24 Hp Mudmotor Finally Finished

[muddin redneck]

over the past several months i have been working on building a 24hp mudmotor using a honda engine. i got the idea to build it from all the posts on the weedeater conversions thread. today was the maiden voyage for it. it ran good but i have to install a cavatation plate for sure. seen a guy at the lake that also had one (factory job) so looking at his helped a lot. hope yall like what ive done. still a few kinks to work out but all in all today was a success. any questions or comments by all means let me know.

parts:

24hp honda engine
3/4" shaft 72" long
1 7/16" x 3/4" u joint
3/4" flange bearing (upper)
3/4" tapered roller bearing and cup (lower)
4- 3/4" oil seals (one in upper part of tube 3 in lower part of tube)
2- 3/4"x1" brass bushing (spaced 20" from top of tube and 20" from bottom of tube)
tube is made from 1 1/4" x1/8" dom tube it is 56" long
upper and lower bearing and seal housing made from 2"x3/8" dom tube and machined to fit bearing cup ,seals and 1 1/4" dom tube
motor base plate is made from 5/16" plate
motor mount is made from angle iron and plate steel
tiller is 1" tubing

the bottom roller bearing is packed in grease and has a grease fitting and then the tube was filled with 80-140 gear oil

[FAST FRED]

Looks like a great simple setup.

How about grabbing a GPS and giving an idea of performance?

RPM vs speed.

FF

[hoytedow]

Looks great.

[muddin redneck]

without the cavitation plate i only got up to 8.5 mph (gps) a little heart wrenching. but today i built the cav plate and will weld it on tomorrow so this weekend if i dont have to work it will be test run #2

[muddin redneck]

got the cavatation plate on today and took it out. there was no speed increase but the motor handle much much better. you can let go of the tiller and the motor we just sit there in the same place and go. gps speed only 8.5 mph. gonna go back out in a day or so with a friend who has one and do some more tinkering with the cav plate and motor depth.

[Erich_870]

You've got a really good looking motor there.:D

Where did you get your roller bearings and cups from?

About your top speed of 8.5mph, what size prop are you running? Mud Buddy recommends an 11x10 prop for your 24hp honda.

Erich

[muddin redneck]

erich
all bearings and bushing came from a company here in my local town which is called motion industries if you need it they got it. as for the speed issue im still trying out different things. going out this weekend to do some more tinkering. i have a new friend i met the other day at the lake on the first day i took it out and he has a go devil and they are recommended to go on a 16" transom boat mine is 21" i didnt think that this would be a big difference but i think that it is now are talking to my new friend b/c he had his on a higher transom boat and it didnt run very good either. my prop size is 9x6 which is the same size godevil puts on there 24 hp longtail. as for your mudbuddy it is a short tail mud motor correct? if so it has a gear reduction to it which will let you run a larger prop. go devil's new short tail mud motors also run a 11x11 prop on their 24hp. do you happen to know what the gear reduction on your mudbuddy is? i am wanting to try to build one of them this coming winter and that gear reduction info would be a great help.

[Erich_870]

erich
all bearings and bushing came from a company here in my local town which is called motion industries if you need it they got it. as for the speed issue im still trying out different things. going out this weekend to do some more tinkering. i have a new friend i met the other day at the lake on the first day i took it out and he has a go devil and they are recommended to go on a 16" transom boat mine is 21" i didnt think that this would be a big difference but i think that it is now are talking to my new friend b/c he had his on a higher transom boat and it didnt run very good either. my prop size is 9x6 which is the same size godevil puts on there 24 hp longtail. as for your mudbuddy it is a short tail mud motor correct? if so it has a gear reduction to it which will let you run a larger prop. go devil's new short tail mud motors also run a 11x11 prop on there 24hp. do you happen to know what the gear reduction on your mudbuddy is? i am wanting to try to build one of them this coming winter and that gear reduction info would be a great help.

I don't have a mud motor, but I'd like one some day. :p You bring up a good point about different props for long and short tail mud motors. Mud Buddy doesn't specifically say which type of mud motor they're talking about in thier prop suggestion guide. http://www.mudbuddy.com/Propeller%20Selection%20Guide.htm

You might give them a call just to double check your current prop size.

Erich

[muddin redneck]

erich
longtail are direct drive no reduction, shorttails are belt or (gear box like prodive motors) so they have a reduction which lets you turn a bigger prop. i went out a few days ago and i tried an 11x11 prop that i got off of ebay for very cheap and this prop had so wear so it was probable around 10-10 1/2 x 11 and with the direct drice on my motor it will kill the engine when it was set in the water so i took it off not wanting to damage my new motor. as far as prop sizes i go to go devils website b/c they list the prop size for ever motor that they sell. for my speed problem i think i am going to has to lengthen the shaft and tube on my motor so that i have a direct corrilation to the original go devil on a 16" transom boat, so i am looking at about a 94"-100" shaft on my motor to compinsate the difference in height.

[Erich_870]

erich
long tail are direct drive no reduction, short tails are belt or (gear box like prodrive motors) so they have a reduction which lets you turn a bigger prop. i went out a few days ago and i tried an 11x11 prop that i got off of eBay for very cheap and this prop had so wear so it was probable around 10-10 1/2 x 11 and with the direct drive on my motor it will kill the engine when it was set in the water so i took it off not wanting to damage my new motor. as far as prop sizes i go to go devils website b/c they list the prop size for ever motor that they sell. for my speed problem i think i am going to has to lengthen the shaft and tube on my motor so that i have a direct correlation to the original go devil on a 16" transom boat, so i am looking at about a 94"-100" shaft on my motor to compensate the difference in height.

