Twin fuel control turnbuckle

[Powdermonkey]

Hi Folks- Since I fired up my 30-2, I've been working on fine tuning the exhaust gas temperature output between the cylinders.  It's generally been pretty good, but I really wanted to get it "right".  A half-turn on that 1/4x20 screw thread can move it too much.  I've generally gotten it within 20 degrees.

I figured there'd have to be a better way.  So, I looked at the riser rod (about 6" long).  Both ends are threaded right handed.  So, if you twist the rod, you wind up going exactly nowhere. Out of one horseshoe brackets goes one side, and into the opposite horseshoe brackets it goes into the other...No change to rod length.  Keep in mind, on a twin, you want to balance the load.  It's all about balancing the fuel load between the cylinders. 

Hmmm....so today I fabricated two new horseshoe brackets.  I threaded them 1/4x28 instead of 1/4x20.  One left-handed thread, the other a right handed thread.  Let's not talk about the 1/4 inch end mill I broke...

On to the listeroid it went.  Worked just like a turn-buckle would.  I was able to balance out the EGT's to within 5 degrees F.  And...I was able to do it with the engine running and under load. 

So, there ya go.  I'm not assuming that there are many folks in need of such a thing.  But should the need arise, you know where to find me. 

[mike90045]

Sweet ! I've got  single, but what a great idea.

[cujet]

Another similar method for those who can't deal with a LH thread is to use fine threads on one end and coarse on the other. It provides very precise adjustment.

This is how Helicopter pitch change links are adjusted, to change blade pitch accurately.

As you might imagine, the coarse threads move more "per turn" than the fine threads do.

[38ac]

Nice work! A multi cylinder engine certainly benefits from equally working cylinders. My past work on CS twins has shown this to be an issue about half the time. My fix has been to place a slight bend in the horizontal rod just beyond the clevises, doesnt take much at all. The first time was to tune up a customer engine where I was away from the shop and fancy tools and it worked so well that I just never have done a proper job of it like you did.

[Powdermonkey]

38AC- by "horizontal rod"...do you mean the main linkage rod which spans across the entire engine?  Academic at this point, but I'm seeking to visualize your adaptation. 

Bend the rod...so that means the fuel rack opposite the side of the governor arms then is further opened than the fuel rack closer to the governor arms...?  If so, I could see that even a slight bend could have a beneficial effect.  Am I right in my assumption?

[38ac]

Exactly, The bend shortens the rod with the target being to get in the middle of that half turn deal you spoke of, it takes very little, almost unnoticeable.  As I said your method is much more processional and I should probably duplicate your efforts on my next twin build.