Rotax fuel fitting torque values

I'm having trouble figuring out what the correct torque values are for the following engine fuel line fittings:

1. VA-216 Fuel return line brass hose fitting to the -4D bulkhead union.
2. VA-216 Fuel pressure sensor line steel hose fitting to steel elbow F4 DTX-S.
3. F4 DTX-S elbow to the brass thread on the fuel pressure sensor.
3. Gascolator to fuel pump line at the gascolator -6D fitting (Rotax Installation Manual says 135 lbin for this one, but seems a bit low for a -6D??).

The Standard Aircraft Handbook Fig 7-13 gives a range of values for different types of fittings, but which ones to use for the above connections? To add to the confusion, the Aeroquip table from Vans gives different values for aluminium fittings than those in the Handbook. I also can't find anything in the various Rotax manuals for these hoses other than the one mentioned above.

What have others done?

It might be helpful if you posted the size and type of thread, and the materials of the fitting and adjoining fitting or hole. Pipe threads, as one example, will not have a torque value, but rather a number of turns past finger tight. Hose type fittings will have a torque value depending on the size and material of the fitting. Same for tube fittings.

novipilot said:

It might be helpful if you posted the size and type of thread, and the materials of the fitting and adjoining fitting or hole. Pipe threads, as one example, will not have a torque value, but rather a number of turns past finger tight. Hose type fittings will have a torque value depending on the size and material of the fitting. Same for tube fittings.

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Thanks for the response:

1. brass hose fitting onto AN832-4D alum union (pipe thread 1/8")
2. alum hose fitting onto AN822-6D alum elbow (pipe thread 1/4")
3. male brass pipe thread (3/8" OD) into steel F4 DTX-S steel elbow
4. steel hose fitting onto F4 DTX-S steel elbow (pipe thread 1/8")

No 2 is specified as 135 lbin in the Rotax manual, so that one is clear enough although the Aircraft Handbook says 75-125lbin, while the Aeroquip table on Van's site says 150-195 lbin. http://vansaircraft.com/pdf/Torque_Spec_Aluminum_Fittings.pdf
It's the other ones I'm really not too sure about.

Hmm, no takers? Well then, unless anyone has any better ideas I'll go with:

1. 80 lbin (based on 135 lbin for No2)
2. 135 lbin (as per Rotax Installation Manual p 88)
3. thread sealant, seat by hand plus 1 to 1-1/2 turns
4. 100-250 lbin (based on Fig 7-13 in the Standard Aircraft Handbook for hose end fittings)

... and check for leaks when I finally get the thing started.

Great post from Down Under!

Thank you Robert for this contribution, right on time when I needed the information. After going through my "trust but verify" routine, I followed your guidelines, except for the fuel pressure sensor fitting where I stopped at 70 lbin, mostly because the sensor was too hard to block while torquing (any suggestion welcome!). I was happy to find out that in these now tight quarters it was possible to squeeze my torque wrench which is more satisfying than counting fractions of turns after bottoming!
I general with RV-12 VANs did a great job writing detailed and very precise instructions, a big change (according to my fellows "RV < 12" builders) from previous kits. I am convinced that it contributes significantly to the RV-12 success, particularly for novice builders like me. But in this particular case, I am at a loss understanding why these torque values are not spelled out where they are needed. After all there are a lot of torque values mentionned throughout the sections of the instruction manual.
Calling VANs did not help as I got the usual reference to the Technical Data sheet from Aeroquip which is more targetted at professionals than guys like us, RV-12 builders. Fuel leaks are serious matter and I hope this omission is not just to avoid liability, leaving builders on their own.

No problem Jean-Pierre, however I still don't know if those values are necessarily appropriate. I had a discussion about torquing with my tech counsellor recently (he runs an engineering business and has built an RV-6 and an immaculate 360hp Culp Special as well as working on many other aircraft projects). He said he's never used a torque wrench on fuel line fittings, and there seem to be plenty of other experienced RV builders on VAF who say the same.

I'm in the process of putting the oil sender on the firewall using Lockwood's kit, and he demonstrated how he would tighten that fitting. It was pretty tight, and was about where I think I would have got it by feel as well. Still, if you're not sure, and you don't have the experience, where do you start? I also think it would be helpful if Vans had some more guidance on this subject in Section 5. There's nothing worse than feeling unsure that what you've done is right.

rgmwa said:

He said he's never used a torque wrench on fuel line fittings, and there seem to be plenty of other experienced RV builders on VAF who say the same.

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Now this is interesting! You would think that fuel lines are the ones that require most precision in torquing but what do I know? May be the reason is that these lines are often so burried into the guts of the airframe that using a torque wrench is just not possible. It is exactly what happens in the RV-12 between the fuel tank and the firewall hense my excitement to find out that the fuel fittings in the engine compartment were torque wrench accessible.
I am also puzzled by the absence of reaction from the RV-12 community on this post when it was created. On the other hand you face this issue of torquing these three fittings once in the build which means that so far it just happened a couple hundred times and mostly with experienced builders. But wait, now the green guys are comin!