Oil Dipstick tube loose

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supertrooper2002

Pre-Flight
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supertrooper2002
I often fly a 172 RG with a O-360-F1A6 engine. Most days when I'm pre-flighting the plane and checking the oil, I find that the dipstick is securely tightened but the tube connecting to the engine is loose and needs to be tightened 1-2 rotations. Anyone have this problem or suggested solutions?
 
supertrooper2002 said:
I often fly a 172 RG with a O-360-F1A6 engine. Most days when I'm pre-flighting the plane and checking the oil, I find that the dipstick is securely tightened but the tube connecting to the engine is loose and needs to be tightened 1-2 rotations. Anyone have this problem or suggested solutions?
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My oil dipstick tube is safety wired to the case. Your engine should also be safety wired. Might need a need a tube and is why it's loose. Safety wire hole wore out?
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More lousy maintenance. No way it should be backed out a turn or two. There is provision for lockwiring it at its base.

Another problem is pilots overtightening the dipstick. That then encourages the tube to come loose when the next guy has to really force it to get it out. No need to be anywhere near that tight.

I had ongoing problems with that in the flight school. Could not get the instructors and students to stop reefing it tight. They even stretched the lockwire while getting the dipstick loose. I finally took those tubes out, cleaned them and the crankcase port faces thoroughly, applied Permatex High-Tack to new gaskets and installed and lockwired them. No more loosening. I wish Lycoming had designed those with a positive rotation stop to make them idiot-proof.
 
When possible my preference is to double safety wire the tube..

If no provision for 2 spots I use a hose clamp around the tube.
 
Dan Thomas said:
More lousy maintenance. No way it should be backed out a turn or two. There is provision for lockwiring it at its base.

Another problem is pilots overtightening the dipstick. That then encourages the tube to come loose when the next guy has to really force it to get it out. No need to be anywhere near that tight.

I had ongoing problems with that in the flight school. Could not get the instructors and students to stop reefing it tight. They even stretched the lockwire while getting the dipstick loose. I finally took those tubes out, cleaned them and the crankcase port faces thoroughly, applied Permatex High-Tack to new gaskets and installed and lockwired them. No more loosening. I wish Lycoming had designed those with a positive rotation stop to make them idiot-proof.
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A good option is to safety wire the tube in both directions so it doesn't rotate either direction.
 
Will Kumley said:
A good option is to safety wire the tube in both directions so it doesn't rotate either direction.
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If it has been properly tightened, it can't go any further unless the pilot uses a tool on the dipstick to tighten it. In that case, we have more serious problems.

I tried everything, from education to softer O-rings to heavier lockwire. Nothing worked until I used the High-Tack on a new gasket and installed it against cleaned surfaces.

The real solution would be for Lycoming to make a dipstick/tube assembly with positive stops. Continental does that, and you don't find those overtightened. Maybe McFarlane needs to develop an aftermarket affair that uses a bayonet-style closure similar to a fuel cap.
 
Perhaps a dipstick with a sacrificial handle? Charging the offender for a replacement dipstick might deter them.
 
Usually this happens when someone squeezes the snot out of the O-ring/gasket at the bottom of the tube where it attached to the engine. The O-ring starts to squeeze out and the tube loosens up. (It also happens when the O-ring gets old and deteriorated.) A new, proper gasket and safety wire usually solves the problem, until the next next time the dipstick is overtightened.
 
Most people (and some mechanics) don't really understand "just tight enough that it will seal and not vibrate loose". As a general rule only 10-20% of the torque contributes to clamping, the rest is to overcome friction, which can vary a lot depending on its condition and whether it is lubricated. One net takeaway is that a lot tighter (torque) is only a little more clamping force, so there's usually no point to securing it gorilla-tight.
 
Dan Thomas said:
If it has been properly tightened, it can't go any further unless the pilot uses a tool on the dipstick to tighten it. In that case, we have more serious problems.

I tried everything, from education to softer O-rings to heavier lockwire. Nothing worked until I used the High-Tack on a new gasket and installed it against cleaned surfaces.

The real solution would be for Lycoming to make a dipstick/tube assembly with positive stops. Continental does that, and you don't find those overtightened. Maybe McFarlane needs to develop an aftermarket affair that uses a bayonet-style closure similar to a fuel cap.
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Yep, see this all the time. Make an oily mess. I usually put new gasket, safety it tight, and apply torque seal just so I can see when it’s moved. I also replace the o’ring more often than normal. Seems to have helped.
 
Will Kumley said:
A good option is to safety wire the tube in both directions so it doesn't rotate either direction.
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This is the winner-winner answer. Dipstick tube will not loosen if it's saftied to avoid movement in both clockwise and counter-clockwise direction.
 
martym said:
This is the winner-winner answer. Dipstick tube will not loosen if it's saftied to avoid movement in both clockwise and counter-clockwise direction.
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It will still move.

Lockwiring isn't that strong. It's there to discourage loosening due to vibration or thermal changes, not to resist someone using a pair of pliers on the dipstick to get it loose. That sort of torque stretches the lockwire, and now we have some play that will only get worse. And if the pulls is bad enough, it will either break the lockwire or rip the lockwire eye off that dipstick stube, which is only plastic, after all.

I, as a mechanic, have seen this numerous times, which is why I cleaned everything off and used High-Tack on a new gasket and cemented it rigidly, as well as lockwired it. Nothing else worked, not even trying to get the guys to stop winding up on that dipstick. They were so afraid it might come loose.

I think someone should come up with a PMA'd aftermarket dipstick and tube assembly that has a quarter-turn cap that can't jam. Or maybe it should be a ratcheting cap like cars use now as fuel caps, to prevent overtightening. If I did it, I would also try to find some way to stop the dipstick vibrating on the intake tubing cast into the sump. That aluminum dipstick gets eaten partway through doing that. Internal guides would hamper oil flow during oil changes or topping up. A brace between the tube and a stud and nut on the accessory housing and a clamp on the tube would reduce tube vibration and also discourage loosening, though with the variety of installations with so much junk in the way, that might be harder to find any commonality on.
 
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