Buying first plane - what should I look out for

Discussion in 'Hangar Talk' started by Micah Powell, Jun 17, 2020.

  1. Micah Powell

    Micah Powell Filing Flight Plan

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    Hello POA,
    I am currently on the hunt for a Piper Warrior II. This will be my first airplane purchase.
    I am looking at one right now and have some questions about it regarding the engine compressions (I haven't seen it in person, I'm going there this weekend).

    TSMOH = 821
    2016 compressions = 76 76 74 76
    2019 compressions = 76 70 74 62

    Between these two annuals the plane only flew 7 hours. (I'm assuming it went out of annual for couple years. I'm just going off some photos of log entries the seller has sent me at the moment). Since the annual in 2019, the plane has flown 13 hours.

    My questions are:
    Should I be worried?
    What could happen that would make compressions change this much in only 7 hours of tach time?
    What, if anything, can be done to improve compression?
    If worst case scenario would require a cylinder head replacement, what should I expect cost wise for that?

    Thanks for your input!
     
  2. Bell206

    Bell206 En-Route

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    FWIW: I'm a big fan of selecting who will be maintaining your new aircraft purchase before even looking at aircraft. Then sit down with them and get a good foundation of basic aircraft knowledge by asking various questions. There are also articles and other guidance that can give you a better idea on what to look for or what to question when you start your search. There is a lot more to buying an aircraft than looking at the compressions which at quick glance appear to be just fine. For example, a more prudent question would be why only 20 hours in 4 years, or why was no annual done for 2017 and 2018? The answers may instead direct you to a different area to review vs engine compression values.
     
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  3. Micah Powell

    Micah Powell Filing Flight Plan

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    Thanks, I have not done this yet and that sounds like a good thing to do. As far as why the airplane hasn't flown much, the owner has been of poor health and sadly, recently passed away.
     
  4. Stewartb

    Stewartb Final Approach

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  5. Micah Powell

    Micah Powell Filing Flight Plan

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    Thanks! That is helpful
     
  6. Larry Vrooman

    Larry Vrooman Pre-takeoff checklist

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    This is worth your time to read:

    https://www.lycoming.com/sites/default/files/Cylinder Compression.pdf

    The short version is:

    1) Less than 65 on once cylinder, Lycoming says check it again in 100 hours;
    2) less than 60 on a cylinder, Lycoming states indicates a top overhaul is in order; and
    3) a 10-15 psi difference between cylinders indicates an investigation as to the cause should be made.

    ----

    That's Lycoming. Many good mechanics will tell you to just go fly it a couple hours and then retest it with the cylinders still at operating temperatures. Some mechanics just warm it up on the ramp before a compression test and that can skew the results. Also, if it has sat for any length of time, a couple hours in flight may well get a low cylinder back in the normal range.

    If it's till in the 60-65 range after a couple flight hours and a retest, I'd borescope it before I pulled the cylinder and look for an obvious issue. Low compression just says something might be amiss, it doesn't really tell you what is wrong. And there may be nothing wrong a couple hours in the air might fix.

    ----

    If it's a prebuy and it's out of annual, and you don't want / can't get a proper retest, I'd still bore scope it and look for obvious issues:

    a) If you see rust or (worse) pitting on the cylinder walls then it's got corrosion issues causing excessive blow by;
    b) If there is rust on the cylinder walls, I'd be even more worried about corrosion on the cam lobes and lifters and the potential for excessive wear and galling than the low compression;
    c) the valves should not have a lot of deposits and the exhaust valve should have reddish and gray coloring with a symmetrical bullseye pattern. If you see greenish hues, its an indicator of high temps. Asymmetric patterns indicate a hot spot on the edge of a valve and a warped valve currently or in the near future. That hot spot can be caused by excessive deposits on the seat that prevent proper heat transfer from the valve, or a worn valve guide (caused by excessive deposits between the valve stem and valve guide); and
    d) if you see none of the above, a couple hours in flight might resolve it. If not, you probably have a ring problem.

