Blue stain - Never a good sign

iflyvfr

iflyvfr

Pattern Altitude
Joined
Sep 20, 2013
Messages
1,794
Location
Columbus, OH
Display Name
Display name:
Greg
I noticed some blue stain on the inside of my lower cowl, directly below my carburetor and decided I might have been to blame - attributing it to poor engine start procedure.

My mechanic found otherwise after decowling today for annual. The hose connecting the intake to the cylinder appears to be the culprit, although it appears to the naked eye the hose is in good shape (see below). Is there anything else you recommend we investigate as the cause?

Details: This is an O-300 motor, right side, center cylinder. The first image is right side, behind the muffler, looking down toward the front of the motor and to the floor. The second is taken from the front, low, looking up and to the left and is large for detail. Third is the hose connection itself. Any (helpful) thoughts?
stain.JPG stain1.JPG hose.JPG
 
Sorry, only help I can give is insert your hand into pocket, pull out wallet, maybe cuss a little..
 
Ha ha, that I'm doing...I'm hoping the hose will resolve the issue. The fuel tank sender and tach rebuild will hurt a little more.
 
iflyvfr said:
I noticed some blue stain on the inside of my lower cowl, directly below my carburetor and decided I might have been to blame - attributing it to poor engine start procedure.

My mechanic found otherwise after decowling today for annual. The hose connecting the intake to the cylinder appears to be the culprit, although it appears to the naked eye the hose is in good shape (see below). Is there anything else you recommend we investigate as the cause?

Details: This is an O-300 motor, right side, center cylinder. The first image is right side, behind the muffler, looking down toward the front of the motor and to the floor. The second is taken from the front, low, looking up and to the left and is large for detail. Third is the hose connection itself. Any (helpful) thoughts?
View attachment 45412 View attachment 45411 View attachment 45413
Click to expand...

Only thought I have is to change your thinking, assume leak first and get something like that checked out rather than thinking it's some procedural error on your part. Eliminate the mechanical possibilities first, then start looking at procedural issues. Gas leaks, especially under the cowling are bad, bad ju ju.
 
Yep, she sits until this is sorted out. I even had the cowl off not too long ago and had the opportunity to chase, but failed to do so. Definitely not happy thoughts.
 
So complete novice thoughts here, but this pipe goes from the carb to the intake port. While the engine is running there should only be vaporized fuel and air in that pipe, I can't think of how you would have raw fuel leaking out of there under power as it should be under vacuum, if there is a leak it would make that cylinder run lean. You may not be too far off with the thought this is occurring during start up, maybe after priming. I would suspect the hose or pipe, in pic two on the bottom of the hose where it touches the pipe, that area looks suspect to me.

Observing it during startup and while running might provide clues, or just replace the hose and make sure the pipe is not cracked. In pic two, if you zoom in, the pipe has a line in it at about 10 oclock where the hose intersects. That looks suspect from the picture, but it might be nothing, hard to tell.

My thoughts, worth what you paid for them, keep us posted as to what it turns out to be.
 
Exactly Paul, that's why my mechanic said I'll replace the hose, but go ahead and post on the forum and ask the collective. What looks suspect to you in that pic, the hose, the pipe, or both? I'll definitely reply with the solution, I consider it my payment in exchange for your thoughts.

Greg
 
I think he means the vertical line on the metal runner at about 10:00 that looks to be a couple inches long, terminating at or under the coupler.

Also, maybe it's just the pic but the hose clamp on the leaking side looks like it might not be tightened (looks like a slight gap under it). Might just be an illusion, guessing mechanic ch checked that.

In my case (front runner to balance tube junction, O470R), mine was leaking and my AP moved the coupler (there was excess) and re tightened the clamps on a fresh section of the coupler. So far no issues but mine wasn't leaking nearly that bad either.
 
Good call out Omalley, I hadn't noticed that nor picked it up from Paul's note! I will definitely point that out to my mech tomorrow when I go back to the hangar.
 
The leak looks like it is coming from the hose/pipe interface at the 7 o'clock position and could be from a deteriorated hose or loose hose. Omalley has it right about the other suspect area on the 10 o'clock on the pipe, but I think it might be a seam or parting line, hard to tell from the picture. Hopefully the hose will take care of it, but were I doing it I would at least prime and crank the engine with an observer if it can be done safely to confirm the leak location.
 
Well I can tell you I would much rather find the blue stain where you found yours vs where I found mine...down the side of the plane!
 
For every ones info, the 0-300 only primes the left bank of cylinders there is no prime given to the right side cylinders.

What he has is a leaking intake tube "hose" any fuel left in the intake of that cylinder will run down until it finds a way out.

