The International Cessna^® 170 Association

How many have had their C145/O300 and fixed-pitch props dynamically balanced..?.. and how significant do you feel the results have been, if any…?

How were the weights applied? Any pics?

i am considering such and thinking of how the application of washers on the standard “bullet” spinner might affect operation and appearance versus perceived benefits. A prop-change at last annual makes me imagine a vibration i never noticed previously, but it’s such a subjective matter I’m curious as to the experiences of others on this particular model airplane/engine/prop combination.

I used to own a 1950 170A with O300 and standard McCauley propeller. History on the propeller from previous owners was not informative. My original experience flying this airplane was consistently smooth operation (approximately 150 hours since buying it). Then, an oil pressure problem came up. This was tracked down to a cracked main bearing resulting in an extensive overhaul with new crank and other major parts. I intended to overhaul prop at same time but delayed due to overhaul expenses. I flew for 100 hours with the old prop and had no vibration problems. Once I could afford it, sent prop out for overhaul to a repair station. It came back with fresh static balance and no major abnormalities noted. Once back on airplane I noted a shudder/light vibration at 2000-2100 RPM. This was present passing through those revs and steady power also. Rest of RPM range smooth.

My IA was highly experienced helicopter mechanic and agreed we need to investigate. Removed prop and did another static balance. Checked bolts/hardware and anything visible on the engine that might be cause. Then we hooked ip a Chadwick Vibration Analyzer. With spinner off, ran engine resulting in a reading (imbalance). Added weights progressively to one of the bolts. These were a collection of various washers as I recall. Once the vibration was completely eliminated, weighed the washers and fabricated a suitable weight which, when installed, resulted in no vibrations. I operated this aircraft for another 10 years or so with no further vibrations, prop, or engine problems.

I never fully understood the source of vibrations from a freshly overhauled propeller. The only explanation I could come up with was the possibility that while dressing it out, the repair station might have made a subtle change in weight or geometry that didn’t show up until the thing started turning. The Chadwick process was quick, inexpensive, and cured the problem. Hope this helps.

Edit: The balance process identified a propeller attach bolt where additional weight balanced the rotation. The final weight fitted beneath the spinner and was not visible. The bolt was able to be torqued to spec and sufficient threads visible for proper installation. There was some concern in the lack of guidance (at the time 2002/2003) to use the Chadwick system on an airplane propeller. No guidance from either Cessna/McCauley or 43-13. That was resolved by the IA making a simple propeller logbook entry record ding the maintenance performed and return to service. He believed he had the authority to perform dynamic balance using a system he had training and experience with.

That is one of my concerns…Where the weights will be mounted….and of what will the weights consists….

The only time I’ve had this done was on larger equipment and the weights were common washers bolted to the spinner backing-plate. Our small spinners and backing plates are so small and light-duty as to cause concern for durability and effectiveness. The clearance from nose cowl leaves something to be desired as well, as compared to some counter-weight installations I’ve seen.

The prop-bolts themselves are so close to the center of the hub that if the weights are attached to them…they would likely be ineffective unless they were more dense than common washers…

Also, removing/reinstalling prop-bolts/nuts more than once concern me. To balance and re-check balance In this installation (6-bolt w/lock-nuts) will require multiple tries… I don’t like re-using hardware, and spares are not plentiful.

As you mention, Harlow, many folks offering this work do not possess any certification or offer any basis of approval to perform this… They expect the customer to provide that.

I’m seeking to know how many of our airplanes have found success.

A 170 that I worked on had been "dynamic balanced" and still vibrated because the prop wasn't in the correct position. After removing all the washers and correcting the prop clocking, it didn't vibrate.

George,
McCauley Service Letter 1989-4D is for constant speed rather than fixed pitch propellers. However, Figure 1 "Mounting Balance Weights" is very similar to their drawing on page 206 of their Owner/Operator Information Manual.I have two different styles of prop spinner rear bulkheads. With the one pictured below a mechanic could mount the AN970 washers anywhere around the circumference, even directly behind the propeller. The drawback is that the weights would have to be mounted closer to the center resulting in having to use more weight than if the weight was mounted as far out as possible. The recess also limits the number of washers that can be stacked behind the bulkhead without interfering with the nose bowl. My Wag-Aero spinner bulkhead is flat so the weight can be mounted further out but not directly behind the propeller.

DWood wrote:A 170 that I worked on had been "dynamic balanced" and still vibrated because the prop wasn't in the correct position. After removing all the washers and correcting the prop clocking, it didn't vibrate.

Thanks, Dan but that is not the issue in this instance. S.N.L.’s 7-8-53 and 3-23-54 address prop “clocking” and that was accomplished at installation.
This current prop came off a 172 with only 681 hrs SOH on the prop removed from the 172 for exchange with a “cruise” prop. It has no damage and ovhl records show it was static balanced. I flew it from TX to MI and to AirVenture and back to TX and it performed fine… I just believe it is not as smooth as the one removed. (this is obviously a subjective opinion)

Thanks, Gary. My spinner bulkhead, like the Wag Aero one, cannot accommodate weights directly behind the blades either. It’s the same spinner as installed in early 172’s except created for 6-bolt prop. (I’ve got a O-300-C with an EM-series prop.)

If I would have done a cursory search here I would have found Brian Olson’s great write up from five years ago here. In that thread Joel advises against mounting the weight as McCauley suggests. Instead he mounts the weights as depicted by ACES here: Reference material on this subject has been added here. See pages 16-20 of the Chadwick manual for their weight mounting instructions.
I see that Doug Mueller is on DynaVibe’s home page. I wonder if he might comment on the difference between their classic model and the GX3 which is more than twice the price, and with ACES’ $2000 ProBalancer Sport Basic Kit.

Prop “clocking” is so important . However I had an issue with a brand new sensenich prop and when engine was running at 2100 rpm , it was a shaking badly . I went back to sensenich [very upset] and they advised to move the prop back one hole against the direction of rotation. This I did and it was perfect . This piece of science i do not understand .

George - shortly after I acquired 62C I had the prop dynamically balanced (I recorded the experience with photos here: viewtopic.php?f=24&t=14029. There is also a photo with the weight and location). It did make a difference. Since that time I have had a top overall, and the prop was "clocked" to the correct position. During an annual two years ago the weight was subsequently removed and there was no real difference with vs without the weight (I suspect the combination of the the new prop position + new pistons/rings, etc negated the need for the original balancing).

Anyway ... see the post for photos.

Brian

Brian I knew about and had read your post and found it helpful. Thank you for being so thorough.

I am hoping a few other owners will contribute their experiences.

I’m scheduling a visit to a nearby shop and will post my results. (I’m also almost due for a 500 hr magneto insp. and want to accomplish that prior to the balance.)

When I bought my plane. The previous owner obtained the prop from an overhaul shop in North Carolina. Well, the prop was anything but balanced and the plane vibrated a fair amount. I had it balanced here in the Chicago area and as I also have the bullet spinner (not the really small one), they had to drill and screw a very large number of washers to the spinner plate. I did not like having to do that but now the engine runs very smoothly with a night and day difference.