First, I'd like to say the information in this thread is worth the price of admission to the 170 Association. I knew I wanted to overhaul the fuel selector valve, but would have had no idea what I was getting myself into were it not for all of the above posts. Thanks to all for their insights, and I am now a member of this exclusive club. Having survived the initiation, I thought I'd try to add to the knowledge base.
1) It's obvious, but loosen the flare nuts on the three fuel lines before going after the two mounting bolts
2) The #10 bolts are relatively easy to drive from the top using a 1/4" wobbly socket, a long extension, and a helper to turn it from above. The 3/8" wrenched #10 locking nuts are what make this job so impossible. They are so close to the back of the valve, that no box end or socket type wrench will fit. I was able to hold them with the open end of an ignition wrench, working my way in from the left rear, loosening the left one first, then the right one. I ended up with my left arm through the opening behind the flap handle, holding the wobbly socket on the bolt, and my right arm through the rectangle opening behind the tunnel, holding a wrench through the hole in the bulkhead that is immediately aft of the valve. My wife turned the ratchet!
3) The valve was easy to disassemble. The 0513120-4 retainers in mine were loose, and flopped around inside their respective cavities. However, they didn't seem to want to fall out, and I didn't try. After learning how expensive they are to replace, I was really careful not to allow one to fall out when I wasn't looking. A dental pick WAS really helpful.
4) My cam did NOT have an extra washer on top, nor did it have any washer or bushing below. There was a very nice wear pattern in the center of the cam. On re-assembly, I did not install the outlet fitting until AFTER assembling the cam, top O-ring, gasket and top cover. At this stage, I could move the cam to the top and bottom of its possible travel, and verify that it did not come close to releasing the two balls.
5) The McFarlane kit I purchased (it has gone up significantly in price) was perfect, except it came with a .093" diameter roll-pin. I'll be calling them next week to inquire into the reason. Fortunately I had the requisite .125" x 0.5" roll pin in stock. Start the roll pin into the block with a brass hammer on a hard surface. Then, holding the valve in a vise, set the ball in the appropriate detent, insert the spring, press down, and squeeze the roll pin the rest of the way in with a pair of channel lock pliers.
6) I didn't see it mentioned in this thread, but elsewhere is the suggestion that the roll pin be backed up by threading safety wire through it. The Aussies have made this an airworthiness directive I believe. Since a roll pin migrating out causes a really ugly failure mode, I considered this a very necessary additional step.
7) On re-assembly, I started the flare nuts, but left them very loose BEFORE installing the bolts. The bolts are difficult to even start in their respective holes. Figure on working almost entirely in the blind.
I personally loved the idea of fabricating a strip of aluminum with two #10 nut plates on it. This makes the job of lining up the nuts a whole lot easier. When one is started, the other one is automatically squared and lined up. I'm attaching some pictures of my finished valve as well as the nut-plate-strip. As an alternative, one could use two "jet nuts," or "K-nuts" in lieu of the original nuts.
http://www.aircraftfast.com/jet-nuts.htm These would allow use of a 1/4" box end wrench to hold the nut while tightening. Starting any type of individual fastener (K-nut or unattached nut plate) is likely to be more difficult, but holding either of them would be much easier.
9) The SafeAir CAV-110H4 drain valve was installed for its obvious safety enhancement. I chose the long-stem version because I was not certain the CAV-110 version would extend far enough below the belly to keep fuel out of the airplane should the drain seep fuel in-flight. In the past, I've had a bit of grit stick in one of these valves and allow a very slow seepage.
I hope the above information will save someone out there some acute future frustration.
Karl
BTW - I took the time to make a very accurate pattern. If anyone should want a fabricated nut-plate-strip, I would be willing to replicate one for a reasonable donation.
