VansAirForceForums  
Home > VansAirForceForums

-POSTING RULES
-Advertise in here!
- Today's Posts | Insert Pics

Keep VAF Going
Donate methods

Point your
camera app here
to donate fast.


Go Back   VAF Forums > RV Firewall Forward Section > Traditional Aircraft Engines
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 06-03-2021, 02:02 PM
mtnflyr mtnflyr is offline
 
Join Date: Mar 2019
Location: Boulder, Colorado
Posts: 18
Default Need Help Analyzing Borescope Images - Leaking Exhaust Valve on Lycoming O-360-A2D

Fired up the O-360 in our RV-6A last week and it ran rough, with EGT in the #3 cylinder failing to come up. Shut down the engine and pulled the plugs - they looked find. Then, a compression test and we could clearly hear air entering the exhaust system. Bought an inexpensive borescope, and the following are video clips and images of the exhaust valve in question. I've not analyzed borescope imagery before and could use some help with what these show. I'm reading everything I can find on leaky exhaust valves and ordered a valve guide reamer from McFarlane in case this is a stuck valve. I'm also looking into lapping the valve in place since it appears to me (remember I've never done this before) that there is significant pitting on the valve and the seat.

Help!

youtu.be/D9OgOrHm-xg
youtu.be/5etTaez_qoA

[IMG]www.dropbox.com/s/ntu56pw54kzi1g7/IMG_0001.JPG?raw=1[/IMG]
[IMG]www.dropbox.com/s/04hggsgiwcyjzho/IMG_0002.JPG?raw=1[/IMG]
[IMG]www.dropbox.com/s/gozttcn6fbdiqt5/IMG_0003.JPG?raw=1[/IMG]
[IMG]www.dropbox.com/s/qh9ltzakxmlthhr/IMG_0004.JPG?raw=1[/IMG]
[IMG]www.dropbox.com/s/cie11t1huskow5o/IMG_0007.JPG?raw=1[/IMG]
[IMG]www.dropbox.com/s/prm2n9q3n0ovueu/IMG_0009.JPG?raw=1[/IMG]
Reply With Quote
  #2  
Old 06-03-2021, 02:22 PM
rocketbob's Avatar
rocketbob rocketbob is offline
 
Join Date: Jun 2006
Location: 8I3
Posts: 3,740
Default

I've had mixed success with in-situ valve lapping. Sometimes its just better to pull the cylinder and have a new guide installed and clean up the valve and the seat. You will have to check the dry tappet clearance if this is done when you put the rockers and pushrods back on.
__________________

Please don't PM me! Email only!

Bob Japundza CFI A&PIA
N9187P PA-24-260B Comanche, flying
N678X F1 Rocket, under const.
N244BJ RV-6 "victim of SNF tornado" 1200+ hrs, rebuilding
N8155F C150 flying
N7925P PA-24-250 Comanche, restoring
Not a thing I own is stock.
Reply With Quote
  #3  
Old 06-03-2021, 02:25 PM
Dan 57's Avatar
Dan 57 Dan 57 is offline
 
Join Date: Sep 2018
Location: LSZF
Posts: 750
Default

Ok, my 2ct...
Quote:
we could clearly hear air entering the exhaust system
This could basically mean 2 things: either a stuck valve, or a leak around the seat... which doesn’t automatically result in a non firing cylinder.
Looking at vids & pics, the valve can be rotated easily, thereby discounting the guide/stuck valve theory.
Valve seat, I don’t see a specific spot, which would show as a black trail, on either the seat nor the seat. The valve burn image shows a quite regular pattern of an engine with a couple of hundred hours, not fully concentric, but regular pizza.

So my quick glance doesn’t reveal any obvious defect. Stupid question, is the «*air entering the exhaust*» happening on cylinder #3?
What were the values of the compressions?
__________________
Life's short... Enjoy!

http://www.aerofun.ch

RV-6.9 #25685, slider, O-360-A3A (carb/dual Lightspeed II), MTV-12-B, HB-YLL owner & lover
RV-4 #2062 HB-YVZ airframe builder
Reply With Quote
  #4  
Old 06-03-2021, 02:53 PM
BH1166 BH1166 is offline
 
Join Date: Nov 2017
Location: Eatonton Georgia
Posts: 513
Default Looks good

Agree with Dan, looks great to me. Compression test, hot or cold? Numbers? Running rough, did you throttle up and try to clear? Any chance your compression testing was flawed.
__________________
Butch
RV6A Purchased N72TX
Reply With Quote
  #5  
Old 06-03-2021, 03:41 PM
YYC650 YYC650 is offline
 
