Thai Longtail/mudmotor With 6hp Lifan/honda

Been asked to let you know how the 6.5 Lifan went so here are the photos and some constructuon details. The tail piece has a taper roller bearing which carries the 12mm stainless drive shaft. Propeller fitting is pin drive for a suzuki prop I had ( 8x 7.5) 14mm bore ..since sleeved up to 17mm to take a Yamah prop from a 20 hp Yamaha ( got 3 props on ebay for $50) this prop is 9 x 10 ish and the engine works hard at 3600 to drive it ..but it stirs the pool up real good !!! shaft tube is 25mm gal steel with ball bearing at engine end and bronze bush in centre . Lubrication is 100 ml of auto transmission fluid . engine plate is 6mm steel plate and chain adjustment by washers under the engine ( only 1 needed )

It has a 2.11 : 1 chain drive so I can use a right hand prop . there is a go cart clutch ( max torque) which comes in at 2200. I am not too happly with this as it means rev range is only 2500- 3600 and if you get into regulated waters at 6 knots then your prop at 2500 needs to give you 6 knots ..hence not much top end ...so am thinking of disableing it so idle will be 6 knots .

Up down rotation is with two bits of box interlocked and shapes to give about 15 deg down. may beef this up and put on adjustable stop...

I have yet to finish the chain guard and throttle linkage as well as moving the electric start to the "front "..hope you like it and have left space below for more pictures....

 

Here are the photos of the articulation joint ..the two U sections are the same size ..bolt stops sideways movement

 

Great job. Well done . What is the rpm limit for the Lifan motor ?

 

Idle seems to be about 1650 and governed max 4000 .research into go kart sites indicates that you can go to 6500 rpm with the standard bits and 8500 with a stronger con rod and valve springs ..HP to about 10 seem possible with new carb/head/rod /camshaft ..thanks for your interest

 

Sweet set up.I was looking at doing one with a 2.5 I posted on the other thread.What is the over all length?I want one for my 10 foot jon boat.My outboard hangs to low.

 

from the piviot point to the prop is 64 inches...remember if you drive straight off he crankshaft you will need a left Hand Prop and the smaller the HP the more difficult these seem to be to get hold of (cheap) You wont build it unless you can weld and it will be difficult to do the bearings without a lathe but not impossible..I have put some notes on where to get left had props in the US on the weedeater post ..thanks for your interest

 

Thanks! and (of course) more questions...

Many thanks for putting your work out for us to learn from.

Can you show a little more detail on the thrust bearing and it's mounting?

Also, is there a 'seal' at the water end, or just the bronze bushing??

THANKS!

 

there should be a picture below ..

Drive shaft is 12 mm stainless steel brazed and roll pinned into the prop carrier
Prop carrier is made from a length of 16 mm stainless bar the idea being that the factory finish 16mm dia will ride inside the oil seal which is 16 x35mm
Thrust bearing is a taper roller 14 x35mm and the thrust is taken on the step down from 16mm to 14mm
Propeller mounting was to suite a Suzuki prop being 14mm bore and with a cross pin drive.
Securing nut is attached to an 8mm SS bolt brazed into an 8mm hole in the end of the shaft.
Engine end of shaft is supported on a 12x35mm sealed ball bearing race and half way down the shaft is a bronze bush 50mm long held with two grub screws
Lubrication is with 100ml of Auto Transmission Fluid and there is a filler hole/plug above the bush
The mounting for the bearings was from a lump of 40mm dia steel bar bored to suit bearings/seal and welded to the pipe ( 25mm galvanised )
Mounting the 26t chain gear to the end of the drive shaft is tricky...make up a boss ..weld to gear THEN with gear held in outside jaws drill the central hole..even though its a chain drive it mist be dead on. Chain is 36 pitch to match the MaxTorque go kart clutch.
If I was doing it again I would put an oil seal at the engine end of the shaft as there is some loss if its not prop down in storage .
If I was going to drive stright off the engine shaft I would not use the universal joint but a straight coupling.Mount a 1/4inch steel plate to the 4 bolts that surrund the output shaft from the engine and then 4 triangular plates welded between that plate and your drive tube .additional support from below.
If you use the chain drive apart from the right hand prop it is much easier to mount he drive tube under he engine rather than try to support it in front of the crankshaft .You can just weld the tube to the plate on which the engine sits ...chain adjustment by washers under the engine mounting bolts .
Not sure if the clutch is a good idea or neccessary as it limits the rev range from clutch engage( 2200 rpm) to 4000rpm . without the clutch you have range from idle to 4000 ..just start out the water and drop it in ...
Balance should be a positive prop down.
Make sure the engine cuts out if you fall overboard.

 

Neat set up. I like the idea of having a thrust bearing. In the swamps here we just use a shaft directly coupled to the engine. Put a shaft tube with a cutlass and you're good to go. Very simple and effective, but the thrust runs through the engine. Haven't had problems with it yet. Trick is to mount the engine on the boat so that it is balanced.

We figured out that with a shorter shaft and a mud prop with extra cup you can run the unit as a surface drive. We can get more speed and get through even more stuff. Run right over mud flats with mud flying. The engine has to mounted lower on the transom though. Thet work great in flat back pirogues. I think that the cost for mine to build was about $1K US. Worth their weight in gold though if you ask me.

Very nice set up.

 

heres some pics of a project last summer

this is one of metalboatkits.com 12 ft. skiff, scaled to 7'6'' .125 5052h32
trans is a comet industries torque a verter.

 

Thanks for the Details!

Thanks! For showing us those details. Always something to learn from someone who is figuring stuff out! When I get home this Summer I'll get a motor on my old 1938 South Bend lathe and see what I can do...

 

What boat did you mount this on? How fast did it go?

 

its all down to if you can get your hull on the plane ....this usually happens at about 15 kts.........then you can run on to 20 kts ...if it wont plane you are probably stuck at about 12 kts.
Of course you need the right pitch prop ..mine is a 10 x10 but remember its geared down 2.11 to 1

 

Thanks for the info Pistnbroke. I'll be mounting my engine on a home-made surfboard, flat bottom, so planing should be easy.

 

Hello Pistnbroke,

I'm doing 17.3kts (GPS) on the surfboard at 5,000rpm WOT, 2-bladed prop 6.75" x 4.7" (crude measurement, crude prop). Engine is 200cc honda clone, kenbo brand rated at 6.5Hp @3,600rpm. Prop is slightly aerated, about 1/2" is out of the water.

The home-made "surfboard" is very flat, no rocker, 12-ft long 3-ft wide 4" thick, plywood & epoxy. No "hump" going from displacement to planing.

Assuming I can get whatever prop I need, will there be any substantial gains if I go for 1:2 gear reduction using the same engine? I figured efficiency will be higher with slower/bigger props but by how much? The propshaft will be turning much slower too, if there's any gain in that. The shaft simply goes through a greased brass tube, no bearings. Thrust is taken up by the engine. Propshaft angle is 14-deg.

Sorry, dunno where else to post my question above.

Thanks,
notsofast