By the looks of it, it's been going on a long time.

to change that hose, that side's muffler must come off, then the "Y" pipe and all 3 hoses on that side must be changed, by removing the 6 hose clamps, and the three bolts attaching the "Y" pipe to the sump. (very difficult to get to two of them) then the "Y" pipe will come off.
 
"Y" pipes
you don't change just one hose
Nice 8 hour job :)
 

Attachments

  • Kens assembly.JPG
    Kens assembly.JPG
    72.9 KB · Views: 50
Think of it this way, you are lucky, the aircraft is in for annual, the mufflers must come off for pressure check for cracks anyway.

No it's not an AD.
No it's not compulsory
Just a damn good idea if you want to stay alive running Hanlon and Wilson 201 mufflers.
 
iflyvfr said:
I noticed some blue stain on the inside of my lower cowl, directly below my carburetor and decided I might have been to blame - attributing it to poor engine start procedure.
Click to expand...

we are begging you to tell us your start routine :)
 
Thanks Tom. I'm headed to the hangar, it's an 1.5 hr drive away...more later.
 
Blue staining on the intake runners like that can also be a sign of a vacuum leak. Any problems starting, running a little rough, running hot on any of those cylinders?

Those clamps can loosen over time. I would start by cleaning it up, tightening the clamps and see what happens before I spend eight hours changing them out.
 
The outside of my cowling won't show 100LL blue (see the picture to the left) but the inside is painted white (at times I curse the guy who decided that the inside of the cowl and wheel wells should be white).
 
Chip Sylverne said:
Blue staining on the intake runners like that can also be a sign of a vacuum leak. Any problems starting, running a little rough, running hot on any of those cylinders?

Those clamps can loosen over time. I would start by cleaning it up, tightening the clamps and see what happens before I spend eight hours changing them out.
Click to expand...
Then why aren't all of them leaking?
 
Tom-D said:
Then why aren't all of them leaking?
Click to expand...

Could be the one that's leaking was insufficiently tightened at original installation, or it was overtightened and the clamp was damaged.
 
Chip Sylverne said:
Could be the one that's leaking was insufficiently tightened at original installation, or it was overtightened and the clamp was damaged.
Click to expand...
Best guess is the cylinder was off and the hose was not changed, I see this quite often.
 
Tom-D said:
Best guess is the cylinder was off and the hose was not changed, I see this quite often.
Click to expand...

That could be as well. A look at the logs wouldn't hurt. Could also be the clamp wasn't square on the tube when it was "tightened", and over time worked it's way square and got loose. Looking at the pic the clamp looks a hair close to the edge of the hose.
 
And while you are in there, look to see if the gasket between each cyl head and the intake manifold risers has pulled in. They are rectangular with straight sidewalls, and somewhat prone to suck into the manifold system. Looking at your pictures it does not appear to be your case, but it is simple to check to see if any of the 1/4-28 inch studs and nuts etc are loose. There are two on each jug as I recall.
 
nrpetersen said:
And while you are in there, look to see if the gasket between each cyl head and the intake manifold risers has pulled in. They are rectangular with straight sidewalls, and somewhat prone to suck into the manifold system. Looking at your pictures it does not appear to be your case, but it is simple to check to see if any of the 1/4-28 inch studs and nuts etc are loose. There are two on each jug as I recall.
Click to expand...
0-300 does not have intake risers, they are intake elbows, I've never seen any of those gaskets fail.
 

Attachments

  • #6 cylinder.jpg
    #6 cylinder.jpg
    69.5 KB · Views: 30
I recently had my plane on a round trip to Manassas & back, about 650 nms and the engine purred the whole time. I lean aggressively and fuel burn was excellent. My compressions are adequate to excellent (62/80 - 78/80).

As for my starting technique, my normal routine in cold weather is 3 good healthy primer shots (e.g. 3 -4 shots to prime the primer followed by three good prime strokes) and she fires off in @ 4 blades. I've also leaned at shut off to ensure I see an RPM rise, which I don't normally do. Now that it's warmed up, I've tried with zero prime shots, and no throttle pumps, to just throttle strokes. THe prior owner told me, if she's been flown for any length of time in the past three hours, two pumps of the throttle and she'd start right up. I've found that to be true and have always done same.

I've been experimenting a bit, and thought this disruption of routine could be resulting in excess fuel dripping out of the carb. But clearly that's not the case, so I will return to my normal start routine and leave well enough alone.
 
Last edited:
So, we pulled the hose off today. We finally have internet at the FBO, so I pulled up the photo and blew it up so my A&P could see the 'blemish' in question. Good news is, that pipe is not cracked, that's just a surface blemish. He said if it were he'd expect to see smoking, which he explained would be dust from the two halves grinding against each other.

