Anybody ever converted a lawnmower or dirtbike engine to a inboard shaft and propeller setup?
 

Hi I am building a little 11 ft. V bottom plywood epoxy speedboat, I am
really interested in installing a 250cc dirtbike engine in it for
propulsion, I would have to use a stuffing box and shaft supports and
rudder, but I live in Chilliwack BC Canada and nobody locally can
supply parts,has anyone ever done such a install? The engine (dirtbike)
would have about 20 to 40 Hp. be watercooled with a small rad, I was
thinking I could use some kind of tranny with F,N,R from a lawn tractor
to obtain reverse in the boat, I know people have told me to use a
outboard but this is a project and I`m going to make it all work one
way or another, any help would be greatly appreciated.

Anybody ever converted a lawnmower or dirtbike engine to a inboard shaft and propeller setup?
 

"rvbilly" wrote in message
oups.com...
Hi I am building a little 11 ft. V bottom plywood epoxy speedboat, I am
really interested in installing a 250cc dirtbike engine in it for
propulsion, I would have to use a stuffing box and shaft supports and
rudder, but I live in Chilliwack BC Canada and nobody locally can
supply parts,has anyone ever done such a install? The engine (dirtbike)
would have about 20 to 40 Hp. be watercooled with a small rad, I was
thinking I could use some kind of tranny with F,N,R from a lawn tractor
to obtain reverse in the boat, I know people have told me to use a
outboard but this is a project and I`m going to make it all work one
way or another, any help would be greatly appreciated.



You stated" I could use some kind of tranny with F,N,R from a lawn tractor"
You need to research the function of a 'thrust bearing' and either add one
to your lawn tractor tranny or use a marine reduction gear which has one
incorporated into the design.

Anybody ever converted a lawnmower or dirtbike engine to a inboard shaft and propeller setup?
 

Hi, I am not following what you mean with with the thrust bearing, and
what would be the advantage of the reduction gear? thanks Bill

Anybody ever converted a lawnmower or dirtbike engine to a inboard shaft and propeller setup?
 

On 30 Oct 2005 13:20:29 -0800, "rvbilly" wrote:

Hi, I am not following what you mean with with the thrust bearing, and
what would be the advantage of the reduction gear? thanks Bill

It is a strange thing when you first hear of it: but the same HP can
give a few pounds of thrust at high boat speeds and hundreds of pounds
of thrust at slow speeds.
The latter place is where marine transmissions live - so they need
buff thrust bearings if they are to last any time at all.
Water props get inefficient at high speeds.

Brian Whatcott Altus OK

Anybody ever converted a lawnmower or dirtbike engine to a inboard shaft and propeller setup?
 

"rvbilly" wrote in message
ups.com...
Hi, I am not following what you mean with with the thrust bearing, and
what would be the advantage of the reduction gear? thanks Bill

When you turn the prop (pushing water aft) the shaft is forced forward. This
forward thrust must be transmitted to the boat through a thrust bearing:
http://science.howstuffworks.com/bearing3.htm

The reduction gear takes the higher input rpm of the engine and reduces it
down to a usable rpm so the prop does not cavitate. It also allows F N R.

Anybody ever converted a lawnmower or dirtbike engine to a inboard shaft and propeller setup?
 

Horsepower is the rate of doing work. Why is it surprising that a small
force at high speed is different than a large force at low speed? It's how
the small displacement car engines at 9,000 rpm are able to compete.

Roger

http://home.earthlink.net/~derbyrm

"Brian Whatcott" wrote in message
...
On 30 Oct 2005 13:20:29 -0800, "rvbilly" wrote:

Hi, I am not following what you mean with with the thrust bearing, and
what would be the advantage of the reduction gear? thanks Bill

It is a strange thing when you first hear of it: but the same HP can
give a few pounds of thrust at high boat speeds and hundreds of pounds
of thrust at slow speeds.
The latter place is where marine transmissions live - so they need
buff thrust bearings if they are to last any time at all.
Water props get inefficient at high speeds.

Brian Whatcott Altus OK

Anybody ever converted a lawnmower or dirtbike engine to a inboard shaft and propeller setup?
 

In my younger days, when I had more time on my hands and little money, I use
a vertical shaft lawn mower engine and the lower unit off a old Johnson
Seahorse.

