VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics


Go Back   VAF Forums > Main > RV Ongoing Maintenance Issues
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 08-17-2015, 06:37 AM
bullojm1's Avatar
bullojm1 bullojm1 is offline
 
Join Date: Feb 2006
Location: Baltimore, MD
Posts: 820
Default Sticking Exhaust Valve - Diagnosis and Fix!

Two Saturdays ago I was on my first instrument rating lesson - something I have been putting off for some time now. The lesson was pretty straight forward - climb up to 6,500' heading 360, following by a series of ascending and descending climbs while under the hood. Next up was a VOR/ILS approach into Capital City airport near Harrisburg, PA. After figuring out how to get the Grand Rapids EFIS to properly display the CDI/HSI from the Garmin 430W, we were in business. Next up was a practice hold followed by a GPS approach into York, PA (KTHV).

As we were approaching the fix for the hold, the airplane developed a very noticeable shake. Clearly something was not right with the engine. Automatically without me even thinking, I pushed the mixture full rich and turned on the fuel pump. My CFII looked out the window to point me towards York airport. I didn't have it in sight, as my mind was going a million miles an hour. I was lucky to have him in the airplane to point me where I needed to be. We were still developing power, and we were within easy gliding distance of the airport just in case the engine had other ideas. A glance at the engine monitor showed what the root cause of the issue was - the EGT for the #2 cylinder was non-existent. The CHT was decreasing quickly. It was clear that the #2 cylinder was not producing power.

We were 2,000' over KTHV when the engine all of the sudden started performing normally again. The EGT immediately came back to normal, and the CHT was increasing. I glanced at my flight instructor and we both thought it would be better to put the airplane down back home at KDMW - a short 10 minutes away. We circled over KTHV gaining altitude and listening to the engine. Things seemed fine. All engine parameters looked to be back in the green. We headed to KDMW.

Roughly half way to KDMW, the engine stumbled very quickly. Not enough for the engine monitor to notice anything, but both of us definitely heard something. We stayed high and circled down to a non-event of a landing.

I was lucky to be in the presence of Captain John and his endless knowledge of everything airplane at KDMW. We decowled the RV and started digging around the #2 cylinder. Both spark plugs looked to be in fine condition (EMAG on the top plug with an auto plug, Slick mag on the bottom with a massive electrode plug). Next up was a compression test - 78/80, with the slight leakage coming through the rings (audible noise through the oil filler tube).

Naturally I would be lucky enough to have an intermittent issue. Now how to figure out how to fix it?!?! An engine needs three basic criteria to work - spark, compression and fuel. If the spark was lost, both the EMAG and Slick mag would of stopped firing in that cylinder. If the EMAG would of quit, the other cylinders would have symptons of elevated EGT's. This wasn't the case. The lack of fuel was a more likely symptom, especially if an injector was clogged. However, I found it to be unlikely that an injector would be clogged so immediate, and then unclogged immediately also. Typically when I have had a clogged injector, I get elevated EGT's, and it typically doesn't cure itself. The last issue is a lack of compression. What could of caused this is a stuck exhaust or intake valve being open. An open valve during the compression stroke of the engine would definitely cause the symptoms I saw.


The first step to investigating a stuck exhaust valve was removing the valve cover.


Next up was removing the rocker valves. To do this, you need to push out the rocker shaft. The rocker shaft is kept in place by the valve cover - the cover prevents the shaft from moving left or right. With the #2 piston at BDC, the shaft pushes out easily with just your fingers.


I removed the shaft and the two rocker arms and stored them with where they were originally on the engine.



This is the top of the cylinder with the rocker arms removed.



There is a cap over the top of the exhaust valve stem. This pulls off easily with a magnet or a dental pick.


Next up was compressing the exhaust valve spring and removing the keys which hold the valve stem to the top of the springs. There are a number of Lycoming valve spring compressors on the market for $60-$150, but from the looks of the pictures of them online, it looked like something I could easily fabricate. This would save me some money, but more importantly, buy me time as I could get the job done ASAP, instead of waiting for a tool to ship.

I ended up purchasing two pry-bars (Stanley 55-515 12-3/4-inch Wonderbar Pry Bar - p/n 1-55-515 - $12 @ Ace and a Kobalt 7-in Pry Bar - Item #: 117699 / Model #: 62897 - $6 @ Lowes). It took about an hour using the angle grinder to get the shape just right, but it worked flawlessly! I wrapped the tool in electrical tape in order to prevent any scratches on the engine pieces.







A poor picture of the took in action. I put a 3/8" socket extension through the holes of the rocker shaft for the valve compressor tool to attach to. Pushing down on the tool compressed the valves enough to get the locking keys out.



After using a dental pick with the spring compressed, the keys holding the top of the valve springs to the valve stem came out.

