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Subject: Ivoprop Magnum & Direct Drive Engines or 2:1 Reductions

Service Bulletin #4 Jul-9-98

Purpose: To detect blade movement inside the hub due to  improper installation and, or harmonic resonance between prop and power plant. To prevent further flight if this situation is detected and develops in unsafe condition (Aluminium bushings inside the blades becoming loose, breaking bolts, blades etc..)

Introduction: Above mentioned combinations produce high level of torsional pulses during their firing cycle which several times exceeds their nominal torque and also torque reversal pulses. If the prop is mounted loose and, or gets in a harmonic resonance with the engine the blades could move inside the hub back and forth in a plane of prop rotation.

What to do: Prior to the next flight or airboat ride accomplish the following:

Get torque wench and check its calibration by hanging a known weight on its arm and multiplying the weight in pounds by arm in feet. This reading should be as close as possible to actual recommended torque on Y2 " bolts (we tried several torque wrenches and most of them were off  by a lot).

Mark the prop position in relation to the crankshaft. There are 2 positions to mount 3-blade prop and 3 positions to mount the 2-blade prop. This makes a great difference in how the prop and engine vibrate together and each position creates totally new situation. It is impossible to determine which position is best for your particular prop engine airframe combination without actual testing it on it. 
Recommended position on 0-360 or 10-360 engine: 
3-blade -# 1 cylinder top dead center & one blade straight up. 2-blade-hand  propping position.

Torque the 1/2" bolts to new torque value of 65 ft. X lbs.

Run the engine momentarily on the ground through the full RPM range.

Check the torque on 1/2" bolts and if you are not using lock nuts safety wire the bolts.

Cut the strips of stainless steel tape about 2 "long and 3/8 " wide (tape supplied with this S B.

Clean the area around gap between blades or gap between blades and blade blocks by rubbing it with clean napkin soaked with ME. K solvent.

Apply stainless steel tape across the gap next and parallel to mold parting line. Use a round object to press the tape on the surface.

Follow this inspection schedule to check if tape is broken:

After short ground run up through full RPM range on the ground and then first 15minutes, 30minutes,

I hour, 2hours, 4hours and then every preflight inspection. Also follow this schedule from the beginning if the prop has been reinstalled in a different position in relation to the crankshaft.

If tape breaks or cracks remove the tape, clean the surface with M E. K and apply new tape and start the inspection schedule from the beginning. ff tape breaks again remove the prop from the service and contact IVOPROP Corp.

Request to dealers: please forward this S.B. and stainless steel tape to your customers who are subject to this S. B. Keep the record of addresses of your customers to which this service bulletin applies. Make sure that any prop being sold to the above-mentioned combinations is accompanied with this Service Bulletin

Compliance.-. Mandatory

Note: Do not use prop in 2-blade configuration without blade blocks (missing pieces of pie, which fill out the big gaps between the blades. 


Not torquing the bolts Do not rely on feel, Get torque wench and calibrate it by yourself. Torque on 1/2 " bolts are 65 ft. X Lbs. (not 65 inch X Lbs.)  

Bottoming the thread of the mounting bolts into the driving lugs or lock nuts. Use extra washers if the bolts are too long. 

Bottoming the driving lugs into the counter bored holes in our thick aluminium plate, always make sure there is some clearance between driving lug and bottom of the counter bored hole.  

Not having driving lugs pushed all the way into the flange. 
Torquing the bolts does not generate enough force to pull the driving lung fully in, however the vibration forces do and you loose the torque on the bolts. Always make sure that there is not even the slightest gap between driving lug head and the back of the flange.          

Inserting spinner composite backing plate anywhere between what bolts are supposed to compress together, these fibreglass or composite backing plates compress with a heat and pressure and you loose torque on the bolts.  

Using wrong hardware 
For instance if you have 1 1/4 " plate which goes on 0-320 and you use it on 0-360 flange the milled notches will fit nicely over the driving lugs, however their original purpose is to hold the lock nuts on 0-320 and not serve as counter bored holes for driving lugs on 0-360.

Another example - if your 2 1/4 " diameter center boss is too long or the radius at its base to big to accept our hardware.

If something does not fit or it does not look right or it has more holes than you need, do not force it together. Contact Ivoprop Corp. and get the right hardware.


Knurled Plates Instructions Magnum Model

The knurled plates shall be installed so that knurling finish on each plate is in contact with the blades. 

The knurled pattern is 60 degrees symmetrical so if you reinstall the blades between crush plates later in different position the imprint on the blades should match the knurled pattern.

However (because the manufacturing tolerances) to get the best match number the blades and plates and always put the blades back in the same place. 

Torque the mounting bolts to 65ft x lb. dry (no oil or lubricant on the thread) and run the prop momentarily through full RPM range. Re-torque the bolts.  

Repeat the above procedure until the torque stays the same.  

Install the service bulletin stainless steel tape and follow the inspection schedule from service bulletin. Any time you inspect the tape check the torque on the bolts during the first four hours. After that check torque every ten hours.  

Make sure that knurled plates supplied to you are counter bored around the bolt holes if your blades have aluminums bushings around the bolt holes.

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