Very light oil leak?

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aharrin1

Filing Flight Plan
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Aaron
I have a Cessna 177B with an O-360-A1F6D engine. It has about 500hrs SMOH, by Pen Yan. Chrome cylinders. In early fall, the plane revealed a very very slight oil leak. It was flown on a 7+hr cross country trip and when the plane got home, there was a small 2" long oil 'streak' coming out of the second from the front cowl fastener on the left side. We had our A&P look at it, took the cowl off, he said it definitely wasnt the prop seal as it was completely dry. We couldnt locate where oil was coming from. We've since been flying the plane keeping close eye on the "leak" It is probably only a drop or two per hour (which can leave a mess that looks bigger than it actually is) recently its been getting more noticeable and when we took the cowl off for its most recent oil change, we scoured the entire engine compartment looking for the leak. It appears the leak might be coming from the seam between the two crank case halves right around the bolt that has the engine hoist 'U'. Is this a simple fix of re-tightening the bolt to the correct torque or is it gonna be a little more involved? I haven't touched it at all yet. As far as our oil consumption is concerned. We have always kept close track of oil consumption and we even keep a chart that we update every month. We are not using any more oil than before we discovered the leak. My guess is that it is becoming more noticeable just by the sheer fact that oil is continually building up one to two drops at a time and has now built up to a point of becoming more noticable. Any ideas?
Thanks
 
Who built the engine? how many hours since last assembly.

I'd retorque the case seam, see what happens.
 
Look for a few drops of oil on the bottom of the rocker covers on that side. Cover gaskets start leaking unless they're silicone instead of cork.

Dan
 
Dan Thomas said:
Look for a few drops of oil on the bottom of the rocker covers on that side. Cover gaskets start leaking unless they're silicone instead of cork.

Dan
Click to expand...
If cork, replace with REAL Gaskets. They are well worth the $.

Not necessarily related, but I once had a thru-bolt on an O-200 that wouldn't tighten (common on those cases so I'm told). You don't want to know what happened to my wallet next...:yikes:
 
iflyvfr said:
Not necessarily related, but I once had a thru-bolt on an O-200 that wouldn't tighten (common on those cases so I'm told). You don't want to know what happened to my wallet next
Click to expand...

I'm curious ... a through-bolt is a simple steel rod threaded on both ends. Nuts on both ends tighten the bolt. How could it NOT tighten?

Jim

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You are right, this was a bolt that went into the case, which needed to be split and helicoiled. Thanks for catching that, though I could swear that's what it was called at the time.
 
The current issue of EAA Sport Pilot has a great Savvy Aviator Mike Busch piece on oil consumption. Lots of common sense ideas and perspective there.

Not sure if you can see this if not a member but here goes:
EAA Mag Savvy Aviator

I'm definitely a big Mike Busch fan.
 
If you have access to a black light, that can help locate a leak. I used one regularly at my last place of work from a florescent penetrant setup. Synthetic oils show up best. Avgas will show a little due to the lead. Jet fuel won't show at all. You could also do a very thorough degrease and dust with baby powder. Check all case halves bolts/nuts and accessory covers for proper torque. If it is a case half, thouroughly clean and put a little fuel/oil resistant pro seal on the seam. That may or may not stop the leak if its a problem with the gasket.
 
If it's coming from between the cases, live with it until you can't, it will require splitting the cases to fix. Either that or see if Penn Yan will fix it under warranty now.
 
UV dye just before the next oil change and a blacklight will make it easy to pin-point the leak.
 
great article. my cherokee burns a quart every 15 hours. and i get oil leaking from the breather. i've been told its normal to leak some. its a 1968. I was told, "if it aint leaking there isnt any oil in it."
 
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