C-170B Pre-purchase Inspection

[wa4jr]

I just made a verbal deal with a fellow on a 1954 C-170B a couple of days ago. Not only my first C-170, but my first aircraft ever. I mailed off the Conditional Sales Contract to him today. Next on the list is the pre-purchase inspection and this is where I need help.

The A&P where the aircraft will be delivered seems quite responsible, but he is not a C-170 expert. What items on a C-170B should he pay close attention to when doing a pre-purchase inspection?

A few other questions regarding this aircraft have me wondering. The aircraft just had ACF-50 applied at last annual. The A&P I talked to says that he does not really like the stuff, as it just covers up the corrosion that may already be there and does nothing to "kill" it. Any thoughts or suggestions?

This C-170B does not have a suction gage. I thought a suction gage was standard on the 170? Is the aircraft illegal without one?

The owner says he has been adding Marvel Mystery Oil at the rate of 4oz per 10 gallons of fuel. Is this practice good or bad? The books show no valve problems at all with over 800 SMOH and compression values are good.

Any help you nice folks can provide will be greatly appreciated. With a bit of luck and a month or so of time, I will be the proud new owner of a C-170 and finally be able to wave goodbye to the commercial airlines for my family's travel! WOOPEEEE!

[N1478D]

I just made a verbal deal with a fellow on a 1954 C-170B a couple of days ago. Not only my first C-170, but my first aircraft ever. I mailed off the Conditional Sales Contract to him today. Next on the list is the pre-purchase inspection and this is where I need help.

The A&P where the aircraft will be delivered seems quite responsible, but he is not a C-170 expert. What items on a C-170B should he pay close attention to when doing a pre-purchase inspection?

A few other questions regarding this aircraft have me wondering. The aircraft just had ACF-50 applied at last annual. The A&P I talked to says that he does not really like the stuff, as it just covers up the corrosion that may already be there and does nothing to "kill" it. Any thoughts or suggestions?

This C-170B does not have a suction gage. I thought a suction gage was standard on the 170? Is the aircraft illegal without one?

The owner says he has been adding Marvel Mystery Oil at the rate of 4oz per 10 gallons of fuel. Is this practice good or bad? The books show no valve problems at all with over 800 SMOH and compression values are good.

Any help you nice folks can provide will be greatly appreciated. With a bit of luck and a month or so of time, I will be the proud new owner of a C-170 and finally be able to wave goodbye to the commercial airlines for my family's travel! WOOPEEEE!

John, I wouldn't give up the commercial airlines totally Even a beautiful 170 can get weathered in. The Marvel Mystery oil added to the fuel is considered by alot of people to be a good thing. It is common practice and should not be a cause of alarm. More than half of the 170 owners in my area use it, including me. Are you in a location where a 170 expert could be brought in to help? Congrads on such a beautiful first plane, there are several experts that can help you on your other questions.

[GAHorn]

I just made a verbal deal with a fellow on a 1954 C-170B a couple of days ago. Not only my first C-170, but my first aircraft ever. I mailed off the Conditional Sales Contract to him today. Next on the list is the pre-purchase inspection and this is where I need help.

The A&P where the aircraft will be delivered seems quite responsible, but he is not a C-170 expert. What items on a C-170B should he pay close attention to when doing a pre-purchase inspection?

A few other questions regarding this aircraft have me wondering. The aircraft just had ACF-50 applied at last annual. The A&P I talked to says that he does not really like the stuff, as it just covers up the corrosion that may already be there and does nothing to "kill" it. Any thoughts or suggestions?


This C-170B does not have a suction gage. I thought a suction gage was standard on the 170? Is the aircraft illegal without one?

The owner says he has been adding Marvel Mystery Oil at the rate of 4oz per 10 gallons of fuel. Is this practice good or bad? The books show no valve problems at all with over 800 SMOH and compression values are good.

Any help you nice folks can provide will be greatly appreciated. With a bit of luck and a month or so of time, I will be the proud new owner of a C-170 and finally be able to wave goodbye to the commercial airlines for my family's travel! WOOPEEEE!

If your mechanic is experienced on Cessna 172's (especially Continental powered ones) he should be comfortable inspecting a 170B.
Pay extra attention to the following:
Rudder circuit cables between the rudder and the aft bulkhead (inside the tail cone.) These are really hard to get to and so are highly-neglected, and frequently chafed/broken/corroded.
Front spar carry-through and internal wing attach blocks. (These blocks are inside the spar carry-through and the bolt that holds the wing to the fuselage pass through this block.) These suffer from 50 years of age in a high water collection spot.
Front/rear doorposts. These are the main strength of the cabin/fuselage and hard landings and high-speed flap abuse will deform them. The front doorposts are often overlooked by tricycle-gear mechanics, but that is where landing shock-loads are absorbed by the 170.
ACF-50 is a good corrosion treatment, and will slow down corrosion already there, but remember, someone was worried about corrosion for some reason. Either because it's already there (always bad) or for preventative purposes (which is OK). Look at the upper cabin above the headliner, especially toward the rear for inside corrosion. Look at wing and tail attach bolts/fittings. Avoid former seaplanes unless they've been totally restored from the "ground up" as automotive collectors say.
Damage histories don't mean a thing in these airplanes as long as it's been properly repaired. Expect wingtip damage histories from ground-loops. Just make sure it's been properly fixed.
I always suggest that the best pre-purchase inspection is an annual inspection performed according to FAA and Mfr's forms. This should insure that the airplane you're about to buy meets the legal airworthiness standards. (Would you want to buy any airplane that didn't?) Remember, you don't have to fix what your inspector finds,...you just want to know about it before it's yours. If, after seeing the inspector's defect-list, you still wish to own the thing, at least you'll be properly informed. (You'll also have a legal standard to base any future surprises or claims upon.) Then if you go through with the deal, you can tell your mechanic to proceed with completing the inspection for an annual sign-off. (And if you reject the airplane, he will make a log entry that it was inspected in accordance with the inspection forms and a list of discrepancies provided the owner.) You're both inclined to deal honorably with each other. An annual inspection only (no repairs) should cost you only a couple hundred dollars and might save you thousands.