I mounted the engine on the keelson with a the shaft going through to the
lower unit, which was bolted to the bottom of the boat. I was using the old
outboard shaft and it ran through a home made stuffing box and a second hole
for the fwd/rev shifter shaft.

It was quite a deal and complex to operate in a 10 foot dingy.. the engine
being between the steer seat and the middle thwart. Lot's of heat on my bare
legs.

Steering was done with the normal sailing dingy rudder.

Had to be careful when running her up on the beach or in shallow water.

Sure was fun to be 'young and dumb and ....'

Steve
s/v Good Intentions


"rvbilly" wrote in message
oups.com...
Hi I am building a little 11 ft. V bottom plywood epoxy speedboat, I am
really interested in installing a 250cc dirtbike engine in it for
propulsion, I would have to use a stuffing box and shaft supports and
rudder, but I live in Chilliwack BC Canada and nobody locally can
supply parts,has anyone ever done such a install? The engine (dirtbike)
would have about 20 to 40 Hp. be watercooled with a small rad, I was
thinking I could use some kind of tranny with F,N,R from a lawn tractor
to obtain reverse in the boat, I know people have told me to use a
outboard but this is a project and I`m going to make it all work one
way or another, any help would be greatly appreciated.

Anybody ever converted a lawnmower or dirtbike engine to a inboard shaft and propeller setup?
 

Hi guys, would it be possible to mount the thrust bearing on the prop
shaft close to the transmission ? I would like to use a prop from a 25
to 40 Hp outboard with a pitch of about 14, will that be to much prop
for the motor as it will have somewheres in the neighborhood of 20 to
30 Hp, it will make this power around 8,000 to 9,000 RPM, I want to use
simple chain and gears to reduce the input(3-1 roughly) to the input of
the tranny, I think with 3-1 it should give a good holeshot. Can the
exhaust be run through a muffler and about 5 ft of pipe into the water,
any chance the water might back up into the engine ? the boat should
weigh in around 650 to 750 lbs fully loaded ( hull,motor,gas,2 adults)
I`m hopeing to achieve the 30 to 40 mph mark, Glen-L has a speedboat
called TNT, it`s the one I`m baseing my modified plans on,it will do 37
mph with a 25 hp outboard pushing it, you guys are really helping me
lots with your feedback and I apreciate this, I`m a little scared of
setting up this engine only to find out I can only get say 20mph, the
specs on everything seem good and possible but theres allways the
chance that I should have say mayby used a little little motor such as
say a 3 cyl. Geo Sprint or 1200cc Toyota,what are your opinions on
this,, thanks Bill--How do we upload pictures into these posts?

Anybody ever converted a lawnmower or dirtbike engine to a inboard shaft and propeller setup?
 

rvbilly wrote:

I`m a little scared of setting up this engine only to find out I
can only get say 20mph, the specs on everything seem good and
possible but theres allways the chance that I should have say mayby
used a little little motor such as say a 3 cyl. Geo Sprint or 1200cc
Toyota,what are your opinions on this,,

I don't have it at hand now, but I remember Dave Gerr's book "The Nature of
Boats" gives quite simple calculations to estimate how much speed you
should be able to get out of your boat. Check it out!

- Heikki



P.S.
How do we upload pictures into these posts?

We don't. Many news servers strip them from all newsgroups not specially
marked as binaries. Better find a website where you can post your picture,
and send a link here.

Anybody ever converted a lawnmower or dirtbike engine to a inboard shaft and propeller setup?
 

"Heikki" wrote in message
. ..
rvbilly wrote:

I`m a little scared of setting up this engine only to find out I
can only get say 20mph, the specs on everything seem good and
possible but theres allways the chance that I should have say mayby
used a little little motor such as say a 3 cyl. Geo Sprint or 1200cc
Toyota,what are your opinions on this,,

I don't have it at hand now, but I remember Dave Gerr's book "The Nature
of
Boats" gives quite simple calculations to estimate how much speed you
should be able to get out of your boat.


How much speed will this motor get?
http://www.weldingfaq.com/turbine2.asp

Anybody ever converted a lawnmower or dirtbike engine to a inboard shaft and propeller setup?
 

You can pretty much make any engine work. Heat is the biggest problem. Even
though the block may be water cooled, you'll still need to get airflow to
the radiator. Exhaust heat will be a big problem and could become a hazard
if the engine is enclosed. Check out www.surpluscenter.com for misc gears
and parts.



