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what is a coupler?

E

ep_brooklyn

Member
Hey guys,

I am in the process of repowering my 33 foot chris craft coho with 2 rebuilt chevy 350's inboards. The boat yard mounted the engines to the transmission over the winter and now I am in the process of installing the heat exchanger/new manifolds/distributors etc....The other day the owner of the yard asked if I had lined up the coupler properly and if I used a feeler gauge. I told him I wasnt sure what a coupler was exactly and that I was waiting for my mechanic to come back from vacation. Does anyone know what the coupler is for or where it is located and in what application a feeler gauge would be used? I apreciate all responses.

Thank You,
Eric
 
G'day Eric,

The Coupler is the unit that connects the Engine/transmission output shaft to the Prop Shaft.

It will consist of a flange that is attacked to the Prop Shaft, and it aligns up with a corresponding flange on the back of the engine/Transmission, and is held together with usually at least 4 bolts.

The idea of using Feeler Gauges to align the units is to stop any chance of vibrations, wear, and damage that can be caused by misalignment.

Firstly, the engine has to be brought up, or down to obtain the height, and sideways so that the gap in the two faces of the flanges are exactly the same from side to side, and top and bottom, and also that the horizontal edges of the flanges are perfectly aligned.

Once all these criterium have been obtained, only then, can the Prop Shaft be bolted up to the engine/transmission.

The only way to obtain the correct alignment is to use shims under the Engine Feet, or if fitted, adjust the Screw Jacks on the Feet, and when everything is correct, tighten the engine to the Beds, and re-check again and again, till you are satisfied that there is no mis-alignment.

In the larger vessels, this final alignment is usually carried out whilst the hull is in the water, as it will be in this environment that the rotating of the shaft is taking place.

Bruce.
 
Bruce's description is dead on........... and make sure that the hull is in the water!
Before any of these feeler gauge measurements are taken (and any engine adjustments are made), be sure to check both flanges on the transmission and on the prop shaft, for any "run-out".
This can be done with a dial indicator!

If you have any unreasonable "run-out", the procedure will render an incorrect adjustment, IMO.
 
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