scsmith
Well Known Member
About four years and 350 flight hours ago, I removed the original MT governor and replaced it with a Hartzell governor. I did this for two reasons. First, there was an AD issued for later versions of the MT governor because they had modified the design and there were some failures, leading to severe overspeed events. While my governor pre-dated the design change and was not subject to the AD, it was more than seven years in service and so was due for an overhaul. The quote from MT for the overhaul was almost as much as a new governor. The Hartzell governor does not have a calendar time for overhauls, so I chose to switch to the Hartzell.
Last week I pulled the RV-8 out and noticed a small puddle of oil on the hangar floor. I pulled the cowl off and quickly figured out that the oil was coming from the control shaft that comes out of the back of the prop governor. I pulled the governor off and sent it off for servicing. The governor shop said that this was very unusual for so few hours on the governor -- only 350 hrs or so. They did indeed find that the seal O-ring had a flat spot on it and was leaking.
When I originally built the airplane, I found the standard Vans governor cable bracket was a difficult installation because it was really hard to get the bolt and spacers and rod-end bearing attached on the "inboard" side of the governor control arm. (By "inboard", I mean on the side of the control arm in between the arm and the body of the governor). So I modified my governor cable bracket to allow attachment on the aft, or "outboard" side of the governor control arm. In the picture below, the original method of installation is shown on top, and my modified installation is in the middle. (click on thumbnail to enlarge image)
With the occurance of this leak at the governor control shaft, it occurred to me that MAYBE my installation was responsible for accelerating the wear on the shaft seal by putting more side load/bending moment onto the shaft by pulling from further behind the governor body. So, I came up with an even better installation, as shown at the bottom in the attached picture. Now I have the control attachment on the 'inboard' side of the control arm, but also it is a straight pull angle rather than at an angle, so no spacers were needed to allow the rod-end bearing to move without binding at the limit of its angular allowance. Without the spacers, I was able to use a shorter bolt, and it was straightforward to assemble the rod-end bearing onto the control arm. The only "down side" to this is that arguably the control cable has to bend a little more to get lined up straight. There is a big enough loop in my control cable that this was not an issue at all.
Now, I don't really know if the outboard attachment hastened the wear of the shaft seal or not. Maybe it would have worn out anyway. But I thought I would share in case anyone else has their control attached on the outboard side, and for any builders that will come to this later.
Last week I pulled the RV-8 out and noticed a small puddle of oil on the hangar floor. I pulled the cowl off and quickly figured out that the oil was coming from the control shaft that comes out of the back of the prop governor. I pulled the governor off and sent it off for servicing. The governor shop said that this was very unusual for so few hours on the governor -- only 350 hrs or so. They did indeed find that the seal O-ring had a flat spot on it and was leaking.
When I originally built the airplane, I found the standard Vans governor cable bracket was a difficult installation because it was really hard to get the bolt and spacers and rod-end bearing attached on the "inboard" side of the governor control arm. (By "inboard", I mean on the side of the control arm in between the arm and the body of the governor). So I modified my governor cable bracket to allow attachment on the aft, or "outboard" side of the governor control arm. In the picture below, the original method of installation is shown on top, and my modified installation is in the middle. (click on thumbnail to enlarge image)
With the occurance of this leak at the governor control shaft, it occurred to me that MAYBE my installation was responsible for accelerating the wear on the shaft seal by putting more side load/bending moment onto the shaft by pulling from further behind the governor body. So, I came up with an even better installation, as shown at the bottom in the attached picture. Now I have the control attachment on the 'inboard' side of the control arm, but also it is a straight pull angle rather than at an angle, so no spacers were needed to allow the rod-end bearing to move without binding at the limit of its angular allowance. Without the spacers, I was able to use a shorter bolt, and it was straightforward to assemble the rod-end bearing onto the control arm. The only "down side" to this is that arguably the control cable has to bend a little more to get lined up straight. There is a big enough loop in my control cable that this was not an issue at all.
Now, I don't really know if the outboard attachment hastened the wear of the shaft seal or not. Maybe it would have worn out anyway. But I thought I would share in case anyone else has their control attached on the outboard side, and for any builders that will come to this later.
Last edited:
