prkaye

Well Known Member
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?

 
Primer line

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

124_2448_1.jpg
 
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.
 
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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).
 
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?

 
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A picture...

... 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.

primer.jpg
 
Primer line

Don, I'm confused as to what thousand words your picture is telling me, other than that your engine has some fitting where a fuel pump would go...

The fitting you see with the 1/8" copper lines coming off of it is the primer connection that as Mel said comes from the primer pump. The lines shown in the picture route around both sides of the engine and attach to the primer nozzles which are screwed into the intake ports. I am pretty sure since you can't find it, it is not installed on your engine.
 
Another pic:

1/8" line off the top of the gascolator. Into the primer mounted sideways; then off the top to two portside cylinders on the bottom fittings. Another line goes to one cylinder on the starboard side.

 
Phil,
The drawing you have is misleading. The primer lines are not a part of the engine and are not normally included with the engine. If you look at Don's picture, you'll see that the lines are only attached to the engine to secure them from breaking due to vibration.
 
Thanks Guys! I think I found the ports Alfio was describing... are these correct (pic labelled below)?



The fitting you see with the 1/8" copper lines coming off of it is the primer connection that as Mel said comes from the primer pump. ... I am pretty sure since you can't find it, it is not installed on your engine.

Does this mean I can't have a priming system? Is the primer pump somethign that has to be built-into the engine? Or can I just slap one on?
 
Many people now use an electric primer. I prefer the old Gerdes hand primer. Of course. I also have manual flaps and manual trim.
 
Thanks Guys! I think I found the ports Alfio was describing... are these correct (pic labelled below)?





Does this mean I can't have a priming system? Is the primer pump somethign that has to be built-into the engine? Or can I just slap one on?


The primer pump, is your electric boost pump that's in the cockpit.......unless it's a hand pump like Mel has. You turn the boost pump on, then hit the prime switch for 2 or 3 seconds, which opens a solenoid , as in my 1st pic. Your engine is all set up for this.

Note: the solenoid is what the arrow is pointing at, in my first pic.
 
The primer pump, is your electric boost pump that's in the cockpit.......

Thanks! I think I get it now... my boost pump (the "automotive fuel pump" that gets mounted to the aft side of the firewall, near the floor?) pumps fuel through the gascolator. When the prime switch is on, the solenoid opens the valuve which allows fuel to come out teh primer line at the top of the gascolator and on directly to the cylinders, bypassing the carbeurator (and intake manifold) completely. Is that all correct?

So does it appear that I have those two ports correctly labelled in the photo?
 
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Thanks! So does it appear that I have those two ports correctly labelled in the photo?

Yes, the labeling is correct. I heard that you could also use the fuel injection ports as primer ports ... can't confirm. It may be easier to route your lines. I used the bottom ports though.
 
Top ports?

I was researching the routing of the primer lines for my O-320-D1A and I'm wondering if there is an issue with using the top ports for the primer? There seems to be some confusion about this. Thanks!