What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Baffle tension rods.

AAflyer

Well Known Member
Van's baffling kit includes some stock steel rod, that I carefully cut to length, and bent to shape, only to find it impossible to thread the ends with my tap and die set.
Can anyone talk me out of using the nice threaded rod available at the hardware store? Zinc-coated steel. Bends easier, so I know it's not as hard, but rated for 200# Safe Working Load. Seems to good to be true at $0.80 each.
 
Maybe you could avoid using rods altogether. Old schoolers use simple safety wire. No bending or threading required. I'm sure there is a thread somewhere on this alternative.
 
I just installed new Van's baffles on my 2000 RV-6. The old ones were secured with safety wire and I did the same with the new set.

My RV-4 also had the baffles secured with safety wire.

YMMV,
 
Maybe you could avoid using rods altogether. Old schoolers use simple safety wire. No bending or threading required. I'm sure there is a thread somewhere on this alternative.

Yep, Andy Karmy did it that way. Since I couldn't directly link to his photo on flickr, I grabbed a screen capture (with apologies to Andy):

AKarmy.jpg
 
I had the same problem trying to thread the SS rod so I did what a lot of folks did with the safety wire. The picture below shows the safety wire with some plastic tubing to protect against chaffing. A word of caution, though. I have seen a fellow RV'er's set up like mine and the plastic tubing that is in contact with the aluminum return tubing can actually cause a scallop in the aluminum tubing over time. I believe he had around 750+ hours on that set up when he noticed it. I think the SS rod is a much better solution. As soon as I get a hold of a capable die set, I'll change out to SS rods during an annual or other down time.
fb069afe3c2ebbff21681ea7c6165ecc24739_1205001340.jpg
 
Rods

Bare mild steel rod is easily threaded and two doglegs per rod provide clearance for the drain tubes. The rods can be painted except for the threaded portion or cad plated including the threads.
A machine shop can thread stainless if its the correct grade. It must be a relatively soft stainless.
 
Don't tie the front and rear cylinders together. Instead wire each to the center baffle plate. Short wire length, and they don't cross any drain tubes.
 
I didn't have much problem threading the rod with my cheap die set from HD. Just used some cutting oil and worked back and forth a lot.

IMG_5038.jpg


As others have mentioned, safety wire works as well, just make sure it's not going to saw through anything.
 
I can only conclude that all these rods are not consistent hardness. I used a not-so-cheap die and it would not get more than 1/4" and snapped, popped and was a significant torsional displacement. I tried several dies, and high sulfur cutting lubes, it was unsuccessful. It was clamped in the vice close to the jaws too. I have tapped and threaded many thousands of things and could not get this job done. An experienced friend had a similar experience.

We got the stainless all thread rod from Grainger. I might use the safety wire technique, but have the rod on hand now.
 
I used SS welding rod and a quality die to thread the rod if you want to go with the rod. Just requires a lot of back and forth so as not to bend the rod and oil. And you need the dog legs to clear the drain-back tubes. :)
 
Doh!

Never thought of using wire. I got the store-bought ones bent, but the holes in the baffles look like they're drilled too close to the bend, that I don't see how a nut, much less a washer can sit flat. Safety wire may be in my future.
Thanks for all the feedback.
Back to the cowling?
cowling?
cowling...
 
Used a good quality split die. You can start it out a little more open then tighten it down. Still lots of back & forth to clear chips.
 
Old thread, comment and new question

First, I may have stumbled onto a way to make cutting the threads onto the rods pretty easy. After having the same difficulties described here, I happened on one that was EASY. It just spun and cut the threads with almost no effort. After examining what I had done differently I realized I had started the threads as usual, got about 4 threads on and took a rest. When I put the die back on I accidentally put it on backwards with the narrow opening of the die first. I intentionally did the same thing on the remaining rods and all were trivially easy to cut. ... Hard to get started but once I had about 4 threads with the wide opening of the die first, I flipped the die and went to town. ... Maybe this might help someone else in the future.

