Sticking Exhaust Valve - Diagnosis and Fix!

[Saville]

Problem found and fixed

I found and fixed the problem.

But first, let me thank everyone here who contributed and offered advice.

Took another look at the engine in the vicinity of #3 cylinder and I noticed something......

a small diameter hose was dangling. It came from the #3 cylinder.

There wasn't similar hoses coming from the other 3 cylinders.

It went to the firewall above the EFIS connectors.

It was the manifold pressure tap that went to the EFIS. It was open to atmosphere.

Reconnected it - made sure it will never come off again. Started the engine.

Runs smoothly

 

[Bill.Peyton]

I’d say that qualifies as a substantial I take leak in number 3!

 

[Saville]

I’d say that qualifies as a substantial I take leak in number 3!

Yeah I'd have to agree.

I'm very pleased and relieved that it was something simple.

 

[pjc]

Add a flow restrictor

In addition to securing both ends, it might be a good idea to put a flow restrictor in that MAP sense line. That way if it falls off again it will present a smaller vacuum leak.

Peter

 

[Aggie78]

Greetings folks,

I thought I would update this topic with a cylinder upper end issue that I had that I've not heard of before...and used Mike's excellent primer on how to do the valve train surgery to R&R the offending item (Thanks, Mike!)

While doing an oil change recently, an add'l item I do at those now is pull an upper plug on each cylinder and use my new borescope to check health. Looking at #2, it looked like I was starting to get a burned spot on the exhaust valve and submitted a ticket to SavvyMx with the pics for some confirmation along with a proposed remedy (lapping in place.)



Brandon at Savvy replied it looked like we caught it early and likely the valve was a good candidate for lapping in place. Using Mike B's tips, disassembly was pretty straightforward right up until getting the exhaust rocker arm off the boss...it seemed "stuck" and took quite a bit of coercion, which I attributed to the fine layer/deposit left behind on the engine parts when using Camguard (so I've heard.) A bit of prying, tapping, some light swearing and I finally had the arm in my hand and expecting a carboned up guide, it was time to check how badly the valve moved. To my surprise, it was as smooth as silk...absolutely no restriction at all. This was a head scratcher to me, because I'd had tunnel vision and just knew the guide had to be fouled (this is the 2nd time this cylinder has had some kind of related issue in ~850 hours TTSN.)

So...I started looking for other causes. One thing I discovered was that the 2 rocker arms on this cylinder, while the same part numbers, did not fit in the cylinder bosses the same. The intake valve's rocker would fit into either boss with no restriction...while the exhaust valve's rocker wouldn't fit in EITHER boss without being restricted. Reaching back out to Savvy with some photos, the tech confirmed the arm must fit into the boss without any restriction at all. Looking at the 2 different arms, it appeared the rocker bushing on the offending valve was not properly installed fully, and protruding just so slightly on the RH side vs the intake valve. The offending item:



Intake Rocker:



To be continued later....

 

[Aggie78]

So, to continue...

I decided pull out the calipers and measure the difference this slight protrusion made between the 2 rocker arms...

Here's the intake, which fits easily:




And here's the exhaust valve's arm:



Edited to add:
Here's a picture of the old rocker arm back from Western Skyways in Montrose, Colorado with the old bushing removed and the new bushing installed. Shout out to them for outstanding customer service as they did it gratis! And no prior customer relationship, either! Great folks! This rocker goes into the spare parts bin if needed for future use.




Replacing the old bushing is a skill set above my pay grade, so a new rocker was ordered from Air Power in the DFW area and in my hands 2 days later. Here's the dimensions on their rocker:



Back out at the hangar with the new part in hand, and the finish up went smoothly. The new rocker went into place slick as could be with no interference. I did use Mike's tip of a 1/2" piece of dowel inserted into rocker shaft bore and rotating the engine to compress the exhaust lifter, which worked nicely and with minimal hassle.



Also installed at this time was a new rocker shaft, a new rotator cap atop the exhaust valve stem, the 2 thrust buttons on either end of the rocker shaft and a new valve cover gasket. Test run went well, I buttoned it all up and have flown it 3 times since with no issues. The plan is to borescope all the cylinders again at annual in April, and especially this cylinder to see if the in-place lapping worked and a more normal pattern resumes on the valve head. If so, I'll consider this item closed and hopefully addressed for the last time.

I did get another rocker bushing and sent the old rocker off to an engine shop to have pressed in....just to have on hand if I run into this issue on one of the other 7 rockers.

I posted this only to make the point that while it's highly likely valve guide carbon fouling can be the source of some of the engine problems mentioned on this thread (heck, I had purchased a ball hone because I knew it would be needed for this job) sometimes it's something out of left field that few folks would be looking at as a causal factor. I will report back with results at annual time on the valve's condition with another 10-15 hours on it and whether it appears the in place lapping job has resolved things.

Cheers,

Rob

 

[KeithB]

Outstanding write up. Thanks for putting it together.

 

[turbo]

one of our pilots from my flying club had a stuck valve Onway to our spring event in sarasota fl this year. he was very lucky the valve stuck open and he was able continue his flights to KSRQ with a rough running engine. he put the plane in a shop on the field for the repairs. what i know is that he had no knowledge of maintaining the health of his engine and of leaning procedures. a new 182 with 400 hours. please educate yourself on these issues and get your exhaust valves checked for wobble measurement. run some fuel additive like TCP or decalin. if you find 'lead' balls in your spark plugs then be for warned of a problem. do you think a simple bore scope would of thrown up a red flag. how does his other cylinders look like? educate yourself and be pro active. this stuff is happening all the time.