Just got the Mad Mud Motor plans from ebay. The instructions look super easy to put together. Has anyone ever built one with a bigger motor? I have a 16hp duromax motor that i want to build a frame for. What sort of modifications would i need to do based off of the plans in order for it to work. Im kind of a green horn when it comes to mud motors. Any advise would be greatly appreciated.

I built one with a 16hp duromax. I just made my motor mount plate 9" wide and I believe 18" long. That should take care of everthing, since all the rest will be built around it. I also needed to add a piece of flatbar going from the top motor mount plate to the bottom motor mount plate, so that the bottom plate would not flex. When it flexes, the holes for the top rear mount plate will not line up when you get it all back together. I also designed my own transom bracket because the one they described was a piece of junk, although I'm sure it works. I actually built 2 of them. I hope you have a portrable band saw--I found mine really handy building the darned thing. May I suggest you take your time and NOT OVERHEAT your welds on the DOM tubing. Only use the lowest heat necessary to make a good weld, and only weld a little at a time, cooling with water in between. Excess heat will deform the inside of the tubing and make getting your sleeve bearings a PITA to get in and out, if not impossible. I used a belt sander to get my sleeve bearings the right size. Mine work great. I got a couple of safety kill switches on ebay for about 20 bucks shipped, and got a universal lawn mower throttle from the local hardware store for $7. I added a piece of angle iron to my tiller to hold both. I found that making the tiller come up pretty high, and staying lined up with the far side of the motor in relation to where you're sitting is handy as well to make it comfortable driving. Safety kill switches are required in my state, but are really pretty darned necessary for one of these, so don't hesitate to go ahead and get one installed before using it. They can and will knock you out of the boat if it hits an underwater object just right. Also, drill and tap your collars on the u-joint in order to add a set screw to hold the woodruff key in place, or it will come out and you'll be paddling.

This maybe a dumb question but when i thread the shaft with #10 are they left handed threads or what?

THey are normal threads, not left handed.

3/4 x 10

sorry im a "rookie" thanks guys!

Hey bayoumonster...I ordered the same plans off of eBay and I'm planning on running the same 16hp DuroMax from MaxTool. I haven't received theplans yet but I have a basic understanding of what I need to do. My one question is, where did you find a u joint that was 1" on one side(for the engine shaft) and 3/4" on the other end(for the driveshaft)? I've looked and tried to figure this out, but I am stumped and I don't know if the plans are going to explain it or not. I appreciate any info.

They provide websites and numbers in the plans.

Ok. I just didn't know if they'd provide part numbers and all if you were building something bigger than a 6.5

The plans will give you that part numbers for the U-joint. I just built one. You will use a 3/4" yolk for the shaft and a 1" yolk for the output shaft and just use a U-joint to hook em up, its very simple.

blackduck, it tried to email you some pictures twice but they keep bouncing back from aol

this is a picture of one of the longtails we build, started by using the plans you have but have since modified them somewhat

Cooling hot welds and hot metal with water is a recipe for disaster.

Other then that, all good info.

Makes them brittle.....

Hey bayoumonster, what size prop are you running with your 16 hp duromax? Happy with it?

do i need to fill the entire shaft with greese?

yes, and most everytime you use it you will want to put some grease in it

in addition to the mud motor plans, put you an extra grease zerk on the shaft
one above the center bushing and one below the center bushing, usually do not
want to put grease into the shaft via the spring loaded grease cup, you will pump
grease into the shaft until it backs up into the grease cup when using the zerk above
above the center bushing.

Thanks man I appreciate it!!

DO NOT ever cool your welds with water. Rapid cooling changes the crystaline structure of the metal making it prone to failure under stress or impact. Mud motors undergo plenty of stress and impacts. Just let the weld cool by itself sufficiently before welding again.

If you cooled your frame with water, inspect your welds before each trip and avoid logs. I wouldn't even leave the dock with it, myself.

Catastrophic motor failure could seriously injure someone. Cooling welds with water could lead to catastrophic failure.

This concludes your Public Service Announcement for this thread.

most people who ever took a welding class or read there instruction manual should know. It is poor practice to put a hot weld in water, unless you are just practicing.

do any of you have a picture of how you assembled your throttle lever assembly

dont have a pic, but on the duromax motor, i took the nut off of the manual throttle handle, take the curved washer that creates friction to keep it in place out and then put it back together, this makes it move very easily instead of having friction on tension on the handle, i drilled a small hole in the manual handle just large enough for the throttle assembly cable to fit the L bent end into, then make a bracket or purchase something at a hardware store that would work as a cable clamp and attach to motor at some point inline with your throttle to secure the cable shield to the motor. that is how you would calibrate the pull on the throttle also, you may find this clamp at a lawnmower shop or off of a junk lawnmower also

i apologize in advance if this seems like gibberish

with the 16hp motor did you make your cav. plate larger to accomidate the larger prop.

1436 jon i ran a 9.9hp on it but needed more ponys for two people. Motor runs good but i am going to build a glasspak exhaust for it

I'm thinking a 12 or 14 hp. It will always have 2 people in it and gear, and we are not goin go be in mud just shallow water and weeds.

Hmmmm,
Been a while since I looked around on this site. I don't throw water on red hot welds. But I do use a wet rag on the DOM tube close to where I'm welding, and once the weld has cooled sufficiently I do use the rag to slurp off the rest of the heat. Welding a short strip at a time and using a wet rag I don't think is a bad idea. However, I can see after rereading my post, that someone might get the idea that I was suggesting putting water on a weld right after it is welded. I just didn't expect anyone would throw water on the weld while it is still red hot. I'm glad that you guys cleared that up before anyone go the wrong idea. Anyway, I am happy with the backwater prop; however, if the boat is lighter than my 15' duracraft I think it might not have enough pitch. I believe it was an 8X5.

Well I'm not too worried about speed, we only have to go a few hundred yards to get to our spot, just want to be sure that it will actually get us there. O

I cannot figure out how to hook my kill switch and tether to this engine, how did you guys do it? Also did you run you throttle straight to the carb or through the governor spring? Sorry to bein this post back up, thanks

what engine are you using

same one as here, 16hp duramax. I also have a 2 prong kill tether

SouthernWake, I just recently went through and had to figure this out. I know this is a late post but its good to have a reference in case anyone else runs into this issue. The cable that runs from underneath the fuel tank is the wire that runs to the magneto. When you ground this it shuts off the motor.