Low Oil Pressure Running Rough

[DXB]

Cool thread- I love it when the mechanics post on here.  Even better when it's a case study on a particular plane known to them.   Way more to learn than when guys like me say stuff like "My cousin Erle once had somethin' like that happen,  and he poured in some pink stuff in there  - think it was Marvel Mystery Oil - cleared it right up.  Y'all should try it..."  

[Yetti]

One day when my father in law was in the ER, I started diagnosing people as they came in.  I was pretty accurate.   Basic IT problem solving of "What changed?"  Works on lots of things.   This one should get professional help.

[jclemens]

 

Well, we found the problem.  Cam lobe gone on the #2 exhaust valve :/  First pic is the bad lobe, second is a good lobe for comparison.  

[chrisk]

Thanks for sharing.   I know this really sucks for the OP, but its way better to find this out now.

 

[Guest]

I can't imagine that with that much of the lobe missing, there was no metal in the oil filter.

Clarence

Edited July 8, 2016 by M20Doc

[jclemens]

Haven't actually looked in the filter yet, it was clean a month ago.  There is some metal imbedded in the piston skirts.  I'll split the case Monday and take some more pictures.  They will get replaced during reassembly anyways though.  With a little over 850 hours on this run, the plan is to tear it down, clean it up, replace the cam and lifters with new, and reassemble with new bearings and gaskets.  Obviously if we find anything in the tear down that needs to be addressed we will fix that too.  Should be done in time for OshKosh.

Edited July 8, 2016 by jclemens

[jetdriven]

13 minutes ago, M20Doc said:

I can't imagine that with that much of the lobe missing, there was no metal in the oil filter.

Clarence

There is, and oil analysis will get it too.  It isnt usually the cam, it's h lifters tha spall then trash the cam. 

[jetdriven]

Just now, jclemens said:

Haven't actually looked in the filter yet, it was clean a month ago.  There is some metal imbedded in the piston skirts.  I'll split the case Monday and take some more pictures.  They will get replaced during reassembly anyways though.  With a little over 850 hours on this run, the plan is to tear it down, clean it up, replace the cam and lifters with new, and reassemble with new bearings and gaskets.  Obviously if we find anything in the tear down that needs to be addressed we will fix that too.  Should be done in time for OshKosh.

 

Just now, jclemens said:

Haven't actually looked in the filter yet, it was clean a month ago.  There is some metal imbedded in the piston skirts.  I'll split the case Monday and take some more pictures.  They will get replaced during reassembly anyways though.  With a little over 850 hours on this run, the plan is to tear it down, clean it up, replace the cam and lifters with new, and reassemble with new bearings and gaskets.  Obviously if we find anything in the tear down that needs to be addressed we will fix that too.  Should be done in time for OshKosh.

The governor will be killed, along with the usual flush of oil cooler, prop, hoses etc.  

[cnoe]

Are the views shown available by pulling only one jug?

Sent from my iPad using Tapatalk

[jclemens]

Yeah, you can see the cam follower face in the photo, it looks like the surface of the moon.  There is still a cylinder on that side, so the valve spring is hold it against the cam.  I'll take some better photos when I get it all apart on Monday (maybe Tuesday).  The governor will be fine, just needs to be flushed properly like everything else.  

[jclemens]

1 minute ago, cnoe said:

Are the views shown available by pulling only one jug?

Sent from my iPad using Tapatalk

Actually yes, they are taken through the hole where the #3 cylinder belongs.  Of course I pulled the #1 cylinder off first, you can't see the damaged lobe from there.  (Well with a borescope you can, but not easily)  

[takair]

Does Lycoming put out measurements such that you could measure how much the valve opens to determine cam wear?  In other words, could this determination be made without pulling a jug?  I know you wouldn't catch the beginnings of this, but this cam is near round....ok oblong.  It does seem that this would have been going on for some time.  Was this engine under oil analysis?

