Silver Hawk cowl interference

Listers,

I am in the process of installing the FAB to the SilverHawk EX servo on a Lycoming O-360 B2B. (parallel valve vertical induction).

The FAB ended up very close to the left side of the lower cowl air scoop, but that was cured by fabricating a new mount plate and moving the whole FAB a little to the right.
I now have a minimum of 1/2" clearance between FAB and left side of scoop.

The problem is now with the servo mixture lever.
in the most forward position it is only 3/16" from le left side of the air scoop.
Doesn't look like much clearance!

Has anyone had the same problem?
Have I missed something?

Regards,
Roberto
RV-8 FWF

similar

My mixture control arm was too close to the cowl, but I have a different cowl (SJ). The arm my engine came with was joggled. I traded for a straight one and gained additional clearance equal to the distance of the joggle. Without a picture, I'm not sure if that will work for you, but maybe it will help.

I-MROB said:

The problem is now with the servo mixture lever.
in the most forward position it is only 3/16" from le left side of the air scoop.
Doesn't look like much clearance!

Has anyone had the same problem?
Have I missed something?

Click to expand...

Roberto, did you get the "mixture arm inversion" option on your Silver Hawk servo? If not, you should.

More info...
http://www.romeolima.com/RV3works/FWF/firewallforward.htm

Randy,
I have the standard configuration.
I was considering the alternate configuration, due to interference with the FAB, but was told to just make a 1" extension below the servo to bring the FAB where it would have been with the original carb. That took care of the FAB iterference, but I just didn't see the air scoop interference coming.

Not sure if I can change now!

I have a similar issue on my Mattituck TMX IO-360. The engine does not come with the Inverted Mixture Arm on the Silver Hawk and it is not retrofitable. I called Precision Airmotive and they said I could send it back to them and for additional $$ they could send me out the one with the inverted mixture arm. Mahlon at Mattituck suggested a spacer.

(Note to Mahlon, you guys may want to address this when you sell an engine for an RV)

I am about 3/4 done with my spacer that is 1" thick. Couldn't find for any reasonable price under $100 a delrin block to make it out of so I used a commercial cutting board which is made of a very similar material and is heat and chemical resistant.

Next week when it's done I'll post a picture of it.

There are some picutes on the Precision site geared towards this as well. http://precisionairmotive.com/

Spacer?

I'm confused, what are you guys spacing off 1"? If you space the FAB down 1" it would likely hit the bottom of the intake scoop and also require the inlet to be at a really awkward down angle.

I had the same issue. I ordered my engine "mixture arm up" or "reversed" but the straight short arm interfered with screws on the servo and the longer bent arm stuck too far out and hit the inside of the scoop.
I took the arm to a trusted tig welder and we cut and modified the arm to be short and joggle only about 1/4". Kind of like a smaller version of the stock mixture arm. Works perfect.

randylervold said:

I'm confused, what are you guys spacing off 1"? If you space the FAB down 1" it would likely hit the bottom of the intake scoop and also require the inlet to be at a really awkward down angle.

Click to expand...

Randy,

the servo is 1" shorter than the carb, so putting a 1" spacer under the servo simply brings the FAB back down to its original place.

Solution!

Ok guys,

thank you all for your help.

Today I found a solution that seems to work.
I tried mounting the rod end bearing from the mixture cable on the inside of the arm.
The throttle cable interfered of course with the servo during movement, but that was taken care of by moving the cable attach bracket 1/2" to the left.
I fabricated a bracket extension that will get riveted to the original bracket.
I now have smooth and clear mixture movement and the whole affair is more than 1/2" from the cowl scoop.
Very nice

I-MROB said:

the servo is 1" shorter than the carb, so putting a 1" spacer under the servo simply brings the FAB back down to its original place.

Click to expand...

That's weird, when I went through this I found that the servo was 7/8" taller than the O-320 carb and the same height as the O-360 carb (MA4-5).

I need to think about this now. I just installed the "arm down" fuel control unit that came with my TMX IO360 on my RV-8. I've been reading this site and websites, and I'm getting mixed reviews on what to do.

Here is what seems to be my options:

1. Keep the standard fuel control unit. This requires me to have a spacer made. I've heard everywhere from 5/8 in to 1.5 in. It might be difficult to find a machine shop to do such a small item. Keeping the standard fuel control unit might also bring up an issue with the mixture arm being too close to the lower cowl, even after the spacer is installed.

