Transom/Gear Case size

[FillupD]

I would like to find out what would happen if a 15" transom(small gearcase) was mounted to a 20" transom. I am trying to swap motors but the 76 55 hp I bought has a small gear case and I have a 20" transom. I have a 73 50hp lark but I'm not sure if the gearcase will interchange.
If I run with the small gearcase, would the cavitation plate just be too high to expect good performance? or would it even work?

 

[Silvertip]

Re: Transom/Gear Case size

That's why they make 15 and 20 inch legs. Generally a 15 inch leg is too short on a 20 inch transom. It will work fine off-plane but when you get on-plane the prop will very likely ventilate.

 

[ondarvr]

Re: Transom/Gear Case size

Are you sure yours is a short shaft? There were short shaft (15") 50's and 55's, but they weren't that common, most were 20" models.

 

[FillupD]

Re: Transom/Gear Case size

I'm going over to IA to pick it up now, I'll know in about 4 hrs for sure. I was just going by what I have read, 15" transom and small gear case. I thought maybe the large gear case would be better though; maybe not, maybe doesn't matter. As you can tell I really don't have a clue about these gear cases and size differences/or why there is. I have a few props for a large case though so I thought switching may be a god idea from that stand point, and possible other benefits?

 

[FillupD]

Re: Transom/Gear Case size

Ok, It is a long shaft with a small gear case. Is there a difference between the gear cases that would merit a change to a large gear case? Would it even work. I'm going to pull the lower end from the motor I just got that's been sitting for awhile and change the impeller, its the same impeller part number maybe the shafts will be the same and I can just swap the cases. I am thinking there has got to be some kind of advantage for a larger gear case versus the smaller one.

 

[ondarvr]

Re: Transom/Gear Case size

I'm not sure what he means by a small gearcase, other than for high performance and racing I don't think there is a small one. The only thing I can think of is that a commercial model may have a larger gearcase than a standard model, but I've never seen one with it and they normally rate the HP lower on commercial models.

 

[FillupD]

Re: Transom/Gear Case size

On my 50 hp the prop is a 4.5" and on the 55 it is a 3". It states in the description for props, small gearcase or large gearcase.
I just wanted to swap my large on on the 50 to the 55 if there was an advantage (other than I have props for the larger one)

I just had a question: Can the gear cases be swapped, and is there an advantage of the large one over the small one?