shorten a long shaft?

[Strecker25]

I have a RU310HP (airfloor/keel) and was able to get a free 2cyl 6HP johnson 2 stroke. I haven't measured it yet, as I just got it home and had to run out, but it might be a long shaft motor. The dink is rated for a short shaft, and while I'm sure it will be fine I likely won't get very good performance if it is the long version. What's the best way to get the motor up higher in the water? Maybe sister in some 1" marine plywood on the transom to extend the mount on the boat up 5" ? I know it sounds nuts to modify the boat to fit the motor, but you can't beat free.

 

[Boston-boater]

You could probably through bolt I piece of starboard onto the existing transom. I would stay way from plywood for this application.

 

[fwebster]

Building up the transom doesn't seem to be a workable idea to me. THe short shaft is 15" and I think a long haft is 20". That means you would have to stack up 5" of shims on an already small transom.

Depending upon the age and design of the motor, some manufacturers achieved a long shaft by selling a long shaft kit (spacer block, longer bolts, longer drive shaft). This allowed the dealers to stock only one motor and with a kit they could change a short shaft into a long shaft with about an hours shop time.

You could do just the reverse if yours is that design……buy shorter bolts, shorter drive shaft and then remove the spacer block, and exchange the long shaft and bolts for the shorter ones.

 

[Sublimetime]

Sister in the plywood, not "free" but darn close. Give it a try. Changing shaft and bots gotta be a lot more than free.

 

[Strecker25]

Thanks guys, a little more info. It is an absolutely immaculate Johnson 6HP 6R-69M, with a 20" shaft. I ran it in a can tonight, and I don't know that I've ever seen or heard a small two stroke idle this smoothly, and it is a two cylinder model.

I think I could build up the transom by sandwiching the same thickness plywood as the original in between two other slabs of the same thickness plywood to achieve that height, but the more I thought about it that changes the force of the motor upwards and likely transfers the energy into an area of the tubes that was not designed for such force.

I think I may just at least run it on the boat and see what happens. I'm sure I'll get plenty wet from the spray, and not get on plane, but we'll see.

Here's some pictures. I am also going to look into the potential to finding the short shaft, as I know they made it that year.


EDIT: A member of another forum just commented that it is in fact a short shaft motor, and that they measure about 17" (which this one does) so we should be ok! Can't wait to give it a try on the water.