corrosion in the center section

Hi Robert, 3800H wassuper clean back in '85 when I got it and remain so thur 2001.Anyway hope you are enjoying her!!!

the best prevention is to get a pre purchase done by someone who knows Coupes or at least classic planes. You pay for experience. someone that works on classics has seen corrosion of all types and locations, they know what to look for.

Just dealt with this on a new purchase. The plane just passed the annual two months before my purchase and it was signed off as all ADs compliant by AI. An AP also looked tat the plane before I purchased it. When I contacted theAI about it, it turns out they never checked for corrosion and only two ADs were signed off on. The AI blamed it on the AP who signed that he complied with two ADs, but the AP never signed off on it. Long story short it was never done. So I had a third party check it out and luckily it is ok. 

This is my first plane purchase and I learned that airplane mechanics are not as thorough as I expected. It seems similar to auto mechanics. You have to find a good one to make sure the plane is properly checked out. There seems to be a tendency to just sign things off which is quite alarming to me. I expected an annual and a SMOH to ensure the plane was safe. Lesson learned: airworthy does not mean safe. I will be double checking everything moving forward and I will trust no one to do what they say since it is my life on the line. 

Do not buy without having the spar caps inspection as jack said inner granduar mean replacement of scrapping because of cost .

It is my understanding that the inner granular corrosion comes from the spars not being correctly heat treated when they were manufactured in the 40's. Apparently there was some that were not treated correctly and got installed in planes. There is no logic to what planes they were installed in just a crap shoot. Just my two cents worth.
Jack

I have a 415-D, made in June 1946. Most of its life in the North West then to GA. from
KY. I bought the kit from Univair for the inspection to cover the AD note, also the drain
kit. The AD note tells you three (3) ways to comply with the AD. Sigh off like C/W
does not comply with the AD. You have to say...C/W by method 1, 2 or 3. No other
sigh off is approved! Lucky, I had no corrosion, but was in need of some corrosion
protection. If you see your IA, ask him or her how they complied with an AD...that
will tell you something! I see so many sigh off's just C/W. I guess I'm from the old
school.