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108-2, Install 25Gal Tank - Connect 3/8" Tank Fitting to 1/2" Fuel Line

Mike Olson

Mike Olson

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All
I am restoring my 108-2. It originally had 20Gal tanks (no longer have), and I am installing 25Gal tanks. The tank connection is 3/8". The fuel line is 1/2". I plan to use a reducer fitting that would connect the 3/8" to the 1/2".
Are there any concerns with this plan?
Thank you so much for your comments.
V/r
Mike Olson
8035K

(If more convenient, please call me at 970-749-0336. Thank you)
 
Mike,

If your engine is 165 HP or higher, you need 1/2” all the way, including the connection. I am surprised you have a 25 gallon tank that is not 1/2 inch as these tanks were only installed in the 108-3s….which all had 165 HP. I have been told the structure of the 108-2 wing, which had the 20 gallon tank, cannot fit a 25 gallon tank….but I could be wrong. When I restored my 108-2, we discovered one tank had a 3/8 inch exit. I had a local A&P, who is good at welding, weld in a new exit pipe and thread it for a 1/2 inch exit. He filled the tank with some type of inert gas to keep things from exploding as he welded. Good luck.
 
By keeping the 3/8 inch fitting, you have a choke point in the fuel delivery system. This could be a potential risk by dropping fuel pressure/volume when you need it most. That being takeoff or go around.
You should maintain 1/2 inch diameter fuel lines throughout the system.
 
All
I appreciate your comments. I will proceed with changing the tank exit orifice from a 3/8" to a 1/2".
Next task is to find an A&P that can perform the task.
Thank you for the insightful responses.
Please send a note if you know of an A&P that I could contact about modiying the tank.
V/r
Mike
N8035K
 
Having talked to Mike this is where he is at with the fuel system for this 1947 108-2:
Mike's 20 gallon tanks that were in this flying airplane were cut open rendering them unairworthy.
Those 20 gallon tanks had 1/2" 90º fittings for hoses and clamps.
The 20 gallon replacement tanks, Mike has, have 3/8" 90º fittings for hoses and clamps.
Mike is searching for replacement 1947 108-2 20 gallon tanks with 1/2" 90º fittings for hoses and clamps.
Steven B
 
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