Annual Maybes - To do or not to do?

[Lax291]

In the middle of my second annual (yikes almost as bad as my first).  It's a 1990 J model and there are some things the shop is pushing to do but are not required.  Some other items are up to me to resolve one way or another.  Interested in your feedback, experience, and knowledge on which ones to do and what to do.

1) No Back Spring Replacement - Seeing on other threads that if it's working fine don't touch it.

2) Air/Oil separator needs to be serviced.  Should I just have them remove it or keep it?

3) Cylinder #1 compression low 62/80 (65 in 2023, 70 in 2022, 65 in 2022, 61 in 2020) with leakage at rings.  Borescope shows cylinder wall corrosion and pitting and piston pin scuffing.  Should I leave it alone since it passed, or have them lap the valve to see if compression can be improved?

4) SB388C Exhaust Valve Inspection overdue.  They really want to do it.

5) Mag was overhauled at last annual but the caps were not replaced.  Should I replace them?

6) Interior & sidewall removal to look for corrosion.  He said it's a SB (don't have the #) but wondering if this will create more harm than benefit with the panels being so brittle. 

 

Thanks.

 

[MikeOH]

Entirely my OPINION, and I am NOT an A&P:

1) NO!  Leave it be.

2) Yes.  I love mine as my belly stays very clean.  They are 'controversial', however. Some think the recirculation is bad for the engine.

3) Tough one, but by what you've shared it's pretty unlikely to be anything to do with the valves (no leak sound in exhaust, right?) so lapping seems a wasted effort.  Based on history, it doesn't look like it's getting worse...and you've been flying it.  Removing cylinders makes me nervous, but at some point you're going to need to.  Me, I'd continue flying and keep an eye on compression and oil consumption.

4) Hmm, I know nothing about that SB. Have they done a borescope?  How much do they want for the SB?

5) Depends on how many hours on the caps, but I'd want to inspect carefully if >1000 hours.

6) That's SB208.  When was the last time it was recorded in the logs?  Did you inspect at pre-buy?  If no to both, then I'd want to inspect.

[Fly Boomer]

32 minutes ago, Lax291 said:

6) Interior & sidewall removal to look for corrosion.  He said it's a SB (don't have the #) but wondering if this will create more harm than benefit with the panels being so brittle. 

The engine stuff gets my attention, but if number 6 has not been done, put it at the top of your list.

[dkkim73]

#3 cylinder issues, makes me wonder about a ring flush. That and valve lapping can make a huge difference. 

Maybe get some advice from an AP and have them review borescope photos.

[NickG]

53 minutes ago, MikeOH said:

6) That's SB208.  When was the last time it was recorded in the logs?  Did you inspect at pre-buy?  If no to both, then I'd want to inspect.

SB208 says for all M20 Series manufactured prior to Jan 1, 1976??

[RangerM20]

For the SB 208, you can inspect the bottom of the fuselage tubes (where corrosion is most likely to be) with just the belly panels removed.

[Lax291]

50 minutes ago, MikeOH said:

Entirely my OPINION, and I am NOT an A&P:

1) NO!  Leave it be.

2) Yes.  I love mine as my belly stays very clean.  They are 'controversial', however. Some think the recirculation is bad for the engine.

3) Tough one, but by what you've shared it's pretty unlikely to be anything to do with the valves (no leak sound in exhaust, right?) so lapping seems a wasted effort.  Based on history, it doesn't look like it's getting worse...and you've been flying it.  Removing cylinders makes me nervous, but at some point you're going to need to.  Me, I'd continue flying and keep an eye on compression and oil consumption.

4) Hmm, I know nothing about that SB. Have they done a borescope?  How much do they want for the SB?

5) Depends on how many hours on the caps, but I'd want to inspect carefully if >1000 hours.

6) That's SB208.  When was the last time it was recorded in the logs?  Did you inspect at pre-buy?  If no to both, then I'd want to inspect.

Thanks for the opinions!  Some answers to your questions:

 

4) It's a SB from Lycoming I believe and estimating $400-$500

5) Don't know but will find out

6) Don't believe it's in the logs and don't believe they did it during the pre-buy. 

[201Mooniac]

I would ensure SB 208 is done if never done, though by 1990, I don't believe there were any issues anymore.  Checking the bottom of the tubes for corrosion is a good idea anyway.  I haven't been worrying about SB 388 which I believe is the exhaust value stem to guide clearance test.  Personally, I don't change the mag cap unless necessary but I never really looked into whether I should.

[PT20J]

SB 388 is the 400 hr wobble test to check valve clearance. Lycoming valve guides before 1998 were prone to wear and excessive clearance allows oil to coke on the valve stem and can cause valve sticking. Your call whether to do this or not, but many just wait for “morning sickness” (very rough engine on start up  when engine is cold due to sticking valve which clears as engine warms). If the engine was overhauled after 1998, it should have the newer high chrome valve guides and the recommendation is a one time inspection at 1/2 TBO. 

[Utah20Gflyer]

1 hour ago, MikeOH said:

Entirely my OPINION, and I am NOT an A&P:

1) NO!  Leave it be.

