Trying to make her purr again

C

C150flyer

Filing Flight Plan
Joined
Aug 28, 2013
Messages
5
Location
Wellsville NY
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Display name:
Pete
Hi I am a first time poster but a long time reader and a scared new owner.
I just recently bought a 1966 150f and have been flying every chance I get. But recently last 2 or so flights I have been feeling a vibration/roughness that has been getting progressively worse. No rpm drop just doesn't purr/sound/feel right. Sometimes when it starts everything feels fine but after warm up I can feel it especially at full throttle. Mag checks drop 75ish both sides I do not have egt gauge so no idea there. I have finally grounded her and decided to figure out what's going on. I have pulled all the plugs and found this:

#1 Top Autolite UREM40E
#1 Bottom Tempest URE138E
#2 Top Autolite UREM40E
#2 Bottom Autolite UREM40E
#3 Top Tempest URE138E
#3 Bottom Tempest URE138E
#4 Top Autolite UREM40E
#4 Bottom Tempest URE138E

I have not cleaned or gapped them yet but personally I would rather get new and have all the same. Also on the right side lower cowl I have a lot of residue from the exhaust and none on the left ( just cleaned entire plane 4 flights prior). My question is this normal to put different heat plugs in and could it cause my issues? (no crazy fouling was found) And if I should replace what plugs have you had good luck with in an 0-200?
 
Not a likely problem, but we had a local C-152 with a major crank flange crack that demonstrated those characteristics. The mechanic pulled the spinner and prop and voila - a $15,000 rebuild.
 
C150flyer said:
Also on the right side lower cowl I have a lot of residue from the exhaust and none on the left ( just cleaned entire plane 4 flights prior)
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This is saying something right here! If you had the plugs in and you pull the prop thru by hand, do you notice any one cylinder compression noticably weaker than the others?


CAUTION: You can be injured or even killed if the magnetos are not properly grounded when pulling the prop thru by hand when the magneto lights the engine up with you on/under/in the prop.

If so, you might want to have someone (or even yourself if you do some research) perform a compression test with one of these:

http://www.aircraft-tool.com/shop/detail.aspx?PRODUCT_ID=2EM
 
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C150flyer said:
My question is this normal to put different heat plugs in and could it cause my issues? (no crazy fouling was found) And if I should replace what plugs have you had good luck with in an 0-200?
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O-200's tend to foul the bottom plugs pretty quickly in my experience and is why you found a different part # in the bottom than in the top. You can mix brands and part # of spark plugs without issues.
 
No but pre bad roughness Aug 21 the pre buy was done and all were 72 and up. But I will do that in the morning.
 
C150flyer said:
No but pre bad roughness Aug 21 the pre buy was done and all were 72 and up. But I will do that in the morning.
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A cylinder can crack at anytime and then you'll have lower compression on that one, causing an unusual vibration. Look very carefully around the cylinders with a bright flashlight for streaking around the cylinder heads, and cracks around sparkplug holes etc. Gray or black streaks coming from between fins on the cylider heads = CRACKED.

The best way to find external cracks IMHO is the compression tester dialed up to 80 PSI and hose them down with some soapy water. Internal cracking is only found after cylinder removal, indicated by low compression and/or hissing sound from exhaust or intake (air filter) that can't be remedied by the usual valve lapping tricks.
 
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What color is the residue? It sounds like you have a valve getting burnt on the side with the residue. Do a rough compression test by rotating the prop through 2 full turns and seeing if you have the same resistance through each compression stroke. If you still have the plugs out, stick the bottoms in and use your thumb to check each cylinder for compression.
 
