c90 fuel pump fittings

[nigel cronin]

I have recently replaced the mechanical fuel pump on my Jodel which has a continental c90 engine. The problem I have is that the two right angle fittings that screw into the pump body when tightened down into the new pump are no longer correctly orientated for the inlet and outlet fuel pipes. In order to connect the pipes the fittings have to be left slightly loose. I tried using a two part sealant to seal the threads and I ran the engine and there appeared to be no fuel leakes. However, I can feel that the fittings can be rotated slightly if I wiggle the pipes. I don't really feel confident to fly the aircraft in this state. I am at a bit of a loss as to what to do. Any suggestions greatfully received. In particular any recommendations of sealants which would seal the threads and be mechanially strong (and fuel resistant). Thanks

[Ian Law]

This is at a bit of a tangent to the above post, but I've been trying to find the exact fittings for the ports on my Cleveland( Parker Hannafin ) master cylinders, which came to me second hand, with AN833 elbow fittings in the 7/16 - 20 straight threaded ports. Sounds similar to the problem mentioned by Nigel. These were sealed by what appeared to be tired looking gaskets/"O" rings, of some sort, that need replacing.

An obvious advantage of this type of fitting is that it appears to be possible to rotate it through 360 degrees so that the outlet (pipe fitting end) ends up pointing more or less in the desired direction, the whole lot being secured by tightening a separate nut.

Parker Hannafin in the US have never responded to my requests for the correct seals.

Suggestions from various other sources have ranged from the obvious "O" rings to boss seals. The Parker catalogues list a vast number of O rings and seals made by them, but matching these up to my Parker fittings is confusing at best. A local Parker "branch" in North Devon(To my surprise, they manufacture stainless steel versions of the AN fittings) recommended a particular "standard" O ring. When looking for this ( the size is, in fact, not all that standard, unless I wish to buy several hundred)I stumbled on an entry in the Aircraft Spruce catalogue for MS28778 Tube Fitting Boss Gaskets. These seem to be exactly what I have been looking for and I will be ordering some to try them out.

Maybe a similar fitting or boss type seal ( for a steel rather than an aluminium fitting ) might work for the fuel pump fitting? The inner edges of the ports on my master cylinders are machined to a small radiused, curved profile in which an O ring or seal would sit and the appropriate edge on the AN fitting is the same, I assume. Not sure if the boss seal will fit this and if not, I'll go back to trying to find the correct size O ring.

Ian

[Rob Swain]

The problem I have is that the two right angle fittings that screw into the pump body when tightened down into the new pump are no longer correctly orientated for the inlet and outlet fuel pipes. In order to connect the pipes the fittings have to be left slightly loose. I tried using a two part sealant...

Sealant? Ugh!

Any indication of what thread we are dealing with here? If it is a 'normal' AN fitting would getting banjo unions and bolts to replace the right angled fittings be a solution - you can point them anywhere you want!

Have you tried swapping the two unions round? Their threads may start and tighten at a different orientation.

Maybe Andair could help...

[nigel cronin]

Thanks for the ideas. The elbow fittings are different on the inlet and outlet. The outlet is 1/8NPTx5/16 tube and the inlet is 1/8NPTx 1/4 tube.

Nigel

[Mark A]

Assuming that the elbow fitting is a standard AN pipe thread, then you should tighten it finger tight and torque a further 2-3 turns to get alignment (-6 and -8 fittings).
I would apply 'Fuel Lube' or 'EZ Turn' to the threads as an anti-sieze on the male thread, avoiding the end few threads.
Avoid backing off after you've positioned it.

[nigel cronin]

problem now solved by being braver tightening the fittings down (Oaksey engineer not me!).

Thanks for all the feed back

Nigel

[MikeM]

Still on the subject of C90 mechanical, engine driven fuel pumps, can anyone explain how the pump avoids over-pressurising the outlet flow to the carb when the carb float bowl is full? Does the outlet valve stay open?

[David Hardaker]

Mike
The arm that follows the camshaft is spring loaded so the pump will only deliver as required to maintain a full float chamber....
D

[MikeM]

thanks David