M20J GAMI spread issue (flow divider?)

[PT20J]

If the engine is running well, why mess with it until you have to? New and overhauled engines can have infant mortality, so you may or may not get better reliability. 

I recently replaced a A3B6D (broken oil control ring took out piston skirt and cam was spalling) with a factory rebuilt A3B6 after duscussions with Lycoming and mag overhaulers. Roller tappets are clearly a design improvement worth the extra cost to me. Dual mags are reliable in my experience, but are no longer made, some parts are hard to get and fewer mag shops will work on them. There are numerous internal differences between A3B6D and A3B6 which has more parts commonality with other engines. The A3B6D will likely end up being more expensive to maintain as time goes by. Lycoming will give you a break to retire a A3B6D core which says something (to me) about its commitment to that engine.

Lycoming has standardized timing at 20 deg on 360 series engines with the exception of the dual mag engines for many years. Some think this is a big deal, some not so much. I don’t want to open that can if worms, but personslly I haven’t noticed much difference. 

Hope that helps.

Still really currious about the injector lines. I think the newer lines are just thicker walled for fatigue resistance and have the same ID, but I’m really interested to know for sure. And, even if the ID is different, it would be interesting to see if that affects the flow rate through the nozzles since the tubing is so much larger than the nozzle orifice.

Skip

 

[Shadrach]

Eight years ago we had a case crack on an engine with 855SMOH. At that time I was very active on the AOPA forum (Red Board). Many folks told me that it was best to just overhaul (what’s $30K to remedy a case crack right?). At the time I had just punched out of a corporate banking position with a nice severance due to a merger. I elected to remove and reinstall the engine myself and utilized a “local” Engine shop about 50 miles away to do the engine work. I learned quite a bit during that endeavor that may be applicable to your situation:

1) There is a tendency in aviation for mission creep towards “while you’re in there” kinds of items without knowledge of the actual condition of those items.

2)  The relative ease with which a case can be split once the engine is off the aircraft. I dropped my engine off at the engine shop around 11:00 AM sans accessories. The case was crated and on its way to Tulsa that afternoon.

3) Owners have a tendency overstate the paper advantage of an overhaul. Some buyers want something run out so they can choose where to rebuild it. Some like to see “Factory zero time”. If you have no reason to sell the plane, the best value is typically to simply correct the problem and get back in the air.  It’s only when you find an engine with multiple issues that an overhaul starts to become a better value. You’re doing a lot of hemming and hawing (just like I did) over what if’s before you really know what you have on your hands. I was terrified that we’d open up my engine and find corroded lifters and a spalled cam. We didn’t, internals were beautiful at 10 yrs and 800hrs. At the end of the day the IRAN with crankcase overhaul and going over the cylinders was about $4000. Engine was returned to me painted and wrapped just like an overhaul. My local IA charged $500 to supervise my reinstallation. If I had paid someone could’ve been closer to 3k to R&R the engine

I was really close to overhauling. At the time I was out of work but has been given a check for more than a year’s salary.  I had both time and money but I’m glad I chose the route I did. I’ve put 400 hours on the engine since and it’s running beautifully. 

Do you have an engine shop close by? This endeavor sounds best suited to a shop that will advise you as more info is garnered. Lycoming won’t give a core credit on anything if the case is split  (must be in running condition).

For what it’s worth, 1 quart every 6 to 7 hours is perfectly acceptable and healthy oil consumption.  

Pull the jug and take a look.

