Well, I made what I could out of that article. I've had about 5 flights or so, frequently ending with the engine going lean from the header coming unscrewed. I suppose I need split washers to help hold it. Today however the engine held the same speed the entire flight, but that was, I believe...too lean. It just sounded a bit lean. Additionally, I was getting about 4.5 laps. So, my question is, am I too lean, (I was also much louder than usual), or do I need a flatter prop.
I used power master 10/22, APC 12.25/3.75, 65' lines. I heard you are supposed to control speed with prop pitch, but it still seemed a bit too lean. Any pointers. Oh, and weather permitting, Nov 21 I think should be tuned pipe day at Napa...weather permitting.
If it is both too fast, and too lean, the obvious solution is to richen it up. Unlike the 40VF, the 46VF was often run into a 4-stroke, and both the 40 and 46 have a *butter-smooth* break from 4 to 2.
Certainly use lockwashers, but as long as you use the sealant properly and have *perfectly flat* mating surfaces, you shouldn't have much problem with the header coming loose. The 40 and 46 have ZERO TOLERANCE for leaks at the header, if they leak, they tend to run with way too much boost and break (because the pipe is no longer constraining it) and also sometimes act like they are running on suction, speeding up/going leaner throughout the flight.
As always,
*face off both mating surfaces with 240 grit wet/dry sandpaper and oil, taped to a perfectly flat hard surface or lapping plate* Don't let it "rock" as you push it back and forth, you much have a perfectly flat surface on both sides from edge to edge
Clean both surfaces with lacquer thinner or acetone until it is perfectly, operating-room clean.
Clean the screws and clean the threaded holes to the extent possible, remove all oil it is possible to remove.
Apply silicone sealant in a thin film all over the mating surface of on the engine side (which is smaller than the header flange, no point on covering that), all around edge-to-edge. DO NOT USE A GASKET OF ANY TYPE. I use Permetex Ultra Copper car exhaust header sealant, but just about any silicone sealant will work.
Put the screws (with split or star lockwashers on them) through the holes, and allow just a touch of sealant to get in the screw threads.
Without allowing the flange and exhaust to touch, start both screws a few turns.
Push the two surfaces together then run the screws down tight. Torque them down until they are tight and read-to-go. Ignore any advice on the tube of sealant about just snugging them, waiting overnight, then hard-tightening them later to form a "cushion" of sealant. You don't want that, it might blow out, you want to squeeze it out as much as possible, leaving sealant only in the scratches made by the sandpaper.
We have *never* had a leak doing it this way, I have them that have been mated for 25 years with no leaks. I have also seen one or both screws back off, but the header stayed on just from the adhesive with no leaks. You *can* get it off later, but it's glued on pretty good.
And I cannot emphasize this enough, *do not, under any circumstances, use any gaskets (paper, aluminum, brass, anything)*. All that does is give something to blow out, and is definitely unnecessary to seal the joint.
Brett