Weed eater engine conversion

[bgtreefrogs]

After years of researching I’m going to take the plunge and build one of these for my kayak. THANKS FOR ALL THE EXCELLENT POSTS! This is the best resource on the web. After reading the posts on the engine sizes I decided on a scooter motor as opposed to an actual Weedeater. The cc’s are larger and they are cheep. It looks like I can also get one with a heavy duty clutch and reduction gear (scooter transmission), also an electric start. I was curious about ripped off’s comments about removing the clutch – it seems that this may not be required if the clutch was actually designed for heavy duty use. You can also get some that have double bearings and three shoes rather than two. Also, the reduction gear might eliminate the need to remove the clutch, since the engine will not be too stressed from the start. I’m going to follow ripped off’s design, which seems bullet proof. Outstanding Design! Any comments? I understand the scooter transmission is a 5:1 reduction. I know this is more than the 2:1 and 3:1 that has been discussed here, but it is already built. Would be great if I could use it rather than use some pulleys and gears.

[crokseti]

I, m working on a project myself and am trying to adapt a Ryobi 31cc motor with a homemade3 bearing shaft conected to a edger gearbox to which a small prop is affixed.
I'll purchase a Sears gearbox with 1-to-1 ratio unless anyone here can direct me to another brand that has 2-to-1 gearing.
Sears-Poulan is around 30 bucks.
I hav'nt found any info on the ratios of any edger gearboxes.
I went to Sears and turned one by hand and verified 1-to-1.
Any help would be appreciated as this project will be done regardless but I don't have much cash to work with.
I will get the prop from Young's.
Thanks,

[evlfkrjohn]

Hey guys i'm new to the site but have been pondering the same ideas! This is the best way that I have yet!! It works flawlessly!!!!!!http://cgi.ebay.com/ebaymotors/ws/eB...215327520&rd=1

[master fisher]

how did u make the weed eater motor please explain if u have time please email me at maddogmd2005@hotmail.com

[master fisher]

Originally Posted by Ward

The engine is really not that loud, but anything beats paddling

It appears that this is the best way to mount the engine. The pull start, handle, and throttle trigger are all in great locations. the handle could be used as a tiller. I do see a couple of problems however. First, this is rotated 90 degrees counter-clockwise from the way you would hold it as a weed eater, which puts the fuel tank filler cap facing forward. Not a big deal, I could always just mount a new tank. This one is part of the handle, so I can't just remove it and rotate it. Another possible problem I see is the location of the spark plug. It looks like its just asking to get drenched, and short out. I'm thinking some sort of small shield to surround it should be sufficient, as this will never see high speeds. Other than that, the only real problems left are figuring out how to mount it to a transomless pirogue, as well as finding/making a suitable prop.

I have thought of one other thing, however. most weed eaters are designed so that the engine can be easily removed from the shaft, in order to change from say a trimmer, to an edger. An edging attachment has a gearbox at the bottom, at a right angle to the shaft, with some gear reduction. I may see if I can find one of these, and see what type of gear reduction it has. I'm thinking it might just be enough to be able to use a small trolling motor prop.

take a pipe and run it from the muffler and run it into the water it is much quieter

[SSNgineer]

Hello everyone. I've been watching this thread for a couple years and I finally have something to contribute. I've been working on a gear drive design based on a 4-1/2" angle grinder head. The gears are made for higher RPMs than a trimmer engine but may not hold up under the higher torque. I haven't done the stress calculations yet. The grinder I bought at Lowe's was $30 and has a 3.08:1 ratio. I am turning an adapter on my mini-lathe that I designed this weekend. I'll try to post some pics soon.

I'm also creating a solid model in Solidworks for a new housing for these gears. It would look better, but I'm not sure how much it would help for reducing drag or cavitation. I plan on using a Weedless Wedge 2 prop that I found on closeout at Walmart and either my 30cc Ryobi (Homelite engine) or Stihl FS46 for power. Using the formula from Minn Kota's FAQ section, I calculate about 8 MPH at 7000 engine RPM (2270 at the prop) assuming 15% slip.

Has anyone tried the grinder gearbox idea before? What do you all think???

[evlfkrjohn]

Hey guys, sorry for the slow responce but my computer has been down for a couple of weeks and i've finally got it back up! The design isn't mine, I got the plans from livetofly57 on ebay. The plans came with all the info on how and where to get all the parts needed to do the conversion. It is a very nice design and was very well thought out! My nephew is welding up an aluminum foot for me in the same design as a 40lb motor-guide trolling motor to make another conversion. I will contact the seller about posting the conversion again, I would do it myself but I assured him that I would not expose his idea to everyone. But I can say this much, it has a 4:1 gear ratio that is awesome!

[evlfkrjohn]

Originally Posted by SSNgineer

Hello everyone. I've been watching this thread for a couple years and I finally have something to contribute. I've been working on a gear drive design based on a 4-1/2" angle grinder head. The gears are made for higher RPMs than a trimmer engine but may not hold up under the higher torque. I haven't done the stress calculations yet. The grinder I bought at Lowe's was $30 and has a 3.08:1 ratio. I am turning an adapter on my mini-lathe that I designed this weekend. I'll try to post some pics soon.

