Pre-buy inspection of a Cessna 175

[Frank]

I am a private pilot, with A&P. I am not current at either, at the moment, although I intend to become current again as a pilot shortly. I am drawn to the Cessna 175, but I am leery of a couple of things. The first is how to inspect the engine, and what to look for in the logs regarding the engine. The second is how to check for corrosion.

My game plan is to find a mechanic to do the prebuy and to take a look with him. I want also to ensure that I can take a preliminary look before I call in the mechanic to do the prebuy.

Step one, before paying for a prebuy inspection, for me would be to review the aircraft logs, and check AD compliance, as well as what was found on annual or 100 hour inspections. A big plus for me would be to find that the owner had been doing oil analysis at each oil change. I won't do a compression check by myself. I probably will avoid any aircraft that has not been kept up with ADs. I don't need the other mechanic to help me on the first run through the books. Then I want to look at the airframe for corrosion. Unless I think the corrosion is really minor, I will steer clear of anything with corrosion. Then I will attempt to do check out the gears. I would really like a simple approach to checking backlash. I saw one entry that said I should get the prop horizontal and check to see how much free play it has. I will also turn on the master switch and see what works or doesn't. I will also do the preflight inspection from the POH. I can see things like flap tracks from the outside.

If I am satisfied at that point then I will attempt to call in the other mechanic with more experience. I certainly want the mechanic to look at what I did already, but beyond that, I am hoping to redo the compression checks, and to use borescopes to see what is going on inside the cylinders, and to check for corrosion, if visible, on the camshaft lobes, or gears ( would like feedback on how feasible this is. I cannot see how I could check the crankshaft. I would also like to use the borescope to check a few critical places for corrosion, such as on the spar, and on low spots where water could pool. Of course, I would hope the mechanic had other ideas, as well.

My questions:

Have I hit the high points, and does this plan make sense?

What would you add?

What other ways can you think of to check the gears mechanism?

How do I find a mechanic in the middle atlantic states who does a lot with 175s?

If the aircraft is out of annual, is there a way to make the prebuy a portion of the annual, should I buy the aircraft?

 

[wabower]

I'd want to check for spalled lifters on all the Continentals that I look at, although I'm not sure of the details with respect to the 175. Ditto upper fuse and wing carry-through corrosion.

I am a private pilot, with A&P. I am not current at either, at the moment, although I intend to become current again as a pilot shortly. I am drawn to the Cessna 175, but I am leery of a couple of things. The first is how to inspect the engine, and what to look for in the logs regarding the engine. The second is how to check for corrosion.

My game plan is to find a mechanic to do the prebuy and to take a look with him. I want also to ensure that I can take a preliminary look before I call in the mechanic to do the prebuy.

Step one, before paying for a prebuy inspection, for me would be to review the aircraft logs, and check AD compliance, as well as what was found on annual or 100 hour inspections. A big plus for me would be to find that the owner had been doing oil analysis at each oil change. I won't do a compression check by myself. I probably will avoid any aircraft that has not been kept up with ADs. I don't need the other mechanic to help me on the first run through the books. Then I want to look at the airframe for corrosion. Unless I think the corrosion is really minor, I will steer clear of anything with corrosion. Then I will attempt to do check out the gears. I would really like a simple approach to checking backlash. I saw one entry that said I should get the prop horizontal and check to see how much free play it has. I will also turn on the master switch and see what works or doesn't. I will also do the preflight inspection from the POH. I can see things like flap tracks from the outside.

If I am satisfied at that point then I will attempt to call in the other mechanic with more experience. I certainly want the mechanic to look at what I did already, but beyond that, I am hoping to redo the compression checks, and to use borescopes to see what is going on inside the cylinders, and to check for corrosion, if visible, on the camshaft lobes, or gears ( would like feedback on how feasible this is. I cannot see how I could check the crankshaft. I would also like to use the borescope to check a few critical places for corrosion, such as on the spar, and on low spots where water could pool. Of course, I would hope the mechanic had other ideas, as well.

My questions:

Have I hit the high points, and does this plan make sense?

What would you add?

What other ways can you think of to check the gears mechanism?

How do I find a mechanic in the middle atlantic states who does a lot with 175s?

If the aircraft is out of annual, is there a way to make the prebuy a portion of the annual, should I buy the aircraft?

 

[Frank]

How much of the lifters can you see without taking them out?

How much of the "some spalling is ok" from the following is TCM CYA,and how much is correct:

http://www.tcmlink.com/pdf2/SID05-1.pdf

 

[wabower]

I've only seen bigger engines. Downey and Charlie are the guys I'd ask.

How much of the lifters can you see without taking them out?

How much of the "some spalling is ok" from the following is TCM CYA,and how much is correct:

http://www.tcmlink.com/pdf2/SID05-1.pdf

 

[Tom-D]

Have I hit the high points, and does this plan make sense?
Sounds good so far
What would you add?

Let's do the easy stuff first, pull the oil filler cap, turn it over and look at the underside, If it is not rusty, the rest of the engine isn't either. if it showing rust that is because the water condenses at the top of the engine, the lifters are at the bottom in the Continental GO-300-D. so they are the last place you'll find corrosion. to see them you'll have to pull a cylinder.

What other ways can you think of to check the gears mechanism?
I't actually pretty easy. place a time rite in any cylinder, move the crank until the pointer on the time rite moves, draw a line on stick held to the prop tip, bump the prop the opposite direction and note the distance the prop moves on the stick with out moving the time rite pointer. any thing in excess of 3/16ths is too much.

