Dynamic Prop Balancing O340

[Dan L]

So it looks like the FX3 doesn't use a plenum. I'm wondering why when it seemed to work so well on the O-340's?

[N867SP]

I finally got around to wrapping up my dynamic balance a few months back. Ended up facing up a bracket that connected to the forward engine case split bolt, allowing the accelerometer to be vertical, centered over the crank and as close to the prop/flywheel as possible. As for the optical sensor I just taped it to the top of the oil cooler, gave it a clear shot to the reflective tape on the back of the master blade. First averaged reading was 0.26ips @ 096 degrees, multiple attempts I was able to get it down to 0.01ips @24 degrees. By temporarily adding washers to the spinner screws to find where the weight was needed. Ended up adding a single AN4-4 bolt, AN960-4L washer and a AN365-428 nut to one of the existing holes in the flywheel that was the closest to the degree needed. Typically anything less that 0.07ips is “acceptable” anything below 0.04ips is “good”. Noticed slight reduction in vibration in the aircraft in our 16hr roundtrip to OSH18.

Forward accelerometer mount




Aft optical mount


First averaged reading


Final averaged reading with permanent hardware installed



Pete Meyer
Severna Park, MD
CCK-1865-0078
✈️N9PW

[Dbro172]

Shouldnt the accelerometer be straight up and down, vertically?


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[N867SP]

Shouldnt the accelerometer be straight up and down, vertically?


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Perpendicular to crankshaft, so with tailwheel Aircraft it’s not vertical to ground.


Pete Meyer
Severna Park, MD
CCK-1865-0078
✈️N9PW

[Dan L]

Aircraft Spruce had a recent sale on the Dynavibe Classic model and I decided to pick one up. I had a top overhaul on my O-340 this fall including new pistons and could tell there was more vibration than it had been. When I’d first changed to the 84x42.5 Catto I’d had it balanced by a shop an hour away and they got it down to .060 IPS.

I’ve watched the balancing process a half dozen times or so and looked at a few you tube videos on the Dynavibe model. In the end I was able to get it balanced down to .080 IPS but it took me quite a few trial runs to get there. I started at .41 so it was a significant improvement.

It is interesting that seemingly minor changes like going from a thin washer to a thick washer can make a big change when you’re getting close to the final solution.

I like the Dynavibe unit. It’s easy to use and tells you where the weight is needed. This model does not tell you how much weight is required but their more expensive version does.

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Here’s a few pictures of my setup.

Also worth mentioning is that in the three times I had props balanced on this EX by others, prior to this balance, we reinstalled the top cowl between trial runs. That kept the section of the bottom cowl behind the spinner from getting blown back into the starter gear. Removing the bottom cowl completely didn’t seem like a good idea because the air intake into the carb would be unfiltered.

This time I make a temporary filter setup from 3” and 2” PVC and a small engine filter from NAPA. This allowed a lot quicker periods between test runs.

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[BC Aircraft]

Awesome Pictures! If anyone wants to rent a Dynavibe, BCAtools.com rents them out by the week.