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RV-9 owners of IO 320-mixture arm rubbing

R

ron sterba

Well Known Member
On my new IO320 it came with a Precision Airmotive servo. The curved mixture arm was right against lower cowling even without bolt installed. Sent for straight arm and installed it with the rod end bearing with AN3 bolt but only have .290" clearance between AN3 bolt head and cowling. Its my understanding that the engine shakes at start up and shut down and will wear cowling but most of all the mixture arm shouldn't be rubbing at ALL! What did you do to elevate the rubbing? I was thinking of a clevis on the arm.

Ron in Oregon QBRV9A
 
You will need more clearance than you have for all the movement the engine will do in the mounts for torque and vibration. I had to cut out the cowl in this area and fabricate a blister for clearance.
 
I had this problem on one plane that I built. I took the arm off which is made of steel and heated it up and reshaped it. Lots of clearance when modified.
 
Dan, This is what I thought of was a blister type bubble but I thought it was a shame to change the slim line of the cowling. Thanks
Ron in Oregon
 
Hi Norman, I to thought on this reshaping of the arm. The other possibility is talking to the manufacturer about maybe the throw to FULL RICH on the TOP swing of the arm instead of the bottom. This would getting rid of the INDENT plate to the airbox. I hope more posts will come as more builders are going to Fuel Injected engines. Maybe there is a horizontal Fuel injection servo with levers that would not have any problems with interferences Dontno. HATE to cut the cowl!

Ron in Oregon

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Thanks Mark, Did you get your servo from Precision airmotive Inc. out of Marysville Washington? Nice fiberglass bubble job! Another idea that's very workable. Thanks Ron in Oregon
 
Do you have a 320 lower cowl or 360? There were issues with clearance for IO-320 when using the 320 lower cowl so Van's recommended the 360 lower cowl for me and I have no clearance issue.
 
kbehrent said:
Do you have a 320 lower cowl or 360? There were issues with clearance for IO-320 when using the 320 lower cowl so Van's recommended the 360 lower cowl for me and I have no clearance issue.
Click to expand...
Kevin I have the 360 cowl. I discovered the clearance problem by accident one evening when I had the work light in the lower cowl. The bent arm without the bolt was against the fiberglasss. I put the new straight lever on and gained a .310 clearance between the AN3 bolt head/rod end bearing to the shell of the cowling. I my 41 years of flying as a club member if there was ever a problem with the plane I justed noted in the log book and it was fixed. Here I Am building my learning curve from you folks. What would be good to know is HOW much swing in the motor mounts does the engine have at that mixture arm location. Kevin does your cowl show any signs of the the bolt head hitting the cowl,wear or chip marks? If not what is your clearance between the bolt head and cowl assuming you have the Precision servo with the lower swing in the arm. Its my understanding that at the website of Precision airmotive that it suggests the upper swing in the arm as Mike Rhodes presented his fix. The parts for the conversion are several hundred dollars plus parts. Again the other fix is modify the fiberglass with a bubble as suggested earlier in these threads. I ordered a Clevis and clevis pin in place of the rod end bearing but will have to modify the mixture cable attach point over so the throw of the clevis is STRAIGHT on or pull, its throw,can't be any benting. Now I have several ways of accomplishing this mod on these posts and all sound good and viable. With out getting to technical here if it was me I would have the lower cowl made a 1/2" wide at that point to remove all doubt. Course sounds like the best course of action maybe to look at the posts and order the reverse throw arm to the servo when the engine is ordered. I'll keep checking the powers to be. I sometimes I get a little lengthy in my posts but Iam a guy thinks about a action and a equal reaction all associated with being detailed builder. Any builder will be a detail RV guy when they are finished.
Ron in Oregon QBRV9A N421HJ
 
Well I got the Clevis and Clevis pin in place and got .615" of clearance now. Vans suggested that a 1/2" clearance would be enough for the shake of the motor on startup and shutdown of the IO 320 and at least 3/4" between the airbox and the skin of the cowling. Make note of it and share with builders.. Having the mixture arm knock against the cowling is looking for trouble.I will have to change the the mixture cable mounting hole on the plate. I am going to try the relocation today. There is one lightning hole next to the mount hole. I'll cut the edge through to the hole and see if I can bend the bracket with the mount hole to be in a position DIRECTLY in line with the mixture arm clevis. The moving cable has to be perfectly straight in the throw. This should fix the problem. Right now all I have is a wear mark on my scalp from scratching and $13 in (Clevis and pin) from ACS. There will be a welders fee still to come on the mount hole repositioning on the bracket. So check those cowls to see if you have wear and if you don't ,post in this thread what model servo and manufacturer so we can ALL avoid this problem. I'll post again in the next week how the mod works.

Ron in Oregon
 
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