(fuel) primer questions

[13brv3]

Greetings,

I have a couple primer questions. First, am I the only one who is bothered by the thought of priming only 3 cylinders?

On the last RV-8 that I built, I used the top ports on my O-360 for primer, so that I could prime all 4 cylinders. To me, this seems like such a logical thing to do, but I can't get over the fact that no one else seems to do it that way.

Is there some reason people don't use those upper ports for primer? I know that using the bottom ports keeps you from having to go into the baffles, but that's really easy with a bulkhead T fitting, so I can't see that being a big reason not to do it.

I also know that it's perfectly acceptable to primer 2 or 3 cylinders, rather than all 4. If it weren't so easy to do all 4 using the upper ports, I would just live with 3. The only other (unlikely) justification for having 4 ports would be to allow some fuel flow if something (did I mention unlikely <g>) happened to the carb.

Second question, is does anyone know if Aeroquip 306 hose (mil-h-5593) is OK for use with gasoline? I'm looking for a flex hose in -2 size to use from the primer solenoid to the T in the baffles, and this is one of the only hoses I can find in a -2 size. Unfortunately, searching the Eaton/Aeroquip site for 306, or MIL-H-5593 comes up empty. Searching the Aeroquip catalog online also has no mention of 306 hose. Is Spruce making this up

http://www.aircraftspruce.com/catalog/appages/aq306.php

Thanks for any info, or engine priming philosophy you care to post.

Cheers,
Rusty (finishing cowl installation, then on to baffles...groan)

[jonbakerok]

If I had it to do again, I'd just route a primer line to one cylinder instead of three. Then I'd have about 6 feet less brittle, fuel-filled copper tubing routed around next to a hot engine, and 7 fewer connectors.

You really only need one cylinder to get it spinning.

[zilik]

Long before Van introduced his primer kit I installed a 4 port primer using the top ports. I am amazed at how many people look at the carb then ask how I like my fuel injected 360.

The system works well and I would bet 3 primed cylinders would work well too!

Gary

[mlw450802]

Originally Posted by jonbakerok

If I had it to do again, I'd just route a primer line to one cylinder instead of three. Then I'd have about 6 feet less brittle, fuel-filled copper tubing routed around next to a hot engine, and 7 fewer connectors.

You really only need one cylinder to get it spinning.

This raises a question I have had for a long time:
Why copper tubing for the primer lines? Why not stainless steel?

Copper has no endurance limit in fatigue and those little lines invariably vibrate until they have a fatigue failure, the characteristic appearance of which makes the stuff seem brittle.

Of course, your suggestion to prime one cylinder seems to have some merit as well.

There are probably quite a few people living in the warmer climes who rarely use any priming to start. Priming only one cylinder would greatly reduce the likelihood of a flooded engine.

I am sure the cold country fliers have a differing experience.

-mike

[Sam Buchanan]

There are probably quite a few people living in the warmer climes who rarely use any priming to start.

Yep, some of us don't have any primer system on our carbed engines. This probably isn't a good option for those above the Mason-Dixon but it works well for me.

[osxuser]

Copper seems to work very well on certified airplanes (30 years of useful life and thousands of hours at least). Typical installation is 1 of 3 cylinders, but why not just run MP gauge to one top, and use the bottom for primer if you want 4?

[vlittle]

I have two cylinders primed using the top ports. Works very well and is much easier to route compared to the bottom ports.

My engine usually starts on the second blade after 2 seconds of (electric) prime.


Vern Little

[13brv3]

Thanks for all the comments. I guess I'm not surprised at all the variations here, but it seems clear that there's no good reason not to use the top ports as planned.

BTW, the Van's FWF kit includes a hose made to length for the bottom port on #3, otherwise, I could consider just running the MAP to an upper port.

I guess I'll give the Aeroquip 306 hose a try, and see how it does with gasoline. Still can't find any info on it.

Cheers,
Rusty (in baffle heck)

[mahlon_r]

306 is OK with fuel.
Good Luck,
Mahlon
?The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at you own risk.?

[13brv3]

Once again, Mahlon comes through

Thanks!
Rusty