How do I find a mechanic in the middle atlantic states who does a lot with 175s?
hard to do, because nobody is doing much with the GO-300-D any more.

If the aircraft is out of annual, is there a way to make the prebuy a portion of the annual, should I buy the aircraft?

That's a good place to start, but will want to know more than what an annual will tell you.
Order the CD from OKC note the last registered owner, he is the person you need signature from, are They alive?
That cd will have all the 337s filed, see if that matches the logs. it will also show all leans filed and their releases.
Airframe corrosion, very easy to spot, it blisters the paint, look for it along the rivet seams, flap wells, and run a borescope into the wing spar carry thru. and note the aluminum block where the wing attach bolt goes thru. and the rear cabin former bulkhead behind the head liner, the glue that Cessna used is corrosive, and that area is very prone to corrosion and very difficult to remove and treat, basically the whole head liner must be removed to clean and treat it. Think about 2500-3000 bucks IF the bulkhead is still airworthy. If the bulkhead is not usable, pack your tool box you are outta here.

 

[Tom-D]

How much of the lifters can you see without taking them out?

How much of the "some spalling is ok" from the following is TCM CYA,and how much is correct:

http://www.tcmlink.com/pdf2/SID05-1.pdf

Spalling on the Continental 0-300 series is a rare occasion, they will dish, which wears the cam lobe all the way across the lobe track. Normal wear track is only half or less of the lobe will show wear. (shinny stuff)

 

[Tom-D]

GO - 300-D lifters

First two pictures are normal wear 3rd and 4th are wear on the side of the lifter, 5th is showing normal wear on a cam lobe. note the milling defect on the cam bearing. Last is showing serious electrolysis, after setting 20 years unpreserved.

 

[Tony_Scarpelli]

Thanks Tom.

This is good stuff.

 

[Skylane81E]

I haven't played with that engine so I cannot comment on specifics for it,

the airframe is basically a 172, door posts are a common point for cracks, the insulation can hold water against the inside of the skins, so look behind it. The carry through on the spar (called a hat section IIRC) should be checked for damage as well

 

[Frank]

I found some nice corrosion articles here: http://www.airmod.com/articles/index.htm

These do seem to indicate that the hygroscopic glues were not used in Cessnas until the '70s, although anything might have been retrofitted to an older aircraft. The articles certainly tell me that there is a lot of effort needed to check for corrosion. Do you find a lot of these glues in 175s? Is there some other product that has the same effect?

It almost seems as though a thorough corrosion inspection would take a lot more effort than a typical 100 hour or annual inspection.

 

[Frank]

By the way, I really want to thank Tom for all his suggestions. I agree that the stuff is terrific. I was so focused that I forgot to express my gratitude.

 

[wabower]

Azure might be able to shed some light on that issue.

I found some nice corrosion articles here: http://www.airmod.com/articles/index.htm

These do seem to indicate that the hygroscopic glues were not used in Cessnas until the '70s, although anything might have been retrofitted to an older aircraft. The articles certainly tell me that there is a lot of effort needed to check for corrosion. Do you find a lot of these glues in 175s? Is there some other product that has the same effect?

It almost seems as though a thorough corrosion inspection would take a lot more effort than a typical 100 hour or annual inspection.

 

[Tom-D]

I found some nice corrosion articles here: http://www.airmod.com/articles/index.htm

These do seem to indicate that the hygroscopic glues were not used in Cessnas until the '70s, although anything might have been retrofitted to an older aircraft. The articles certainly tell me that there is a lot of effort needed to check for corrosion. Do you find a lot of these glues in 175s? Is there some other product that has the same effect?

It almost seems as though a thorough corrosion inspection would take a lot more effort than a typical 100 hour or annual inspection.

A bore scope takes a lot of the time involved out of the inspection.

What the aft cabin bulkhead former looks like.
The yellow stuff is glue, you can see where the aluminum has cast off the dried glue, and left an etched area.

 

[Frank]

A bore scope takes a lot of the time involved out of the inspection.

What the aft cabin bulkhead former looks like.
The yellow stuff is glue, you can see where the aluminum has cast off the dried glue, and left an etched area.

Thanks. That could be quite a mess to fix, or even to inspect. I don't think I can get under glue with a borescope, so I cannot tell if the corrosion is serious or not. Is the etched area typically easy to fix by removing surface corrosion or is it usually seriously pitted?

At this point I would be switching my focus to Warriors, but the recent spar AD and pictures of messed up spars (I saw a picture of one that was just peeling) means there is no refuge there either. Oh well, at some point if I want to get an airplane I just have to do the best I can, and accept that nothing is ever 100 percent. So far this has been one of the most illuminating threads I have ever participated in, in any kind of forum. Again thanks.

 

[Tom-D]

Thanks. That could be quite a mess to fix, or even to inspect. I don't think I can get under glue with a borescope, so I cannot tell if the corrosion is serious or not. Is the etched area typically easy to fix by removing surface corrosion or is it usually seriously pitted?

At this point I would be switching my focus to Warriors, but the recent spar AD and pictures of messed up spars (I saw a picture of one that was just peeling) means there is no refuge there either. Oh well, at some point if I want to get an airplane I just have to do the best I can, and accept that nothing is ever 100 percent. So far this has been one of the most illuminating threads I have ever participated in, in any kind of forum. Again thanks.

YAVW.