    ----

    The big concern with 7 hours between 2016 and 2019, with no annuals in 2017 and 2018 is that it wasn't flown for an extended period. That can result in corrosion on the cam lobes and lifters. Those parts are face hardened for wear resistance. However, if that surface is compromised by corrosion and pitting, then the exposed softer metal underneath will quickly start to gall, and you'll need a new cam and that involve a very expensive tear down to replace.

    *If* the engine was properly pickled with storage oil and desiccant plugs in the exhaust and the cylinders, it might not be an issue, (However the preferred storage method is to do the above, plus invert the engine so the cam and lifters are submerged in oil.)

    If the aircraft was stored in a dry climate the odds improve a bit. Similarly, if the aircraft was stored in a hangar, the day to night temperature differentials are lower. That results in both less air exchange in the engine and less condensation in the engine. If it's both hangared and in a dry climate it's less risk than if it was parked outside in a wet climate.

    Straight weight mineral oils adhere better to the cam than multiweight and synthetics, and Cam Guard or Shell W100 Plus oil also helps reduce corrosion in infrequently flown engines.

    ----

    Look for all of the above. My major concern would be that it runs fine now, but starts making metal due to corrosion in the engine. That'll be evident in an oil analysis but you also need some basis for comparison.

    ----

    Also be aware that the FAA has been mulling over a wing spar AD for all PA-28s with more than 5000 "factored service hours.

    https://www.federalregister.gov/doc...iness-directives-piper-aircraft-inc-airplanes

    The short version is that there was a wing spar failures on a PA-28-200R operated by ERAU with >7000 hours, but the FAA is concerned about all PA-28s.

    Given the effects of how the aircraft is used in service the threshold is proposed to be 5000 "factored service hours". The number of 100 hour inspections is used as a measure of how intensively the aircraft has been used. The formula is (N × 100) + [T-(N × 100)]/17 = Factored Service Hours, where N = number of 100 hour inspections and T = total hours in service.

    This is pretty good news for PA-28 owners with complete logs and no or few 100 hour inspections.

    An aircraft with 14,000 hours but no 100 hour inspections:

    [0 x 100] + [14,000 - (0 x 100)]/17 = 823 factored service hours.

    The same 14,000 hour aircraft with 45 100 hour inspections:

    [45 x 100] + [14,000 - (45 x 100)/17 = 5056 factored service hours.

    Some commenters objected to the use of 100 hour inspections as it's more complicated and would require complete logs. I don't really get that reasoning as if you are missing logs and can't prove no, or a low number of 100 hour inspections and have 5000 hours total time on the aircraft, you are no worse off than you would be with a mandatory inspection at 5000 hours, which is where the FAA is setting the bar.

    Other suggestions were made that the only cracks found in the lower spar cap on PA-28s and 32s were in the PA-28-235 PA-28R models and the PA-32-260 and PA-32-300 models. However, the is applying it to all PA-28 aircraft. The FAA did the same thing with the Champion 7 series. They found failed wing spars in a few 8 GCBC aircraft that had accident histories where the spars were most likely cracked, but then applied the AD to all 7 and 8 series aircraft with 85 or more horsepower.

    At best it's an expensive annual inspection requiring eddy current inspection and replacement of the wing bolts (probably $500 per year) and if a crack is suspected it's a very expensive process to remove the wing to confirm, and if it is indeed cracked it'll be around $8-$10K to replace the cracked spar on that wing (and you'd still have to annually inspect the other wing spar.)

    This is the long way of saying, check the logs carefully for complete logs and little or no intensive use with 100 hour inspections.

    -----

    The important thing with a pre-buy is to be fully prepared to walk away. There are a lot of Warriors out there, so don't feel you need to buy this one.
     
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  7. Dana

    Dana Cleared for Takeoff

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    Camguard, yes. The Lycoming additive in the Shell Plus oils (also in the Phillips Victory oils now) is an anti-wear additive, not a corrosion inhibitor.

