Silver Hawk EX to FAB plate issue

This has been an ongoing situation for me since the plane started flying. At first, I made a cork gasket to put between the Precision Airmotive Silver Hawk EX and the FAB plate (.090) I made but the compression of the bolts that hold the plate in place against the gasket resulted in a depression on the plate and, ultimately, cracks around the edges near the washers. And the cork was pretty damp too.

So at the annual this year, I went dry.



This was right after I changed the oil and rolled the plane out to start the engine to check for leaks etc.

I had just taken a paper towel to the FAB plate to gussy it up. As you can see there's fuel leaking out between the plate and servo.

I'm GUESSING that this occurs when I have mixture and throttle full open and hit the boost pump for five seconds, as instructed by Mattituck for the engine. But it's only a guess.

How serious is this? And what are the solutions to having a better seal here?

BTW, for no particular reason, when I shut down the engine, rather than pull the mixture, I shut the fuel valve off in the cabin and let it die.

Hi Bob. I have been getting the same, plus a dark blue black mess around the top plate of the FAB. Just reinstalled the plate with red RTV in between, and am hoping that might help.

I'm reluctant to put anything down there that could get sucked into the servo.

Bob, Have you tried the factory gasket? I got one from Precision Airmotive. It is more of an airframe part but they should be able to set you up. If you have problems let me know and I will dig up the part number for you. DO Not use RTV.

I would use larger washers under the heads of the bolts to spread the load. If you want to get serious you might make a reinforcing plate from 0.090 and sandwich the existing plate to stiffen the area. The bolts are lock wired so materials washers should not be ingested. Along with a gasket and some fuel lube, that should work.

It also might be that the attachment is to rigid/or close between the FAB and the cowl, leading to the cracks you found.

Whatever you do the excess fuel is going to wind up somewhere. Typically it drops out of the alternate air door (after mixing with the grease you used to seal the door). You should have a drain hole at the bottom to let excess fuel escape.

If you haven't done so already, give some thought to putting some aluminium in the bottom of the bowl, where the filter rubs the fibre glass. They all wear through once the filter shrinks from AVGAS exposure.

rwtalbot said:

It also might be that the attachment is to rigid/or close between the FAB and the cowl, leading to the cracks you found.
..
If you haven't done so already, give some thought to putting some aluminium in the bottom of the bowl, where the filter rubs the fibre glass. They all wear through once the filter shrinks from AVGAS exposure.

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There is no attachment that connect the FAB to the cowl (vertical induction).

And, yes, I have a plate bonded to the bottom of the bowl.

Same here, how about a doubler

LettersFromFlyoverCountry said:

I'm reluctant to put anything down there that could get sucked into the servo.

Click to expand...

I created a doubler about 1/4" larger than the bolt pattern on the top. This stiffens up the FAB and also helps with possible cracks around the main bolts.

For myself, I just used a small amount of permatex smeared on a finger to seal the surfaces as a tiny air leak here will not change the mixture.

FYI, Precision is recommending reducing the amount of prime. Currently, I'm following the Mattituck instructions of full throttle/mixture, boost pump for 5 secs, throttle/mixture to cutoff, throttle open 1/8.

I'll try 2 secs and see how that works.

Start proceedure

Bob,

Your procedure sounds more like my hot start procedure (only 3 seconds of boost pump for mine). Normal cold starts are about 2 seconds of boost pump (full throttle and mixture) then throttle 1/8" in with mixture about 3/4" in. I get a slight greasy coating on the fab plate over time.. A combination of gas and oil, slightly blue in color. I have been told this is normal. 240 + hours and still going strong.

Superior IO-360 VI Silverhawk.

LettersFromFlyoverCountry said:

There is no attachment that connect the FAB to the cowl (vertical induction).

Click to expand...

What I meant was if the snorkel end is to close to the cowl or the rubber is too stiff it will transfer additional load to the FAB, and the plate may crack at the bolts.

If you do not like fuel leaking on the nose fairing, the RV10 drawings show an optional drain hose which you could retrofit. It is made from a piece of 035X1/4 plastic tube, plugged with an AN470AD6-7 rivet. You epoxy/glass it to the bottom of the FAB and drill a #19 hole back through the FAB into the tube. You can probably find pictures on someone's build site.