Yesterday I successfully completed my second annual on our 205. For the most part, it went off without a hitch. We had two items creep up on my #6 cylinder and wanted to see what you all thought about it.

While doing the compression check my #6 cylinder was leaking air past the exhaust valve. At last annual the pressure was 75. This time it was 64. This same cylinder had an exhaust gasket that was leaking, which we replaced. It has flown 98 hours since the last annual one year ago. I run approximately 60-65 degrees LOP in cruise using a EDM 700 and Gami injectors. Gami spread is 0.2 and this cylinder consistently runs at 350-365 degrees. The engine is an IO-470-S with 807 hours on it. I run it at 2100 RPMs and between 19 and 21 inches MP in cruise depending on altitude which yields BHPs well below 65%...usually below 60%.

After discovering the leak, we got a Snap-on scope and got some pictures and video of the valve. The resolution isn't the greatest, but hopefully some useful info can be gleamed from them. The Dropbox link below will take you to them. You can see that it has that symmetrical ring like it is supposed to, except for the forward area where the ring is wider and the metal is polished and shiny.

Any insight and recommendations anyone can give would be appreciated. My mechanic wants to just watch it and replace the cylinder in the near future. From reading the few articles below, it seems like there are other options out there to prolong the life of the valve/cylinder. Adrian Eichorn works at B6 with me so I'm trying to get his input on this as well.

https://www.dropbox.com/sh/n9224pexdmq5m22/AABlghhgsmlc8qtNSPcNGkvTa?dl=0

AOPA's article on healthy exhaust valves.

http://www.aopa.org/Pilot-Resources/Air-Safety-Institute/Valve-Safety

http://www.aopa.org/News-and-Video/All-News/2014/June/Pilot/pe_ownership

Thanks,
Cory

Why replace the cylinder? Worst case would be changing the valve guide when you grind the valve and seat, which is still cheaper than replacing the cylinder.

I just went through the same thing. Check out my post:
https://www.backcountrypilot.org/community/forum/latest/techron-is-amazing-15920

Bore scoping is an art-form as much as a science.
Things always look different under a scope, things look bigger, rougher, shinier, etc. Interpreting what you see can be tricky unless the driver knows -very well- the wear modes and failure mechanisms of the parts they are looking at....
All I am saying is, much like with a doctor, it can be helpful to have a second opinion before going in for elective surgery.

I'd Lap that valve and see if the compression goes up. If it's the guide then you may need to replace that. But Lapping is what I've done a few times.

had that problem on my tripacer years ago... My mechanic staked the cylinder.... whole bunch of shit came out the exhaust......problem solved would that be a possibility for you... not a mechanic but the mechanic types here might know....

You can get the valve lapped without removing the cylinder. That is what I would do unless it is determined you have a guide problem.

My cylinder with a leaky exhaust valve went from 70 to 79 by having the valve lapped. The shop that did it said they lap the valves on continentals almost every annual.

Easiest thing to try first is to pressure up the cylinder and hit the exhaust valve with a brass punch or brass hammer. If it's just a small piece of carbon, the air pressure blows it out. If that doesn't work then you have to relap the valve.

Thanks for the replies everyone. I'll check out the ither thread.

ajfriz wrote:Why replace the cylinder?

This is exactly what I am thinking.

Ok, this is all new to me. What is lapping? I've heard of staking and have that in the list if options.

The article mentions that a cause can be poorly adjusted valve guides...so I'm guessing these can be properly readjusted?

Grassstrippilot wrote:Yesterday I successfully completed my second annual on our 205. For the most part, it went off without a hitch. We had two items creep up on my #6 cylinder and wanted to see what you all thought about it.

While doing the compression check my #6 cylinder was leaking air past the exhaust valve. At last annual the pressure was 75. This time it was 64. This same cylinder had an exhaust gasket that was leaking, which we replaced. It has flown 98 hours since the last annual one year ago. I run approximately 60-65 degrees LOP in cruise using a EDM 700 and Gami injectors. Gami spread is 0.2 and this cylinder consistently runs at 350-365 degrees. The engine is an IO-470-S with 807 hours on it. I run it at 2100 RPMs and between 19 and 21 inches MP in cruise depending on altitude which yields BHPs well below 65%...usually below 60%.

After discovering the leak, we got a Snap-on scope and got some pictures and video of the valve. The resolution isn't the greatest, but hopefully some useful info can be gleamed from them. The Dropbox link below will take you to them. You can see that it has that symmetrical ring like it is supposed to, except for the forward area where the ring is wider and the metal is polished and shiny.

Any insight and recommendations anyone can give would be appreciated. My mechanic wants to just watch it and replace the cylinder in the near future. From reading the few articles below, it seems like there are other options out there to prolong the life of the valve/cylinder. Adrian Eichorn works at B6 with me so I'm trying to get his input on this as well.

https://www.dropbox.com/sh/n9224pexdmq5m22/AABlghhgsmlc8qtNSPcNGkvTa?dl=0

AOPA's article on healthy exhaust valves.

http://www.aopa.org/Pilot-Resources/Air-Safety-Institute/Valve-Safety

http://www.aopa.org/News-and-Video/All-News/2014/June/Pilot/pe_ownership

Thanks,
Cory

Don't freak out just yet! if you still have 64 that's not too terrible. Try staking it and run it a few hours and test it again. Most likely some lead deposits that could blow out.

whee wrote:You can get the valve lapped without removing the cylinder. That is what I would do unless it is determined you have a guide problem.