__________________
Mike Bullock
RV-7, Flying!
http://www.rvplane.com
The Best FAA N-Number Availability Search Engine -TailNum.com
Reply With Quote
  #2  
Old 08-17-2015, 06:37 AM
bullojm1's Avatar
bullojm1 bullojm1 is offline
 
Join Date: Feb 2006
Location: Baltimore, MD
Posts: 820
Default

Now, the moment I have been waiting for - is the exhaust valve sticking, or is there something else going on with my engine.



Within about 0.000001 seconds of touching the exhaust valve stem, it was very clear what my issue was - sticky valve! The valve stem was very very tight in the valve guide. I could not spin the valve. I could not wobble it. I could barely push it into the cylinder. I called up Daryl at Superior and let him know what my issue was. His recommendation was to purchase a 0.4995" reamer and clean out the valve guide.

A 0.4995" reamer is on it's way ($25 shipped via Ebay), and I should hopefully have this fixed by the weekend. More pictures to follow of the process.
__________________
Mike Bullock
RV-7, Flying!
http://www.rvplane.com
The Best FAA N-Number Availability Search Engine -TailNum.com
Reply With Quote
  #3  
Old 08-17-2015, 06:38 AM
bullojm1's Avatar
bullojm1 bullojm1 is offline
 
Join Date: Feb 2006
Location: Baltimore, MD
Posts: 820
Default

Fast forward a week, and today was the day to fix my sticky #2 exhaust valve. After doing some research, it seemed to make sense to drop the exhaust to get access to the exhaust port on the #2 cylinder.


It's not much access, but it's enough to be able to grab the exhaust stem once it is out of the guide.


I used a 7/16 wooden dowel to use a hammed against to push the valve into the cylinder.


It's tough to see, but I used a set of mechanical pickup jaws to grab the step of the exhaust valve once it exited the guide.


This tool is amazing - the jaws have a fantastic amount of strength, and there is a built in LED light at the end of the tool. For $8, it's a bargain.


I bought this 0.4995 reamer off of EBay for around $25 shipped. The total cost to fix this issue is under $50! I'm thrilled with this!.


I chucked the reamer into my tap-and-die tool and added a fair amount of Aeroshell #5 wheel bearing grease. The grease not only lubricates the reamer, but it also catches any shavings the reamer removed from the guide.


Rotating clockwise, the reamer is fully inserted into the guide.



I only went in as far as I needed to with the reamer.
__________________
Mike Bullock
RV-7, Flying!
http://www.rvplane.com
The Best FAA N-Number Availability Search Engine -TailNum.com
Reply With Quote
  #4  
Old 08-17-2015, 06:39 AM
bullojm1's Avatar
bullojm1 bullojm1 is offline
 
Join Date: Feb 2006
Location: Baltimore, MD
Posts: 820
Default

Pulling the reamer out revealed some interesting black gook it removed from the guide.


Next was cleaning any shavings out of the valve guide. I inserted a rag into the exhaust port, and then sprayed carb cleaner down the exhaust valve guide.


Next up was the fun task of getting the valve back into the guide. I used a telescoping magnet down the valve guide to attach to the valve stem. However, the valve needed to be lifted in the cylinder to line up properly with the guide. This modified Popsicle stick did the job. It took about 5 minutes to get the valve back in the guide.


The valve now moves effortlessly in the guide. I consider this issue fixed!


Next up was getting everything back together. I re-inserted the rope into the cylinder to keep the exhaust valve closed while I installed the keys.


A few moment later, the two keys to the exhaust valve are installed.


And then the cap.


This is where I lost a little momentum. I had a hard time getting the rocker arms compressed enough for the rocker shaft to be pushed through the arms. It was almost like the pushrods grew longer by a few mills. After doing some research, it seems this is caused by the tappets/cam followers (aka hydraulic lifters) filling with oil and expanding, making the pushrods seem longer.

There were three possible solutions I read on how to overcome this:

1) Remove the pushrods and shroud tubes, remove the hydraulic lifters and bleed the oil out of them with a toothpick.

2) Apply some force to the pushrods for a few minutes - this will cause oil to be bled from the lifters.

3) Use a valve spring compressor to compress the springs on the valve enough for the rocker shaft to fit into the rocker arms.

For the intake valve, I was able to place an Irwin clamp to apply a slight amount of force to the pushrods. This worked great.


Success! The shaft is through the intake rocker arm.


Unfortunately the Irwin clamp trick did not work on the exhaust side. One issue was the baffle material got too tall and the clamp didn't have much to grab onto. I did not have a proper spring compressor, nor did I want to remove the shroud tubes for the exhaust pushrod. The last option was to find a way to compress the hydraulic lifter by applying a force to the pushrod.