2) Yes.  I love mine as my belly stays very clean.  They are 'controversial', however. Some think the recirculation is bad for the engine.

3) Tough one, but by what you've shared it's pretty unlikely to be anything to do with the valves (no leak sound in exhaust, right?) so lapping seems a wasted effort.  Based on history, it doesn't look like it's getting worse...and you've been flying it.  Removing cylinders makes me nervous, but at some point you're going to need to.  Me, I'd continue flying and keep an eye on compression and oil consumption.

4) Hmm, I know nothing about that SB. Have they done a borescope?  How much do they want for the SB?

5) Depends on how many hours on the caps, but I'd want to inspect carefully if >1000 hours.

6) That's SB208.  When was the last time it was recorded in the logs?  Did you inspect at pre-buy?  If no to both, then I'd want to inspect.

In regards to oil air separators being controversial.  It seems like if you have an oil/air separator and your oil analysis comes back fine then I can’t see a rational reason to be against them.  Personally I want to see objective data indicating there is a problem before I go along with someone’s hypothesis and oil analysis will definitively demonstrate whether there is a problem.  

[OR75]

item 6)  why no inspect yourself .... easy to remove the seats and take your time to not break the brittle plastic ... a good project for rainy day (assuming you have a hangar)

[M20F]

2 hours ago, Lax291 said:

3) Cylinder #1 compression low 62/80 (65 in 2023, 70 in 2022, 65 in 2022, 61 in 2020) with leakage at rings.  Borescope shows cylinder wall corrosion and pitting and piston pin scuffing.  Should I leave it alone since it passed, or have them lap the valve to see if compression can be improved?

 

 

The valve has nothing to do with wall corrosion, wall pitting, nor piston pin scuffing.  Did your AI suggest valve lapping as a solution to these 3 problems?

[EricJ]

2 hours ago, Lax291 said:

In the middle of my second annual (yikes almost as bad as my first).  It's a 1990 J model and there are some things the shop is pushing to do but are not required.  Some other items are up to me to resolve one way or another.  Interested in your feedback, experience, and knowledge on which ones to do and what to do.

1) No Back Spring Replacement - Seeing on other threads that if it's working fine don't touch it.

Yes, leave it be unless there is solid reason to do something.

2 hours ago, Lax291 said:

2) Air/Oil separator needs to be serviced.  Should I just have them remove it or keep it?

3) Cylinder #1 compression low 62/80 (65 in 2023, 70 in 2022, 65 in 2022, 61 in 2020) with leakage at rings.  Borescope shows cylinder wall corrosion and pitting and piston pin scuffing.  Should I leave it alone since it passed, or have them lap the valve to see if compression can be improved?

If the leakage is at the rings (by listening through the oil filler tube during a compression test), then there is zero reason to lap valves.    It also looks like the compression has been stable for a long time, so if there's no metal in the oil filter or the oil analysis (or not enough to worry about), it's probably fine to just leave it be.   When they're like that it's always good to keep an eye on them with oil analysis, borescopes, etc., just to see if the situation changes.   A ring flush during the next oil change might help to get some of the compression back.

2 hours ago, Lax291 said:

4) SB388C Exhaust Valve Inspection overdue.  They really want to do it.

Why do they want to do it?   Unless there's a compelling reason to suspect that you have valve guide problems, there's no reason to do this.

2 hours ago, Lax291 said:

5) Mag was overhauled at last annual but the caps were not replaced.  Should I replace them?

Do you mean the condensers?   If so, then, yes, those should be replaced at mag overhaul, or even at mag iran, imho.   They're a wear/failure item.

2 hours ago, Lax291 said:

6) Interior & sidewall removal to look for corrosion.  He said it's a SB (don't have the #) but wondering if this will create more harm than benefit with the panels being so brittle. 

You can do a reasonable job of tube inspection by just loosening the screws around the window sills and sending a borescope down between the interior piece and the outside wall.   I've done this a few times and you can get a good representative view of things without taking the panels off if you're worried about that.

[PT20J]

There is a philosophical issue here.

Some people like to try to get all their maintenance done once a year during the annual. But this often leads to expensive annuals and the airplane being in the shop for weeks waiting for parts and mechanic availability.  

Others (and I’m firmly in this camp) like to take care of things as they come up and want the inspection to just be an inspection. Certainly if an airworthiness item comes up, it will have to be addressed. But I’d just like a list of the non-airworthiness items so I can address them (or maybe not address them if I determine that to be the prudent decision) at my leisure.

[NickG]

10 minutes ago, PT20J said:

There is a philosophical issue here.

Some people like to try to get all their maintenance done once a year during the annual. But this often leads to expensive annuals and the airplane being in the shop for weeks waiting for parts and mechanic availability.  

Others (and I’m firmly in this camp) like to take care of things as they come up and want the inspection to just be an inspection. Certainly if an airworthiness item comes up, it will have to be addressed. But I’d just like a list of the non-airworthiness items so I can address them (or maybe not address them if I determine that to be the prudent decision) at my leisure.

