Merc Prop to jet when an extension kit is on the prop.


New member
Apr 25, 2006
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I have a 1994 150 optimax. The motor was originally a 20 inch and someone put a 5 inch bay manufacturing extension kit on the motor before i bought it. I am now looking at putting on a jet.

I took the lower unit off, and the extension housing comes right off with it, however the 5 inch SHAFT extension stayed inside the housing of the motor. I took the copper water tube off and I was able to get the shaft extension out that hole, as it would not fit out the normal shaft hole. It was a pain in the butt to do.

We then put the lower unit back on, to do this we had to put the shaft extension up the water hose housing and slide it to the drive shaft spot. Now this is the part that seemed TOOO easy, we slide the prop shaft into the 5 inch extension and it slide right in nicely, and then with a little turn of the flywheel we were able to get it all the way up and back on. I am curious if we got lucky having the extension slide on the shaft that easily or if it always works that way? It just seemed to easy since the 5 inch shaft extension is just resting freely in the housing.

When we change jets out here we do it on a gravel bar upriver. So i am curious if I should buy a new shaft for my lower unit that is 25 inch so i don't have to mess with the shaft extension.

The copper water hose also has a 5 inch extension on it.

I am curious then if i should run a 20 inch jet and take the extension housing off? or if I should run a 25 inch jet and get longer studs on it to go up through the extension to where it mounts to the motor?

Or just sell the motor and buy a new one LOL, i hate to do that as i just put a new power head on it.

I can't be the only guy this situation applies too, anyone have any insight on what would be best to do?

I will also add I have a power lift so I am ok with either a 20 inch jet or 25 inch jet, I would just have to change the height the motor mounts on the lift a bit depending on which jet i picked.


New member
Nov 1, 2009
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I would leave it the way it is. We do it here on the Stikine all the time.


Well-known member
Apr 7, 2008
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Last civilized place on the planet
Maybe I am missing something......
you should be able to install a 20" jet on that motor after removing the bay kit and be set, or at least real close. (jets come with a shaft).
A lift is handy but there is no real need to use the bay kit and a lift.
The lift will allow for some fine tuning that you will not have with a bay kit, however you did not say what size the motor or boat (bottom width) is... Lifts set the weight of the motor back ~ 5" and can affect how the boat sits at rest, narrow hulls can be adversely affected and will affect the hole shot.....also the lift weighs another 50 some pounds....most lifts seem like they are just over 5" of travel. Power trans is 7"....all alllows for some adjustment on each end.