"rvbilly" wrote in message
oups.com...
Hi I am building a little 11 ft. V bottom plywood epoxy speedboat, I am
really interested in installing a 250cc dirtbike engine in it for
propulsion, I would have to use a stuffing box and shaft supports and
rudder, but I live in Chilliwack BC Canada and nobody locally can
supply parts,has anyone ever done such a install? The engine (dirtbike)
would have about 20 to 40 Hp. be watercooled with a small rad, I was
thinking I could use some kind of tranny with F,N,R from a lawn tractor
to obtain reverse in the boat, I know people have told me to use a
outboard but this is a project and I`m going to make it all work one
way or another, any help would be greatly appreciated.

Anybody ever converted a lawnmower or dirtbike engine to a inboard shaft and propeller setup?
 

"Mark" wrote in message
...
You can pretty much make any engine work. Heat is the biggest problem.
Even
though the block may be water cooled, you'll still need to get airflow to
the radiator. Exhaust heat will be a big problem and could become a hazard
if the engine is enclosed. Check out www.surpluscenter.com for misc gears
and parts.

Even though the block may be water cooled,
you'll still need to get airflow to the radiator.

The "raditaor" is called a Heat Exchanger (in a boat) and is cooled by
seawater not air.

Anybody ever converted a lawnmower or dirtbike engine to a inboard shaft and propeller setup?
 

On 30 Oct 2005 12:16:41 -0800, "rvbilly" wrote:

Hi I am building a little 11 ft. V bottom plywood epoxy speedboat, I am
really interested in installing a 250cc dirtbike engine in it for
propulsion, I would have to use a stuffing box and shaft supports and
rudder, but I live in Chilliwack BC Canada and nobody locally can
supply parts,has anyone ever done such a install? The engine (dirtbike)
would have about 20 to 40 Hp. be watercooled with a small rad, I was
thinking I could use some kind of tranny with F,N,R from a lawn tractor
to obtain reverse in the boat, I know people have told me to use a
outboard but this is a project and I`m going to make it all work one
way or another, any help would be greatly appreciated.

I built an inboard canoe once. I used a Briggs & Stratton 2hp
horizontal shaft engine from an edger. I mounted it where the rear
seat was and used a shaft and gears from old weadeaters to get the
power to the prop with a belt and pulley dealie. In order to keep the
shaft from leaking and filling the boat with water I made one end of
it protrude above the "deck" of the canoe. It had no reverse. I made a
rudder to steer it and a seat in the middle with a steering wheel
hookup. The weedeater gears are really tough. I used a wooden block
behind the housing that was screwed into the transom (it was a flat
transom canoe) so it wouldn't push out. The prop came off a 15hp
outboard engine. It went pretty fast for a 11ft canoe. I rode that
thing around for a while. Lots of fun. Eventually ants invaded the
transom and ruined the wood. I gave it to my uncle so he could rebuild
it and make it something else. Got a lot of use out of that $20 boat.

Anybody ever converted a lawnmower or dirtbike engine to a inboard shaft and propeller setup?
 

Also try posting this question in
rec.crafts.metalworking

"rvbilly" wrote in message
oups.com...
Hi I am building a little 11 ft. V bottom plywood epoxy speedboat, I am
really interested in installing a 250cc dirtbike engine in it for
propulsion, I would have to use a stuffing box and shaft supports and
rudder, but I live in Chilliwack BC Canada and nobody locally can
supply parts,has anyone ever done such a install? The engine (dirtbike)
would have about 20 to 40 Hp. be watercooled with a small rad, I was
thinking I could use some kind of tranny with F,N,R from a lawn tractor
to obtain reverse in the boat, I know people have told me to use a
outboard but this is a project and I`m going to make it all work one
way or another, any help would be greatly appreciated.

Anybody ever converted a lawnmower or dirtbike engine to a inboard shaft and propeller setup?
 

Ookie Wonderslug wrote:
On 30 Oct 2005 12:16:41 -0800, "rvbilly" rvbilly@shaw.


Hi, did you have any problems with that 2 hp trying to turn the 15 hp
prop? Would it stall out at any point? thanks Bill

Anybody ever converted a lawnmower or dirtbike engine to a inboard shaft and propeller setup?
 

