walkman

walkman

Well Known Member
Today in an attempt to diagnose some potential morning sickness I started the old rope trick on my O-360-A1F6D.

Got the #4 checked out. Smooth as silk, just perceptible play, valve face looks gorgeous.

However, when I came to reassemble I was unable to get the rocker aligned to get the rocker arm pushed in enough to get the pin through. It was like my push rod grew. Yes, piston is in the right position. Both valves definitely closed. I removed the pushrod tube and fished out the tappet, cleaned, put back in. Same problem.

Any ideas? I'm loath to start the engine with no clearance. Am I being stupid? What is up with my magically growing push rod?
 
It sounds like the tappets/cam followers are full of oil, not collapsed. Try pushing as hard as you can on the pushrods, for several minutes. See if they don't 'shrink'. You must not let up the pressure while you re-install the rocker arm, or the tappets will expand and fill up with oil again.

I didn't think the tappets were removeable, except on the H engine???
 
Remove the hydraulic lifters, disassemble, clean out the old oil, reassemble and install, then check valve lash. See Lyc overhaul manual and various Lyc letters and documents for more info.
 
I wouldn't take the lifters out, just borrow a valve spring compressor if you can. But if you cant find a valve spring compressor you can take the lifter bodies out with a bent piece of safety wire. To make the lifters leak down before disassembly I always bring a valve open and leave it there for 2-3 mins, then do the same to the other valve. Enough leakdown occurs to get the rockers and pins off easily.
 
... I ... fished out the tappet, cleaned, put back in....
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See image from overhaul manual (below). If all you pulled out was a single piece, then it is likely #2 and you didn't get the actual hydraulic lifter plunger assembly (the plunger body and spring).

A couple of things -

When reassembling the pushrod socket (#2), if you put this in backwards you'll have exactly the problem you describe - worth checking out.

When pulling the plunger body and spring - don't drop them and be sure to keep the parts together - don't mix them. (To remove them, use a piece of safety wire with a hook on the end - don't use a magnet.)

To get a good indication of the go/no-go clearance, I'd probably pull the plunger assemblies and clean them up.

kf1j6f.jpg


Dan
 
I agree with Dan, if you put the socket in backward(easily done) then the pushrod will appear long as you describe.
 
Not tappet

Or Lifter body. Misspoke. Push rod socket only. Lifter body would not clear the metal cap on the casting where the push rod tube fits. Removed socket, cleaned, and put back in correct orientation.

I did not realize the lifter could re-expand afterwards. Perhaps that is all I am seeing. Engine had not run in weeks, I assumed they would be completely collapsed.

Are pushrods different end to end? Looked identical to me although I'm pretty sure I did retain orientation.

Btw, strong recommend on Valve Wizard from Jolly Time Tools. Much better than traditional valve spring compressor.
 
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The hydraulic lifters need to be bled before you can reassemble the rockers. If you just use the brute force method (rocketbob), the valves might be held off their seats for a while after engine start, with that cylinder misfiring until then.

What happens when the pushrod is removed is, the plunger spring (#3 in Dan's pic) expands the lifter and fills the rest of its travel with oil, making the lifter a now-full-length rigid block.

The proper way to do this is remove the pushrods and shroud tubes, then using a piece of safety wire bent into a small hook, pull out the pushrod sockets and then the hydraulic lifters. Use a toothpick and depress the ball check valve (#10) and simultaneously collapse the spring-loaded plunger on the opposite end. The oil in the lifter will squirt out. Then, reassemble everything. The lifters will refill with oil in a few seconds after engine start.
 
hgerhardt said:
The proper way to do this is remove the pushrods and shroud tubes, then using a piece of safety wire bent into a small hook, pull out the pushrod sockets and then the hydraulic lifters. Use a toothpick and depress the ball check valve (#10) and simultaneously collapse the spring-loaded plunger on the opposite end. The oil in the lifter will squirt out. Then, reassemble everything. The lifters will refill with oil in a few seconds after engine start.
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I agree with the above procedure, this is way I was taught and has always been the way I've done it.
 
If you have a valve spring compressor I'd follow RocketBob's method, it's a lot less work. The valves will not be held open during the next start. The lifters on any open valve will bleed down in the time it takes to screw the valve cover back on.
 
walkman said:
Got the #4 checked out. Smooth as silk, just perceptible play, valve face looks gorgeous.
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Your comment above is tangential to the thread topic, but since it's in the original post, maybe worth a response.