[Guest]

1 hour ago, takair said:

Does Lycoming put out measurements such that you could measure how much the valve opens to determine cam wear?  In other words, could this determination be made without pulling a jug?  I know you wouldn't catch the beginnings of this, but this cam is near round....ok oblong.  It does seem that this would have been going on for some time.  Was this engine under oil analysis?

There are no published limits that I've seen.  But if you compared the rocker arm lift to all of the others there would be an obvious difference.

Clarence

[ArtVandelay]

How would this affect EGTs, could an engine monitor diagnosed this, I assume at least pinpointed the cylinder?

[jclemens]

You can pull the valve covers and use a dial indicator.  I think the lift is .350 or something similar on all the lobes.  You don't really need to know the exact number, just compare them all, usually only one lobe goes, so that one will be a lot less than the others.  I find it to be just as easy and more definitive to pull two cylinders so I can look at everything.  No oil analysis on this engine.  

An engine monitor would have absolutely shown this.  EGT would have been low on the #2 cylinder during engine roughness (real low).  In cruise when the engine wasn't noticeably rough, The EGT would fluctuate, on a datalog graph it would show as a "jagged" line rather than a basically smooth one.  CHT would most likely be high due to improper exhaust scavenging.  You don't really need to know any of that, just know what your engine monitor is supposed to look like when everything is good, and if it ever looks any different, have it checked out.  

 

[carusoam]

JC great photos and explanation to go with them.

Thank you very much.

I used the photos to educate my children regarding cams and cam wear.  Fun stuff for the engineer house!

Best regards,

-a-

[Yetti]

I would be interested to know if the valves are sticking and that is what spalled the cam

[cliffy]

One of the best and definitive diagnosis I've ever seen. 

Nice write up!!!!

And in time for Oshkosh? WOW!

You wanna open a shop in my city? :-)

[jetdriven]

4 hours ago, jclemens said:

Yeah, you can see the cam follower face in the photo, it looks like the surface of the moon.  There is still a cylinder on that side, so the valve spring is hold it against the cam.  I'll take some better photos when I get it all apart on Monday (maybe Tuesday).  The governor will be fine, just needs to be flushed properly like everything else.  

I couldn't find z shop that would flush the governor. It's like the DG knob spring that breaks, once they open it up they pull the repair station thing, everything has to be new limits. And they pull out the service letters that have updated flyweights and pilot control valves. 4 grand later in some cases, you get your governor back. 

[Cwalsh7997]

I know a lot of people on this site, Jake at Daytona aircraft Service is highly recomended! Been with them over a year, and as a Mooney Service Center, they truly care about customer service and quality work, be sure to stop by!

[jclemens]

8 hours ago, jetdriven said:

I couldn't find z shop that would flush the governor. It's like the DG knob spring that breaks, once they open it up they pull the repair station thing, everything has to be new limits. And they pull out the service letters that have updated flyweights and pilot control valves. 4 grand later in some cases, you get your governor back. 

Call a prop shop.  We are a repair station, so is the prop shop I use.  This governor was just overhauled last month.  They will tear it down, clean it, stick it on the test bench and set up the pressures again.  I'd be surprised if they even charge me for more than a gasket.  I just bought an overhauled governor outright with no core for $2600 for another aircraft.  Sounds like you have had some bad experiences, I suggest you find better people to deal with.  Unfortunately, there are some unscrupulous prop shops out there, other vendors as well.  There are also some very good ones.  I think the key is to find a respected high volume shop, such as mine, that has a good rapport with their vendors and let them handle it for you.  When owners start price shopping repairs at specialty shops themselves, it usually ends poorly because they typically pick the cheapest quote.  That usually doesn't end up being the best option.  The pros know who we can send stuff to that will return a quality product at a predictable price.  I have done business with every prop shop in this state and many others, I now only use one.  If I need something that's outside of their capabilities I let them send it to their preferred vendor. 

