injector O-ring sealing - sides and bottom or just sides???

[fury fan]

I'm still in my fuel hardware R&D stages; I'm working to convert a cast-iron manifold. For the bottom injector boss I'm drilling 3/8 pipe plugs out to injector size - I found a handy counterbore bit that does the job nicely (but requires a delicate touch on the drill press). Upper end of injector fits to a standard Edelbrock fuel rail.

So the question:
Do the injector O-rings need only the sides for sealing or do they need the bottom also?

The reasons I don't know:
1. I have some Delphi injectors with a plastic collar on the bottom below the O-ring. The top end of the Delphi injectors has a metal snout, above the O-ring, where it fits my Edelbrock fuel rail. Both these O-rings appear to only seal along the sides. The Bosch I looked at, though, could potentially seal either way. The Delphi could seal via the O-ring at the top if my fuel rail hole was slightly larger than the metal snout.

Here is a good pic of the Bosch-type injectors:
http://www.hotrodsolutions.net/injectors.html

2. I see some aftermarket aluminum bungs that appear to be simply pieces of CNC-machined pipe. There appears to be no step in them, so it looks like the injector would bottom out on its body ILO the bottom O-ring. This would also suggest side-sealing is all that is required (assuming these suppliers are selling a well-engineered product).

FWIW, I have drilled and pressure-tested several of my fittings with 40PSI shop air, soapy water, and an injector pressed in. One Delphi injector *slowly* started to walk out of one fitting, but besides that I saw no bubbles and no troubles with either injector type in 3 different fittings.

It may seem like I've answered my own question, but I wanted to start some dialogue with you more experienced fabricators. What are your thoughts???

[devastator]

I've been replacing injector o-rings a lot lately, and I can tell you that mine definitely seal on the side only.
I machined my own fuel rails as well, and they seal on the sides of the o-rings. My injectors look a lot like yours, only with a metal end.
Hope this helps.
Dev

[airfueleddie]

I'll attempt to find the correct answer to that 'problem' or potential problem.

[Heribert]

The injectors are designed with one O-ring sealing the fuel pressure side and another oring sealing the manifold vacuum/pressure side.
Both o-rings shall seal by being radially compressed.
For this to work well and last :
Make sure you have a 45 degree chamfer some 1 mm deep where the Oring enters. Smooth any burrs with 400 grit carborundum paste. Break all edges
Apply a thin film of good quality grease when mounting. Dry Orings tend to shear off a little bit of the circumference and thus loose compression.
Sorry for going metric on you but the standard injector Oring fits in a 13,50 mm hole

Replace the Orings whenever dismantling.

Klotzakk

[airfueleddie]

Thanks Heribert. Answers some very specific questions I had. Radially compressed. Makes perfect sense now!

[np75]

I just thought I would add for reference that while they are typically a radial seal (sealing on the bore OD), some are a face seal (seal on the bottom of the bore). Some late model Toyota injectors like the Scion tC have a square section o-ring on the manifold side that is at least primarily a face seal.