I agree with your methodology and that’s what I do as well

[Joshua Blackh4t]

As for 6 (tube frame inspection) the SB is only recommended, but the way I read it Ad/m20/32 A6 means its mandatory every annual.

I don't know what others' thoughts are on this, but that seems overkill if in a hangar, and very sensible if in the tropics outside, and near the coast. (As I am about to be soon for a few months. Poor baby)

[PT20J]

30 minutes ago, Joshua Blackh4t said:

As for 6 (tube frame inspection) the SB is only recommended, but the way I read it Ad/m20/32 A6 means its mandatory every annual.

I don't know what others' thoughts are on this, but that seems overkill if in a hangar, and very sensible if in the tropics outside, and near the coast. (As I am about to be soon for a few months. Poor baby)

Apparently, if your airplane is registered in Australia. 

[Joshua Blackh4t]

7 hours ago, PT20J said:

Apparently, if your airplane is registered in Australia. 

Thats the kicker then. I was wondering why people here thought it was optional.

We have some annoying rules.

[Lax291]

19 hours ago, 201Mooniac said:

I would ensure SB 208 is done if never done, though by 1990, I don't believe there were any issues anymore.  Checking the bottom of the tubes for corrosion is a good idea anyway.  I haven't been worrying about SB 388 which I believe is the exhaust value stem to guide clearance test.  Personally, I don't change the mag cap unless necessary but I never really looked into whether I should.

Looking more closely at SB 208, looks like this doesn’t apply to my year. 

[Lax291]

18 hours ago, PT20J said:

SB 388 is the 400 hr wobble test to check valve clearance. Lycoming valve guides before 1998 were prone to wear and excessive clearance allows oil to coke on the valve stem and can cause valve sticking. Your call whether to do this or not, but many just wait for “morning sickness” (very rough engine on start up  when engine is cold due to sticking valve which clears as engine warms). If the engine was overhauled after 1998, it should have the newer high chrome valve guides and the recommendation is a one time inspection at 1/2 TBO. 

Was overhauled in 2004 so sounds like I should be good. She starts up great so no signs of morning sickness but will still be keeping that in mind. Thanks. 

[Lax291]

18 hours ago, Utah20Gflyer said:

In regards to oil air separators being controversial.  It seems like if you have an oil/air separator and your oil analysis comes back fine then I can’t see a rational reason to be against them.  Personally I want to see objective data indicating there is a problem before I go along with someone’s hypothesis and oil analysis will definitively demonstrate whether there is a problem.  

Haven’t done an analysis yet but I’ll be doing my own oil changes starting with the next one and already received a blackstone sample bottle to fill up. Thanks. 

[Lax291]

18 hours ago, M20F said:

The valve has nothing to do with wall corrosion, wall pitting, nor piston pin scuffing.  Did your AI suggest valve lapping as a solution to these 3 problems?

No, he was making me aware of the corrosion and pitting. He said the lapping could help bring up the compression number. 

[PT20J]

59 minutes ago, Lax291 said:

No, he was making me aware of the corrosion and pitting. He said the lapping could help bring up the compression number. 

You can tell where the leak is by listening for the hissing during the compression test: Out the oil filler tube = rings, out the exhaust tail pipe = exhaust valve, out the air filter = intake valve. If the air is getting past the rings, lapping won't do a thing except empty your wallet. Even if some air is leaking out the exhaust, it might be prudent to run it a few hours and recheck. Sometimes there is just a bit of carbon between the valve face and the seat. Lapping is generally done when the heat signature on the face of the valve is not concentric but before it gets bad enough that the valve has burned. If the valve face looks good in the borescope pictures, I wouldn't mess with it.

Piston pin scuffing on the cylinder walls is common on Lycomings. The piston pin floats in the piston and the plugs on the ends can rub on the cylinder walls by design and leave a witness mark. If there is some roughness in the cylinder wall due to corrosion, it might cause more wear. As long as it's not making metal, I wouldn't worry about it.

[Ragsf15e]

1 hour ago, Lax291 said:

No, he was making me aware of the corrosion and pitting. He said the lapping could help bring up the compression number. 

To add to what @PT20J said (he already got the most important parts), the compression checks are pretty “flukey” (that’s a technical term).  They can change a lot based on who did them, how hard they tried and what state the engine is in - hot, warm, cold.  The usual method for “fixing” a failed compression check (I understand yours passed) is to fly the airplane and do the check again on the hot engine.  That gives the best results.  Then if it’s still leaking, you can slowly tweak the prop to find the closed position on the valves and listen for where the leak is coming from.

Then, if it’s leaking from the rings (oil filler port), you don’t go lapping valves.  Maybe ring flush or whatever.  If it’s leaking at a valve, replacing rings won’t help.  This id why lapping valves in your case seems strange?

Edited July 19 by Ragsf15e

[PT20J]

I own a 20 year old Volvo XC90 5-cyl turbo airport car. I do 5000 mi oil changes, but I've never cut open the filter. I don't do oil analysis. It sits a lot. I have no idea what the compression is. I never worry about it, and it always starts (hot or cold) and runs fine.

I own a 30 year old airplane, and .... oh, never mind