time I had a Lycoming exhaust valve stick it cost me an overhaul from cam and lifter body wear. Too much surface pressure between components I assume. Do whatever satisfies to ensure that didn't happen.

Gary
 
Can someone explain how leaning prevents a stuck valve?

This problem has been solved years ago - run Marvel (or like-product) in the gas (and oil, if you want)...the old mechanics/aviators been using it for years to free/prevent sticky valves. I don't recall hearing them say to lean it more though.
 
Last time I had a Lycoming exhaust valve stick it cost me an overhaul from cam and lifter body wear. Too much surface pressure between components I assume. Do whatever satisfies to ensure that didn't happen.

Gary

My guess is, like a real cold engine without lifters pumped up, The stuck OPEN valve, allowed the cam lob to STRIKE the lifter, instead of riding it up the lobe. 2 very hard surfaces.


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…. I get better results using Lucas upper cylinder treatment to reduce carbon buildup then I ever did with MMO. Cheaper too.....

Per your link, MMO is $15.87 per gallon.
Lucas shows at $8.87 for 32 ounces, which is a quart- so twice the price of Marvel.

It might be better, I never heard of it before.
I used to use MMO when it was 2 or 3 bucks a quart at Walmart,
but quit when the price started going up.
I think it's about $5 a qt at the stores now.
The airplane never seemed to notice the difference.
FWIW I burn about 80/20% mogas /avgas mix.
 
Probably should be something mainly added to fuel to reduce valve sticking, and MMO 2oz/5gal is my choice. Think about it. If it depended only on an oil additive to move it around that would mean same oil (with dispersed engine contaminants) would have to get to the sticking area between the valve guide and valve stem in sufficient quantity. And then somehow avoid cooking under heat and possibly form even more deposits. Something has to clean and not leave a big mess behind. Periodically checking valve to guide clearance and centering, and if plugging up reaming the exhaust valve guide or applying penetrating solvents like Kroil to clean helps.

Gary
 
In general, how common are sticky valve stems?

Seems to me that if the guide/stem clearance is correct, and if the guide axis is co-axial to the valve seat, and if the valve is straight and correctly ground, all should be good.

Am I wrong about this? If I am, what happens to cause sticky valves?
 
Exhaust valves should rotate some and not wear in one position. Grinding the rocker arm face off flush, building the arm slightly offset, or using an STC'd rotator like ECI did are some means to help (theory). There may be others. If they don't and clearances between the stem and guide increase due to wear (inevitable but slow is better), then exhaust gas can interact with lube to form coke (not cola) and slowly fill the void. When the clearances reach minimum sticking can occur. That's what I was taught 50 some years ago but newer experience might make that BS.

I might add that a mechanic noted to me that if exhaust gas is getting past the exhaust valve guide with time it'll show as cooked oil around the valve springs, rocker arm, and inside the valve cover. Engine oil can turn black just like with excessive piston ring blowby.

Gary
 
AKWING
Exhaust byproducts are what cause the valve to stick, so the less fuel you dump in the less byproducts you will have. Now excess leaning can cause several other problems (high CHT, excessive valve guide wear, ect). Having a good multi cylinder CHT/EGT allows you to see what the CHT's are and adjust accordingly. 100LL contains 5 times the lead that many of the low compressions engines design called for, that is why you see problems. If you do a internet search on Camguard. You will find a good article on the chemistry involved as the lead is burned.
DENNY
 
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he cylinders are Lycoming 220hrs since new, ported and polished by Lycon.

Ask why the problems and how the remedy.

Gary
 
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