For those with a lycoming valve train...?

[bradp]

Thinking about DXBs thread.  I'm aware of recommendations to perform a wobbble test every 400-500 hrs.  Seems like good preventative maintenance with little risk for MIFs.  For those in the know are there certain details about this recommendation that come into play when deciding when to do the test / ream the guides? Do angeled or parallel designs come into the equation? How much notice will a valve give you before it becomes a critical issue ... i.e. Is there a typical progression to morning sickness before valve failure?  The later is not something I want to mess around with.   Can savvys platform identify valve issues at the "need to team the guide / stem" phase rather than "need a new cylinder but didn't yet become a semi powered glider" phase ?  

I have almost 600 hrs on the engine with no history of a wobble test having been performed per the books.  I'm thinking about just doing it with my IA at next annual but wanted to hear what the group consensus is. 

The two things I have the least confidence on a Mooney are the mags (if slick) and the lycoming valve train.   

[cnoe]

A few of us here have experience with this. I am one of them.

My great-running 600 hour IO360 experienced a brief episode of morning sickness on a cool morning departure from Durango in September. It ran rough for 30 seconds with the #2 cylinder's EGT dropping out during that time. It cleared up immediately and didn't show any further symptoms after returning back to the hot Texas coast. Still I'm a pro-active sort of flyer and after running the data by Savvy (I pay for their service) they confirmed my suspicion. I immediately began a search for a shop who is experienced in Lycoming on-plane valve-guide reaming. Let me tell you, there are LOTS of mechanics who won't do this and/or know nothing about it (even popular, well-known mechanics).

We ended up doing the wobble test on all 4 cylinders and I decided to go ahead and ream all 4 at the same time though truly only #2 was below spec. We also pulled all the stems up through the spark plug holes and polished them with scotchbrite. I haven't had any hint of a problem since and I feel much better knowing that this work was done.

Now I don't think the wobble test is warranted for checking too MUCH clearance as the newer guides are really tough and I haven't heard of this being a problem. I also doubt I'd routinely do a wobble test every 500 hours without seeing any prior symptoms. I'm no expert but I believe that if you're attentive you would notice a problem with a sticky valve before you run the risk of catastrophic failure in flight, but that is JUST MY OPINION. The key IMO is to NOT IGNORE the onset of morning sickness.

Having been through it I would still consider the whole operation to be somewhat invasive making you more prone to a MIF. The hydraulic tappets have to be removed and bled, the pushrod tubes removed and resealed, and valve cover leaks can occur just to name a few things. Also, on planes with the rear-mounted oil cooler, it must be removed partially along with some baffling in order to get the #4 rocker shaft out. It's a bigger job than what you might expect.

I may do a write-up on the job sometime when I'm not so busy but will post a couple of pics here as a teaser. One more thing, I don't believe that SAVVY is going to catch a sticky valve that you yourself don't notice. I love their service but not for that reason.

[1964-M20E]

Talk about laparoscopy surgery.

[Mooneymite]

Of interest:

 

[Jsavage3]

In the "Modern Mooney Discussion," do a search for...Sticky Valve_Lycoming IO-360-A3B6D. It's a very lenthy thread with a lot of pertinent information.

Good luck!!

Edited October 22, 2016 by Jsavage3

[MHemperly]

16 hours ago, cnoe said:

A few of us here have experience with this. I am one of them.

My great-running 600 hour IO360 experienced a brief episode of morning sickness on a cool morning departure from Durango in September. It ran rough for 30 seconds with the #2 cylinder's EGT dropping out during that time. It cleared up immediately and didn't show any further symptoms after returning back to the hot Texas coast. Still I'm a pro-active sort of flyer and after running the data by Savvy (I pay for their service) they confirmed my suspicion. I immediately began a search for a shop who is experienced in Lycoming on-plane valve-guide reaming. Let me tell you, there are LOTS of mechanics who won't do this and/or know nothing about it (even popular, well-known mechanics).

We ended up doing the wobble test on all 4 cylinders and I decided to go ahead and ream all 4 at the same time though truly only #2 was below spec. We also pulled all the stems up through the spark plug holes and polished them with scotchbrite. I haven't had any hint of a problem since and I feel much better knowing that this work was done.

Now I don't think the wobble test is warranted for checking too MUCH clearance as the newer guides are really tough and I haven't heard of this being a problem. I also doubt I'd routinely do a wobble test every 500 hours without seeing any prior symptoms. I'm no expert but I believe that if you're attentive you would notice a problem with a sticky valve before you run the risk of catastrophic failure in flight, but that is JUST MY OPINION. The key IMO is to NOT IGNORE the onset of morning sickness.

