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Mixture Arm Interference with Starter

walkergp

Member
I have installed Van's mixture bellcrank and bracket for an IO-360A1B Horizontal Induction. When I connect to the mixture arm I am unable to get full throw due to interference with starter (see pic). This engine installed in another aircraft was configured with the arm in the down position where there would be no interference. Van's said I either need a shorter starter or modify the arm to avoid the contact. Even if I use the lower hole and cut off the top portion it does not look like I will still get full throw.
25673709810_bf46b90554_m.jpg


Any suggestions?
Thanks,
Greg Walker
RV-8A
 
Thanks for the ideas!

airguy - Rerouting the cable could be done from the bottom like the prior installation of this engine. I assume Van's had a reason for routing it above the sump. My exhaust is supposed to be delivered any day so that will give me a better chance to look for alternate routing.

Mike S - Not sure I understand clocking the injector servo?

Boyd - I think a straight arm would clear the starter. Might need a longer bellcrank as it appears the angle would be too oblique for the mechanical advantage. Do anyone have a source for these arms?

Thanks,
Greg
 
Just did this

Hi Greg,

Just went through this last week. You'll notice the arm attached to the mixture is locked by teeth like a gear. Loosen the nut and move it forward one tooth at a time. I think I moved mine a tooth or two. Check the travel.

I am clear of the starter but only by 1/8," but it is clear and everything is smooth with full travel.


I have installed Van's mixture bellcrank and bracket for an IO-360A1B Horizontal Induction. When I connect to the mixture arm I am unable to get full throw due to interference with starter (see pic). This engine installed in another aircraft was configured with the arm in the down position where there would be no interference. Van's said I either need a shorter starter or modify the arm to avoid the contact.
 
Interference

I did not use the Van's bracket. Flipped the arm down and made a simple bracket of bent steel, attaching by two bolts to a flange on the case of my IO-360M1B. This allowed direct movement with no reversal of action and has worked flawlessly for 50 hours. Will try to post pic. I believe others have done something similar. Good luck and please post your solution. Thanks.
 
Remember, if you flip the arm the opposite way, you reverse the operation.


Yes, but when you dump the Rube Goldberg bellcrank, you "unreverse" the action, and it works fine.

I did this change on the -8 and it works great. With Van's focus on simple and light, I never could understand why he added the extra complication of a bellcrank.
 
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Not accurate. The bell crank assembly keeps it proper.

Proper to what? Flip it again, and you reverse the problem. See ToolBuilders post right ahead of yours.
By the way, I have seen some creative fixes when changing to counter rotation. One of my least favorite, but have seen it more than once, is bringing the mixture cable in from the front.
Also, you can order the SilverHawk servo counter rotating. That is what I did. Not sure about the other manufacturers.
 
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In my 9A I'm running an IO-360 in M1B configuration with forward facing induction and Vetterman crossover exhaust. Not sure what you've got coming but here is what I ended up doing. I routed it below my intakes and above the exhaust, installed some radiant heat shields to protect it somewhat, and manufactured a custom bracket to bring it at the bottom of the servo, works like a charm. These pictures were initial install, it was cleaned up a bit later but you get the idea. My arm on the servo was originally a straight arm that would not allow me to do this, I traded it for an offset arm.

IMG_0805_zps4bazxpcq.jpg


IMG_0863_zpstp9hdpci.jpg
 
How about this?

Can't tell if this would work in your particular situation, but this is how I did it. 300+ hours and gets special attention/inspection at every oil change.





 
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Didn't make this up!!!

See post #14 below. This is the bracket I'm referring to. Despite flipping the arm the, bracket that is a bell crank keeps everything as it should be on the controls. The geometry is correct!!!!

Darwin N. Barrie
Chandler, AZ




Proper to what? Flip it again, and you reverse the problem. See ToolBuilders post right ahead of yours.
By the way, I have seen some creative fixes when changing to counter rotation. One of my least favorite, but have seen it more than once, is bringing the mixture cable in from the front.
Also, you can order the SilverHawk servo counter rotating. That is what I did. Not sure about the other manufacturers.
 
See post #14 below. This is the bracket I'm referring to. Despite flipping the arm the, bracket that is a bell crank keeps everything as it should be on the controls. The geometry is correct!!!!

Darwin N. Barrie
Chandler, AZ

If you come in from the top left, yes. If you come in from the bottom left, no.
 
Thanks for all the ideas, guys! I need to cogitate on these and see which one will work best.

My Vetterman crossover exhaust is due to be delivered on Monday.
The starter is a Sky-Tec 149-12HT that came with the engine.

Thanks,
Greg
Aledo, TX
 
With Van's focus on simple and light, I never could understand why he added the extra complication of a bellcrank.

Because a conventional push/pull throttle control as used in the side by side airplanes doesn't have as long of cable travel as the RV-4/8 quadrant does.

If you lengthen the arm when using the side by side throttle control you would not be able to get full throw on the arm.
 
....and for those contemplating shorter arms, be aware that the shorter arm is more sensitive (or less sensitive depending on how you look at it). Smaller motion equals more change. You can still dial in your mixture accurately enough, but you do need to be more conscious of the slight amount of slack in the push/pull cable actuator when changing mixture settings. A slight amount of drift can occur if you don't. Not a big deal but something to be aware of.
 
Because a conventional push/pull throttle control as used in the side by side airplanes doesn't have as long of cable travel as the RV-4/8 quadrant does.

If you lengthen the arm when using the side by side throttle control you would not be able to get full throw on the arm.



Ok, but it seems odd that the selection of a short travel cable assembly drives the engineering requirement to add a belcrank.

Anyway, There is a choice to use the "standard" throw vernier mixture control from ACS or the "special" (short throw) Vans version from ACS.

I went with the "standard" vernier for both the -8 and Rocket and lengthened the arm specifically to match the available travel of the cable. This was done to increase the resolution of the vernier action.

This same vernier control (or push pull with more travel) would fit the side by sides just as easily as the tandems, no?
 
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Ok, but it seems odd that the selection of a short travel cable assembly drives the engineering requirement to add a belcrank.

Anyway, There is a choice to use the "standard" throw vernier mixture control from ACS or the "special" (short throw) Vans version from ACS.

I don't know anything about a short throw vs standard throw control.
The ones sold by Van's are produced by ACS and I assume (possibly incorrectly) that they have the same throw as any vernier control ordered from their catalog.
 
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