Cowl interferes with mixture linkage

[rwtalbot]

Hi Everyone,

I have a Mattituck IO-360 engine fitted to my 7A. The induction is vertical and I have the Precision fuel injection servo mounted underneath the engine. After checking the brass plug as per the AD, I have fitted the servo to the bottom of the engine.

My issue is that the servo does not hang down the engine centreline. It actually sits to the left (as viewed from the rear). This causes the servo to be extremely close to the lower cowl. I can see that the mixture linkage is also going to interfere with the cowl were the scoop area intersects with the rest of the cowl. This was the best picture I could take of the area. You can see when the cowl is raised to its normal position the linkage will interfere in the areas marked.



I'm wondering if this is a common problem and what people have done to address it?

I can see I could swap the servo round 180 degrees but all of the linkages will be reversed so surely this is not a good solution. The cowl is centred properly at the firewall and around the prop flange so I cannot see this being an alignment issue with the lower cowl.

Thanks
Richard
RV-7A Finishing

[hevansrv7a]

My case was the same problem with different engine and cowl. The solution I selected was a different mixture arm - I swapped with Superior for one that was straight and thus closer in. They did suggest changing sides, but like you that seemed like too much work if another solution could be found.

[Jamie]

Hi Richard:

I have the same setup except for on a Superior engine. How much clearance do you have? You say it is extremely close.

Mine was closer than I thought and after a few flights the bolt put a nice little hole through the side of the cowl (thank goodness I waited to paint). The fix was two-fold.

1) I had the bolt with the threaded portion pointed outboard. I had more than enough threads showing so I cut the bolt down so that just two to three threads would show.

2) I also removed the arm from the unit and 'tweaked' it inboard a bit in my bench vice.

These two fixes have given me enough clearance.

Hope that helps,
Jamie

[rwtalbot]

Hi Jamie,

The arm is sitting in the ICO position at the moment and it basically touches the cowl. Perhaps a different arm will help but I think I need at least another 1/2 inch.

Richard

[Capflyer]

First be sure it clears the airbox.

I did a couple of things to fix my clearance issues. First, I made a spacer to drop the FI unit down 1/2". Second, I made a new top plate for the airbox that centered the airbox in the cowl. Third, my mixture arm showed about a 1/2" clearance between it and the cowl but after 40+ hours I saw it was gouging the cowling so I trimmed out the cowl and built up the outside of the cowling to give it some structure. This has all worked fine and all is ok now.

I had a similar issue with the alternator pully. 1/2" clearance but after some time I had a 1/2" gouge in the cowling so did a similar fix.

Good thing my cowling is not painted yet.

What all this tells me is that the engine is moving around on the mounts while the cowling is in a fixed position. I found this really made a difference after some aerobatics which increased the G's on the plane.

Hope this helps.

[JonJay]

http://www.vansairforce.com/communit...ical+induction

or search for vertical induction

[rwtalbot]

Thanks everyone. I thought this might not be a new issue. I found most of the answers in the previous thread.

Cheers
Richard

[Jekyll]

Richard:

Same set up, 7A, TMX-IO-360-B1B, (180 horses, vertical Silver Hawk induction).

You did nothing wrong. You just don't have everything you need.

Vans has a cut-out modification plate to provide clearance for the mixture arm. Ask for the VA-131-Q and instruction sheet. It will take several hours to install. It provides the clearance for the arm with respect to the FAB. It doesn't alter the cowling clearance.

I made a new top plate to move the FAB 1/2 inch to the right. I recommend doing this to give adequate clearance between the FAB and cowling - another couple of hours. Repositioning the FAB greatly improves the alignment of the FAB with the cowling intake mouth for a better installation. This is a result of using Vans using the same parts for a plethora of different installations and models. They should have sent this with the FAB unless you didn't specify you were using the vertical induction. Get a 12 inch x 12 inch piece of .060 sheet. Vans might even cut you a new top plate without the servo holes cut (I think I read where another builder got one from them).

Do all this and it will fit perfectly. You will need to make a small height adjustment on the throat to align it vertically with the intake mouth. This is easy and won’t take too long.

Get some ballons for the intake set up. You need several of those high tech aircraft construction jigs. Buy a bag and your kids/grandkids can play with the left over construction jigs

Jekyll