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Easy Exhaust Valve Wobble Test Lycoming IO-360

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proppastie

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Having had a stuck valve and bent push-rod once a long time ago I was worried about my engine because of the rough running at full throttle if the engine was not fully warmed up. Looking at the weather I saw 2 warm days in a row so decided to take a look.....there are two Lycoming service bulletin/instruction as regards the sticky valve problem....1425A and 388C....One requires dropping the valve in the cylinder and ream of the guide and the other requires special tools to measure the wobble to see if you need to ream the guide of the carbon. There was a phrase in 388C about pressing the valve in to get it off the seat to measure the wobble, which when the special tool is on and the rocker arm is off and the springs are still attached I have no idea how it could be done.

Thinking about it I rotated the prop until the exhaust rocker was just pushing the valve in and off the seat....I then took a screw driver and pushed against the cap between the rocker arm and valve stem and "eyeballed" the movement......There is very little play maybe .001 between the cap and the stem so whatever the movement was it was close to the wobble of the valve stem. The spec. is between .015 and .035 and it looked as I had more than .015 and in any case there was wobble and I do not have to worry about a sticky valve. This method should work for any of the Lycoming engines when one suspects a sticky exhaust valve because of carbon or lead fouling.
 

Dan Thomas

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Having had a stuck valve and bent push-rod once a long time ago I was worried about my engine because of the rough running at full throttle if the engine was not fully warmed up. Looking at the weather I saw 2 warm days in a row so decided to take a look.....there are two Lycoming service bulletin/instruction as regards the sticky valve problem....1425A and 388C....One requires dropping the valve in the cylinder and ream of the guide and the other requires special tools to measure the wobble to see if you need to ream the guide of the carbon. There was a phrase in 388C about pressing the valve in to get it off the seat to measure the wobble, which when the special tool is on and the rocker arm is off and the springs are still attached I have no idea how it could be done.

Thinking about it I rotated the prop until the exhaust rocker was just pushing the valve in and off the seat....I then took a screw driver and pushed against the cap between the rocker arm and valve stem and "eyeballed" the movement......There is very little play maybe .001 between the cap and the stem so whatever the movement was it was close to the wobble of the valve stem. The spec. is between .015 and .035 and it looked as I had more than .015 and in any case there was wobble and I do not have to worry about a sticky valve. This method should work for any of the Lycoming engines when one suspects a sticky exhaust valve because of carbon or lead fouling.
The spring has to come off to get a reliable reading.

If your engine was built, or overhauled with new Lyc cylinders in 1999 or later, the guides don't wear much at all. Lyc changed the guide material to a high-chromium-content bronze.

The wobble test is to check for guide wear, not carbon buildup.
 

proppastie

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Well the valves were not too loose or not too tight and were overhauled in 2013 so that does make sense.
 

TFF

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It’s a pain to do but not all that bad if you have the spring compressor, a magnet or two, a grabber tool, and some rope. It is actually kind of fun at the same time as long as you don’t have a boss or customer breathing down your neck. Once you get the tool order figured, it goes easy. If you don’t have reusable gaskets, it’s more of a pain to clean the cover and head than really do the real work. You need more rope than you think.
 

rotax618

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I recently made a Lycoming valve wobble tester for the helicopter guys in the next door hangar, milled it out of I think 16mm alloy tool plate using my CNC, I don't have a photo of the finished device but this is a photo of the base.
there was a square block mounted on one end to attach the dial gauge.
 

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proppastie

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It’s a pain to do
I have done it the old way once after my stuck valve and bent pushrod. .....really this way is no comparison......I did all 4 cylinders from cowl on to cowl on in less than 3 hr. I was only looking for movement and yes did not get an accurate reading.....however given my experience I certainly am able to estimate more than .015 movement and less than .035 movement by eye........I easily could have added a small dial indicator to measure the movement......one might have to account for the fact that the cap is not out as far as the measuring point with the tool, given the small angles involved that probably is a very small difference.
 
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delta

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I can't help but think there's a oil or gas treatment that would prevent or at least delay the buildup. I'm thinking techron, 44-k, marvel mystery oil etc. I found this guy talking about temperatures that seems logical,
 

TFF

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Like I said, I kind of enjoy it except for bosses and owners. Probably 4 hour job start to finish. Depends on how cold or hot the shop is of course.
 

proppastie

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Probably 4 hour job start to finish.
well you have done it many times on the helicopters I would guess.....now me....well needless to say knowing what is involved I like the method of post 1
 

TFF

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It’s not really a problem anymore if the engine has been rebuilt in recent times. Lycoming can do a lot of CYA even if they fixed it. I learned from a friend that updating the service bulletin would start the clock over on liability, so today manufacturers will never update except to cover something worse, never better.
 
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