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  #1  
Old 11-16-2008, 06:15 PM
RV7ator RV7ator is offline
 
Join Date: Jan 2005
Location: Boise, ID
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Default Required FAB Alterations

The as-manufactured updraft FAB doesn't fit in the 7 cowling. (I'm sure this holds true for the 9 as well.) Threads abound regarding the narrow clearance between the port side of the air box and the nearby inside surface of the updraft induction cowl. It's way too tiny, so the engine whacks the FAB against the cowl, especially at start-up, unless you alter the FAB design. It's one of those Van's things they simply will not fix.

Alteration for me always meant making a new mount plate, relocating the carb interface as far to port as possible, about 3/8 inch, limited by the FAB-to-carb screws fouling the filter element. That may not seem like much, but it doubles the as-manufactured FAB-cowl clearance at the port side. Watch out, though. The clearance is smaller still where the lower radius of the air box and the cowl radius almost nest.

This project I'm also modifying the top plate, as the above approach still yielded only a 1/4 clearance between FAB and cowl. (It would have touched otherwise.)

Open up the top plate oval hole to port so the filter element can remain closer to its natural round shape. How far is controlled by the bottom edge of the element; it can only round out so far before it starts riding up the radius of the air box. Check that you also have at least 1/2" between the filter's outside surface and the fiberglass airbox for placement of retaining clips and platenuts, as well as allowing the carb sump cutout to remain inside the filter. Now, the carb stud and intake hole pattern can slide about 3/4 inch to port of the factory punched mount plate. The mount plate also must have it's circumference swelled out to overlap the new expanded top plate cutout, and you need to be creative about placement of the platenut/retaining clips. Obviously, you need a piece of 1/16 aluminum sheet for this custom part, so order it with the FAB.

This works for carbs. I know the mixture arm recess won't fit in this modification, so the AFP servos will need the optional mixture arm relocation, which brings with it another set of installation problems. YMMV.

Nothing is ever simple.

Hope this helps.

John Siebold
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  #2  
Old 11-17-2008, 04:32 AM
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plehrke plehrke is offline
 
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Location: Defiance, MO
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Default Modify the filter

Quote:
Originally Posted by RV7ator View Post
Alteration for me always meant making a new mount plate, relocating the carb interface as far to port as possible, about 3/8 inch, limited by the FAB-to-carb screws fouling the filter element.
I moved it further over then that and carved out recess holes in the top of the filter for my fuel injection servo mounting screws to fit. That got me another 0.5" of clearance. Only down side is that the filter has only one position to be installed and can not be rotated.
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  #3  
Old 11-17-2008, 02:53 PM
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jimski9 jimski9 is offline
 
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Location: Tauranga, New Zealand
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Default Modify the Cowl

I took a different approach and modified the lower cowl. Several cuts were made in left side and the bulge was spread open a bit to allow better clearance alongside the FAB. After re-glassing, filling, priming and sanding, the slight asymmetry in the cowl at this point is not noticeable.

Jim Talbot
RV7A - last 90%
New Zealand
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  #4  
Old 11-17-2008, 04:35 PM
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robertahegy robertahegy is offline
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Default

Not sure what engine you used, but on my 7A with an 0-360 A1A (from Van's) I had no trouble fitting the FAB to the engine and cowl. I did make a small indentation on the back of the FAB to clear the nose gear leg. I heated the fiberglass with a hair drier and formed a small indentation with a pipe. Never noticed any hitting, rubbing, or degradation in 4 years.

Roberta
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  #5  
Old 11-18-2008, 07:43 PM
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jimski9 jimski9 is offline
 
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Default

I have a Mattituck TMX O360 A1A. The sump places the carb and FAB well to the left. There is plenty of clearance between the FAB and nosegear leg but not enough between the left side of the FAB and cowl. There were several posts about this some time ago but I can't recall whether other engines were mentioned.

Jim Talbot
RV7A - "last 90%"
New Zealand

Last edited by jimski9 : 01-08-2009 at 02:10 PM.
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  #6  
Old 11-19-2008, 01:18 PM
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robertahegy robertahegy is offline
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Must be certain engines position the carb such that there is a clearance problem. I know there are many variations out there.

Roberta
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  #7  
Old 11-19-2008, 01:38 PM
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Brantel Brantel is offline
 
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Default

With mine (O-360A1A and RV7) it had only 1/4" clearance in the stock configuration.

I remade the mount plate shifting the box over as much as possible without modifying the filter. It is fine now.

Quote:
Originally Posted by robertahegy View Post
Not sure what engine you used, but on my 7A with an 0-360 A1A (from Van's) I had no trouble fitting the FAB to the engine and cowl. I did make a small indentation on the back of the FAB to clear the nose gear leg. I heated the fiberglass with a hair drier and formed a small indentation with a pipe. Never noticed any hitting, rubbing, or degradation in 4 years.

Roberta
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  #8  
Old 01-07-2009, 11:31 AM
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lucaperazzolli lucaperazzolli is offline
 
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Default Fab 360 carb O-360-A1A * More photos.

Hope this helps !



http://www.rv8.it/log/fab360/index.html
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  #9  
Old 01-12-2009, 03:03 PM
jbDC9 jbDC9 is offline
 
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Default

So I guess it's my turn to have air box issues; I'm currently doing the 2nd condition inspection on my RV-8 (O-360, carb) and noticed the top plate mounted to the carb has finally cracked at the 420 hour mark. Not helping the crack issue is the fact that the clearance between the FAB and and the left side of the cowling is so snug that on start up and shutdown the FAB bumps into the cowling.

I've read many threads covering this issue and I know what I need to do: re-make the top plate, but offset to the right for more cowling clearance. The problem I'm running into is what type material to use and where to get it? I don't want to use the standard 2024 aluminum and would prefer to try a bit thicker piece of 6061. I only need one square foot and I can't find any vendors that'll sell it that small. I could get a piece from ACS, but the smallest size they'll do is 4 sq feet. Add in the fact that my tools to work with are a hacksaw and a Dremel tool and these larger metal blanks are just too much to work with.

Any ideas on what to material to use and where can I get a small quantity?
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  #10  
Old 01-12-2009, 05:05 PM
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DanH DanH is offline
 
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Default

John,
Aircraft Spruce has never been the only game in town. Great service here:

www.wicksaircraft.com

....and if I may say so, we should all make it a point to send them some business. Competition is good for the consumers.

Material choice: 6061T6 has lower yield and tensile strength compared to 2024T3 or T4, so just "a bit thicker" won't help.
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