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  #1  
Old 06-09-2016, 09:40 AM
scard's Avatar
scard scard is offline
 
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Location: Cedar Park, TX
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Default Rope trick gone bad

The other day I performed some minor exhaust valve maintenance using the standard rope trick. I used 3/8" rope, which I'll never do again. Somehow I must have hit the lottery because the rope tied itself into the most perfectly tight slip knot inside the cylinder. I was on the verge of pulling the cylinder because there was just no way this knot/rope was coming out.

Tanya said, "Don't pull that cylinder just yet. Not until I get a crack at it." She loves puzzles and this one was a doozy. So I took a deep breath and sat for a few minutes, all the while thinking "I could have this #2 cylinder off and back on in an hour and a half."

Was I really going to let her show me how this is done? I don't think so!

I drug out the borescope and computer for detailed evaluation. Yep that is one tight slip knot. With the borescope in the bottom plug hole, looking at the computer screen, a hemostat and flat head screw driver went in the top hole. To my amazement, in about 45 minutes, I was able to mostly untie the knot in the cylinder and extract the rope. Wow, that was close.

I think a smaller rope, maybe 1/4", would be more appropriate such that if it tied itself in a knot, it could still be pulled out. I'm sure some unsuspecting mechanic has already learned this lesson. Now I have too.
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  #2  
Old 06-09-2016, 09:43 AM
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Default

Been there, done that.

Only, I ended up pulling the cylinder.

You win
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  #3  
Old 06-09-2016, 09:54 AM
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Default

Hemostats are God's gift to surgeons and mechanics!
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  #4  
Old 06-09-2016, 10:40 AM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
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For the benefit of those learning from this...

In the automotive world, compressed air is the common method for holding the valve while compressing the spring and removing the keepers. Just hook up your compression tester (leak-down type) then throw 80 or 100 PSI at it. Works well. It is common for the hot rod guys to go through several sets of valve springs when tinkering with cams and valve float (i.e. hitting max rpm) and we always use air.

Be sure that have someone hold the prop for you so you don't hurt yourself or tie it to something.

Larry
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Last edited by lr172 : 06-09-2016 at 10:42 AM.
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  #5  
Old 06-09-2016, 10:54 AM
BillL BillL is offline
 
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Quote:
Originally Posted by lr172 View Post
For the benefit of those learning from this...

In the automotive world, compressed air is the common method for holding the valve while compressing the spring and removing the keepers. Just hook up your compression tester (leak-down type) then throw 80 or 100 PSI at it. Works well. It is common for the hot rod guys to go through several sets of valve springs when tinkering with cams and valve float (i.e. hitting max rpm) and we always use air.

Be sure that have someone hold the prop for you so you don't hurt yourself or tie it to something.

Larry
+1

The rocker assembly is off, so push the piston to BDC, quite safe there. The retainer will have to be smacked off axis with an inertial tool to loosen the keepers as they are usually pretty tight. Then, you are golden. 100 psi is a lot of force on that valve to keep it there during spring removal.

Scott, Good you ( and Tanya ) were persistent and got it out.
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  #6  
Old 06-09-2016, 11:12 AM
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Never thought of that. Thanks for going through that for me
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  #7  
Old 06-09-2016, 11:30 AM
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az_gila az_gila is offline
 
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Question

One online source said they used 1/2" mountain climbing rope, not the 3/8" nylon rope suggested by the Lycoming SB.

I think the demo I saw at a Grumman convention also used 1/2" rope.

Do you think fatter rope would be harder to get knotted internally?
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  #8  
Old 06-09-2016, 11:40 AM
jimbo jimbo is offline
 
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I'm at a loss here...what minor exhaust valve maintenance work was Scott attempting to do with the rope?

Jim
RV9a
160 hours
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  #9  
Old 06-09-2016, 12:05 PM
lr172 lr172 is offline
 
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Quote:
Originally Posted by jimbo View Post
I'm at a loss here...what minor exhaust valve maintenance work was Scott attempting to do with the rope?

Jim
RV9a
160 hours
,
I would speculate he was doing the "wobble test" looking for valve guide wear or carbon build up. The spring needs to come off for that test. The standard "in situ" test for valve guide/stem clearance is measuring the lateral movement of the stem tip.
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Last edited by lr172 : 06-09-2016 at 12:10 PM.
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  #10  
Old 06-09-2016, 12:08 PM
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Quote:
Originally Posted by jimbo View Post
I'm at a loss here...what minor exhaust valve maintenance work was Scott attempting to do with the rope?

Jim
RV9a
160 hours
Lapping exhaust valves. And sure, a wobble test while we're at it. It's time to make sure you're ready for Oshkosh you know .
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