2. Exchange the standard fuel control unit for the "reversed arm" unit. This will require some new hoses and their routing. It might have some issues with the mixture control cable routing. Is forward still rich? Also, is the air box then up too high?

Craig,

There is a third option which is what I did. I modified the filtered airbox with a cutout to allow the mixture arm its full range of movement. I also had to modify the front of the airbox to angle it down slightly to mate up with the scoop on the cowl. I have not had any issues with airbox or servo arm and cowl interference. I'll post a picture of the problem and fix. The fix picture was taken as I was making the cutout so it doesn't show the finished re-glassed airbox, but I think you'll get the idea. On the first picture you can also see the cut at the front of the airbox which shows how I angled the airbox down. This is just another option to consider, and has worked for me. It will allow you to stay with the standard fuel line and mixture cable routing.

Mark

For what it's worth, here's my solution. I'll also take this opportunity to try and clear up the confusing and somewhat conflicting information in some of the threads on this topic.

First of all, for a 360, the Silverhawk throttle body is ~1 inch shorter than the carb. The opposite is true for a 320. That is my experience and Mahlon Russel has confirmed it.

I went with the standard, non reveresed arm throttle body. The reason is that the cables and fuel lines work nicely that way. Adding the spacer puts the airbox in the right place and really makes it easy to install. With the spacer, there is no need to notch the airbox.

My spacer was made by a good friend, but it isn't a complex part and could be made cheaply by any shop. I suppose you could also make one on a drill press if you had the patience. I can try and find the drawing I made if it is useful to others. Just PM me.

My mixture arm was awfully close to the cowl scoop. This has nothing to do with the spacer, just the placement of the throttle body on the sump. Since I was painting prior to flight, I decided to avoid any potential problems by putting a small blister on the cowling. I'm not sure if it was needed, but it's better than touching up paint. I'm not the first one to do the blister, I got photos of a similar job from another VAF member.

Here's some photos:

Papa said:

Craig,

There is a third option which is what I did. I modified the filtered airbox with a cutout to allow the mixture arm its full range of movement. I also had to modify the front of the airbox to angle it down slightly to mate up with the scoop on the cowl. I have not had any issues with airbox or servo arm and cowl interference. I'll post a picture of the problem and fix. The fix picture was taken as I was making the cutout so it doesn't show the finished re-glassed airbox, but I think you'll get the idea. On the first picture you can also see the cut at the front of the airbox which shows how I angled the airbox down. This is just another option to consider, and has worked for me. It will allow you to stay with the standard fuel line and mixture cable routing.

Mark

Click to expand...

My airbox came with a molded aluminum piece that you stick into the side of the airbox, looks just like the above pic.

Thank you all.

I'll probably try to make it work with the existing fuel control unit.

By the by, I'll need to reindex the control arm. As received, it is way too far forward in the full rich postition. Does precision make a shorter control arm? That would get it further from the lower cowl without making a blister, and also minimize the size of the spacer.

Give Precision a call

They are friendly and talkative,.. and willing to work with you. However,.. said they had been stiffed by several builders (of undisclosed plane type) and no longer exchange mixture arms through the mail, without first getting the old one. I am just getting a straight versus offset arm,... but understand they have different throw lengths also.

Craig said:

By the by, I'll need to reindex the control arm. As received, it is way too far forward in the full rich postition. Does precision make a shorter control arm? That would get it further from the lower cowl without making a blister, and also minimize the size of the spacer.

Click to expand...

Precision wants way too much money for their parts. Just drill a new hole farther up the arm. I had to do this for both the mixture and the throttle.





And for what it's worth, here's a shot of the spacer. It's a lot cheaper to have a spacer made than it is to get a new servo and new hoses. If you go with the "reverse" servo, you have to move the fuel inlet to the right side so it doesn't interfere with the upward-pointing mixture arm. Then you need a whole new hose configuration.

Thanks again.

I opened up the FAB kit, and it does indeed have a formed aluminum piece to allow for the mixture arm movement. It seems better in the long run, however, to get a spacer made.