[wa4jr]

Thanks Joe and George for the tips. No I do not have a 170 expert to look at the plane with me...so this will be a crash-course in C-170 dos and don'ts.

George, I unzipped the headliner in the cabin, and did see some corrosion...not bad I would say...just powder that scraped off easily. No pits in the metal. Not too worried if this is the extent of the problem. The airplane is a Florida Panhandle bird, with some history in Annapolis, MD as well. I will forward your comments on to the mechanic down in Alabama that will be doing the inspection.

Where can you get an annual for $200? I remember them costing that much several years ago on a C-150, but then only if my dad and I took all the inspection plates off ourselves. The mechanic that is doing the inspection for me on the 170 is charging $350
and his base annual fee is $750 Perhaps I should be working on planes rather than flying them for a living

Should corrosion be found that is more than just "powder", how much is too much and where does one draw the line? Finding C-170s is getting harder and harder...not like the glut of 172s.

[GAHorn]

Think of corrosion like cancer. How much is OK?
Imagine if you were in the position of having to sell the airplane to someone else? How would you feel about the corrosion and how would you represent it to a potential buyer.
There is an insidious opinion that has crept into the vintage/classic airplane marketplace, that a "little" corrosion is OK,...to be expected even. I personally do not accept that. If I were looking at any corrosion, then I'd argue the price downward sufficiently to make a repair to rid it.
Both previous domiciles of the subject airplane were coastal areas,...not to say coastal airplanes are always problems, ....only to say they will need particular scrutiny, re: corrosion, ...and that any corrosion found will never get better unless the metal is replaced. The regs say a repair (i.e., replacement) should be performed whenever 10% is damaged. I'd say that a white, powdery surface indicates that damage has already occured, and further that the protective "Alclad" and/or anodizing has already been penetrated and the base metal is already under attack. So, what will that cost to replace? That is how much the average airplane is below average in value.
When we buy airplanes we all tend to lose our ability to make "arm's length" judgements. My advice: Be critical now, before you own it. After you own an airplane is not the fun time to become disappointed in your own judgement. There are excellent condition airplanes out there, and the money spent finding them is better spent that way unless you are looking for a project and are qualified to do a lot of sheet-metal work yourself.
Re: the $200/annual,...I said a "couple hundred" but meant that loosely depending upon how long it takes to get through logs and do compression tests and confirm the aircraft condition. Remember you're not expecting the mechanic to repack the wheel bearings and lube the controls. You're not even expecting him to top the battery with water. You're expecting him to inspect the airplane in accordance with industry/FAA standardized forms, for airworthiness. Annual Insp. forms would require him to confirm that engine is a C-145-2 or a O-300-A, ...not an O-300-C. If the engine is not according to the Type Cert., then it would require the inspector to determine the basis for the difference,....Is there a field approval or STC to support that difference? If there's an unapproved prop on this airplane, it could end up costing you money when you try to annual it next year, unless you've already required a mechanic to determine all this in a prebuy (using annual insp. forms. A prebuy under any other name has no legal standing. If you let a mechanic do a "prebuy" according to anything other than annual inspection forms, then you have no legal basis to hold his feet to the fire later when it's discovered he missed 3 AD notes that have never been performed or that theres an O-300-A installed allright, but it's one manufactured by Rolls-Royce under license, not a genuine TCM. See what I mean?) This would likely only take about 2 hours with the airplane (single-engine, fixed gear), ane 1 hour with the logbooks. Does your IA charge more than $200 for 3 hours work?

[N4316B]

I just made a verbal deal with a fellow on a 1954 C-170B a couple of days ago. Not only my first C-170, but my first aircraft ever. I mailed off the Conditional Sales Contract to him today. Next on the list is the pre-purchase inspection and this is where I need help.

Be sure to have your inspector check the rib on which the pilot's right brake master cylinder is attached. It is pretty common for them to break. If it's broken, it'll need to have a doubler riveted, which takes ~8 hours.

[russfarris]

Good advice, N4316B! I checked my airplane (52 B model) today...the longeron that the right master cylinder is attached to WAS broken! Probably for decades. It does look like a tough repair; at my IA's rates I hope it doesn't take eight hours! I would suggest everyone check their airplanes. Russ Farris