Theres a very high probability that the governor on this plane wasn't even subjected to metal contamination.  It was put on with clean oil and nothing in the filter or screen was found.  If the filter and the screen are clean now (yet to be determined), this cam damage could have been there for a while.  It could have been the cause of the prop governor needing to be overhauled before though.  Several pre-existing indication errors and power problems lead to the OP flying at lower power settings than he though he was at, cruising at 2000 RPM and 20 MAP.  Those have been corrected and now he's flying at normal power settings that are higher than before.  The cam lobe problem has probably been there for a while, but just didn't present itself as noticeably due to the way the engine was being operated.

[MooneyBob]

45 minutes ago, jclemens said:

Call a prop shop.  We are a repair station, so is the prop shop I use.  This governor was just overhauled last month.  They will tear it down, clean it, stick it on the test bench and set up the pressures again.  I'd be surprised if they even charge me for more than a gasket.  I just bought an overhauled governor outright with no core for $2600 for another aircraft.  Sounds like you have had some bad experiences, I suggest you find better people to deal with.  Unfortunately, there are some unscrupulous prop shops out there, other vendors as well.  There are also some very good ones.  I think the key is to find a respected high volume shop, such as mine, that has a good rapport with their vendors and let them handle it for you.  When owners start price shopping repairs at specialty shops themselves, it usually ends poorly because they typically pick the cheapest quote.  That usually doesn't end up being the best option.  The pros know who we can send stuff to that will return a quality product at a predictable price.  I have done business with every prop shop in this state and many others, I now only use one.  If I need something that's outside of their capabilities I let them send it to their preferred vendor. 

Theres a very high probability that the governor on this plane wasn't even subjected to metal contamination.  It was put on with clean oil and nothing in the filter or screen was found.  If the filter and the screen are clean now (yet to be determined), this cam damage could have been there for a while.  It could have been the cause of the prop governor needing to be overhauled before though.  Several pre-existing indication errors and power problems lead to the OP flying at lower power settings than he though he was at, cruising at 2000 RPM and 20 MAP.  Those have been corrected and now he's flying at normal power settings that are higher than before.  The cam lobe problem has probably been there for a while, but just didn't present itself as noticeably due to the way the engine was being operated.

Please stick around on this forum. We need you. 

[DXB]

17 hours ago, jclemens said:

 

Well, we found the problem.  Cam lobe gone on the #2 exhaust valve :/  First pic is the bad lobe, second is a good lobe for comparison.  

 

Dang.  So much for a happy ending to this thread.  Informative though.  I'm curious - were there any other signs of corrosion in the engine that would go along with demise of a cam lobe?  Everything else looks pretty clean in the pix.

[mike_elliott]

15 hours ago, takair said:

Does Lycoming put out measurements such that you could measure how much the valve opens to determine cam wear?  In other words, could this determination be made without pulling a jug?  I know you wouldn't catch the beginnings of this, but this cam is near round....ok oblong.  It does seem that this would have been going on for some time.  Was this engine under oil analysis?

I don't think there is a procedure published by Lyc, but the cam lift I believe is .35", and I have put a dial indicator on all of the valve spring retainers and measured lift for comparison on IO360's to get  a tell tale indication. Normally one finds the shared lobe bad since it is doing twice the work, but in Conner's case, it was the ex.  Could it have been coked causing the demise, Jake?

 

[N601RX]

It's unlikely you will be able to get an absolute cam lift measurement without at least removing the spring. The lifter is hydraulic and will bleed down under the valve spring pressure. The lifter clearance is originally set up o something like .025 to .080 when new but will change as the engine gets hours on it. 

Rick Romans took me on a tour of his shop a few years ago when I dropped som parts off for him to recondition.   I remember him showing me his cam grinding machine and asking him what then lift on my io360 cam was.  I think he said .308". If measuring on top of the valve spring you would also have to account for the rocker ratio which is probably on the 1.3 to 1.4 range.