I just went through this a couple of months ago. Factory-new Superior XP-IO360. Had what I realized in hindsight were classic morning sickness symptoms on #2. Several people told me it couldn't be, since the engine was barely broken in. I'm new to air-cooled aircraft engines, but not engines in general, so I was inclined to agree. Eventually ran out of other explanations. #2 exhaust looked clean, moved smoothly, but a local veteran mechanic wiggled the stem and declared it too tight. I bought the low-budget version of the checking fixture that Aircraft Spruce sells and checked the end play per Lycoming SB-388C. The inexpensive fixture requires a valve spring compressor, unlike the factory version, but I had bought one of those already since I figured on having to ream the valve. The measured play was .013"- outside the lower limit. Now to me, .013" feels like a LOT of play. Hard to imagine a valve that's at, say, .025" (but still in spec). I reamed the guide, which brought it to .015". At the hairy edge of the spec- but noticeably sloppier- and the problem disappeared.

Long story short: just because it's smooth, appears clean and has barely perceptible play, don't assume it's ok.
 
Lars said:
Your comment above is tangential to the thread topic, but since it's in the original post, maybe worth a response.

I just went through this a couple of months ago. Factory-new Superior XP-IO360. Had what I realized in hindsight were classic morning sickness symptoms on #2. Several people told me it couldn't be, since the engine was barely broken in. I'm new to air-cooled aircraft engines, but not engines in general, so I was inclined to agree. Eventually ran out of other explanations. #2 exhaust looked clean, moved smoothly, but a local veteran mechanic wiggled the stem and declared it too tight. I bought the low-budget version of the checking fixture that Aircraft Spruce sells and checked the end play per Lycoming SB-388C. The inexpensive fixture requires a valve spring compressor, unlike the factory version, but I had bought one of those already since I figured on having to ream the valve. The measured play was .013"- outside the lower limit. Now to me, .013" feels like a LOT of play. Hard to imagine a valve that's at, say, .025" (but still in spec). I reamed the guide, which brought it to .015". At the hairy edge of the spec- but noticeably sloppier- and the problem disappeared.

Long story short: just because it's smooth, appears clean and has barely perceptible play, don't assume it's ok.
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Thanks Lars.

I have a dial gauge so I may just fab up a fixture to check it properly. Or I may just ream anyway.
 
Question for Rocket Bob

Bob

Can you explain how compressing the valve springs solves this problem?

What I am wondering is whether this works both ways. What I mean is does the oil drain back out of the lifter body if there is too much in it by unloading the pushrod. Would it not just self level if the engine were turned over?
 
WAM120RV said:
Bob

Can you explain how compressing the valve springs solves this problem?

What I am wondering is whether this works both ways. What I mean is does the oil drain back out of the lifter body if there is too much in it by unloading the pushrod. Would it not just self level if the engine were turned over?
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When one compresses the springs, the valves open and thus the rocker pin can move freely regardless of the lifters being pumped up. I really never do things this way. Like I mentioned previously I turn the prop to bring a valve open and leave it there for a couple of minutes, then turn the prop again to bring the other valve open. Then turn the prop where both valves are closed. This causes a small amount of lifter bleed down, sufficient enough to easily push the rocker pin thru by hand. To me taking the pushrods out, lifters out, etc. is just additional work with no benefit.
 
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I was taught it is good practice anytime doing cylinder work to remove the lifter and check it. In fact I was told it is "standard procedure".

I think it is important for all of us to remember with these public forums that there are various levels of skill and experience here. Just like the filter inspection thread a while back. Why take a short cut unless your making a living out of it and know what your doing, expecially something that takes so little time.
 
Why take a short cut unless your making a living out of it and know what your doing, expecially something that takes so little time.
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Because you open yourself to more screwup opportunities. You may drop the lifter in the dirt, get the socket on backwards, mix up the lifters, screw up the pushrod shroud seals, drop a gob of grit in the tappet, knock the skin off your knuckles on the fins, break the aforementioned toothpick off in the lifter check valve, all kinds of fun stuff.
 
aerhed said:
Because you open yourself to more screwup opportunities. You may drop the lifter in the dirt, get the socket on backwards, mix up the lifters, screw up the pushrod shroud seals, drop a gob of grit in the tappet, knock the skin off your knuckles on the fins, break the aforementioned toothpick off in the lifter check valve, all kinds of fun stuff.
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yep, exactly!!
 
aerhed said:
Because you open yourself to more screwup opportunities. You may drop the lifter in the dirt, get the socket on backwards, mix up the lifters, screw up the pushrod shroud seals, drop a gob of grit in the tappet, knock the skin off your knuckles on the fins, break the aforementioned toothpick off in the lifter check valve, all kinds of fun stuff.
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Good points, but what if the problem is the lifter. I am the novice here so I will bow out and leave it to the experts.
 
JonJay said:
I was taught it is good practice anytime doing cylinder work to remove the lifter and check it. In fact I was told it is "standard procedure".

I think it is important for all of us to remember with these public forums that there are various levels of skill and experience here. Just like the filter inspection thread a while back. Why take a short cut unless your making a living out of it and know what your doing, expecially something that takes so little time.
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Not only good practise, but actually required by the Lycoming SB 388C, aka Valve Wobble Test, so yes, I would call it a "standard procedure".

