Weed eater engine conversion

Discussion in 'DIY Marinizing' started by Ward, Jun 2, 2003.

  1. John O`Neal
    Joined: Sep 2007
    Posts: 85
    Likes: 1, Points: 0, Legacy Rep: 29
    Location: Lenexa Ks.

    John O`Neal Junior Member

    Duckho; Here is some information I hope will help in your build. If you are using a U-joint configuration "driveshaftparts.com" offers the most reasonably priced unit I have been able to find. Their needle bearing 3/4' X 3/4" U-joint costs $19.80 plus shipping. The caveat is you must use stepped key stock as the key way is cut 1/4" and the engine output shaft is cut 3/16". This is not a problem as Fastenal, Grainger, Mc/Carr all carry stepped key way stock, it`s pretty common.
    [​IMG]
    Since you indicated an intent to upgrade the performance of your engine I have included some pics and sources of information and parts.
    The 6.5 hp Lifan is commonly known as a Honda clone, or clone motor. Using those terms as keywords will allow access to a myriad of information on the net.
    As a former stock car racer I still have a lot of hot-rod tendencies so I couldn`t resist the desire to hop mine up a little. Kart racers are able to extract up to 15+ hp from these little motors.
    Here are the changes I made to my motor .
    I first removed the governor that limits the eng. to 3600 rpm. This by itself will free up a little hp, as out of the box these motors will make a little over 7 hp @ 4400. Nr-Racing.com has a video on their site on how to accomplish this. affordablegocarts.com also has a step by step tutorial on governor removal. I advanced the timing 6 degrees using an offset crank key. I removed the head and port matched the port openings to the gaskets. I also blended in the short side radius behind the valve seats. I then took the head to Scott racing engines and had 50 thou. milled of the head surface . This raised the compression from the stock 7.?? to 1 to 9.3 to 1. It really helps the torque output, and since these motors have a compression release built into the cam it doesn,t make them harder to pull start. While the head was off I installed 18lb valve springs to help control the higher ratio (1.3 to 1) rocker arms I planned to equip it with. The higher ratio rocker arms have the same effect on the motor as installing a higher lift camshaft.
    [​IMG]
    [​IMG]
    [​IMG]
    I modified the carb by drilling the main jet to .038 and the starting jet to .024 . Affordablegocarts, NR-Racing and 4 racer.com provided the info on what size and how to do it. I then installed a hi-flo filter adapter and a K&N style pleated filter.
    [​IMG]
    On the exhaust side I removed the stock muffler and made my own exhaust header to fit the engines intended use as a mud-motor. I purchased a s-shaped 1" tube $9.50, an exhaust flange $3.50, and a muffler $4.50 from boomerangracing.com and fabricated the new system.
    [​IMG]
    The dyno charts displayed by 4 racers.com shows engines with these mods easily making 9+ hp. My motor starts easier now than before the mods and really barks when you throttle it . I am eagerly looking forward to getting it wet and throwing a little mud. I hope this Info. will help you with your own build. Good luck and keep us informed on your progress.
     
  2. ben2go
    Joined: Jul 2008
    Posts: 187
    Likes: 4, Points: 18, Legacy Rep: 13
    Location: Upstate, South Carolina,USA

    ben2go Boat Builder Wanna Be

    Thanks for posting that.It will help greatly when I build a motor for another use.
     
  3. goose_716
    Joined: Oct 2008
    Posts: 10
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Roy UT

    goose_716 Junior Member

    Question

    I have located a 4 stroke 49 cc motor as opposed to the 2 stroke. Short of not having to mix the fuel and oil what other advantages is there or is thee any
     
  4. goose_716
    Joined: Oct 2008
    Posts: 10
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Roy UT

    goose_716 Junior Member

    Question

    I have located a 4 stroke 49 cc motor as opposed to the 2 stroke. Short of not having to mix the fuel and oil what other advantages is there or is thee any
     
  5. pistnbroke
    Joined: Jan 2009
    Posts: 1,405
    Likes: 34, Points: 48, Legacy Rep: 404
    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    It is much easiier and more satisfactory to use a honda/lifan clone .....come on you americans know there is no substitute for cubes ...you can always throttle back on 200cc but if its flat out with a 49cc thats it .....


    ++++++++++++++++++++++++++++++++++++++++++++++

    My rep is bad because I speak the truth ....some dont like it ....
     
  6. mudman
    Joined: Mar 2007
    Posts: 88
    Likes: 5, Points: 0, Legacy Rep: 72
    Location: Madisonville, LA

    mudman Junior Member

    I am a believer in BIGGER IS BETTER!!!!!!!!!!!!!!!!!!!
     
  7. Mark Wo
    Joined: Dec 2007
    Posts: 143
    Likes: 5, Points: 0, Legacy Rep: 56
    Location: Minnesota

    Mark Wo Senior Member

    4 stroke verse 2 stroke


    They are quieter and they tend to have more torque throughout the entire rpm range.

    Sometimes, depending upon size of the motor and hp out of that motor, 4 strokes can be harder to start. Watch a motorcross event and see how much trouble they have starting those motors. Granted, we're talking high hp motors and all and they are much bigger than what you are talking about.

    Other things to considerr on the 4 stroke. Does it have an oiling system designed to lubricate the motor at the angle you will be using it as a mud motor? And, if something goes wrong with a 4 stroke, they are much more difficult to repair.