    Some mechanics will recommend running it with some Marvel Mystery Oil for awhile, too... :popcorn:
     
  8. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    Only the dumb ones.
     
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  9. Huckster79

    Huckster79 Cleared for Takeoff

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    Hey if this is your first purchase- take this from a guy whose only owned a year and a half... realize you don’t know Jack crap about biting a plane... not personal .

    I realized I did t know jack crap when I found out it wasn’t only hours since major but also years and amount of use vs sitting... so I reasesrched and read all I could, and I talked with multiple knowledgeable people, my IA to be,Experienced owners, and even the technical director of the type club I wanted. Guess what I got a great plane! 170 hours later- no big gotcha surprises- I figure now anything that goes couldn’t have been caught in prebuy... I’ve put her through her paces now...

    move had two friends go it alone for the most part- both got screwed! One bought a plane too dollar that was Unairworthy... and they ended up parting out once they flew it home... another friend found out his bargain was no bargain, he has an airplane but one that’s needed significant attention cancelling out and like surpassing any amount of “bargain” he got...

    Aacept that if you’ve not done this before know that ya don’t know what ya do t know... you are on a good path already asking questions here :)
     
  10. Kenny Phillips

    Kenny Phillips En-Route

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    That good old differential cylinder pressure test (AKA "leakdown") will let you know where most of the loss is occurring. Not to be confused with a dynamic compression test, of course, though some have used the term interchangeably. I have a nice Snap-On tester; it has a warning to watch out for the prop!
     
  11. Bob Noel

    Bob Noel Touchdown! Greaser!

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    or, to put it another way, there is nothing like buying an airplane to learn about buying an airplane...
     
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  12. Micah Powell

    Micah Powell Filing Flight Plan

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    Thanks Larry for the detailed post. I will definitely have an oil analysis done in the prebuy although I doubt there have been any previous oil analyses done by which to compare.
    As far as the wing spar AD, this plane has less than 5000 total so it shouldn't be an issue for a while. Thanks for the heads up.
     
  13. Micah Powell

    Micah Powell Filing Flight Plan

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    Could you tell us a little bit more about your two friends? What were the things they overlooked when purchasing their planes?
     
  14. Huckster79

    Huckster79 Cleared for Takeoff

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    both skipped prebuy... that’s the long and short of it... the crazy stuff in both could have been found by any pilot w even the slightest mechanical aptitude. neither set eyes on their planes nor paid anyone to look for them, until they owned them.

    that’s the lesson... the particular deficiencies aren’t as of interest as every make and model is different- the lesson is a good pre-but... what that entails is a debated item tho too...
     
  15. MooneyDriver78

    MooneyDriver78 En-Route

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    I would used a local CFI that’s experience with the model, have them fly it to verify everything works, they should also be able to do a rudimentary inspection to check for corrosion in the airframe, etc.
    Saves you a trip, an hour or so of their time should only cost you ~$100.
     
    Last edited: Jun 19, 2020
  16. Kristin

    Kristin Cleared for Takeoff

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    I would use a CFI that is also an A&P. Using someone like that who can also mentor you through the purchase process.
     
  17. frfly172

    frfly172 Touchdown! Greaser! PoA Supporter

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    Find a mechanic you trust to do a thorough pre buy inspection.also worthwhile to pay the mechanic to review all logs and AD compliance.
     
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  18. WannFly

    WannFly Final Approach

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    I have a diff story, I bought sight unseen, but I did hire a pro to review logs, since I didn’t know jack crap about airplanes back then. In fact I don’t know jack about them even now, other than the fact that you throw enough credit cards at a problem and it goes away. That’s true in any situation though
     
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  19. Larry Vrooman

    Larry Vrooman Pre-takeoff checklist

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    I can't speak to the Phillips Victory oils, but the Plus in the Shell oils is both an antiwear additive and corrosion inhibitor. From the Shell site:
    https://www.shell.com/business-cust...centre/technical-talk/techart14-30071535.html

    "Not only does AeroShell Oil W100 Plus have this anti wear additive, but it also contains a "metal passivator" and a corrosion inhibitor.