Having been through it I would still consider the whole operation to be somewhat invasive making you more prone to a MIF. The hydraulic tappets have to be removed and bled, the pushrod tubes removed and resealed, and valve cover leaks can occur just to name a few things. Also, on planes with the rear-mounted oil cooler, it must be removed partially along with some baffling in order to get the #4 rocker shaft out. It's a bigger job than what you might expect.

I may do a write-up on the job sometime when I'm not so busy but will post a couple of pics here as a teaser. One more thing, I don't believe that SAVVY is going to catch a sticky valve that you yourself don't notice. I love their service but not for that reason.

What shop did the job for you? How much did they charge? 

Mike

[Yetti]

So I helped ream 2 cylinders and did not think it that invasive, just a step above cleaning spark plugs.   I am trying to figure the need to pull the rods and bleed the tappets other than measuring clearance.  Even that is simple to do.  If you have silicone gaskets, there should not be leaking from the covers.  I would say it is a 2 person job to get the valves back into the holes, and getting the keepers back on.  We used 2 springy grabber things through the spark plug holes.  It took about an hour for 2 cylinders.  everything is pretty accessible. Not sure why competent AP would not be able to carry out a Lycoming SB

[DonMuncy]

On ‎10‎/‎22‎/‎2016 at 8:01 AM, Yetti said:

So I helped ream 2 cylinders and did not think it that invasive, just a step above cleaning spark plugs.   I am trying to figure the need to pull the rods and bleed the tappets other than measuring clearance.  Even that is simple to do.  If you have silicone gaskets, there should not be leaking from the covers.  I would say it is a 2 person job to get the valves back into the holes, and getting the keepers back on.  We used 2 springy grabber things through the spark plug holes.  It took about an hour for 2 cylinders.  everything is pretty accessible. Not sure why competent AP would not be able to carry out a Lycoming SB

It appears pretty obvious that to get the valve stem out through the spark plug hole, you first must push it down into the cylinder. Then I can see how you can fish in there and get it up through the spark plug hole. But how do you then get it back into the valve guide hole.

[cnoe]

On 10/22/2016 at 8:01 AM, Yetti said:

So I helped ream 2 cylinders and did not think it that invasive, just a step above cleaning spark plugs.   I am trying to figure the need to pull the rods and bleed the tappets other than measuring clearance.  Even that is simple to do.  If you have silicone gaskets, there should not be leaking from the covers.  I would say it is a 2 person job to get the valves back into the holes, and getting the keepers back on.  We used 2 springy grabber things through the spark plug holes.  It took about an hour for 2 cylinders.  everything is pretty accessible. Not sure why competent AP would not be able to carry out a Lycoming SB

"Invasive" may not be the proper term but if you follow the prescribed procedure as outlined in Lycoming Service Bulletin 388C it is a fair amount of work. I entirely agree that a competent A&P would be able to perform the work but I can't imagine how you could complete the required steps in one hour, even for just one cylinder.

The SB states "4. All Engines:  Remove push rods, shroud tubes and hydraulic tappet assemblies. Disassemble tappet and clean as described in the applicable overhaul manual" as part of the procedure. As it was explained to me the hydraulic tappet assemblies may accumulate and retain oil as the crankshaft is rotated to allow clearance for removing the valves and reaming the guides. Lycoming also states "Any disassembly of the valve train must be followed by removal of all oil from the hydraulic lifters prior to reassembly" which can be accomplished by inserting a small brass rod into the lifter to unseat the check valve ball. Doing this allows one to reinstall the rocker arm without any issues. I guess one could compress the valve instead (to install the rocker arm) but there may be some risk of damaging a dislodged lifter using this technique. We simply followed the detailed instructions in the SB.

Regarding the amount of time required to do the operation in accordance with the SB (at a minimum) the following steps must be taken:

Remover upper and lower cowlings, remove ignition leads, remove spark plug, remove valve cover, remove rocker shaft cover, compress valve spring (requires special tools), remove valve keepers and rotator cap, remove rocker shaft, remove rocker arm, remove push rod, remove push rod shroud tube, remove hydraulic lifter, clean/inspect/test hydraulic lifter (IAW Lycoming Service Instruction 1011K), remove valve springs and retainer, set up fixture for measuring wobble, measure wobble, push valve into cylinder, fish valve stem out of spark plug hole, clean/polish valve stem, ream valve guide (as needed), flush and clean guide of contaminants, fish valve stem back into guide. At this point you will need to scrape/clean the old rocker shaft cover gasket material prior to reinstalling everything in reverse order of above. Anybody who can perform the entire procedure in than an hour or two per cylinder should be revered.