    Mark W
     
  8. duckho
    Joined: May 2009
    Posts: 4
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: mo

    duckho New Member

    Thanks for the info John. Very much appreciated!

    duckho
     
  9. wac m trac m
    Joined: Jun 2008
    Posts: 75
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Texas

    wac m trac m Junior Member

    My briggs 34cc is finally getting tired. It gets real hot after running 30 min or so.. Time for a new powerhead..more power erghgh erghh!!!


    John that's some cool stuff you did there. Cant wait to hear how it does in the marsh.
     
  10. Jimideaman
    Joined: Apr 2007
    Posts: 8
    Likes: 1, Points: 0, Legacy Rep: 11
    Location: EAST IOWA

    Jimideaman Junior Member

    Back in March I posted re a "mudmotor" made using a 40 CC 4-cycle Briggs weed trimmer head ("HP rated" at 3600 RPM) driving a Youngs T10 prop which I feel is loading down the engine excessively. I received a number of suggestions and then I got busy on something else. I have some 1 & 1/8" brass rod and some 3/16" brass plate which I think I could frabicate a prop (versus trimming the T10) from without an excessive (?) amount of work. I was going to work from instructions Rich Willoughby gave me but noted he was basing that on 7200 RPM. I thought I'd ask again in case anyone has some newer experience before I do serious metal work. I'm thinking that unless I get more data or get really lucky I'll have to do a lot of "trim and try" and may have to build a "water box" -- a bit far from the work shop to a body of water. (I never got around to getting a tach so I can check the RPM drop when I drop the prop in the water -- If that's the best route to go to determine a starting point I guess I'll have to get one.) Advice will be appreciated. Jim H.
     
  11. pistnbroke
    Joined: Jan 2009
    Posts: 1,405
    Likes: 34, Points: 48, Legacy Rep: 404
    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    good job you did not trim the young as reducing blade area does not have as much effect as pitch ...and as its cast you carnt change that ...
    with your motor doing 3600 raather than 7000 you will need twice the pitch suggested for a 7000 rpm motor .....if you could measure it you would need about a 2 inch pitch. for 6 mph ...I would silver solder the brass to the hub but I dont think you have any choice but to start with little pitch and increase it ...I use my swimming pool but an old bath would do ...remember it will speed up when you get it on the boat and are moving ...

    If you take a 5 in circle in card with 1 inch hole in centre ..split it to the centre and then pull the outer edges where you cut apart 1 inch thats a 1 inch pitch prop ( one blade ) ...that will give you an idea of the angle required
     
  12. Stumble
    Joined: Oct 2008
    Posts: 1,913
    Likes: 73, Points: 48, Legacy Rep: 739
    Location: New Orleans

    Stumble Senior Member

    I was wondering if any of you that have been through this process a few times could write up a tutorial on how to do the conversion? I tried reading through the thread but there are so many specific questions and asides then it is pretty confusing to follow. I also ran across some plans that were being sold, but there seemed to be some disagreement about wether they are worth persuing or not. At this point (37 pages) it may be time for a beginners guide to the conversion process.
     
  13. ben2go
    Joined: Jul 2008
    Posts: 187
    Likes: 4, Points: 18, Legacy Rep: 13
    Location: Upstate, South Carolina,USA

    ben2go Boat Builder Wanna Be

    There are a couple PDF guides out there,but they use some machined parts.It would be nice to have plans for a unit that could be built with hand tools.Leave out the power grinders,welders,lathes,and mills.Most people on this forum do not have this type of equipment available to them or the knowledge of how it operates.I am one of few with free accssess to this type of equipment and at 60 to 80 an hour,it can get expensive.Then this project becomes more costly than it's worth.
     
  14. mudman
    Joined: Mar 2007
    Posts: 88
    Likes: 5, Points: 0, Legacy Rep: 72
    Location: Madisonville, LA

    mudman Junior Member

    I have plans for a small mudmotor, It is not the weedeater type, It is for at least 5 hp. It does require some machining, but if you buy a stock shaft, any machine shop will machine it for about 100 bucks. Other than that, you are just buying couplings, and maybe using a drill press. Some welding is required, but most people have a friend that will do this for a case of beer.

    We build 2 types of straight shaft mud motors, a longtail and a short tail. The short tail uses a surface prop and gets better speed and can go through more in the soupy type mud that we drive in.

    I will look for the drawings and post when I get a chance. I'd say the cost is about 300 for an engine, 150 bucks for a shaft, 200 in materials and 200 for a good prop, with a grand total of about 850 to 1000. of course you can go bigger and get a 25 hp and be at 2000 to 2500 or so. The parts would look just like these kits http://www.boghogmudmotors.com/lt_u_weld_it.php
    These are good kits, but still expensive IMO.
     

  15. Mark Wo
    Joined: Dec 2007
    Posts: 143
    Likes: 5, Points: 0, Legacy Rep: 56
    Location: Minnesota

    Mark Wo Senior Member

    The information you are looking for is in here

    The first motor I built was done with only the following tools:

    Tap and Die set (not needed by any stretch, it just made a nicer looking unit)
    Hack saw
    Jig saw (once again, not needed but made a prettier skeg)
    Drill
    Screwdrivers
    Allen head sets
    Conduit bender for tiller (once again, not needed but made a nicer more uniform bend)
    Sandpaper

    I then took the skeg to a local welder who charged me next to nothing to weld the skeg to the drive tube.

    If you don't have these tools, I don't think I would look any further into building one of these motors.

    Mark
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.