I have a Irwin 27 with an atomic 4 motor. When I put he boat in reverse, the shaft has come loose and seperated from the coupling at the transmission. There is a set screw and it was tight. It would appear something besides the set screw is needed to take the backing down load. With the set secrew out the shaft slips out easily from the coupling. The shaft has a key for handeling the rotational load, but no "C" ring or other device to take the back down load. Is something missing? Does the coupler need to be replaced? Should it be a compression tight fit? Could I through bolt it in place of the the set screw? I have already dimpled the shaft to give the set screw a better bite which worked for a while, yet it still pulled out when in reverse after the winter layup.
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You need a new coupling if it is that loose. Take your shaft and coupling to a good machine shop and have them build you a new coupling. Have them tap it for 2 set screws that interface with dimples in your saft.
A coupling that loose is going to cause bigger problems with your transmission if left alone.
A coupling that loose is going to cause bigger problems with your transmission if left alone.
Steve, you probably have two problems.. one is a too loose coupling fit and the other is some misalignment which is working the screw loose. Ross is right, as a stopgap, you can drill and pin it, but that and the new coupling, as Tim states along with alignment will put it all back better than new.. Good luck with it.
The set screw
The "set screw" serves two purposes. It holds the shaft in the coupler and to distribute the torque from the shaft to the coupler.
No matter how close the fit, the shaft will still move. There is a lot of torque exerted by the prop. It is pushing or pulling thousands of lbs. The set screw must go into the shaft for about 25% in order to send the torque to the coupler. The set screw is usually black steel high tensile with a nut on the coupler as locking nut. If you are missing the nut, it will backout.
I use a Hex bolt and drilled across the head for a security wire.
The "set screw" serves two purposes. It holds the shaft in the coupler and to distribute the torque from the shaft to the coupler.
No matter how close the fit, the shaft will still move. There is a lot of torque exerted by the prop. It is pushing or pulling thousands of lbs. The set screw must go into the shaft for about 25% in order to send the torque to the coupler. The set screw is usually black steel high tensile with a nut on the coupler as locking nut. If you are missing the nut, it will backout.
I use a Hex bolt and drilled across the head for a security wire.
I must correct a statement here. The set screw should NOT be carrying the torque load. The shaft key does that. The set screw(s) secure the coupling to the shaft and a drill point dimple the same diameter as the set screw is adequate. Proper grade screws and correct tightening torque are vital.
SHaft
Shaft couplings are and should always be machined to a light press fit or interference fit. This means most of them require a light tapping with a wood or brass mallet to seat it in the coupling. This light press fit combined with a shaft key and dimpled set screws will hold your shaft just fine.
The set screws are not designed to take the load but when slop is present and the shaft comes out of the coupling easily they begin to take a load they were not designed to. They are a last stop safety measure.
You really need a new coupling at a minimum. A new coupling should be fitted and faced to the shaft by a machine shop or a prop shop that does shafting work. If you have had slop for a while there is a very high likely hood that the shaft is also damaged from the wear induced by the slop.
Over the years a couple of builders, mostly Canadian, used key less straight couplings and the set screws did take the load but these shafts failed more often and did not meet industry shafting construction standards. I don't believe there is any builder today using key less straight solid couplings.
Shaft couplings are and should always be machined to a light press fit or interference fit. This means most of them require a light tapping with a wood or brass mallet to seat it in the coupling. This light press fit combined with a shaft key and dimpled set screws will hold your shaft just fine.
The set screws are not designed to take the load but when slop is present and the shaft comes out of the coupling easily they begin to take a load they were not designed to. They are a last stop safety measure.
You really need a new coupling at a minimum. A new coupling should be fitted and faced to the shaft by a machine shop or a prop shop that does shafting work. If you have had slop for a while there is a very high likely hood that the shaft is also damaged from the wear induced by the slop.
Over the years a couple of builders, mostly Canadian, used key less straight couplings and the set screws did take the load but these shafts failed more often and did not meet industry shafting construction standards. I don't believe there is any builder today using key less straight solid couplings.
Spring Pin Type > Diameter
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Pins
6 products match your selections
Material TypeStainless SteelFinishPlainStainless Steel Type420 Stainless SteelPin TypeSpring PinsSpring Pin TypeCoiledCoiled Spring Pin TypeHeavy-DutySystem of MeasurementInchDiameter1/4"Specifications MetAmerican Society of Mechanical Engineers (ASME)ASME SpecificationASME B18.8.2
Overall LengthThe overall length of pins is measured from end to end, except for clevis pins with heads. For clevis pins with heads, measure the overall length from under the head to the tip of the pin. 1" | 1-1/8" | 1-1/4" | 1-1/2" | 2" | 2-1/2"
These 6 products match your selections
Overall Length
1"95765A516$12.98 per Pack of 10
1-1/8"95765A5247.33 per Pack of 5
1-1/4"95765A5337.72 per Pack of 5
1-1/2"95765A5399.10 per Pack of 5
2"95765A5459.54 per Pack of 5
2-1/2"95765A55110.46 per Pack of 5
Just do what mainesail suggests or drill it and pin it. Be sure to install a Drive Saver coupling.
http://www.marineparts.com/mpf/mpf204.aspx
View catalog page
Compare products (6)
Pins
6 products match your selections
Material TypeStainless SteelFinishPlainStainless Steel Type420 Stainless SteelPin TypeSpring PinsSpring Pin TypeCoiledCoiled Spring Pin TypeHeavy-DutySystem of MeasurementInchDiameter1/4"Specifications MetAmerican Society of Mechanical Engineers (ASME)ASME SpecificationASME B18.8.2
Overall LengthThe overall length of pins is measured from end to end, except for clevis pins with heads. For clevis pins with heads, measure the overall length from under the head to the tip of the pin. 1" | 1-1/8" | 1-1/4" | 1-1/2" | 2" | 2-1/2"
These 6 products match your selections
Overall Length
1-1/8"95765A5247.33 per Pack of 5
1-1/4"95765A5337.72 per Pack of 5
1-1/2"95765A5399.10 per Pack of 5
2"95765A5459.54 per Pack of 5
2-1/2"95765A55110.46 per Pack of 5
Just do what mainesail suggests or drill it and pin it. Be sure to install a Drive Saver coupling.
http://www.marineparts.com/mpf/mpf204.aspx
shaft comes loose when in reverse Fixed
This happened this weekend when comming into the dock what a nightmare. when pulling out the shaft the set screw was loose and the keyway fell out when we reasembaled the prop shaft I placed a split collar around the shaft it will ride up to the cutless packing nut but not let the shaft back out.Hope this is a fix.
This happened this weekend when comming into the dock what a nightmare. when pulling out the shaft the set screw was loose and the keyway fell out when we reasembaled the prop shaft I placed a split collar around the shaft it will ride up to the cutless packing nut but not let the shaft back out.Hope this is a fix.
Steve:
Here is an example of a shaft coupling with bolts that will accept safety wire. If you have bolts with heads you can drill them and safety wire them or get bolts that can be wired.
Be sure that the holes is the shaft are deep enough too.
Here is an example of a shaft coupling with bolts that will accept safety wire. If you have bolts with heads you can drill them and safety wire them or get bolts that can be wired.
Be sure that the holes is the shaft are deep enough too.
For reference, the max allowable "slop" between shaft and straight couplings is NONE! You really need a new coupling not a band aid for the long term. Losing a shaft is potentially a boat sinking event.. A proper straight coupling fit to the shaft is an interference fit.
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