[jkarch]

So the issue is, a few days ago I took my last oil filter, which when visually inspected, did have just a few flecks of metal in it, and swiped a mechanic's magnet through each and every rung of the filter.  I did find finely ground magnetic material attaching to the magnet.  It wasn't much, sum total much smaller than a third of a grain of rice, grayish in color, with one shiny.  I saw photos of this in another forum, where someone else installed a magnetic pickup in the drain plug and got their answer more quickly.   I immediately connected this to cam steel.  I have access to mass spectroscopy at work, so I may bring my sample in to see what its composition is.  I know the recommendation from lycoming is change the oil, filter, and check the screen and filter, then recheck in 10 hours, but because of the 75F difference in peaks between 1&2 and 3&4, even if the tubes may be responsible for some of the spread, the engine has started making metal, and while it could be other things, the cam is definitely suspect as part of the issues.  I've had this issue for many years now, however-- who knows if I've been flying with a wiped cam all along and didn't know it, or if it's just starting to make metal.  It does run amazingly well, and I've had no jug issues.   I'll know more when I check the sample that has 40ish hours on it tomorrow and the screen.  Something tells me there will be more.  How much more I don't know, and while lycoming has specific guidance about knowing when to say when, I don't know if I have personally the same tolerance.  However, paying $500 to pull a jug when the metal in the oil filter is giving clues seems like another $500 I could pay on a monthly payment for a factory rebuilt engine, or for engine removal costs.  The valve lift test is something that seems easier and less invasive to do, and seeing 10 thousandths difference between the front and back intake lobes will answer that question.

[Shadrach]

4 hours ago, jkarch said:

So the issue is, a few days ago I took my last oil filter, which when visually inspected, did have just a few flecks of metal in it, and swiped a mechanic's magnet through each and every rung of the filter.  I did find finely ground magnetic material attaching to the magnet.  It wasn't much, sum total much smaller than a third of a grain of rice, grayish in color, with one shiny.  I saw photos of this in another forum, where someone else installed a magnetic pickup in the drain plug and got their answer more quickly.   I immediately connected this to cam steel.  I have access to mass spectroscopy at work, so I may bring my sample in to see what its composition is.  I know the recommendation from lycoming is change the oil, filter, and check the screen and filter, then recheck in 10 hours, but because of the 75F difference in peaks between 1&2 and 3&4, even if the tubes may be responsible for some of the spread, the engine has started making metal, and while it could be other things, the cam is definitely suspect as part of the issues.  I've had this issue for many years now, however-- who knows if I've been flying with a wiped cam all along and didn't know it, or if it's just starting to make metal.  It does run amazingly well, and I've had no jug issues.   I'll know more when I check the sample that has 40ish hours on it tomorrow and the screen.  Something tells me there will be more.  How much more I don't know, and while lycoming has specific guidance about knowing when to say when, I don't know if I have personally the same tolerance.  However, paying $500 to pull a jug when the metal in the oil filter is giving clues seems like another $500 I could pay on a monthly payment for a factory rebuilt engine, or for engine removal costs.  The valve lift test is something that seems easier and less invasive to do, and seeing 10 thousandths difference between the front and back intake lobes will answer that question.

What you describe is not a lot of metal.  Typically the lifters fail before the cam.  Lifters breakdown rapidly when they stop rotating.  The cam typically follows rather than leads the this type of failure.  I do not understand why you've not had the cam lift measured.  This should not be a major endeavor. A dial indicator and a few ours max for an experienced A&P.  This is the first thing I would do.

[jkarch]

So before moving forward with all new tubes, I wanted to ask about the cam.  Let’s say the problem is the cam.  What is preferable, IRAN or overhaul on an engine with 1200 SMOH and 14 years? This engine came from a 1978 J model and was overhauled in 2005 by LASAR.  The engine has the Ney Nozzle Mod.  Will Lycoming accept the “D” engine as a core if I switch to an IO360-A3B6? Are the new DLC tappets (via Zephyr overhaul) considered an alternative to roller tappets? So I guess this is the IRAN, factory overhaul or remanufactured versus Solid field overhaul by Zephyr question.  Compressions are all high 70s.

[jkarch]

So this is what I found in the last filter. I’ll see if I can get my mechanic tomorrow to measure lift while we drain the oil. Does this seem like a lot of ferrous material? This is from 30 hours.  -J

Edited January 11, 2019 by jkarch

[Shadrach]

18 minutes ago, jkarch said:

So this is what I found in the last filter. I’ll see if I can get my mechanic tomorrow to measure lift while we drain the oil. Does this seem like a lot of ferrous material? This is from 30 hours.  -J

As I said, not a lot of metal.  You're getting way ahead of yourself.  Check the valve lift...