See page 2 -

http://www.caa.si/fileadmin/user_upload/pageuploads/AD-NOTE/AD-2006/093_sb_SB388C.pdf
 
Well I think SB388C overall is a complete waste of time, but thats besides the point of this thread. Anyone that has worked on enough Lycoming stud assemblies will know that just about every engine will not pass the wobble test with a couple hundred hours on them in perfectly good working order.
 
rocketbob said:
Well I think SB388C overall is a complete waste of time, but thats besides the point of this thread. Anyone that has worked on enough Lycoming stud assemblies will know that just about every engine will not pass the wobble test with a couple hundred hours on them in perfectly good working order.
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That is the problem Bob, many of us have not had your kind of experience, but are mechanically inclined enough, have the interest, and wish to venture into it. No offense to aerhed, but if you are concerned about messing things up even further you shouldn't take off the valve cover. This is where having some kind of standard procedure for the work we do becomes important to guys like me.
Sorry for the thread drift, but for me, short cuts are just ways for me to miss something important, perhaps a partially blocked orrifice or sticking lifter body, I don't know, if I did know, I probably would know to take the short cut.:)
 
First, do no harm...

I think the point is that even an experienced mechanic thinks he is more likely to create a problem than find one by digging down into the lifter bodies, so why go there when there is no reason to suspect a problem?
 
No offense to aerhed, but if you are concerned about messing things up even further you shouldn't take off the valve cover.
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I posted all those bad things from memory. They've all happened to me. Those particular things no longer happen because now I know about them. New ones come along every day. If you're lucky, you get to repeat the operation and glean the benefit from the former screwup. Otherwise you just become an "expert" and write Lycoming Service Bulletins for a living.
 
BobTurner said:
I think the point is that even an experienced mechanic thinks he is more likely to create a problem than find one by digging down into the lifter bodies, so why go there when there is no reason to suspect a problem?
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I understand Bob and I certainly respect that. I follow the same dont't fix if it aint broke philosophy when i know what i am doing. Not to flog the horse anymore, but have the lifters been ruled out or is that just highly unlikely they are the problem or a contributor to it? Personally, I found the lifter to be very easy to remove and check and I was directed by my engine builder to do so because according to him "you are supposed to". This is a prominent builder with hundreds of engines in RV's. I will listen to him as I have the total experience of doing this on one aircraft engine cylinder so I accept the fact that I don't know what I am talking about, but I will do it again if he tells me too. If Rocket Bob or Aerhed where in my hangar, I would listen to them too.
 
rocketbob said:
Well I think SB388C overall is a complete waste of time, but thats besides the point of this thread. Anyone that has worked on enough Lycoming stud assemblies will know that just about every engine will not pass the wobble test with a couple hundred hours on them in perfectly good working order.
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OK, so what is the criteria for a too loose or too tight valve?

How wobbly is OK?
 
Actually just kidding. I don't know what optimum would be, but it sure doesn't hurt to go by new limits on guides and stems instead of the wobble check.
 
aerhed said:
Actually just kidding. I don't know what optimum would be, but it sure doesn't hurt to go by new limits on guides and stems instead of the wobble check.
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...but to measure accurately - to 0.0005 inch or so - a worn bore that may not still be round is pretty difficult. The stem of the valve probably will also not be worn evenly at different distances from the head. New numbers are for new, not worn stuff that is still serviceable.

The wobble test gives an "effective" looseness/tightness of the valve in it's actual bore.

Waiting for the valve to stick or break is a little like determining max. torque by wrenching 'til it breaks and backing off a 1/4 turn...:D
 
rocketbob said:
Well I think SB388C overall is a complete waste of time, but thats besides the point of this thread. Anyone that has worked on enough Lycoming stud assemblies will know that just about every engine will not pass the wobble test with a couple hundred hours on them in perfectly good working order.
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My limited sample does not show that.

My Tiger engine failed 2 cylinders at 600 SFRM (Lyc. reman. with new cylinders) on the loose end.

Mine also had the newer, harder valve guides.

After that, we checked a few other Grummans and RVs with O-320s and O-360s around the area. All of the others with time varying from 200 to 2000+ TT passed.
 
High chrome guides are advertised to "solve the problem" but I've seen a few cases where the guides were worn out and were high chrome. There are several variables in the valvetrain geometry that I believe cause the guides to wear. They will all wear to the point of failing SB388 but the vast majority of guides wear so badly that the .035 wobble limit seems like nothing since most engines aren't checked. I've developed and have had manufactured my own adjustable roller rockers which hopefully make this problem go away entirely, at least on my engines.
 
az_gila said:
OK, so what is the criteria for a too loose or too tight valve?

How wobbly is OK?
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The original problem is not a "too loose or too tight valve" but an occasional momentary rpm drop out when at idle or close too it that is not related to ignition.

A sticky valve was an easy thing to check especially as it has been noted cold more than hot.

I have experienced it with a hot motor as well tho. Lifter is still in play as problem source afaiac.
 
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