Cracks in aft bulkhead

[snellbob]

Finally removed the complete empenage to replace the rudder cables and tailwheel cables for broken wires and corrrosion. Little bit of surface corrosion down in the hole but for 58 yrs it all looked pretty good, EXCEPT.....
Found 2 small cracks in the aft bulkhead in the lower right bolt hole where one of the tailwheel steering pulley bracket mounts. This appears to be not too uncommon! I've searched this forum and found some great info dated June 10, 2013 regarding repair to this area.
Does anyone know if there has been a Cessna service bulletin published on this topic as of yet? OR is there a 337 floating around somewhere with this repair procedure? I looked thru the library documentation and did not see anything published. Also is McFarlane still a good source for cables?
Thx in advance

[c170b53]

You'd have to post a pic I think before someone could give good advice. Cracks can be stop drilled and doublers or stiffeners installed as repairs but stop drilled cracks must be closely monitored for crack progression. That may be an issue with your situation. Again you might consider posting a pic.

[snellbob]

Will try to submit pics seperately. I have done additional research and have not found any SB from Cessna regarding this issue. This area had been stopdrilled previously and a large area washer installed on the front side of the bulkhead. This is more of a temporary repair but now it is in need of a correct fix via AC 43-13 which is currently underway. The correct springs are installed as per the IPC but I suspect at one point in time maybe adjusted too tight and probably the rudder banging around in a high wind created the issue. The issues with late model steering cables that I have seen regarding bulkhead cracking so far have all been on the right side. The elevator bellcrank structure is mounted slightly left of center on the bulkhead which gives the bulkhead additional strength reducing the possibility of cracks on the left side in my opinion. If anyone has a form 337 copy from this repair that is willing to share please send it my way.

Thx

[snellbob]

Bulkhead cracks

[voorheesh]

From what you show in the pictures, this looks like a pretty straight forward repair and I am not sure why you think a 337 is needed. Is it going to affect a flight control cable routing or support of a pulley/something of that nature? That would need a 337/field approval if it differs from type design. AC 43-13 provides guidance for simple repairs and I would check the Cessna Maintenance Manual to see if they have any data for this type of bulkhead. Sometimes I hear from FSDO Inspectors that 337s are filed unnecessarily probably with the idea that the form itself will make a repair or alteration legal. (Not always the case) There could be a 337 out there with a good drawing describing a repair scheme, but I would think those small cracks would be repaired and documented with a maintenance logbook entry unless there is more to it. Hopefully, you are working with a qualified mechanic or are one yourself. And of course, maybe I am missing something. Incidentally, rather than a Cessna Service Bulletin, you should download their Supplemental Inspection Document (SID) for Single Engine Airplanes which contains some good guidance for inspecting these old aircraft. I believe the work you are doing is probably very close to what the SID calls for in the rear fuselage and your airplane will greatly benefit from your efforts.

[snellbob]

After a period of time and labor of love, our 170B is back taking flight. Original reason to pull the tail off was the fact in 58 yrs I found no record that the horizontal stab had been removed. This alone was reason enough to expose the "hole" as I call it. Fortunately the 0-300 leaks enough oil to preserve the aft most tailcone area, at least in my case. Only lite surface corrossion found that was soda blasted and removed followed by epoxy primer. Rudder and tailwheel steering cables indeed were rusted but worse than that was the wear of the rudder cables passing thru the penolic fairleads that are attached to the tailcone on both sides. After removal, bending these cables at the worn areas produced multiple broken and frayed wires. UGLY!
The other problem as noticed on the previous post was the crack at the aft bulkhead. Attempting to post good quality pics now of before and after, probably not in that order. Apology in advance if the pics are bad. I can walk, chew gum, drive and even fly, but photo editing ain't my bag!

[snellbob]

More pics, hopefully

[snellbob]

Hopefully this may help in the future for anyone progressing to this point.