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R22 exhaust valve stuck again


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For the second time we have a stuck exhaust value on our Beta II. The first time we had around 600 hours on the ship, we now have a tad over 900. The cause the first time was carbon buildup, and (I'm no A&P, so I'm not positive this is right) the A&P had to ream two of the valve guides.

 

I've heard talk that if you don't stay at 75% RPM long enough before reducing the throttle to idle and disengaging the clutch, that you can get a buildup of carbon around the #1 and #2 exhaust valves. Does

anybody know if this is true? Do we need to stay at 75% for a little longer after the CHT drops? Or is something else maybe going on?

 

Any thoughts appreciated!

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I would have a look at your shutdown procedure. You can't rush the cool down process. This is true with all piston engines, whether car, boat, lawn mower etc..etc.. If it should be a minute, then give it the full minute. It sounds like you are not cooling the engine for long enough after having run it.

 

A rapid shut down will cause carbon deposits as the high temperature oil meets the relatively lower temperature metals (or is it the other way around?). (A mechanic can explain this better.) The valve then must be reamed back to the correct size.

 

In short, you need to cool everything down slower so that it (the engine components and oil) all cools at the same rate.

 

The other possibility is that your filters need changing.

 

 

I found this very clear article right from the Lycoming factory. Some good advice here.

 

Lycoming Information - Avoiding Stuck Valves

 

Joker

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I would have a look at your shutdown procedure. You can't rush the cool down process. This is true with all piston engines, whether car, boat, lawn mower etc..etc.. If it should be a minute, then give it the full minute. It sounds like you are not cooling the engine for long enough after having run it.

 

Joker

The Robinson POH is kind of vague about this -- all it says is that you should run at 70-75% until you get a CHT drop before proceding with the shutdown. Maybe that's not sufficient -- perhaps we should wait a minute or so after the drop stops, particularly with high OAT's.

 

We are downlight religious about filters and oil changes, and the helicopter is flown around 250 hours/year.

 

Maybe one of us (we have 5 pilots) is getting too impatient in the shutdown...

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At our school, we also do a full 3 minute cool down at 75% with the Beta II. I would suggest implementing this because just waiting for a CHT drop is not always good enough.

 

For example, on a hot day (correct me if I'm wrong for I'm not a mechanic either), the CHT may stop dropping after just a short while because of the high OAT. You'll start sweating like a pig sitting there just waiting but it'll be better in the long run if you wait a full 3 minutes.

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Now it's been a while since I flew a Robby and in about 1800 hours I had two stuck valves. The first was on start up and didn't happen until I picked up to a hover. The cyclic began to shake very violently, I sat it down and end of problem. The second was on start up as we went to 100%. The engine started to run rough, so I turned it off. No damage either time. It's important to recognize there's a problem and do something about it as the amount of damage that can occur is considerable.

 

We always did a 3 minute cool down and the two stuck valves I had were on the right hand side of the engine(sitting in pilots seat) and were on the forward cylinder, number 3 if I remember correctly. The reason the mechanics gave me is that the number 3 cylinder has less airflow going over it because there is air ducted down from that side to ??? (can't remember). The machines had oil changes every 25 hours.

 

Maybe someone is trying to keep the hobbs time down a bit and doing an improper cooldown.

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Did they do the Lycoming SB about the valve stem "wiggle check" at 300 hrs? I've seen that pencil whipped most of the time because people don't own the measurement tool. I always reamed all the valves at 300 hrs whether or not they needed them just to make sure.

 

Other options.....

 

Run TCP. It's a lead scavaging agent added into avgas. Expensive, but helps prevent valve sticking. Last time I bought a can it was $40-50 a gallon and you used about an ounce per 10 gallons I think.

 

Run AvBlend. It's an oil additive that leaves that helps prevent lead build up. Again, expensive--about $20/can used every oil change.

 

Make sure you have an oil filter. If your R22 didn't come with one, buy an aftermarket ADC or Airwolf kit. (I like the ADC kits much better since they have a 15/16" 6 point head on the top so you're not torquing the a/f. You can get a chip detector for it too.)

 

Get an autogas STC and run 93 premium (w/ no ethanol additives) and you will never have to worry again about stuck valves. We used to run about a 50/50 blend with 100LL just to be safe. Best $700 you can spend since it will save can save you over $10,000 over the life of the engine running a 50/50 blend.

 

All of these options are kind of expensive, but they'll hopefully save you from buying $1000 cylinders around 1200 hrs when they like to smoke valves and/or seats. Not to mention the downtime and the fact that they're a pain in the azzzzzz to replace.

 

And one other note.......cooling the engine down for TOO LONG will cause problems--especially in turbines. The engine isn't hot enough to burn off the junk anymore.

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The Robinson POH is kind of vague about this -- all it says is that you should run at 70-75% until you get a CHT drop before proceding with the shutdown. Maybe that's not sufficient -- perhaps we should wait a minute or so after the drop stops, particularly with high OAT's.

 

We are downlight religious about filters and oil changes, and the helicopter is flown around 250 hours/year.

 

Maybe one of us (we have 5 pilots) is getting too impatient in the shutdown...

We run at 75% for 100 seconds before reducing throttle to flight idle, then wait until CHT is 300° or below (if not already) before disengaging the clutch, waiting the 30 seconds, pulling the mixture, etc...

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As Joker mentioned above all engines need a cool down period. It sounds like the 3 minute mark seems to be working.

 

the enginge cool down time comes from the manufacture ( Lycoming ) this should be incorperated into the POH, if you think you've waited long enough for the cool down give it 60 more seconds to be sure.

 

having your machine down because I need to ream the valve guides from the carbon deposits left from improper cool down is only going to hurt your flying time and the company's money.

 

life is short, no reason to be in a hurry.

Edited by 67november
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The school I attended in Florida had a cool down procedure (Schweizer 300). I can't remember the specifics (gettin old) but after set down, something like 2500 RPM until 350 on the CHT, then RPM to 2000, until 300 on the CHT, then idle, clutch disengage, shutdown. The process took 3-4 minutes. They also had installed engine monitors with digital CHT readouts, takes the guesswork out of the readings. I'm in an R22 now, I adapted my own version of the above by maintaining 104% after set down if the CHT is above 350, then to 75% until CHT at 300, then Idle and shutdown. Usually takes right at 3 minutes. When its really hot and humid as it has been lately, I try to do any hovering maneuvers, slopes etc. at the beginning of the flight, and finish with a normal landing and set down.

I always thought that young students would be the worst at abusing the helicopter, trying to get the meter stopped as soon as possible, but I think the older guys, and the owner/pilots are the worst I've seen. There is one R44 owner I know that can land, shutdown, blades stopped, and in the car headed home in 3 minutes! :o No joke

 

Fly Safe

Clark B)

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  • 3 weeks later...
For the second time we have a stuck exhaust value on our Beta II. The first time we had around 600 hours on the ship, we now have a tad over 900. The cause the first time was carbon buildup, and (I'm no A&P, so I'm not positive this is right) the A&P had to ream two of the valve guides.

 

I've heard talk that if you don't stay at 75% RPM long enough before reducing the throttle to idle and disengaging the clutch, that you can get a buildup of carbon around the #1 and #2 exhaust valves. Does

anybody know if this is true? Do we need to stay at 75% for a little longer after the CHT drops? Or is something else maybe going on?

 

Any thoughts appreciated!

I have found 75% for 2min then idle to disingage belts for shut down

and keep up with the 300hr valve-to-guide check - have had very good results over the years

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