He did say he could get about a 1/2 turn on the clamp, but since he had a new one, we're just replacing that and the gasket to see if the issue goes away permanently. I also have a mag that needs a new gasket, a fuel sender that needs rebuilt, and an overhaul/replacement of the tach coming, so it will be weekend after next before we can ground run her and check for leaks.

My untrained eyes couldn't see anything wrong with the hose after it was removed and cleaned up. Since I have had 3 cylinders reworked in the first few years of ownership, it's entirely possible hoses were reused, but I seem to recall we normally replace hose and gaskets when we do cylinders.
 

Attachments

  • inside1.JPG
    inside1.JPG
    97.4 KB · Views: 41
  • inside2.JPG
    inside2.JPG
    158.9 KB · Views: 39
  • hose1.JPG
    hose1.JPG
    134.5 KB · Views: 38
  • hose2.JPG
    hose2.JPG
    135.6 KB · Views: 40
P.S. Thanks for the input everyone. I really enjoy learning about my engine and helping maintain my bird. Today I spent an hour gapping and installing my REM37BY plugs. I'm amazed at the difference in the lead buildup between these and the normal plugs: very little to clean out. My mechanic made me redo my safety wire on the oil filter 4 times until I got it perfect.

I also cut the oil filter and there was nothing to see, not a single fleck of metal.
 
Have you double checked your primer lines? Fuel flows downhill. Look at everything uphill. Broken primers are common. Have somebody watch them as you prime.
 
Stewartb said:
Have you double checked your primer lines? Fuel flows downhill. Look at everything uphill. Broken primers are common. Have somebody watch them as you prime.
Click to expand...
Wrong side of the engine, the 0-300 only has one primer line to the engine, it connects to the left "Y" pipe. at the sump level.
You can see the 1/8th pipe threaded hole in the "Y" pipe in the picture
 

Attachments

  • Kens mount.JPG
    Kens mount.JPG
    77.2 KB · Views: 19
Tom-D said:
Wrong side of the engine, the 0-300 only has one primer line to the engine, it connects to the left "Y" pipe. at the sump level.
You can see the 1/8th pipe threaded hole in the "Y" pipe in the picture
Click to expand...

I haven't seen the whole setup, but I would think the fuel would go to the lowest point in during the prime and be sucked into all cylinders.
 
Regardless, we are definitely doing a ground run or three before I fly it to ensure no leaks.
 
PaulS said:
I haven't seen the whole setup, but I would think the fuel would go to the lowest point in during the prime and be sucked into all cylinders.
Click to expand...
Not if you are cranking the engine as you should be.
Prime,,, prime,,, prime,,, prime, let's see what's next on the check list, Oh yeah, let's start,, yes it will be in the cowl ready to be ignited.
It will run down past the throttle plate and out the bottom of the carb, into the airbox then on down into the cowl continuing down to the tire and on the ground.
 
iflyvfr said:
Regardless, we are definitely doing a ground run or three before I fly it to ensure no leaks.
Click to expand...
Simply clean your spark plus as you should, then at 5 hours look at them you will see which is running leaner than the others. those are leaking.
Or
Lean on the ground until it skips, and do the cold cylinder test.
 
After a couple of weekends, the plane comes out of annual today. Yesterday I did a 5 minute test run to check for leaks, then a 20 minute shakedown flight in the pattern. This annual was a little more involved: we replaced a magneto gasket, replaced the intake hose (the subject of the OP), checked the output on the voltage regulator (trivial), replaced a main gear tire & tube with a Monster retread (6x6x4), and R&R the right tank fuel sender. That's a bit of a chore. At first it seemed as though it wasn't functioning: after filling the tank to 1/4 with avgas the needle didn't budge off its stop.

After some t-shooting we decided to add more gas to bring it to 1/2 full and the needle now showed 1/4 tanks. So, we removed the sender unit 3 more times - bending the wire until it displayed 1/2 tanks properly. I am now a pro at seating the unit into the tank (takes some finagling) and even managed to get the ground strap on there too. Not only did my mechanic let me do most of the work under his watchful eye but then he bought me lunch! I'll make up for it in the check I write him shortly. Planning on bringing her home later today.

We were in awe of the new fuel sender. I sent it to Lockhaven, PA for a rebuild ($175 w/ new gasket and screws) but the unit came back looking brand new. I'm going to call them tomorrow and ask if they replaced my old unit or if this is my original. As far as I can tell this is probably the first time it's ever been off the plane in 50 years.

A good annual over all: compressions checked out OK, oil filter was spotless, and some problems were fixed/replaced. Somehow cash doesn't seem like enough for my mechanic. I think I'll find a couple of really nice steaks and drop them off to his wife today.
 
You must log in or register to reply here.
Back
Top