Now for my question. Standard IO-540 D4A5 for the RV10. Followed the plans, interpreting best I could. The pictures below are of my left and right outboard tension rods. As I tighten the ends the rods bow upward in the center putting pressure on the oil return lines. Am I doing something wrong? These are the second set of rods I've made. Increasing the angle where they attach to get more clearance makes no difference. They just bow up in the center and contact the oil lines. In the pics I've backed off the pressure to the point where I can just move the sheathing. If I tighten to the point where the baffles are tight against the cylinder fins, there's enough pressure on these return lines to see them flex upward. This just doesn't seem right to me. But maybe it's OK??

Am I missing something here? Any advice?

IMG_20170225_172538_018-768x432.jpg


IMG_20170225_165056_448-768x432.jpg
 
Last edited:
I was able to buy SS all thread from my local RC airplane hobby shop. I slid it in plastic tubing prior to bending for oil return tube clearance. Worked great!
 
I was able to buy SS all thread from my local RC airplane hobby shop. I slid it in plastic tubing prior to bending for oil return tube clearance. Worked great!

Doesn't the center of the rod bow upward against the oil lines as you tighten it? It seems for me to get it tight enough to make the baffle lay firmly against the fins the rod is putting a lot of upward pressure on those oil return lines. Am I making the rods too tight? Am I just overthinking it? ... I just don't like seeing the oil line flex as I tighten the tension rod. Seems like a bad thing.
 
Doesn't the center of the rod bow upward against the oil lines as you tighten it? It seems for me to get it tight enough to make the baffle lay firmly against the fins the rod is putting a lot of upward pressure on those oil return lines. Am I making the rods too tight? Am I just overthinking it? ... I just don't like seeing the oil line flex as I tighten the tension rod. Seems like a bad thing.

Hi Joe,
I had to 'over bend' the jog so the rod just touches as it gets tight. I also used brake line tubing over the rod to protect the return tube from rubbing.
DSCF5573.JPG

DSCF5574.JPG

DSCF5575.JPG
 
Doesn't the center of the rod bow upward against the oil lines as you tighten it? It seems for me to get it tight enough to make the baffle lay firmly against the fins the rod is putting a lot of upward pressure on those oil return lines. Am I making the rods too tight? Am I just overthinking it? ... I just don't like seeing the oil line flex as I tighten the tension rod. Seems like a bad thing.

Joe,
After looking at your pictures closer, I think you need offsets/jogs closer to where the return lines are. Just bend a relatively short section near the lines to go down and then back up near the tubes.
 
tie rods

A few comments:
Welding rod is usually under the nominal size so easier to thread but not as good a thread.
The holes in the baffles for the outboard rods can be moved 1/8 or so lower. Install a doubler with just two rivets and relocate hole.
With a proper joggle and proper tightening the rod will not contact the oil drain tube. Some of the rods in the pictures do not have enough joggle and/or are overtightened.
If you carefully shape the radius where the baffle contacts the cylinder fins the rods can be installed with less tension.
The allthread is an invitation to problems. The nylon tubing melts depending on the individual temperatures and then the allthread can saw thru the drain tube.
My preference is to make the rods from mild steel and either paint the non threaded portion or cad plate.
 
Joe,
After looking at your pictures closer, I think you need offsets/jogs closer to where the return lines are. Just bend a relatively short section near the lines to go down and then back up near the tubes.

Thanks. Sounds like an easy solution. I'll try this.
 
A few comments:.....
The allthread is an invitation to problems. The nylon tubing melts depending on the individual temperatures and then the allthread can saw thru the drain tube......

Hi Jim,
You raise some valid points and I check that area when ever the bottom cowl comes off for the reasons you've stated. I have 140 hours on the Hobbs now with no signs of melting or rubbing. That includes flying on many of those 100+ days we get out here in the high desert as well as a 50 minute taxi and hold at OSH last year (lousy thing to do to your engine!).
Regards,
 
Back
Top