My cylinder with a leaky exhaust valve went from 70 to 79 by having the valve lapped. The shop that did it said they lap the valves on continentals almost every annual.

I looked up lapping on youtube. So I've got an idea of what they are doing.

Whee, which shop was it? Would you recommend them?

Thanks Trent. I just want to get out in front of this sooner than later...before a larger issue can develop.

It was Aerohawk here in Idaho Falls. I haven't dealt with them much but I told them what was going on and they said the thought lapping the valve would take care of it. Quoted me $35 to do it but I knew it would be more because on the Luscombe you have to pull the prop and cowl to get the rocker cover off. So instead of paying $1100 to replace the cylinder I paid $75 and got the problem fixed. Good guys and always been helpful.

There has got to be someplace closer to you that can lap a valve but it not, yeah I'd give Aerohawk a call.

Do you run 100LL only? Buy the peterson STC and start running mogas mixed in (1/3rd 100LL and 2/3 mogas) and splash in a little mystery oil. If your mechanic wants to replace a cylinder because of a sticking exhaust valve, you should probably be looking for another mechanic.

See my post on the rope trick - where I detail what happened to me recently with a stuck exhaust valve. Lapping the valve might help - but I don't agree that you can do a good job with the cylinder on - need to pull it. Far more likely is lead deposit build-up on the valve stem. Staking may get it unstuck but not likely the fix much. Need to pull the exhaust valve and ream the guide and clean it out. You probably should do all of them. Borescoping won't show you squat in the valve guide.

I'd ream the guides first before anything else. A good mechanic with the right tools (and a clean rope) can do all 6 in a few hours. Or you can do 1 in a full day on the side of the runway in rural Minnesota with nothing but screw drivers, dental floss, and Corona.

https://www.backcountrypilot.org/forum/the-rope-trick-field-repairs-101-15650?p=212406#p211932

No you do NOT need to pull the cylinder to lap it! At least on a lycoming you don't. I've had to do it a few times now as I mentioned. You do the rope thing. Then you put some valve grinding compound on the valve and use a drill to spin the valve into it's seat. Then you clean off the compound (just a dab btw) with something like brake clean. It works great! Try the staking, if that doesn't work then do the lapping.

Most mechanics have heard of this, if they haven't then find a new one!

Btw when I did mine it took all of about 30 minutes total...then I put the cowl back on and flew off into the wind!

Here's another article with useful information:

http://www.avweb.com/news/maint/182894-1.html

Is your mechanic using a big bore cylinder compression tester or small bore? The readings will be massively different between the two. Find out! If you are using a tester with a .040 orifice (small bore) and are getting a 60/80 you might get a 70 to 80/80 reading with a big bore .060 orifice tool.
Either way changing a cylinder or making a repair to a cylinder reading 64/80 is usually a waste of time and money. When I get a 60 cylinder more then likely it is in the 70s come the next 100hr or annual.
If you or your mechanic have a hard on for exploritory surgery on a serviceable engine at least do yurself a favor and fly it for an hour or more and re check.

Cory,

I had the same symptoms in my O360. #1 was at 65, leaking through the exhaust valve. Pulled the jug and found valve guide worn. Replaced guide, valve seat and rings. Cost was minimal with me doing most of the grunt work. Pull the jug.......peace of mind.

soyAnarchisto wrote:.... If your mechanic wants to replace a cylinder because of a sticking exhaust valve, you should probably be looking for another mechanic.
See my post on the rope trick - where I detail what happened to me recently with a stuck exhaust valve............I'd ream the guides first before anything else. ................

He didn't say he has a stuck valve, he said he has a leaky valve. . Probably the opposite problem...quite likely the guide is worn, allowing the valve to wobble around which prevents it from seating properly, and also causes the seat to erode further. Quite likely needs a new guide and the valve seats recut. I've never had much luck staking a leaky valve, but it's worth a try before tearing the cylinder off.
FWIW I've done the rope trick several times to fix sticky valves (or check for them) and it works great. Just make sure to get the correctly-sized reamer for reaming the guide-- I used a .437" reamer on the exh guides of the O-300 cylinders on my old C170.

[quote="soyAnarchisto"]
Far more likely is lead deposit build-up on the valve stem. Staking may get it unstuck but not likely the fix much. Need to pull the exhaust valve and ream the guide and clean it out. You probably should do all of them. Borescoping won't show you squat in the valve guide.

I'd ream the guides first before anything else.
quote]


Soy, 2 totally different animals, O-470, 0520's don't have the same guide problems that the Small continentals have. His problem is the valve not seating 100%