Motor Mount Variations

Over the years , I have seen many different types of engine mounts. Some used bars bolted to the root tube via angles with matching bars on the motor. They have worked very well and offered little maintenance problems.

The GT used a plate bolted to the engine and four Lord mounts which provided a slightly superior vibration dampening system.

What I would like to discuss here, is the evolution of the motor mount system with the motor plugs down, long shaft drive, v-belt and pulleys, to the latest system with the motor plugs up, gear boxed and at the rear of the wing underneath.

Shown to the left is the HP belt drive on my first MXII following a total rebuild of the airframe at 2000 hours and on the right, the latest design, the underneath, right side up mount here shown on my first "Captain America "trainer.

The first Quicksilver with the Cuyuna engine had a set of four bars with small rubber bushings. The upper bars were bolted to the root tube angles and the bottom two were bolted to the engine. Vertical bolts connected the plates and the rubber spacers, 16 of them, offered vibration dampening.

The engine transmitted power to the rear end of the root tube via a shaft attached to the engine with a coupler. This coupler was rigid keeping the engine and shaft aligned. The aft end of the shaft had a pillow block bearing and a pulley. It drove a larger pulley on the prop shaft with a 2 to 1 reduction. This pulley was clamped to the shaft with 2 5/16 bolts.

The propeller was bolted to a prop flange with a front plate. A cross bolt securely located the prop and hub to the shaft. The main hub was located behind the prop so that the side loads would be taken by the shaft ahead of the cross drilled hole. This made for a stronger design.

The first drive belt was a cog belt. It drove very reliably with no slip. It was not totally satisfactory since when it failed from teeth shearing, the prop stopped turning immediately. Belt life was about fifty to one hundred hours for the first belt. We found that subsequent belts failed after fewer and fewer hours. We found the cause to be a build-up of dirt in the bottom of the notches of the small pulley. Cleaning the grooves prior to replacing the belt gave nearly the service of a new drive.

The change to vee belts was done in the spring of 1982. I saw the first set of four belt pulleys with the purchase of my first two-place. The vee belt change solved the teeth shearing problem of the cog belts but offered a new set of problems.

Belt tension had to be greater for the vee belts as they relied on friction for power transmission. If the belts were run loose, they would score the bottom pulley and remove the hard anodizing. This would lead to rapid wear of the pulley and necessitate a replacement.

On at least one occasion, I ran a non-anodized pulley and it was ruined in about ten hours. The black coating of aluminum oxide was very necessary to the life of the pulley. I suggest that a new belt set be broken in so to speak, by readjusting it after the first few minutes of operation.

Subsequent tensionings should be done after twenty minutes, then an hour, then two hours and so forth. This will allow the belts to seat into the pulleys but never run loose enough to remove the anodizing. Belts properly broken in will offer years of trouble free service.

This drive design had some problems which would only show up after hundreds of hours of operation. A few problems were obvious when sitting in the seat. The motor was very close to your head. The engine fan was also very close to your ears. The bumping of the head and whining in the ears was considered a small price to pay for flying in those days.

The more serious problem was that of the coupling of the engine to the long shaft running back to the reduction pulleys. Any misalignment of the shaft and the motor resulted in a 5500 rpm vibration. The rear pillow block bearing held the rear of the shaft a a given point. The crankshaft through the coupling had to follow the misalignment. The rear bearings of the engine frequently failed due to this vibration. The high speed wobble also broke the coupling which was 1 1/2 inches in diameter on the early MXs. It was replaced with a stronger coupling that was 1 3/4 inches in diameter.

Shown here on the left is the original Eipper Aircraft Quicksiver 'E' model. It was responsible for the invention of the flex coupler. Shown to the right is what some do to reduce noise and increase headroom, flip the motor and drive up.

Only after the motor mount bars, mufflers and even the carburetors fell off on the newly introduced Quick E weightshift model was the problem fixed. A flex coupler was designed that allowed for about 3 degrees of angular misalignment of the shaft and the crank centerline. This solved the serious problem of failed bearings, broken cranks and broken couplings forever.

The bearings at the rear had their own special needs. The early bearing carriers had no provision for greasing the rear shaft bearing. This was solved by adding some internal passages and a grease fitting.

The pillow block bearing initially had an eccentric lock collar the cut into the shaft to maintain the shaft and bearing alignment. This collar and its set screw made nicks in the shaft which, when combined with belt tension, led to failures of the long drive shaft. This problem was solved by the use of a finger lock bearing with an outer lock ring. It no longer cut into the shaft for alignment and therefore had to be Loctited in position.

The proper method of greasing the two bearings requires that the prop be removed and the engine idled while ONE shot of grease is given to each bearing. Over greasing will lead to early failure of the seals and the bearings. The bearings are greased from the factory. No initial lube is required. Once a year or every one hundred hours is the proper frequency for subsequent greasings.

Shown below, on the left , is the first of the top mount motors. It was a 582 on an MXLII. It had the C-box and a 66 inch prop. Shown on the right, is the same mounting system but turned upside down.

My experience with both the 'plugs up' and the 'plugs down' arrangement convinced me that starting, bearing life and ring freeness was better with plugs up and the accessibility was better with the engine on the bottom, plugs down. The bottom mount also was a faster plane since the air over the top of the wing was kept very smooth.. The best of both worlds would be the motor under the root tube but with the plugs up.

Shown below are pictures of the engine located below the root tube with the plugs up.

My first trainer with the motor located under the root tube and right side up is shown below. It flies very well balanced with two people and is an ideal training craft. The dual landing gear downtubes take the loads directly to the axle and the lightly aired tires.

Return to Main Page