#5 lower case the same as a #4?
 

interchangeable?

Yes

I don't think you can put #4 gears, shafts and bearings in a #5 case or vise versa, can you? I think to do the swap, the lower would need to be complete with the correct internals in it.

Complete will bolt up.

Good question and I'd like to know the answer as well. As for a complete lower swap I believe one potential issue could be the polygon vertical shaft in a SSM IV, not sure the V used a polygon shaft.

So what is the weak area of the #4? The upper or lower? I know that Gary sells straight cut gears for the #4 that will make it equal to, or close to as strong as a #5.

A SSM4 is a shortened SSM3. A SSM5 is a shortened SSM3A. I believe the main difference is 3A and 5 have bigger shafts.

The gears are better in the 5 vs 4 and the bearings are bigger as well. Other than the prop shaft, I don't think there is much difference in the actual shaft size in 4 vs 5. They are cut different. Splined (5) vs polygon (4), but as far as I know, the overall diameter is the same.

Finally got a hold of Collabella ,.. the 2 are not interchangeable.
The 5 lower has bigger stuff in it..

That makes sense 'cause I researched putting 5 lower intervals in a 4 housing and that wasn't an option.

Dan,

Do you have a set of 5s already?

I do not ..looking for a set ...

Justin... sell Dan yours... and go Arneson !!!! it's time for a new project....

From what I know, the #5 lower, has 1 inch thick spur gears. #4 has .750 thick spur gears. The #4 has a polygon vertical shaft, the #5 has a splined vertical shaft. The #5 has a 1.750 propshaft, the #4 has either a 1.375 or 1.750 propshaft.

From what I have heard, is the #5 case, is stronger, and beefed up. The guys racing the #4's back in the 80s were cracking the lower case housing, on fast catarmarans. I dont know if the actual lower gears are physically any larger in a #5, but I do believe the way they are supported in the case, is better. Larger support bearings and stuff like that. Gary K might know the answer on the gears, as he sells the replacements for the #4 and #5 lowers, and had the original blue prints from mercury on them.

The #5 was simply a updated version of the #4. And the 3A, was an updated version of the #3.

Some info ..

It's pretty obvious what the weak link is in the #III drive, when looking at the first image.

Buy some 3As, Todd beats the living Piss out of his 900s in front of them. and for all the major Airtime over the years they have lived with no damage,

Gotta give him Kudos on the throttles though. He is Johnny on the spot with them,Richie Powers would be proud.

some people can blow up a brick **** house tho while others can drop a duke on lace and never get a stain on it.... its more the person than the strength of the equipment on how well things last

They`re 6" longer. What are you thinking I start second job dredging canals?

drives last longer when they are deeper . Mount a trs even with the bottom on a 38 flatdeck with 900s. Should last a new York minute before they send a mirage plus 100 feet in the air