Black not dripping oil out or anything just looks like what I cleaned off way sooner then the left side I would post a pic but POA doesn't trust me yet
 
C150flyer said:
Black not dripping oil out or anything just looks like what I cleaned off way sooner then the left side I would post a pic but POA doesn't trust me yet
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That would be carbon, product of incomplete combustion most likely due to low compression, most likely caused by a sticking or already burnt valve. Hate to say it, but you likely need to repair/replace a cylinder. Always operate as lean as you can make the engine run smooth to prevent this from happening.
 
ok that sucks but since that comes up I trained in a 150 and I was taught back it off till it starts to get rough and 3 turns to rich is that correct? I know I'm opening a can of worms but I can't get a straight answer from anything I read
 
C150flyer said:
ok that sucks but since that comes up I trained in a 150 and I was taught back it off till it starts to get rough and 3 turns to rich is that correct? I know I'm opening a can of worms but I can't get a straight answer from anything I read
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Yep, that's the way. On the ground, lean very aggressively to the point that you have to be careful and slowly advance the throttle to keep it from dying. This not only assures you of leanest operations on the ground and not loading up the cylinders and plugs, it also serves as a reminder to enrichen the mixture for take off.
 
I've found flowers, a small diamond something, and a good dinner out work wonders ...

oh ...

you were talking about airplanes :cheers:
 
Oh, c'mon, guys, you are scaring the $#!+ out of the poor kid.

Yes, small bore Continentals are notoriously hard on valves. More notorious on the exhaust than the intake. Remedy is a Tijuana valve job that doesn't even require pulling the cylinder.

Blackish residue on one side vs the other? Never saw a COntinental yet that didn't try to mark its territory out the pushrod tubes. Most probably not the problem.

But the BEST advice you got was to do nothing. NOTHING!! until you have somebody help you troubleshoot the problem to find the actual cause rather than throwing parts at it hoping you find the right one. That is called shotgunning and isn't the best way to isolate the problem.

So calm down, put your big boy panties on, and calmly and logically fix the problem rather than the symptoms.

Jim
 
I gave him a free way to do a basic compression check, how much cheaper does it get?
 
Henning said:
I gave him a free way to do a basic compression check, how much cheaper does it get?
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Well, I wasn't going to criticize your answer, but since you gave me the opportunity ...

Why would a burnt valve leave a sooty residue in the exhaust (I don't buy the unburnt fuel explanation)? Did you bother to tell him to shut the mags off before doing the thumb test? I know what a proper thumb pressure is, and I presume you do. This is the kid's first airplane...how do you expect him to know what that feels like?

How about, "What did the plugs look like ... sooty, oily, white, gray...?" How about, "When you use the starter to turn the prop over, do you hear a wheeze out of the exhaust? Out of the carburetor?"



Like I said, let him find somebody that knows what they are doing to help him troubleshoot ... or were you born with that intrinsic a-priori knowledge?

Jim
 
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weirdjim said:
Well, I wasn't going to criticize your answer, but since you gave me the opportunity ...

Why would a burnt valve put a deposit on the INside of the cowl? Why would a burnt valvue put a deposit on ONLY the one OUTside of the cowl? Did you bother to tell him to shut the mags off before doing the thumb test? I know what a proper thumb pressure is, and I presume you do. THis is the kid's first airplane...how do you expect him to know what that feels like?

Like I said, let him find somebody that knows what they are doing to help him troubleshoot ... or were you born with that intrinsic a-priori knowledge?

Jim
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I missed where it's on the inside of the cowl, still don't see it mentioned in the OP, perhaps I'm blind. Why would the mags make a difference with the thumb test? Besides, I don't expect him to be stupid. He doesn't need to know the proper pressure, just comparative as in "these three I can't hold against, this one I can". Wasn't born with it, but I started working on engines at 11, I'm 48 now, that includes 4 years working in aircraft shops.
 
C150flyer said:
ok that sucks but since that comes up I trained in a 150 and I was taught back it off till it starts to get rough and 3 turns to rich is that correct? I know I'm opening a can of worms but I can't get a straight answer from anything I read
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What mixture control do you have?

most have the click type.

if you have the vernier type 3 turns is too rich.

now we know why the plugs foul.
 
Tom-D said:
What mixture control do you have?

most have the click type.

if you have the vernier type 3 turns is too rich.

now we know why the plugs foul.
Click to expand...

Yeah I was gonna say the same thing.

Lean until it gets rough, then slowly enrich the mixture until it runs smooth again. Leave it there.
 
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