[ArVeeNiner]

I have a MA-4SPA carb. Van's drawing OP-28 says that a AN823-6D fitting gets installed into the carb. That fitting has a pipe thread that goes into the carb and it takes about 3/4 of a turn to get snug.

When I look into the female fitting on the carb, it looks as though there is some sort of flare in there that is made to take a male tube fitting. See the pictures below. My question is, is Van's correct in calling out the AN823-6D?

 

[osxuser]

Yes, it's a pipe thread fitting.

 

[DickDe]

Carb Fittings

The fitting you have on the carb. in your picture appears to be anodized aluminum. On the engine most will use steel fittings here as well as on the gascolator. I don't know if that is a requirement but I was told it is accepted good practice because of the added strength and the relatively severe consequences if it fails. I used steel and my Cessna had steel as well.

Dick DeCramer
RV6 N500DD flying
RV8 fuselage
Northfield, MN

 

[osxuser]

I concur that steel or brass would be better choices than Aluminum, but it's not unacceptable to use aluminum.

 

[Rick_A]

Steel

I used steel on most of the fuel and oil fitting FWF. I've got a bunch of aluminum AN fitting that came with the FWF kit that I never used.

 

[Beancounter]

Carb fitting

The finger screen female fitting on my Marvel carb was NOT national pipe thread. It was straight thread just like the mechanical fuel pump fittings. Please check yours. I dont know how safe it would be to rely on 3/4 of a turn with an NPT fitting in a straight thread.

 

[osxuser]

Hmm, how old is your carb? The finger screen itself isn't pipe thread, but usually the inlet side of it is... I've never see one otherwise.

 

[ArVeeNiner]

I'm not sure how old the carb is. It was rebuilt a couple of years ago for a guy with a Vari-Eze but never used by him.

I'll go with steel. I was just following Van's drawing but that has bit me on a few occasions during this build.

Honestly, it feels like it's made for a pipe thread. The 3/4 turn I'm referring to is until it gets finger snug. I have yet to put a wrench on it. It threads in quite easily. I wonder how trying to thread a pipe thread into a straight hole would act. Would the end of the pipe thread actually be smaller in diameter than the straight thread diameter?

 

[osxuser]

Hmm, If it starts to tighten up really quickly, and you can't get 3-4 full turns in before it becomes really tight (with a wrench), it's possible you don't have a NPT fitting, i've never seen one, but they I guess they exsist (see above). My solution if that was the case would be to buy a new finger screen rather than deal with a straight fitting.