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Pre Buy Tips

cplne

Registered User
Found a nice 12 that I am going to do a pre-buy on Tuesday. I'm having the local maintenance person do an annual on the plane which will constitute the pre-buy. The plane has a Crosswind STOL Wing on it, 18 gear and tail, ABW 31 with most of the Alaska Mods I'm most interested in. Anything that I really need to pay attention to during the inspection. The engine has 1300 hrs on her with 800 since TOP and well aware of the cam spalling isues but without removing the cylinders I can't check the condition and honestly wouldn't ask the owner unless we come up with a flat cylinder. Any advice is much appreciated.

FYI I am buying the plane for my wife and will fly it to our place in Alaska this spring.
 
OK, here's my 2c. If the plane has done any sitting pull the cylinder and know for sure? It's not a big job at all. A couple hours of labor and done, then even if you don't buy it the owner will have something to advertise or repair as the case may be. Check around the tail from in front of thejack screw area to the end for cracked or broken tubes, rudder post etc.
; pulleys for the flaps in the top of the cabin where the cables come up and out to the wings. The mounting brackets welds brake. Then general stuff.
 
Punch the lower tubes at the tail for corrosion, check lower tubes under the battery box (see recent post by colorguns). Whypull a cylinder if compressions good. Look for unauthorized mods.
 
Not to be argumentative but you can have good compression and a good amount of rust inside, seen it.
 
An inspection is not just to tell you what is wrong, but what repairs you might be facing in the near future.

Pull cylinders on one side and inspect the cam and lifters. sometimes you can save a cam by changing lifters that have begun to show rust, other times you find that the cam is having issues and can at least save the engine from sending metal flakes through all of the oil system.

I am much more careful about my wife's car's condition than mine. If she was flying the plane I would be a whole lot more diligent in my inspection prior to purchasing.

The only reason not to pull cylinders is that the plane has been flying 100 hours in the last six to nine months, or I had a borescope I was able to look inside with.
 
Had two O-320's eat cam and lifter bodies in the '80's and early 90's. Never any significant metal in the screen. Some silvery sheen in the drain oil like very light suspended silver dope, maybe from piston skirt wear from cam/lifter particles...they were scored at removal. Magnet stuck in drain oil overnight caught it first...real fine ferrous metal. Hydraulic lifters maintained clearances as cam lobes wore (shared one was the worse). Valve guide sticking on one was suspected but not confirmed...ran rough briefly once. The other had original Shell multi-vis also suspected. Both flew 200+ hrs/year on 80/87.

Almost had a third on a potential purchase. Sharp mechanic pulled and had a look at the visible cam and lifter rust. Engine ran less than 5hrs/year for a few but supposedly "pickled". Saved me $$$$, cost the owner more than he expected.

Gary
 
An original airframe is 71 or 72 years old. Inspect what you can and expect future repairs to happen. They weren't built to last forever.
 
Magnet stuck in drain oil overnight caught it first...

BC12D-4-85;

Would you mind expanding for my learning purposes what you mean by this? I'm imagining a hand held magnet picking up bits in the drained oil?

Ta.
 
Here is a link to an article I wrote on this subject. Pre-Purchase Inspection
If you search "pre-purchase inspection on this site you will find lots of threads on the subject and things to look for. Fuselage corrosion is the biggest issue I have seen with PA12s.
 
Really good stuff here guys. I’ll see if the owner will let me pull two cylinders to check the cam but doubt he will go for it. Yes I will check for corrosion. And yes that’s why I’m spending so much time checking the old girl out, the airplane!
 
Good stuff Steve. If the airplane checks out I’ll bring her home to Dallas until spring when we head for AK.
 
All owners I have dealt with have been fine with pulling cylinders as long as I had a qualified mechanic do the work. Also, have all new soft lines and orings so when she goes back together she is tighter than before; owners appreciate that.
 
BC12D-4-85;

Would you mind expanding for my learning purposes what you mean by this? I'm imagining a hand held magnet picking up bits in the drained oil?

Ta.

If an owner suspects internal engine wear have a look at the drain oil visually and with a hand held magnet. On my two engines that had excessive cam wear I started to see a very light sheen of suspended fine particles as soon as the oil was drained into a clean container every 25 hours of flight (use a flashlight). Seen it twice so my mechanic dropped the clean end of a hand held magnet into the drain oil and let it sit over night. Next day it was covered with a thin layer of ferrous metal. The visible sheen was still there and was probably aluminum. Nothing abnormal was found in the oil filter screen and I had no canister oil filter for him to open and examine. We pulled a cylinder and the rest was only money and time.

There's no reason a similar magnet couldn't be stuck into the oil filler neck if wear is suspected, but how much is normal and how much is excessive wear? I'd like to know more about that. We have better oils and additives like Cam Guard now to protect the engine.

Gary
 
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