On 10 Nov 2005 19:55:13 -0800, "rvbilly" wrote:


Ookie Wonderslug wrote:
On 30 Oct 2005 12:16:41 -0800, "rvbilly" rvbilly@shaw.


Hi, did you have any problems with that 2 hp trying to turn the 15 hp
prop? Would it stall out at any point? thanks Bill

It wouldn't stall out because of belt slip. I used the engaging pulley
like a clutch. I'd give it full throttle and let the power build up,
then slowly engage the pulleys. I had it geared down 3 to 1 also. It
would bog a little, but not too bad. An outboard runs around 9000 rpm.
My prop was barely doing 1000 rpm full speed. So it wasn't really a
problem. I'd say top speed was around 10 or 15mph. Fast enough for me
in that boat. It was great for puttering around the local 50 acre
lake.

Anybody ever converted a lawnmower or dirtbike engine to a inboard shaft and propeller setup?
 

Hay Ookie can you imagine what that canoe would have done with a 250cc
2 stroke dirt bike engine hooked up, it would have been crazy fun,
that`s what I am hoping to hook up, of coarse with the boat wieghing
more it won`t be as fast but I still figure I should be able to get 30+
mph out of it, I still haven`t located a suitable transmission out of a
wrecked ride on tractor yet but something will turn up. Think I`m going
to run the exhaust through a muffler right into the water and mayby put
the rad or heat exchanger right in the water at the transom to keep it
cool, Bill.

Anybody ever converted a lawnmower or dirtbike engine to a inboard shaft and propeller setup?
 

On 11 Nov 2005 19:24:27 -0800, "rvbilly" wrote:

Hay Ookie can you imagine what that canoe would have done with a 250cc
2 stroke dirt bike engine hooked up, it would have been crazy fun,
that`s what I am hoping to hook up, of coarse with the boat wieghing
more it won`t be as fast but I still figure I should be able to get 30+
mph out of it, I still haven`t located a suitable transmission out of a
wrecked ride on tractor yet but something will turn up. Think I`m going
to run the exhaust through a muffler right into the water and mayby put
the rad or heat exchanger right in the water at the transom to keep it
cool, Bill.

Why not use the tranny from the bike? That way all you have to do is
couple it to a shaft. You could even go further and couple it with a
jet pump from a jet ski. That way you don't have to worry about a
rudder and could go into much shallower water.

I had intended to do the same thing with a 600cc street bike engine I
have. Unfortunately if seized up. I went out to crank it over like I
used to do every couple weeks and it just wouldn't kick over. It's
grown up in the weeds now, useless. Until it seized up I was going to
build a large jon type boat and use the pump out of a jet ski to
propel it. Those pumps are hard to find for cheap though. Still might
build one if I can find a pump for less than $50. Don't think it's
going to happen anytime soon though.

If you do go the prop route, it may be possible to use the back
pressure of the exhaust to keep the shaft free of water like an
outboard seems to do. I would get it to the water somehow. I have a
weedeater that I bent the shaft to 90 degrees on and put a trolling
prop on it. It works, but it's LOUD. For some reason that thing echoes
all over the lake. Not at all like it would if it was being used to
cut weeds. Something about the water carries the sound more.

Anybody ever converted a lawnmower or dirtbike engine to a inboard shaft and propeller setup?
 

Hi Ookie, how are things,I`ve been checking, and I1m now thinking it
might be cheaper to use a outboard, the shaft supports, shaft, prop,
tranny, engine and other parts needed are adding up to alot, more than
a cheap 25 hp. outboard, I don`t have alot of money to play with, the
actuall boat has only cost me $ 135.00 to build the frames and all
plywood skin ( 4 sheets 1/4 inch) I have a supplier searching for me
on all the fiberglass needs right now, should be about $ 200.00
$250.00 for fiberglass. thats not bad for a 11 ft. speedbout, as
compared to $3000.00 or more for a boat of this size that is on a
greedy salesmans lot, I`ve found a few 1980`s 25 hp. outboards in the
papers ranging from $500.00 $875.00 and I can afford that, I think
the second boat I build will be a 8 ft for the kids, that one I will
try the Briggs and Straton setup. send me your email so I can send you
a few pictures Bill, have a great day.