[jkarch]

6 minutes ago, Shadrach said:

As I said, not a lot of metal.  You're getting way ahead of yourself.  Check the valve lift...

I’ll have my mechanic do that tomorrow. Is there a particular document we should use for the procedure? I asked him to grab a dial indicator. I’ll check this and the screen tomorrow when I do the oil change.  Isn’t any amount of magnetic material long past the initial break in a sign that a failure is within sight?

[Shadrach]

10 minutes ago, jkarch said:

I’ll have my mechanic do that tomorrow. Is there a particular document we should use for the procedure? I asked him to grab a dial indicator. I’ll check this and the screen tomorrow when I do the oil change.  Isn’t any amount of magnetic material long past the initial break in a sign that a failure is within sight?

My airplane has produced very little ferrous metal over the years.  I have several cars on the road that have shown way more metal then what's in your photo with no detrimental effects years after.  There could be an issue and the metal could be a symptom of the problem...or not.  It's not a good thing to have metal in your filter but it's not a "tear it down now" situation either. 

It's running well. Do the easy stuff first. 

[jkarch]

Much appreciated! I was checking the bank accounts to get ready and calling overhaul shops. Even if I’m 2-300 hours plus out it’s good to take stock.

[jkarch]

Well here’s an update. No surprise here. Started leaking oil out of front and rear cylinders.  So finally had no excuse but to pull the cylinder I expected was a victim of a bad cam.  Engine still ran great other than the annoying egt indications. But when front cylinder was pulled the answer was clear. Yup, John Paul nailed it. The damn cam and lifters.  Time for a reman. -Josh 

[carusoam]

Great picture, Josh!

I believe that part is called the cam follower... because that is what it does... it is the business end of the valve lifter...

It Will look like the lunar surface, with craters on it...

Corrosion usually causes the craters... the craters in turn carve through the hardened surface of the cam lobe...

 

When the parts come out, See if you can get a good pic of the cam follower surfaces...

 

PP thoughts only, not a mechanic...

Best regards,

-a-

 

 

[jkarch]

What’s rather strange is what precipitated the cylinder pull. It wasn’t related to the cam. Oil was weeping out of the cylinder to crankcase seal on front #2 and rear #3. I will be getting a factory rebuilt from AirPower so I probably won’t know what becomes of this single dual mag engine ... even better, the roller tappets will preempt this from causing overhaul in the future, and I will have a dual mag setup. I may even be able to eventually go 50 hours between oil changes now, as I usually do 28 between changes. While the new fuel lines actually smoothed out engine operation, it did not fix the GAMI spread too. Exhaust lobe looked good comparatively. Just as expected and predicted! And just prior compressions were all in the 70s so exhaust lobes were likely ok.

Edited June 9, 2019 by jkarch

[Shadrach]

7 hours ago, jkarch said:

What’s rather strange is what precipitated the cylinder pull. It wasn’t related to the cam. Oil was weeping out of the cylinder to crankcase seal on front #2 and rear #3. I will be getting a factory rebuilt from AirPower so I probably won’t know what becomes of this single dual mag engine ... even better, the roller tappets will preempt this from causing overhaul in the future, and I will have a dual mag setup. I may even be able to eventually go 50 hours between oil changes now, as I usually do 28 between changes. While the new fuel lines actually smoothed out engine operation, it did not fix the GAMI spread too. Exhaust lobe looked good comparatively. Just as expected and predicted! And just prior compressions were all in the 70s so exhaust lobes were likely ok.

It usually starts with a follower and progresses.

[jkarch]

So now that the dirty deed is done, what should be redone along with the remanufacture? New vacuum pump, prop governor overhaul(or IRAN), and prop reseal and new mounts? I assume it makes sense to clean the gunk out of the prop and governor.

