Request for photos

[48RagwingPilot]

Could someone with an A or B model either take a photo of one of the fuel lines passing through the rear gear box bulkhead forward toward the fuel selector valve or describe in detail the method used by Cessna to penetrate that bulkhead and support the fuel line? I need this info to move forward with removing the fuel pump from my '48. Any assistance would be greatly appreciated. Thanks.

[Bruce Fenstermacher]

The fuel line goes up the middle tunnel which also houses control cables. Here is a few drawings from the IPC.

[n2582d]

My '52 B model is a little different than Bruce describes. On mine the line runs to the right outside the tunnel. The line passes through three 1" dia. holes that call for AN931-6-16 grommets. The IPC shows two lines (p/n 0500106-60 (forward), and p/n 0500106-89 (aft)). The IPC forgets to include a union, AN815-6D, between the two lines. In the second picture you can see where my two lines join. I assume this is original but have not compared this to other 170's. Threading the forward line without having the firewall off will be a real challenge.

[48RagwingPilot]

Thanks to you both for the replies, drawings and photos. It appears the fuel selector valve in the A and B models is located at the aft end of the tunnel, aft of the gear box bulkheads, while in the '48 it is located in the middle of the tunnel, forward of the gear box bulkheads. So, it looks like I'll be able to penetrate the gear box bulkheads on both sides of the tunnel using 1" holes and grommets and then into the fuel selector valve, which should work out well.

[hilltop170]

Those bulkhead grommets are very important! Without them, the bulkhead will eventually "saw" its way thru the gas line if it touches the bulkhead. Vibration wear is very patient and will eventually get the job done even if it takes 50 years. One of the grommets was missing on my plane and was caught by an astute IA during an annual. When the line came out, one bend at the abraded area and the line broke in two! It was just thousanths of an inch away from wearing thru. If it had broken, the entire contents of the fuel tanks would have dumped into the belly. I don't even want to think about the enevitable outcome had that happened.

Another thought, bulkhead fittings on the fuel line at each bulkhead would have good and bad points. With them, each section of line between bulkheads could be individually replaced without having to snake a pre-bent line into confined spaces. The fittings themselves would prevent bulkhead chafing and rigidly support the lines. On the other hand, it would cause the fuel line to weigh more and have more potential leak spots.

[48RagwingPilot]

Excellent information, thanks. I'm going to propose to my A&P/IA using a combination of grommets and strategically placed Adel clamps. I hope to document the project with photos so the next guy won't have to reinvent the wheel.

[n2582d]

Another thing you may need to consider is where water may collect in your new layout. The low point with the tail down in the B model is between the door posts and the fuel selector. The later style fuel selector has a pipe plug in the bottom that some have replaced with a drain valve.

[Bruce Fenstermacher]

Another thing you may need to consider is where water may collect in your new layout. The low point with the tail down in the B model is between the door posts and the fuel selector. The later style fuel selector has a pipe plug in the bottom that some have replaced with a drain valve.

The early A model selector also has a pipe plug that a drain valve could be installed. However the plug is not often found above a hole in the belly for easy access and if you care about such things the STC which is available only covers the B model.

[mike roe]

Also if you search the forums you can find where some have replaced the fuel selector mounting hardware with nutplates to make removing anytime at a later date much easier working thru the access hole. Excellent idea.
Mike Roe

[48RagwingPilot]

Thanks again for all the great comments and ideas. If possible, I'd like to install a drain valve in the fuel selector. Does anyone have information on the applicable STC? My field approval is pretty broad and authorizes alteration of the existing fuel lines to mimic the B model, so it may be possible.

[GAHorn]

I installed the CAV-110H-4 , which allowed a short drainpipe to extend below the belly.

Saf-Air 1/8" pipe

cav-110h-4.jpg (16.47 KiB) Viewed 9445 times

IF you decide to actually mess with an STC to install an operable drain plug in lieu of a plain drain plug.... don't forget to fill out Form 337.

Also, do not use much torque to install, remembering that it is only gravity pressure that exists in this location. Do not use Teflon pipe thread tape either, particles can drift downstream and end up in your carb. (Use a small dab of Permatex No. 2 instead on only the second thread, IMO.)

[blueldr]

The threads, on the above picture of the CAV-110H-4 drain fitting, look to me like straight machine threads rather than tapered pipe threads. If such is the case, some sort of a gasket would be required.

[GAHorn]

Nope, ...they're NPT.

[48RagwingPilot]

Thanks, fellas. More to follow as the project progresses.