Hey guys, here is what I am faced with, and keep in mind that I am just now starting to do my homework before I start anything. I have an old hyperdrive with a kohler 18 pro motor on the frame. The frame is a first generation, and does not have reverse and overall, the unit just works. I picked this unit up used, and had a local shop go through the motor and it runs like a champ. I have run it for 3 seasons with 0 issues and I also use it to fish out of all summer long. I have been terrible about logging the hours on the motor but I change oil and spark plugs frequently and keep an eye on the belt, and the frame gets greased often. With that all being said, no issues. I AM TIRED OF GOING SLOW THOUGH! I have 2 buddies with the 35hp vanguards and they blow by me on the water (WELL DUH). So i am looking to upgrade my motor and maybe just keep the kohler as a backup because it has been so good to me. Here are my questions...
1) What motor would you all go with? Briggs & Straton, Honda, Kohler, Etc....
2) If I am correct, if I upgrade motor size, I am pretty sure I have to upgrade the prop as well?
3) As I am shopping for motors, I see different horizontal shaft diameters and lengths, so what is the measurements I would need to order in the new motor to fit the frame?
4) Depending on motor, what upgrades would you all do? I do not need to fly or do 50mph (although that would be freaking sweet), but I may want to upgrade the motor a little without making it unreliable.

Your responses are appreciated, thanks for the input and the read, once I start the project, I plan on keeping this thread updated with photos and problems encountered.

if it's a sweet little mudmotor, maybe keep it and buy a 25 or 35hp outboard to get you around when u need speed.

good luck with whatever u choose!!!!

What size boat do you have? You could go with a 23 brigs and mod it.


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Check and see if the 18 Kohler and the 25 Kohler mount on your frame the same way. If it does, that is your easier route.

Years ago we put a 35hp Vanguard Commercial on a 2004 18hp short transom MB frame. We had to modify the motor mount plate adding 1 1/2" by 1/4" flat stock to the frame and redrill the mount bolt holes, and elongate them to allow for forward and backward movement. We also had to elongate the holes in the frame where the belt housing bolts went thru, The BB vans output shaft is taller than the small blocks so we had to allow for the extra height, and still be able to use the same length belt.. We cut off and moved tiller bracket, and moved it to clear starter motor. We also fabed up a new belt tensioner bracket, and repositioned it. We installed a 48" prop shaft off a tall transom MB to the belt housing. The 18 Hp came with a 32-50 gear set, we got a 36T upper gear and had the taper lock bored out to match motors output shaft dia. and broached to a larger key way to match motors key. This motor is still running today, with a BB prop and home made dual exhaust.

First off, thanks for the responses guys.
1)The boat size is an old 17 foot polarkraft modified v. A lot of work has been done to the boat and the transom so I know it would support the extra weight of the new motor if I were to upgrade. That i am in no way worried about.
2) Some very valid points have been made and I appreciate the input. I did not even think about the heights of motors being an issue. Now what I am not sure about still, is that one of my buddies who has the 35 hp has the exact same frame as mine. So i am still not sure if I would have to modify the mounting plate to put the new motor on. The height in which the shaft goes into the gear, where the belt meets is my big question now.
I have a few months before I start to do anything. Need to graduate school in a few weeks and start working but this is one of the projects I want to tackle once I have some more free time. I think the best thing to do is get my frame and my buddies frame side by side and get some measurements of everything and see if there are true differences in the frames to support the different motors.

Again, thanks for all the help. I will keep this thread updated with pictures, measurements, etc. as it keeps coming along.