Replies to This Discussion

Permalink Reply by Tim Croy on July 18, 2017 at 12:56pm

Jan, I have the number / lines engraved into the hub with a central plastic dial dart and tach indicates ~3100 at climb out WOT about 90mph at index number 2.

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Permalink Reply by Jan Eggenfellner on July 18, 2017 at 2:36pm

There is your vibration.

2 problems

1. The plastic dial is not even close enough for accurate pitch setting.  Get a Warp Drive protractor or a digital level and set the pitch manually.
2. The propeller is likely to not hold the blades from turning in the hub.  Carefully inspect the hub and blades for signs of movement.  

If, after you set the blades manually and the engine is initially smooth running, then after a couple of flights, the vibration return, then the blades are moving in the hub

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Permalink Reply by John Austin on July 18, 2017 at 10:20pm

Ditto Jan's remarks and a couple of additional observations:

Although the Sensenich GA prop is supposed to simultaneously adjust pitch on both blades, there is enough slop in the system that you can't rely on setting the pitch on just one blade - you need to fine-tune the pitch (I use a digital protractor) and check the pitch on both blades. I snug the bolts to lock-in the pitch on one blade and then adjust the other blade to match - then, I torque all the bolts to final specs.

The Sensenich GA prop uses Nord-lock washers to hold the torque on the prop bolts.  I've had zero problems with blade movement/pitch change after torquing the bolts to spec and running the engine.

John

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Permalink Reply by Tim Croy on July 18, 2017 at 10:37pm

Thanks Jan and John. I'll do that. Part of the maintenance I just did was torquing cylinder head bolts and the propeller clamping bolts. Before I did the clamping bolts I noticed I could turn the plastic dial about an 1/16-1/8 of an inch back and forth and hear a metallic knocking sound in the hub. After I loosened them (the shop who put the propeller back on my plane in March torqued them unevenly, that is all top then bottom bolts leaving a difference in the gaps when comparing top and bottom gaps) and torqued them down to 220-240 in-lbs there was very little if any turning of the dial after that. 

Also, I noticed when I torqued the nordloc washers some of them would creak loudly and I'd just keep torquing until my torque wrench clicked once. I think this is the way to do it. I never used a torque wrench before. I also used the star pattern to evenly torque them.

Thanks again for all your help,

Tim

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Permalink Reply by John Austin on July 18, 2017 at 10:53pm

The knocking sound might have been the metallic pin on each blade that nests in the plastic adjuster in the center of the hub - you probably heard a pin hitting the plastic.Make sure the pin is firmly attached to the blade and not loose!  If it is loose, it needs to go back to Sensenich for repair.

Sounds like your torquing sequence is right-on!  Torque up all the bolts in two or three stages with the last sequence arriving at the final torque.  Yes, Nord-lock washers can make some unnerving cracking or popping sounds, but that's normal and they work great!

John

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Permalink Reply by Darryl Legg on July 19, 2017 at 12:10pm

Hi Tim,

Sounds to me like your engine is a bit out of tune, maybe a bit rich. You might have a blocked air filter or might need to drop down 1 size on the main jet. Backing off the throttle a bit then it smooths out is a good indicator. Do you have EGT monitoring?

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Permalink Reply by Tim Croy on July 19, 2017 at 5:25pm

Hi Darryl,

Yes I do. It's funny you mention that since during each of the five take-offs I did that evening I would always get an EGT temperature span too great warning from the GRT EIS on my EFIS display. I'm not sure what that might mean at this point.

Tim

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Permalink Reply by Darryl Legg on July 20, 2017 at 11:32am

Hi Tim, have attached a carby tuning guide, have a good read and then see if that might be your problem. Running rough at that RPM could just be your vibration.

Attachments:

• CarbyTuning.pdf, 736 KB

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Permalink Reply by Tim Croy on July 20, 2017 at 11:49am

thank you

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Permalink Reply by Tim Croy on May 3, 2018 at 3:18pm

Just wanted to provide a quick update. I have some time now to dedicate to the plane again. Last time I flew about a month ago I discovered at cruise if I increased RPMs over 2950 or so it would vibrate and the EGTs dropped 70-100F so I ordered the 250 and 245 main jets. My condition inspection is due now so we'll probably change the main jet after we see what size it's currently using - it's been changed at least twice so far according to my engine log book. Hopefully, this will help. I received this tip from Nick at Arion Aircraft in Shelbyville, TN (taking over much of the work Pete Krotje at Jabiru NA used to do, both great, knowledgeable guys), and now I understand better what Darryl was saying.

Thanks again. I'll let you know how it all turns out.

Blue skies, Tim

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Permalink Reply by Tim Croy on November 1, 2018 at 8:41am

Update 2: We didn't change the main jet during the condition inspection. It's been flying great with no vibration up to ~2950 RPM before I get a little stutter in the engine at wide open throttle. I made a thicker, modified oil cooler hose bracket (old one was cracked a little) that keeps the line from hitting the cowling. That may have helped also. I will update after main jet is replaced. Thanks.

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Permalink Reply by Louis W. Ott on March 2, 2016 at 12:21am

Exactly why I chose the flat 6 Corvair when I was going through this decision process 6 years ago. Smooth. No airframe shaking on startup or shutdown.

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