Tip: Oil restrictor fitting

[koda2]

There have been a number of ways posted out there to make your own oil restrictor fittings and save some money, from using JB weld to rivets but here is another that I am trying.

The ID of the AN fitting was 3/16" so I used 3/16" bronze welding rod for the restrictor. A 3-ft stick was $2 and it is slightly oversize.

The key is getting the rod to just a slight press fit so it will go in place with just enough force. If you don't have expensive machine tools, you can manage it with a sturdy drill press to both file the rod diameter(smooth file) and to press the bronze in place.

I cut a .500 piece and drilled the back half 3/32" and the front half #60(.040) to make the orifice. I also took the "belt and suspenders" route of applying a miniscule amount of JB weld to the bronze before inserting it and also staking the steel very carefully around the edge with a sharp punch (arrow).

You can check the orifice with the #60 bit for patency and the opening from the back side by looking thru it at a bright light.

Brass would have been better and easier to work with but I am not aware of any compounds in aviation oil that will affect bronze.

Dave A.
6A build

 

[LarryT]

Exactly what we used...

...in our small block Chevy engines for racing. The oil flow to the top end was biased to keep hydraulic lifters pumped up for the street. Racing engines don't use hydraulic lifters and don't need all that oil pumped away from the crank. The plugs you described work perfectly.

LarryT

 

[gasman]

Brass would have been better and easier to work with but I am not aware of any compounds in aviation oil that will affect bronze.

Dave A.
6A build

How is brass affected by aviation oil?

 

[koda2]

Brass

As far as I know brass is not affected by aviation oil or any petroleum compound but am not a "tribologist". I know that aviation oil differs from automotive oil by the additives in it.

Some gear oils supposedly affect bronze. Gear boxes with cheap bronze gears interact with some compounds, I think the sulfur based ones, that are present in API -GL5 oils. So a GL 4 gear oil is a better choice. I know this because I used some expensive GL 5 gear oil in a Harbor Freight machine and it quickly etched a bronze gear.

The rocker arm bearings in a Lycoming engine are sleeve bearings and I bet are bronze-based so theorectically there should not be be a problem with either bronze or brass.

Brass is also much easier for me to work with in a lathe. It cuts more cleanly on my low-end equipment. If I am not mistaken, most carb jetting is brass.

Maybe someone with a more knowledgeable background could comment.

Dave A.
6A build

 

[Danny7]

this thread mentions oil affecting copper

http://www.vansairforce.com/community/showthread.php?t=69925

 

[rocketbob]

The wrist pin and rocker arm bushings are bronze. Bronze and Brass are both copper alloys; brass being alloyed with zinc while bronze is alloyed with tin. So there isn't a problem with brass fittings and oil.

I have made these fittings many times by simply tapping the ID of the fitting for a 10/32 AN bolt. The bolt is then drilled with a small hole with on my lathe. I booger the thread on the bolt slightly to get it to lock in place when threaded in the fitting then cut the end of the bolt off with a cutoff wheel.

 

[pierre smith]

Is the wall thickness of the fitting...

...I have made these fittings many times by simply tapping the ID of the fitting for a 10/32 AN bolt. .

...enough to not lose much strength after the tapping?

Best,

 

[rocketbob]

...enough to not lose much strength after the tapping?

Best,

On the 1/8" NPT fittings the hole is large enough that there is not very much left to run the tap thru, so it creates a minimal thread, and thus wall thickness is not affected much. I use steel fittings anyway for anything -4 and under on the engine.