primer line connection

[prkaye]

I'm having trouble identifying the primer line connection on my O-320 from Aerosport. According to the manual it should be in the area shown in this photo (of my engine)... where should it be?

[Don Jones]

There is not one in the photo. There should be a "T" fitting with 1/8 copper tubing running off of it to the primer nozzles fitted into (in most cases) 3 cylinders. It is usually near the oil pan rail.

[Mel]

The primer line should come off the gascolator or somewhere upstream of the mechanical fuel pump. It will not come off the engine itself.

[prkaye]

The primer line should come off the gascolator or somewhere upstream of the mechanical fuel pump. It will not come off the engine itself.

So if I understand correctly, the priming system will take fuel from the gascolator, and pump it into the carb? (why is this necessary in cold weather?)

But why then does the O-320 manual depict a port for the primer on the engine itself? Is this an older way of doing it?

[vlittle]

Phil, the primer pumps fuel from your gascolator directly to the intake of your cylinders.

You will find 1/8" hole plugs on the heads of all of your cylinders. One of these holes is used for the manifold pressure sensor, leaving 3 cylinders left for priming.

Some of the new engines have two ports per cylinder. The upper ports are for fuel injectors but can be used for primers as well--- that's what I did.

If you look carefully you'll see the copper primer lines in this photo:

[Mel]

Not sure I understand. Your manual must be different from mine. The only primer ports shown in my manual are the ones that go into the cylinder head just behind the intake valve. Page 6-8 of the 0-320 parts manual shows the routing of the primer lines. The input for the primer is item 9, a union "T". The input to this "T" normally comes from the gascolator, through the primer pump, then on to this "T". I've been working on Lycomings since the early '70s and to my knowledge, it's always been done this way.

[Lycosaurus]

Originally Posted by prkaye

So if I understand correctly, the priming system will take fuel from the gascolator, and pump it into the carb? (why is this necessary in cold weather?)

But why then does the O-320 manual depict a port for the primer on the engine itself? Is this an older way of doing it?

Phil,

Each cylinder should have two ports, in your case both are plugged. The upper port would be for fuel injection, and the lower one for priming, or in the case of cylinder #3, for vacuum. You can thus use up to 3 ports for priming.

Most planes have 1 port used for priming. This allows fuel to be sprayed close to the intake valve, allowing for an easier start in cold weather. I decided to use the full 3 ports, cause it gets pretty cold here, and better it fire on 3 cylinders than just one.

Some have done away with primers ... You could pump your throttle to drop fuel in the in the carb, however there is a greater risk of causing a fire if it backfires. Play it safe, use the primer.

The primer line starts off from the top of the gascolator, onto the solenoid valve, then onto a distribution lines (some T fittings) to each of the primer ports (if doing the multiple cylinder thing).

[prkaye]

i'm looking at fig 7-7... the following is a photo of it. On the cylinder it shows the "primer or manifold pressure connection (what Alfio was talking about). BUt towards the bottom right of the figure there is that "primer line connection". What is that?

[Don Jones]

... is worth a thousand words. This engine does not have a mechanical fuel pump, but this is in the area where the fuel pump would be.

[prkaye]

hmmm... let me see if I can find that on my engine...