Assembling a fuel-injected engine: What about sealants and fuel line routing?

I have nearly finished assembling a Lycoming O-360 that will be fuel injected. I am trying to find information regarding what kind, if any, sealant I should use and how to apply that sealant should one be used. I am assuming that careful application would be required in this area, specifically the fuel flow divider. Also, any information about the routing of the fuel line from the throttle body to the fuel flow divider would be a big help.

Jim George

via email

The nozzles are installed with no lubricant, but the threads should be nice and clean, as well as the threads in the cylinder. Keep in mind that these are a pipe thread, so don’t over torque them.

I’d also suggest you review a copy of Service Instruction 1414A, for some good information, including proper torque, for the nozzles and the attaching fuel lines. There have been instances in the past where the fuel line to nozzle was over torqued and it actually cracked the top of the nozzle, causing erratic engine operation and a slight fuel leak.

With the new design cowlings most aircraft use today, we are unable to do a good visual inspection of the engine compartment during a preflight, so a small fuel leak may go undetected for some time. In the old days, when you could open up the side cowls and get a good look around under the cowl, situations like this were less likely to go undetected.

The best information on proper routing and clamping of the lines is available in Service Bulletin SB342E. This SB is also covered in the FAA AD Note 02-26-01. This AD Note was introduced following the discovery of improper routing and clamping of lines that could lead to the lines breaking and spraying fuel in a hot engine compartment, resulting in a potential fire hazard.

The routing of the fuel line from the fuel injector body to the flow divider is really up to you, but I’d recommend that you check out a current IO-360 parts catalog for the various options for the different models. The PC also would provide the hose part number that connects the injector to the flow divider and provide you with the specific part number for the inner cylinder baffle that the fuel line passes through between the fuel injector and the flow divider. You also can get the part number for the mount bracket for the flow divider and any attaching hardware that may be required.

Paul McBride, recognized worldwide as an expert on engines, retired after almost 40 years with Lycoming. Send your questions to:

Almost all of the mail I receive from readers is positive and educational. The number of responses to the column on static electricity (What’s the proper way to ground during refueling, June 9) was certainly a learning experience for me. For example, Doug Millard wrote, “”I do know for a fact that there is almost universal misunderstanding on the subject (of static electricity).””

William Hougland noted the correct term is bonding, not grounding. Bonding refers to connecting a cable from the aircraft to the refueling system and not necessarily to ground. The main concern is for both the aircraft and the refueling apparatus to be at the same electrical potential. He also raised the question of how to bond a composite aircraft. It is much more critical to establish a proper bonding connection point on composite aircraft than on aluminum aircraft since most of the airframe is nonconductive.

Another interesting note was from Tim Zuck from Racine, Wis., who noted that most pilots do not want a bonding cable connected to the exhaust since the clamp will scratch the coating and lead to rust. This rust can reduce the life of the aircraft’s exhaust system. Tim’s training recommends that “”the ground cable be attached to either the tie-down or a bare spot on the wheel.”” (I assume he meant a spot on the axle or strut since if one connected to the wheel itself, the conductive path would need to go through the wheel bearings, which may not be that conductive.)

Another point was made by William Belleau, who pointed out that on later model aluminum-skinned aircraft the filler neck is part of the skin. On these models, most people will let the fuel filler hose sit on the wing and the nozzle can put pressure on the filler neck. (Remember that the fuel filler hose is conductive.) However, on a rag wing aircraft, the hose and nozzle could damage the wing surface and filler neck. Therefore, many pilots will hold the nozzle away from the neck sides. This can create an electrical potential differential that could lead to arcing and a fire if the aircraft tank is not properly bonded.

He also told about a helicopter operator who lost a JetRanger that was being refueled. One of the crew was wearing a nylon jacket. He heard a snap inside the tank, then the tank was on fire. He also told about an airman who went onto a storage tank during a snowstorm. He could not get the small sample access cap off so he opened the manhole cover and let the sample jar down on a string. When it got the right distant from the fuel, he heard a snap. The explosion threw him off the tank.

The main problem for most of us is that we become complacent. We do the same thing time and time again with no problem. But static electricity is always there. If we miss a small step just one time, it can really bite us.

If you have an aircraft, designate a bonding point. Check the conductivity between that point and your fuel fill neck on a periodic basis. Finally, use a bonding strap each and every time you refuel your aircraft.

Ben Visser is an aviation fuels and lubricants expert who spent 33 years with Shell Oil. He has been a private pilot since 1985. You can contact him at

Leave a Reply

Your email address will not be published. Required fields are marked *