After battling with different ideas for over an hour (very long frustrating hour, I might add), I came up with the idea to allow the engine to do the work. Although the rocker shaft was too big to insert, I thought I could insert a 1/2" wood dowel, and then rotate the propeller so the camshaft would push on the exhaust pushrod, applying pressure to the exhaust valve spring, and compressing the hydraulic lifter in the process. This worked amazingly well! Within one minute, the lift was compressed enough to allow the rocker shaft to be inserted into the rocker arm!
__________________
Mike Bullock
RV-7, Flying!
http://www.rvplane.com
The Best FAA N-Number Availability Search Engine -TailNum.com
Reply With Quote
  #5  
Old 08-17-2015, 06:39 AM
bullojm1's Avatar
bullojm1 bullojm1 is offline
 
Join Date: Feb 2006
Location: Baltimore, MD
Posts: 820
Default

The rocker shaft is in place, and the job is done!


I did go around to the other 3 cylinders to make sure the exhaust valve was not sticking. Good news was no other exhaust valve seemed to have any major friction with the guide. I buttoned everything up and went for a successful 0.7 hour test fight. It's great to have the RV back in service, and I learned a TON about how the topend of this engine works.
__________________
Mike Bullock
RV-7, Flying!
http://www.rvplane.com
The Best FAA N-Number Availability Search Engine -TailNum.com
Reply With Quote
  #6  
Old 08-17-2015, 06:53 AM
LettersFromFlyoverCountry's Avatar
LettersFromFlyoverCountry LettersFromFlyoverCountry is offline
 
Join Date: Jan 2005
Location: St. Paul, MN.
Posts: 4,597
Default

Great write-up which is really going to help me.

Just one question. You mentioned you RE-inserted the rope, but that was also the first mention of rope. When had it been inserted previously?
__________________
Bob Collins
St. Paul, MN.
Blog: Letters From Flyover Country
RV-12 empennage completed. Waiting for wings.
Builder log
Reply With Quote
  #7  
Old 08-17-2015, 07:00 AM
bullojm1's Avatar
bullojm1 bullojm1 is offline
 
Join Date: Feb 2006
Location: Baltimore, MD
Posts: 820
Default

Quote:
Originally Posted by LettersFromFlyoverCountry View Post
Great write-up which is really going to help me.

Just one question. You mentioned you RE-inserted the rope, but that was also the first mention of rope. When had it been inserted previously?
Bob,

I originally inserted the rope thinking I needed to to remove the exhaust valve spring. However, the valve was so tight in the guide, I didn't end up needing the rope to push between the top of the piston and the valve. After cleaning out the guide, the valve slid freely in the guide, requiring some force to keep the valve as closed as possible to install the keys.

I am torn on the rope method. I have always used it in small motors to be able to pop the flywheel nut off of outboard engines and lawn mowers. However, I read an article recommending against the rope as it could potentially become knotted in the cylinder, causing you to most likely remove the jug. Alternatively, you can use compressed air in the cylinder to push the valve tight against the top of the cylinder in lieu of using the rope. My air compressor is at home for a new wood floor project, so it was either rope or rope for me.
__________________
Mike Bullock
RV-7, Flying!
http://www.rvplane.com
The Best FAA N-Number Availability Search Engine -TailNum.com
Reply With Quote
  #8  
Old 08-17-2015, 07:09 AM
pa38112 pa38112 is offline
 
Join Date: Mar 2008
Location: Clarksboro, NJ
Posts: 370
Default

Yes, great write-up. It looks like your exhaust flange has some erosion. Were there indications of an exhaust leak?
What do you think lead to the valve sticking in the first place? I know these engines suffer from that, but why one cylinder and not the other three? Does this cylinder run hotter or colder than the others? Is it first or last to peak when leaning?
__________________
http://aprs.fi/N153MC
2004 RV6A Flying
Reply With Quote
  #9  
Old 08-17-2015, 07:12 AM
Rupester Rupester is offline
 
Join Date: Dec 2005
Location: Mahomet, Illinois
Posts: 2,116
Default

Great write-up with perfect pics, Mike. Thanks much!!
__________________
Terry Ruprecht
RV-9A Tip-up; IO-320 D2A
S. James cowl/plenum
(Dues paid thru Nov '17)
Reply With Quote
  #10  
Old 08-17-2015, 07:16 AM
bullojm1's Avatar
bullojm1 bullojm1 is offline
 
Join Date: Feb 2006
Location: Baltimore, MD
Posts: 820
Default

I never noticed the bit of metal missing from the cylinder around the exhaust valve flange. It looks like there has even been some leakage here. Is this anything to worry about?

__________________
Mike Bullock
RV-7, Flying!
http://www.rvplane.com
The Best FAA N-Number Availability Search Engine -TailNum.com
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 04:58 PM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.