    What does this mean?

    Metals such as Copper are normally a problem for oils as they cause oil to degrade quicker than they would otherwise. This can be a problem as many General Aviation engines contain Copper - the largest area is normally found on cam shafts which is left over from the manufacturing process.

    When cams are manufactured the cam face is often hardened using a process called Nitriding. This leaves a hard, but brittle, surface - ideal for the cam face, but not for the rest of the shaft.

    The rest of the shaft does not need to be hardened and it performs better if the surface is not brittle from the Nitriding process. So to protect the rest of the shaft, a thin layer of Copper plating is used to cover all the areas which do not need to be hardened.

    Once the cam has been manufactured this Copper serves no useful purpose, but it is not removed. This can be a problem for the oil in an engine because, as I have mentioned, the copper acts as a catalyst to make the oil degrade faster than normal - and a degraded oil does not make a good lubricant.

    This is where the "metal passivator" comes in. This additive reacts with the surface of Copper components forming a protective layer which separates them from the oil, thus preventing the Copper from degrading the oil.

    One more additive is used in AeroShell Oil W100 Plus and that is a corrosion inhibitor. This inhibits the formation of rust in the engine - a common root cause of engines not reaching TBO. Rust is often found in engines as used oil is acidic and, combined with dissolved water from the atmosphere, causes corrosion."
     
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  20. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    The copper remains to protect cam from corrosion, The only thing that rusts is the area in contact with the cam.
     
  21. DFH65

    DFH65 Pattern Altitude

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    "Buying first plane - what should I look out for"

    Advice from POA. :)
     
  22. Micah Powell

    Micah Powell Filing Flight Plan

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    Thanks for all the replies. The prebuy is scheduled for today. The mechanic is doing everything for an annual without the servicing and additionally he is going to bore scope all the cylinders. We discussed doing an oil analysis but there is nothing to compare it against, unfortunately.
     
  23. MrPutz

    MrPutz Filing Flight Plan

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    I'm in the same boat. Buying my first plane (67 Piper Cherokee 235) and just got the Pre-buy report. Found about 10 things that needed attention, 2 of them reskins of control surfaces. With the pre-buy, annual, and fixes I'm looking at $12 grand. I got the plane at a good price so that's not the end of the world. but my question is when a broker sells a plane advertised as "ready to fly" and 2 control surfaces needs replaced.. should they help with the some of the costs to make it air worthy? No ADSB, 2 bad control surfaces, and no navigation. As mentioned the initial purchase price is good and the engine is great. But 500hr magneto, and replacing all the fuel and oil lines add up to $3300 right there. Reskinning 2 control surfaces another $3300 there. So my choice is sink money into this one and know what I've got or take a chance on another more expensive plane and hope the same 40+ year old parts are better??? hmmmm
     
  24. Kristin

    Kristin Cleared for Takeoff

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    Do you have the option of getting your deposit back and walking away? I always advise my clients that they need to be able to walk away without forfeiting any deposit, based on the pre-purchase inspection, without any limitation.
     
  25. MrPutz

    MrPutz Filing Flight Plan

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    That shouldn't be an issue. As an update though a big red flag for me was the 8hr charge at $105 per hour to pull and reinstalled the magnetos. I've approached another A&P and after discussions with him I feel much better about the purchase and will probably pay about 65% of the first quote to get this plane up to standards. :) I don't believe in cutting corners but sure feels like I was being taken advantage of.
     
  26. Larry Vrooman

    Larry Vrooman Pre-takeoff checklist

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    Agreed. A purchase agreement should include the option to back out with a full return of the deposit if a pre-buy identifies (non cosmetic) issues that require expensive repair, and/or render the plane non airworthy and/or indicate the aircraft was not properly represented by the seller - intentionally or unintentionally.

    If that happens, the next step is a renegotiation of the the sale price and or agreed upon split of the repair costs, and failing that return of the deposit, limited the bu
    yer's risk to the cost of the pre-buy inspection.