I should also add that on angle valve cylinders for those who have the rear-mounted oil cooler you should add a couple of more hours minimum to complete this work on cylinder #4. In addition to all the steps above you must also remove the engine baffling at the rear of that cylinder which means removing the retaining springs underneath the cylinders as well as the oil cooler itself (hoses remain attached).

IMO to complete this job on all four cylinders (including reaming guides and cleaning valve stems) a reasonable time allotment would be 10-12 hours. In my instance it took even longer than this. An A&P that is very experienced in this specific procedure may be able to do it in less time but I can't imagine anybody doing all this in a few hours. YMMV.

And in answer to the question about the shop and cost, the work was supervised by a local A&P who was paid for supervision only. The mechanic was not personally experienced in the procedure, and none of the other shops I contacted were familiar with the procedure either, even shops recommended by SAVVY.

[Yetti]

We skipped the wobble test, probably saved an hour there. No need to when the valve was all froze up and we had to beat it out with a punch and hammer. Also the valve cover seals had already been scraped off and replaced with silicone seal.

To get the valve back into the guide, we used two of these.  http://www.homedepot.com/p/GrabEasy-Grabber-and-Retriever-PF0401/202505170

One grabber in the top spark plug hole one in the bottom. And lots of finesse.  Have seen some people suggest dental floss tied to the valve, which will go into one of the flutes of the reamer.

for spring compression we used a breakdown version of this, http://www.pilotshop.com/catalog/topages/compressor.php?utm_source=google&utm_medium=cse&utm_term=12-00202&gclid=CjwKEAjwv7HABRCSxfrjkJPnrWgSJAA45qA2RaTYSfEZyz-shXPtKY_4zzYUSOMbH8x3O9Gg260VBBoCidTw_wcB

We put two cylinders on and reamed the other two went and had lunch.  Put the plane back together in the afternoon. 

two people really helped the process move along.

 

 

 

[cnoe]

It appears pretty obvious that to get the valve stem out through the spark plug hole, you first must push it down into the cylinder. Then I can see how you can fish in there and get it up through the spark plug hole. But how do you then get it back into the valve guide hole.

Don, we had good success using a magnetic pick-up tool thru the guide (to line up and pull the valve) and a bent-wire hook thru the spark plug hole (to hold the valve level). This was described in a couple of online postings elsewhere. With a little practice it becomes easier.

We had mechanical fingers too but that seemed harder than the magnet and hook technique. I talked to someone who used floss but it still has to be lined up and the floss must clear between the tip of the valve and the guide. I'm told you can tie it to the valve as it sticks out the plug hole then use a vacuum to suck the free end out the guide hole to pull on.


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[DonMuncy]

Thanks for the information. If your magnetic tool is smaller than the diameter of the valve stem and the guide was reamed nicely, I suspect that would work out pretty well. I didn't see how a fingered tool, or even floss would clear the guide.

[cnoe]

Thanks for the information. If your magnetic tool is smaller than the diameter of the valve stem and the guide was reamed nicely, I suspect that would work out pretty well. I didn't see how a fingered tool, or even floss would clear the guide.

Lycoming specified the magnet tool and mechanical fingers in the SB. We found the fingers more difficult to manipulate than a simple stiff wire hook lowered through the upper plug hole which actually worked quite well with the magnet. Shining a bright light into the bottom plug hole allows you to sight down the open guide to get the valve stem properly lined up.

Dropping the exhaust and working through the open ports would make it even easier but that's more work that we didn't find necessary.


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[Wes Peters]

On the Robinson R44 helicopters we do the valve clearance check every 300 hrs . We used to run Aeroshell 15W50 and we always had issues with exhaust guides being to tight. We switched to Aeroshell W80 and now its a rare thing to have a tight valve . R44's run " full rich" always so that contributes to the problem . Also new Lycoming cylinders are not within the 388 specification 0f 0.015" - 0.030" wiggle clearance !! The new cylinder clearance is about 0.012". They must be reamed/honed to bring it into tolerance . Meny of the stuck valve issues were on new cylinders that had not been reamed. We set the wiggle to 0.017" and have had no issues. We use a 1/2" flex hone to clean/ enlarge the guide . The company I work for runs ten R44s.

[carusoam]

Welcome aboard Wes!

Great tech details you got there.

Best regards,

-a-

[Planegary]

when i have had to do the morning sickness repair in smaller continentals i tied a piece of dental floss to the corrugations on the valve to make it easier to get the valve back into alignment with the valve guide. always worked easily and the floss can be fished thru the guide with a pait od flexible grabbers after the reaming is done but what do i know i am not a professional mechanic so take everything i say with a grain of salt