This page created 11/9/99; Updated 12/14/11
The original fuel selector valve for the Stinson 108 series is a brass valve that has a history of becoming difficult to operate over time. Finally, there is a modern replacement valve available. Bruce Plendl of Everett Washington (Email: email@example.com) developed the new replacement using an Allen Aircraft Products valve. The valve kit is available from Univair. Here's what Bruce had to say about the kit when it was introduced in 1999:
"Univair has improved fuel tank selector valve kits now available for the Stinson to replace the original style brass tank selector valves. This is Univair's design kit equivalent of the single-use STC modification made to my airplane over two years ago, utilizing an Allen Aircraft Products valve. The Allen fuel valve is an aluminum valve of modern design and on my airplane operates as nicely as the day it was purchased. The selector rotates smoothly and easily with positively felt detent positions. (I sure don't miss draining my tanks yearly to lubricate the old valve.) Even though I only have two years time on my installation, the Allen valves have been used for several years on Piper products.Bruce offered these additional words in January of 2007: "Regarding the fuel selector, I am now approaching 10 years with the Allen fuel selector and have not had to perform any maintenance on it. It works as well as the day it was installed." Bruce also provided, in February of 2007 a comprehensive "10 year Update" report, in PDF format, on the development of his original fuel selector valve STC. The report describes in detail the testing that was done to receive FAA approval. Included in the update is a discussion of the issues that would be involved in seeking approval for use of the Allen valve with alternate engines and a summary of applicable FAA regulations relative to the fuel system. This report is an extraordinary resource for those interested in engineering data on the Stinson fuel system.
Back in 1999, I spoke with Bill Little of Univair who offered this information:
The valve is installed according to "Univair Aircraft Corporation Service Information Letter No. 80" dated 2/22/99. Since Univair holds the Type Certificate, this change can be accomplished in accordance with this Service Letter and no STC is required. Appropriate log entries are required and the instructions that accompany the kit should be kept with the aircraft logs for future reference if needed for maintenance purposes.
Included in each kit is the U491-947 valve, screws, flareless line fittings, a collar that fits between the valve and the fuel selector torque tube, washers, clevis pin, etc. The torque tube needs to be cut and drilled to fit onto the collar with a clevis pin. The fuel lines are trimmed and cut squarely to a length where they will bottom on the seat within the flareless line fittings that are used with this installation. Detailed installation instructions are included in "Service Information Letter 80."
Installation of one of these kits eliminates the requirements of Service Bulletin No. 250 and Service Letter No. 77.
In posts on the Yahoo Stinson discussion board in January 2007, it was noted that the valve supplied by Univair is the same for either the 3/8" or 1/2" lines, only the fittings are different. This is confirmed by the parts list included in Service Letter No. 80. In fact, the the ONLY difference between the 2 kits is the number for the flareless fitting (68x8x4 for the 1/2" kit and 68x6 for the 3/8" kit). The part numbers for the valves are identical, U491-947.
As of this writing, the fuel valve kits are not approved for alternate engines, only the stock 150 or 165 HP Franklins. Bruce Plendl indicates that this is not necessarily because the valve does not provide sufficient fuel flow, but rather that the engineering required for FAA approval has not been pursued. Bruce stated, in an email dated Jan 11, 2007, "As I have said in past discussions, the 1/2 inch fuel system with this selector flows an incredible amount of fuel." Bruce believes that the valve could support up to 180 HP. Beyond that, other solutions would probably be needed, including the addition of a fuel pump.
At Oshkosh 2010 Univair had a prototype of a valve that they plan to approve for the Lycoming O-360 installation. On December 22, 2010, Bill from Univair said they are still working on it - nothing new to report yet. For the latest update on this, you could contact Univair.
I ordered and received the 1/2" kit for my Stinson, but decided not to install it because of uncertainty over future engine upgrades. I had Frank Bailey in California overhaul my original valve in 2005, but Frank is up there in years and is no longer providing the service.
Original Imperial-Eastman brass 1/2" fuel valve installed on my Stinson 108-3. Shown with firewall off. Earlier aircraft that had the 150 HP Franklin were originally equipped with 3/8" fuel lines and a 3/8" brass valve.