I'm also creating a solid model in Solidworks for a new housing for these gears. It would look better, but I'm not sure how much it would help for reducing drag or cavitation. I plan on using a Weedless Wedge 2 prop that I found on closeout at Walmart and either my 30cc Ryobi (Homelite engine) or Stihl FS46 for power. Using the formula from Minn Kota's FAQ section, I calculate about 8 MPH at 7000 engine RPM (2270 at the prop) assuming 15% slip.

Has anyone tried the grinder gearbox idea before? What do you all think???

I've never thought about using a grinder gear box before, but it may work well! I guess you won't know until you try! Good luck and keep everyone posted!

[Rick Willoughby]

Originally Posted by SSNgineer

.....
Has anyone tried the grinder gearbox idea before? What do you all think???

The attached pictures shows internal of a small grinder box after 20 hours use swinging an 8" prop. It was pedal powered with speed steup up to the prop so would be better in the other direction. The prop shaft was connected to the tiny pinion. I was surprised that it held up for a reasonable period.

It was very easy to replace the armature with an 8mm aluminium shaft and use the plastic case for shaft support. The removal took about 1 hour.

Rick W.

[John O`Neal]

Originally Posted by bgtreefrogs

After years of researching I’m going to take the plunge and build one of these for my kayak. THANKS FOR ALL THE EXCELLENT POSTS! This is the best resource on the web. After reading the posts on the engine sizes I decided on a scooter motor as opposed to an actual Weedeater. The cc’s are larger and they are cheep. It looks like I can also get one with a heavy duty clutch and reduction gear (scooter transmission), also an electric start. I was curious about ripped off’s comments about removing the clutch – it seems that this may not be required if the clutch was actually designed for heavy duty use. You can also get some that have double bearings and three shoes rather than two. Also, the reduction gear might eliminate the need to remove the clutch, since the engine will not be too stressed from the start. I’m going to follow ripped off’s design, which seems bullet proof. Outstanding Design! Any comments? I understand the scooter transmission is a 5:1 reduction. I know this is more than the 2:1 and 3:1 that has been discussed here, but it is already built. Would be great if I could use it rather than use some pulleys and gears.

Scooter motors are available in larger cc and hp ratings . The Chinese versions can often be purchased for around $150.00 with electric start and a 76mm clutch. I have seen transmissions offered in a 3 to 1 ratio. Try a Google search for motorized bicycle, scooter parts ,mini bikes, you will find an abundance usable parts. A simple method to the bulletproof design that Turn4fun offered up is to start with a brushcutter. They come with much larger cc motors than weedeaters and make a simple ,lightweight more powerful mini-longtail conversion. examp. www.Duropower.com offers a 51.7cc brushcutter for $179.00.

[smoothseas200]

Hello Everyone,

I have the plans for this conversion for sale on Ebay. Many thanks to
evlfkrjohn for referring me to this site. This is a proven design, take the time to read the entire ad as it is a bit lengthy but well worth your time. It has been designed as simply as possible. Please see Ebay Ads :
250217316299 and 250217516279, both are my ads and both ads represent the same plans. This little motor will get the job done ! Who ever thought a weedeater could be this much fun !

Thank you,

Dean / jeta2008@netcommander.com

[smoothseas200]

Hello,
I am new to this site and I have posted my Ebay Listing Numbers to purchase the plans for a proven, easy to build, lightweigt Weedtrimmer Outboard using a 31cc engine. Anything less is fruitless. I spent a fortune in the design of this outboard. Please see the ads, this is your answer to your problems. This is the design evlfkrjohn was refferring to. I am a Aeronautical eng, so I crunched some numbers and created this little monster. It can handle a 24' sailboat with ease and larger, and cost around $ 140.00 to build as "New".
I wish you the very best, please let me know if I can help.
Sincerely,
Dean
jeta2008@netcommander,com

[realmanofgenius]

I've been using this site as a reference and have tried making one of these darn things but have hit some snags. First of all I tried to keep the lower gearbox on my Stihl FS85 trimmer/brushcutter. The problem that I experienced with this is that the force of the water being pushed by the prop would push it deeper and deeper into the water. To correct this problem I need to either shorten the shaft to about 35" so that the prop is pointing more horizontal, or I need to take off the gearbox and have the prop directly off the back of the driveshaft. I would like to have the prop directly off of the driveshaft but am stumped on how to do so without my driveshaft sliding out the back end??? Any help would be much appreciated!!!

[crokseti]

Ive almost got one built and am waiting for the prop from Youngs.
Cant wait to try it.

[crokseti]

I made my shaft out of 1 in. pipe and inserted a bearing in either end.
Had to ream it out a little to accept it but its snug. Then I used set screws to hold the gearbox and motor on the shaft.
I sealed the gearbox as best I could with form-a-gasket and painted the whole thing with hammertough paint.
I added grease fittings in the gearbox and the shaft also.
Come on Young's.