I'm familiar with the differences between long and short tails ;) It sounds like your well on your way to figuring out how to improve your performance. I agree that lengthening your shaft to reduce the angle should yield some improvements. Keep us posted :)

How long is your shaft right now?

Erich

[muddin redneck]

the shaft is 72" so 24" or a bit more may be needed

[pistnbroke]

I think its a well engineerd professional job . Note how you need much extra Iron to brace it all if you go for the direct drive rather than the underslung chain drive system.
Your speed problem is all to do with the prop..your motor has a govener and I suspect its running at governed speed ..say for your motor thats 4000 rpm ...you need to increase prop pitch to get it down to say 3750 or its not at full throttle ..the governer is throttleing it back to 4000. you need a tacho like a tiny tach to see whats going on
You need to get the boat up to about 15 mph to get it on the plane ..dont see why you should not get 25 mph + easy. dont be tempted to take the govener off ..its not more revs you want its more pitch and leave that shaft alone till you get the pitch right .

[muddin redneck]

pb,
thanks for the info. i do know that a worn out 11x11 is way to big. a friend of mine has a factory built go devil it has a 24 hp honda on it it same as mine and it uses a 9x6 prop (factory recommended). when i run mine i can tell that the prop is cavitating so i think if i can get that to stop it will go faster any suggestion on that?

[pistnbroke]

your motor is governed to 3600 rpm (honda site) so with a 6 inch prop your max speed with no prop slip is 20.45 mph.....that to me sounds too slow for a 24 hp on a small tin boat......you need to measure the revs and put a prop on the get the revs a little below 3600 at WOT ...your problem is that a prop thats ok at max throttle is too much load at idle...certainly a cavitation plate but is the iron work above and in front of the prop drawing air down?
my 6.5 hp is driving a 10 x10 with a 2.2 reduction..so thats equivalent to a 10x4 if direct drive ...if you got a swimming pool thats a good place to experiment with a bracket on the edge or set something up on the river bank where its deep.
Addition
Looking at it again the shaft does look a bit short.....thats the other advantage of the under slung shaft with a drive chain you can get the shaft right down on the transom

[muddin redneck]

i moved the cavitation plate back away from the prop a few inches which increased my speed to a whopping 10 mph. but with the cav plate moved forward the prop the prop rises out of the water will running so i am going to put a wing on the back of the cav plate at about a 45 degree angle up to help push the prop down while running will hopfully be able to test this idea in a few days. if any body has any other ideas on this please let me know im running out of ideas
thanks

[pistnbroke]

your cav plate should be parallel with the water surface ...so no need for bends an things ...suspect you have it angled up too much at the front

[FAST FRED]

Keeping the prop submerged with a cavitation plate will have to cause drag.

How about controlling the depth of immersion with a push pull cable as found on the steering of many outboards?

FF

[pistnbroke]

thats a daft idea most of these longtails have a plate above the prop parallel with he water surface to stabilsie the positon of the prop under the water

[FAST FRED]

"ABOVE the prop parallel with he water "


Perhaps it is working as an end plate to stop airation , as well as a depth of immersion device?

[muddin redneck]

when the cavation plate is parallell with the water there isnt enough force of water riding over it to keep the prop in the water. that is why i am thinking of adding the wing to the back of the cav plate. i have included a crude sketch of what i a going to try. the cav plate is to keep the prop from cavatating and the wing will be to help keep downward force on the prop from water running over it

[mudman]

Put some cup in the prop. Happened to me with my boat. Learned on the forum here that I wasn't cavatitating, I was sucking air. More cup in the prop and I went from about 20 mph to 35 mph. Thats 65 HP though. You should see around 18 to 20 with that engine. Go devils engines are direct drive. A 23 HP has a spec at 18 mph. Check out Go devils props. Alot of cup.

[pistnbroke]

I think we have discovered that these longtails work better when geared down about 3 to 1 the genuine Thai item is even lower geared . What we have on an outboard is a max prop rpm of about 3000 but thats with the motor sized to get the boat up on the plane at about 20 % slip. What you have with your 24 hp is the prop going too fast and pushing a heavy boat so the slip is probably 50 % hence you only go slow. Reducing your slip with cupping may help but even the weed wacker brigade have discovered gearing down helps a lot as have the 6.5 lifan Honda users.

[muddin redneck]

i think your all probably right to some extent. i am going to keep the motor as is for right now so i can still use it this year to go out on the water but when fall gets here i am thinking of doing some kinda gear reduction to the motor. thanks for all the in put

[mudman]

I don't know..... Manufactureres make em 1:1. But I haven't read too much about the reduction on the forum here. Reduction seems complicated and unnecessary. Especially when prop can fix the problem.

[pistnbroke]

well if its geared down its probably easier to match a prop .....less of an egg beater ......I notice that the genuine longtail props for the 24 hp have about 80 % blade area ( is 80% of a full circle)...I carnt see what prop you have but getting it at the right depth with the right prop and shaft length should cure it