Geoff, thanks for the pictures. I have your website bookmarked. Although getting more travel out of the linkage is one feature of where you have the hole drilled in the mixture control arm, I'm thinking that a shorter control arm will also keep me from having to install a blister in the cowl.

Craig said:

Thanks again.

I opened up the FAB kit, and it does indeed have a formed aluminum piece to allow for the mixture arm movement. It seems better in the long run, however, to get a spacer made.

Geoff, thanks for the pictures. I have your website bookmarked. Although getting more travel out of the linkage is one feature of where you have the hole drilled in the mixture control arm, I'm thinking that a shorter control arm will also keep me from having to install a blister in the cowl.

Click to expand...

I had no interference problems with the control arm. It doesn't extend beyond the confines of the FAB in any position, and that's even after I remade the mounting plate for the FAB to slide it farther inboard. Even if the arm did hit the cowl, you could always grind off the end of it after drilling a new hole. I was initially leary of drilling a new hole, but one look at Precision's price list convinced me to try it. What's the worst that could happen? You'd have to buy a new arm -- which you were planning to do anyway.

I did notice after a few hours of operation that the head of the bolt contacted the inside of the cowl. Notice the paint in this picture. There was plenty of clearance in a static condition, so I can only assume that it occurred during startup/shutdown. I removed a spacer washer and that solved the problem. The alignment between the arm and the steel anchor plate isn't 100% perfect without the spacer washer, but it works.

Now that I've thought about it for a bit, I realize that drilling the hole up on the arm like you did will also of course move the rod end further away from the lower cowl - just like a shorter mixture control arm would. The remnants of the original arm won't be a factor.

When you remade the top mounting plate of the air box, how far over did you move the holes? As long as I'm getting a spacer made, I might as well have the skin mill machine guy make me a new plate.

It's another of those chicken-or-egg things. I haven't mounted the cowl yet, so I don't know how much, if any, I need to move the FAB over to miss the cowl. I test fitted the lower cowl, and it looks close on the port side. I won't know the exact location until the cowl is final fitted.

Once you moved the FAB further starboard, did you have to notch the upturned top edge of the FAB for the mixture linkage?

Craig said:

When you remade the top mounting plate of the air box, how far over did you move the holes? As long as I'm getting a spacer made, I might as well have the skin mill machine guy make me a new plate.

Click to expand...

I moved it over as far as it would go and still have all of the FAB parts fit. If you move it too far, you won't have room for the filter. It isn't really something you can do ahead of time. You have to build the top of FAB first because the top of the FAB, the filter, and the fiberglass are fixed with respect to each other. Once you know where all of those parts go, then you can determine how far you can move the holes in the mounting plate without interfering with the rest of the stuff. The bolts that hold the mounting plate to the servo have to remain inside the filter. If you move it too far over, those bolt heads will interfere with the filter. Build the stuff in this picture first and then you'll know how far you can move it over.



Additionally, don't match drill the holes around the edge of the mounting plate until you finish with the ones in the center. After moving the FAB over, you'll have to rotate it slightly because you still want the front of the FAB pointing at and centered on the intake hole in the cowl. You can't do any of this until the lower cowl is mounted because until then you don't know where the intake hole is going to be.

It's another of those chicken-or-egg things. I haven't mounted the cowl yet, so I don't know how much, if any, I need to move the FAB over to miss the cowl. I test fitted the lower cowl, and it looks close on the port side. I won't know the exact location until the cowl is final fitted.

Click to expand...

You know you need the spacer, so you can do that ahead of time. The rest of it you can't do until the cowl is fitted, as I mentioned above. So just put it off and don't worry about it until then. But next time you place an order with Vans order up a blank piece of 063 sheet to use when you make the new mounting plate.

Once you moved the FAB further starboard, did you have to notch the upturned top edge of the FAB for the mixture linkage?

Click to expand...

No notch required with a spacer. You will need to buy some longer bolts, though, to hold the mounting plate to the servo. By the way, don't use those cheesy bent-tab lockwashers that Vans wants you to use to secure those bolts. You don't want one of those coming loose and potentially getting sucked up into the engine. Use some drilled head bolts like these and safety them. You can see the holes I initially drilled for use with the bent-tab lockwashers before I threw them away. The other big hole was for an air temp sensor that I decided not to use.

Got it.

Gracias.