Join Date: Apr 2017
Location: Calgary, Alberta
Posts: 17
Default

Nice images. What borescope did you use?
__________________
RV-7a @ CYBW
2020 dues paid
Reply With Quote
  #6  
Old 06-03-2021, 07:45 PM
mtnflyr mtnflyr is offline
 
Join Date: Mar 2019
Location: Boulder, Colorado
Posts: 18
Default

Quote:
Originally Posted by YYC650 View Post
Nice images. What borescope did you use?
https://www.amazon.com/gp/product/B0...0?ie=UTF8&th=1

Not sure I'd recommend it. The first one I received wouldn't hold a charge. I returned it to Amazon and they sent me a new borescope and this one won't charge past halfway and runs out of juice in around 30 minutes. It's also a chore to get it oriented correctly - bend, install, pull it out, bend it again, hold your tongue just so . . . . If I return this borescope, I think I'll go with one of the Vividia products. The VA-400 is recommended by Mike Busch and it was after watching his AOPA presentation on exhaust valves that I bought this unit. I think the ability to bend the head from outside the cylinder would make this job a whole lot easier.
Reply With Quote
  #7  
Old 06-03-2021, 07:55 PM
mtnflyr mtnflyr is offline
 
Join Date: Mar 2019
Location: Boulder, Colorado
Posts: 18
Default

Quote:
Originally Posted by BH1166 View Post
Agree with Dan, looks great to me. Compression test, hot or cold? Numbers? Running rough, did you throttle up and try to clear? Any chance your compression testing was flawed.
Ran the engine long enough for the EGTs to come up and #3 was hardly rising at all. Very rough. Compression test the next day, cold. 30/80 in #3. Very obvious air sound in the exhaust pipe. Definitely leaking.

I'd been getting a "pop, pop, pop" at full throttle on climb out for a couple of flights earlier, and that concerned me. Running a bit rough, but everything smoothed out once she warmed up.

Funny thing is, before that the engine had been running the smoothest it has since we bought the airplane and the compression tests were the highest and most consistent ever at this year's annual done last month (78/80).

Sent the pics to a cylinder shop and they said the pitting was consistent with a mid/high time engine. They recommended trying to lap in place and when that didn't work, pull the jug and send it to them. They said to expect the lapping in place wouldn't fix the issue.
Reply With Quote
  #8  
Old 06-03-2021, 07:57 PM
akarmy's Avatar
akarmy akarmy is offline
 
Join Date: Jan 2005
Location: Auburn, WA
Posts: 677
Default

I've lapped a number of valves in place on my 0-360 which on average raised each cyl about 15lbs. I did this over a 2 year period but it would always start leaking again. We pulled the Cyl's and found very worn valve guides on the exhaust valves.
__________________
Andy Karmy
Covington WA

RV-8 - Flying!
RV-9A - sold

Dec 2020 Paid
Reply With Quote
  #9  
Old 06-03-2021, 08:02 PM
mtnflyr mtnflyr is offline
 
Join Date: Mar 2019
Location: Boulder, Colorado
Posts: 18
Default

Quote:
Originally Posted by akarmy View Post
I've lapped a number of valves in place on my 0-360 which on average raised each cyl about 15lbs. I did this over a 2 year period but it would always start leaking again. We pulled the Cyl's and found very worn valve guides on the exhaust valves.
I think that's the next step for this valve. Worth a try as it doesn't cost me more than the price of some lapping compound. Couple of questions:

- What lapping compound did you use?
- I'm worried about getting the grit on the cylinder walls and the valve stem. How did you get things cleaned up in between changing grits and when you were all done?
- How hard do you pull on the valve stem? Is this just a light pull, or lots of pressure?
- Thinking of making a jig to hold my dial indicator to do a wobble test. Did you do that?
Reply With Quote
  #10  
Old 06-03-2021, 08:47 PM
akarmy's Avatar
akarmy akarmy is offline
 
Join Date: Jan 2005
Location: Auburn, WA
Posts: 677
Default

Quote:
Originally Posted by mtnflyr View Post
- What lapping compound did you use?
- I'm worried about getting the grit on the cylinder walls and the valve stem. How did you get things cleaned up in between changing grits and when you were all done?
- How hard do you pull on the valve stem? Is this just a light pull, or lots of pressure?
- Thinking of making a jig to hold my dial indicator to do a wobble test. Did you do that?
I just used permatex valve lapping compound from the auto parts store. 2 grits
We sprayed the valve with brake cleaner through the spark plug hole with the lower plug out to drain the excess out.
Pull as hard as you can while spinning it.
I didn't do the wobble test (looks like I should have as that's where mine failed in the end)
__________________
Andy Karmy
Covington WA

RV-8 - Flying!
RV-9A - sold

Dec 2020 Paid
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 06:43 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.