[ArtVandelay]

Well here’s an update. No surprise here. Started leaking oil out of front and rear cylinders.  So finally had no excuse but to pull the cylinder I expected was a victim of a bad cam.  Engine still ran great other than the annoying egt indications. But when front cylinder was pulled the answer was clear. Yup, John Paul nailed it. The damn cam and lifters.  Time for a reman. -Josh 

 

#1&2 cylinders intake lobe?

 

 

Tom

[jkarch]

12 minutes ago, ArtVandelay said:

 

#1&2 cylinders intake lobe?

 

 

Tom

Yup, looks pretty worn down. 1&2.  I wonder if I would get back a few kts with the new engine. I have been slowly going down to about 150 kts over a long time. It was closer to 154-155 when I got it although the cause may be related to sitting for five months outside before I bought it, or when removed from service for avionics upgrade which took six weeks about 4 years ago. 

[jkarch]

I’ll start a new thread on the “what next” section. I know there are some mods to upgrade to the true dual mag version with roller tappets.

[mike_elliott]

11 hours ago, carusoam said:

Corrosion usually causes the craters... the craters in turn carve through the hardened surface of the cam lobe

That is certainly the party line of Lycoming's legal dept. but yet they have the DHC tappets now to solve the problem ,. Oh, and a roller tappet engine to solve cam corrosion . There back is turned on the lubrication design or metallurgy because, well, it just can be that, now can it?

[jkarch]

1 minute ago, mike_elliott said:

That is certainly the party line of Lycoming's legal dept. but yet they have the DHC tappets now to solve the problem ,. Oh, and a roller tappet engine to solve cam corrosion . There back is turned on the lubrication design or metallurgy because, well, it just can be that, now can it?

Question is, what's better, roller tappets, or Diamond coated flat ones?  I guess for me the other biggie is no more D2000 mag which was expensive to overhaul a couple of times.

[mike_elliott]

The Roller tappets make sense, other than the mandatory replace of $ame anytime you have the case opened. They are priced to keep Lycoming profitable for a long time. The DHC (with a cam that doesnt suffer "corrosion " issue metallurgy) have had lasting results in the field.

The centrilube STC has some "followers" that might be worth looking at in conjunction with the DHC. Scott Sellmeyer may be able to opine with authority here.

 

[jkarch]

9 minutes ago, mike_elliott said:

The Roller tappets make sense, other than the mandatory replace of $ame anytime you have the case opened. They are priced to keep Lycoming profitable for a long time. The DHC (with a cam that doesnt suffer "corrosion " issue metallurgy) have had lasting results in the field.

The centrilube STC has some "followers" that might be worth looking at in conjunction with the DHC. Scott Sellmeyer may be able to opine with authority here.

 

My other concern is what might be causing oil to leak through the through bolts, that might imply issues with the case as a simple press fit keeps oil out.  At this point, I'd rather just divest myself of this engine.  But I have heard that's a silly thing as the roller tappets taken out of a sudden stoppage engine looked okay and they still had to replace.  I'm not sure what that's all about, though I've never so much as removed a cylinder in 800 hours since buying the plane.

Edited June 9, 2019 by jkarch

[ArtVandelay]

Yup, looks pretty worn down. 1&2.  I wonder if I would get back a few kts with the new engine. I have been slowly going down to about 150 kts over a long time. It was closer to 154-155 when I got it although the cause may be related to sitting for five months outside before I bought it, or when removed from service for avionics upgrade which took six weeks about 4 years ago. 

Yep, as I said in post #6, I had same issues with the cam. My oil leak was because of a crack in the case, if I had known I would have considered a factory reman.


Tom

[mike_elliott]

27 minutes ago, ArtVandelay said:

My oil leak was because of a crack in the case, if I had known I would have considered a factory reman.

I think this might preclude using your existing engine as exchange core from what I have heard.

[ArtVandelay]

1 minute ago, mike_elliott said:

I think this might preclude using your existing engine as exchange core from what I have heard.

Oh, I didn’t know that, I thought if it ran, it was good. PO had already upgraded to A3B6, so there wasn’t a big incentive for me to go factory at the time. It went 2200+ hours without roller tappets.