O-360 - Primer Fittings in AN-3 Size??

Canadian_JOY · #1 05-28-2016, 08:29 PM

I had stainless braided conductive teflon primer lines made by one of the VAF-supporting vendors. They were made with AN-3 fittings on each end. Our engine is a carb'd O-360 and I have a hand-operated Essex-style manual primer pump installed in the panel.

Where I'm a bit stumped is with the primer nozzles which will be threaded into the cylinder heads. If I just use a regular AN-3 /1/8NPT AN fitting, the fuel will sort of drizzle into the cylinder head, as opposed to producing anything like a mist. Regular primer nozzles are brass AN-2 size. I'm kinda scratchin' my noggin trying to figure out where I go from here.

Anybody have any good ideas?

BTW, this aircraft will be operated in very cold weather - think arctic-like, -20C or colder, so doing without primer lines to 3 of the 4 cylinders is simply not an option (the port on the 4th cylinder is used as a manifold pressure pick-off point). Even with pre-heat, when it's that cold, you want to be sure your engine will start reliably every time. I've had great success with manual priming systems in the past, so that's what I wish to stick with.

Thanks for your well-considered replies.

lr172 · #2 05-28-2016, 09:55 PM

They make special primer nozzles (designed to atomize the fuel) and fittings for them (not standard AN fittings, but same as Injectors) The tube end fittings are designed to be soldered on to 1/8" OD tubing (softwall copper is typical). The tube ends and nuts are the same as those used for injector lines, except brass. I think it is AN-812 or something like that. The primer nozzles are NOT AN-2 and an AN-2 hose fitting will not attach. I am aware of no primer or injector nozzles that use AN-2 or 3 fittings.

If you just pour the fuel in with the system you set up, all the fuel will run down the intake pipes and pool in your FAB (fire risk with a backfire). With a restricted fitting, like a primer nozzle, the pressure will force most of fuel to pool around the intake valve, where you want it.

I just converted to FI and pulled a complete 3 cylinder primer setup from my engine. Worked great during Chicago's winter season. I was about to post this set up in the classified section. PM me if you interested.

Larry

TS Flightlines · #3 05-29-2016, 06:32 AM

Mark---you can make hoses with -2 primer ends to connect to primer nozzles.
We typically do it with -3 teflon, since getting -2 is difficult, as well as collars and such.
Tom

Canadian_JOY · #4 05-30-2016, 06:07 AM

Thanks for the inputs, folks. The challenge is I already have the hoses with -3 ends, so now I'm working on resolving exactly which fitting to use in the cylinder head. I'm leaning toward using steel fittings and silver soldering restrictors into them, or perhaps using JB-Weld to hold a restrictor in place.

While I have the brass primer fittings and lots of copper line, I'm not inclined to go back to that technology, especially now that I've got a bunch of nice stainless braided conductive teflon hoses in hand. Time for another trip to the shop to work out a way to make these work effectively.

aerhed · #5 05-30-2016, 07:40 AM

You could just put restrictors in AN3 fittings. There are two styles of brass primer fittings. The old style are just plain with no restrictor anyway (no it doesn't just dribble down the intake tube).

TS Flightlines · #6 05-30-2016, 02:32 PM

you can make an adapter from -3 AN to -2 to convert your hoses,if you wanted to go that way.
Tom

Canadian_JOY · #7 05-31-2016, 09:02 AM

A brief follow up and a word of thanks and commendation to Tom Swearengen.

Without prompting, Tom contacted me off line and has patiently walked me through the most viable options. This is the kind of service that puts TS Flightlines at the top of the heap when it comes to suppliers who go the extra mile to earn and keep your business.