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  #41  
Old 06-28-2018, 10:16 AM
rv7charlie rv7charlie is offline
 
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A thought from the scrounger gallery. If you're going to do heat shields as Dan mentions, you can use stainless instead of aluminum. Really thin stainless doesn't weigh much (if any) more than aluminum that's thick enough to be stable. Added advantage is less re-transmission of heat.

Now for the scrounger reference. Check the local Wally World or other discount chain for a cheap stainless 'stock pot'. It cuts & deburs easily with an abrasive cutoff wheel, and you can shape the pieces with your seaming pliers, vice, etc.
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  #42  
Old 07-09-2018, 08:08 PM
crabandy crabandy is offline
 
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Quote:
Originally Posted by rv7charlie View Post
A thought from the scrounger gallery. If you're going to do heat shields as Dan mentions, you can use stainless instead of aluminum. Really thin stainless doesn't weigh much (if any) more than aluminum that's thick enough to be stable. Added advantage is less re-transmission of heat.

Now for the scrounger reference. Check the local Wally World or other discount chain for a cheap stainless 'stock pot'. It cuts & deburs easily with an abrasive cutoff wheel, and you can shape the pieces with your seaming pliers, vice, etc.
I like the tip, I've scrounged cutting boards and various layup shapes from Wally World numerous times.
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  #43  
Old 07-09-2018, 08:25 PM
crabandy crabandy is offline
 
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I had some scrap stainless, FiberFrax and foil tape so I went to work making a heat shield.

I used my roller a second time (only had it 3 years) to roll my over-sized piece of stainless and fit it over the exhaust.





I made some trim marks with a marker and scrap cardboard and went to work cutting out my piece with the die grinder. I like to use scrap angle as a cutting guide for straight lines, works well for filing too.





Heat Shield with the edges cleaned up.



I made and riveted some attachment brackets to the heat shield and covered the side opposite the exhaust pipe in Fiberfrax and aluminum tape.



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Last edited by crabandy : 07-09-2018 at 08:29 PM.
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  #44  
Old 07-09-2018, 08:37 PM
crabandy crabandy is offline
 
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Heat shield in place.









I don't have any "before" temp measurements, but will try to get a guesstimate based off the distance from the exhaust pipe. The opposite side has the standard vetterman crossover heat muff I suppose acts as a radiant heat shield as well.
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  #45  
Old 07-11-2018, 09:37 AM
crabandy crabandy is offline
 
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I placed my temp probe just in front of the fuel elbow on the carb.



I don't have any "before heat shield" temps, but this location by the carb/fuel line is 35-40*F hotter than the rest of the lower cowling. In cruise I was seeing 205*F with OAT's of 65*F. After a 30 min shutdown and taxi back to the runway with 86 *F OAT's the temp was 245. Only 2-3 seconds of engine stumbles right after the heat soaked engine start, aggressively leaning the mixture stopped the stumbling.
At the completion of the flight I left the airplane idling for an extra couple minutes at full rich with no stumbles. I need to fly in hotter temps and longer taxi times for further evaluation.
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  #46  
Old 09-04-2018, 12:59 PM
crabandy crabandy is offline
 
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After flying 20 hours with the larger heat shield, I'ld have to say it has helped with the fuel boiling in the carb. I haven't had an issue on my hot quick turns, but its been a little cooler than normal with lower 90's.

It's condition inspection time and I would like to further improve my fuel cooling by :
1. Removing the Gascolator
2. Installing a Phenolic spacer between the carb and the sump

Is there any reason I should not remove the gascolator? As a taildragger it is not the lowest point in the fuel system and I do have a filter between the fuel selector and the electric boost pump.

I believe I could replace the gascolator with an AN6 90* bulkhead fitting like this one.



Either I have Tom S make me a new hose with a 45 end, or a hard AN6 45* like this may work with the existing hose.



I think the AN6 90* bulkhead fitting would fit perfectly with the existing hard line from the fuel pump inside the cockpit.



For the phenolic spacer (Thx SnoperCod!) between the carb and the sump I think I would need to pull the studs and replace with longer ones. Perhaps use a low profile metal lock nut instead like a MS21042.


Thoughts?
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Last edited by crabandy : 09-04-2018 at 01:02 PM.
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  #47  
Old 09-04-2018, 03:44 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by crabandy View Post
Is there any reason I should not remove the gascolator? As a taildragger it is not the lowest point in the fuel system and I do have a filter between the fuel selector and the electric boost pump.
Conventional wisdom says carbs do need a gascolator.

That said, have you ever seen any water in yours?
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  #48  
Old 09-04-2018, 05:05 PM
rvbuilder2002 rvbuilder2002 is offline
 
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I know of gascolators being found 1/2 full of water on RV's, so it probably depends on many factors (sumping diligence of pilot, etc.)

It is a misconception that gascolators are supposed to be installed at the low point of a fuel system.
That would probably be the optimal (but not always practical) location, but the primary purpose is to act as a filter by artificially positioning a low point within the flow path of the fuel. This low point, along with the fine screen filter that the fuel must flow through leaving the gascolator, separates water and other debris from the fuel before it gets to the carb.
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  #49  
Old 09-04-2018, 06:30 PM
rv7charlie rv7charlie is offline
 
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I know of at least one carb'd -4 that started life with a gascolator and is now flying without; it's in my hangar. It lost the gascolator after near engine stoppage at ~1k' agl after takeoff on a 100 degree day. Since the plane has a real fuel filter, and any water in the tanks will be gone if the pilot does their job, it was decided that the gascolator's primary function on this plane was heat collector.

No more rough running in several years since.

Not telling anyone else to do it; just passing on one person's experiences.

Charlie
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  #50  
Old 09-04-2018, 07:07 PM
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rocketbob rocketbob is offline
 
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For some reason we still have gascolators. Why? Because reasons! That's the way its always been!

Would you ever drink a coke by skimming the top of the cup with a straw? That's how a gascolator works.
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