Will my O-320 Sump Work with the RV-6A

This is my first post here. I have just begun my journey to build an RV-6A and it will be my first aircraft build. I have just put a deposit on previously started QB kit without too much work done on it. I also picked up an O-320-B1A engine this evening that I will be overhauling (top end already done).

While the engine is a B1A model from a twin Comanche, the sump is not what I thought was on that model. This sump has a vertical carb inlet on the bottom. However, this opening is positioned at the rear of the sump and not in the middle as I thought was the most common for the 320. While this image is a sump for a 235, it looks identical to mine.



I am hoping someone can let me know if this will work with the RV-6A. I won't be picking up the kit for a couple of weeks, so I have no way to measure clearance. From pictures, it looks like it will be close. I fear the carb may interfere with the point on the mount/frame where the four support tubes meet up with the front gear strut.

I would appreciate any guidance that you could provide.

Larry

Difficult to say for sure without comparing with other pictures, but I suspect it won't work as the carb will foul on the nosegear. There used to be a sketch on the Van's site somewhere, and/or in the build instructions that shows what is required. If your engine was an IO it would be worth retaining the injector.

Pete

lr172 said:

This is my first post here. I have just begun my journey to build an RV-6A and it will be my first aircraft build. I have just put a deposit on previously started QB kit without too much work done on it. I also picked up an O-320-B1A engine this evening that I will be overhauling (top end already done).

While the engine is a B1A model from a twin Comanche, the sump is not what I thought was on that model. This sump has a vertical carb inlet on the bottom. However, this opening is positioned at the rear of the sump and not in the middle as I thought was the most common for the 320. While this image is a sump for a 235, it looks identical to mine.

I am hoping someone can let me know if this will work with the RV-6A. I won't be picking up the kit for a couple of weeks, so I have no way to measure clearance. From pictures, it looks like it will be close. I fear the carb may interfere with the point on the mount/frame where the four support tubes meet up with the front gear strut.

I would appreciate any guidance that you could provide.

Larry

Click to expand...

Larry:

I will have to say NO it will not work. My RV-6 has been flying over 16-years. I have a B2B converted to Constant Speed Prop operation. Back when I got my engine, I got it because it could NOT be used with the -6 because of how far back on the sump the carb mounted. The above image looks like the carb is in the same location as it is on my engine. IF you go look at some of the engines produced in the last 20-years, you will find a sump where the carb is almost directly centered on the sump. That will work on the -6A RVs.

RV6_flyer said:

Larry:

I will have to say NO it will not work. My RV-6 has been flying over 16-years. I have a B2B converted to Constant Speed Prop operation. Back when I got my engine, I got it because it could NOT be used with the -6 because of how far back on the sump the carb mounted. The above image looks like the carb is in the same location as it is on my engine. IF you go look at some of the engines produced in the last 20-years, you will find a sump where the carb is almost directly centered on the sump. That will work on the -6 RVs.

Click to expand...

I *think* where Gary says "-6" he actually means "-A".

I suspect the rearward mounted carb will interfere with the nose gear leg/engine mount on the -A model.

-Brad

It will not work. I built an RV-6A in the 90's that had a Lycoming 0320H2AD engine. The back of the oil sump hits the engine mount. I had mine rewelded to go around it.
I believe there is a special engine mount you can buy from Vans that is made for this issue.

Larry,

The 320 B1A has a few drawbacks but don't be discouraged. If it came out of a Comanche you should have injection with it as well. Replace the existing sump with the D1A type sump and you should be on your way. Another thing to confirm is the engine mount - you will need the type 2 dynafocal mount for that engine, and if you are running with the Bendix injection you will need the O 360 airbox to complete the mount to the cowl. We had an IO 320 B1A on our first 6 and were very pleased with the performance.

Good luck,
Chris

This is the sump layout you need for a -6A

Thanks for all of the replies and assistance here. I was told it was from a Twin Comanche, but I guess you never know. It has conical mounts and has a Marvel MA-4 carb(-12). The carb was recently rebuilt (relative to engine time) and is in good shape. Maybe needs a few seals for comfort.

I have done some research on the carbs and sumps. Apparently the sumps like mine used the -12 carb and the sumps with centrally mounted carbs, called Vertical risers, used the -32 carb. I called Marvel to find a rebuild kit and they told me the two carbs are externally the same, but have different jetting and tubes. I suspect the differences in the two sumps creates different flows through the carbs. I am wondering if I will be safe in using the -12 carb in the vertical sump. I have already found an affordable vertical sump to swap to.

Does anyone have experience in performing these carb swaps? I could also consider an FI upgrade, but I am trying to keep the cost in check.

Thanks again for the assistance.

Larry

Sumps

All Twin Commanches were either I0-320 B or C series engines.
All were fuel injected with rear mount injector and all were type 2 dynafocal.
The sumps as shown with the large hex plug in front of the carb flange are not compatible with fuel injection, regardless of other issues.
The Twin Commanche sumps, most other narrow deck sumps and some late model sumps all have slightly smaller intake fittings, the short steel tubes that are swaged into the sump. These will cost you a couple horsepower.

Thanks for all the assistance guys. I have done a bit of research today. I have found an E2D sump that has the straight riser in the center of the sump, so that should help avoid the gear interference issue. While the -32 is specified with this carb, it seems many run the -12 as it runs a bit leaner. I will probably keep the -12 and replace with a -32 if I have problems with leaning.

I also found that ECI (who will be doing the inspecting and machining of my case) can convert the case from conical mounts to dynafocal I. That will be cheaper than buying a new engine mount from Vans.

Larry

Hopeless case...

lr172 said:

Thanks for all the assistance guys. I have done a bit of research today. I have found an E2D sump that has the straight riser in the center of the sump, so that should help avoid the gear interference issue. While the -32 is specified with this carb, it seems many run the -12 as it runs a bit leaner. I will probably keep the -12 and replace with a -32 if I have problems with leaning.

I also found that ECI (who will be doing the inspecting and machining of my case) can convert the case from conical mounts to dynafocal I. That will be cheaper than buying a new engine mount from Vans.

Larry

Click to expand...

Larry,
There is a solution to all your woes...build a Tail Dragger...
BTW, there is a guy on Barnstormers looking to trade his RV6 conical mount for a dynafocal...


V/R
Smokey

Dynafocal 2 to 1

Just had a 320 case converted from Dyna 2 config to Dyna 1 by Divco in Tulsa for $250

What you need to shop for is a "straight riser sump" and the matching induction tubes.
The reason it is call a straight riser sump is that the induction tubes travel in a straight line between the outlet ports of the sump and the inlet of the cyl heads. They only have a single (upward) bend in them. On the sump you have, the induction tubes have two bends in them (one forward, and one upward), because of the aft position of the carb. inlet. So make sure you get a set of induction tubes when you get a different sump. I am pretty sure the flange rings (or what ever the official Lyc. name is) that attach the tube to the cyl. head are the same for both tube styles so you should need to get new ones.