31cc Ryobi Conversion Engine, and more...

Zippster

New Member
Oct 8, 2008
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Austin Texas
Hey guys I'm new - I've been reading various posts on these forums for a couple days, and hope that I've garnered enough info to justify posting myself.


That being said, on with the questions!

I plan to add a 31cc WW engine to my mountain bike in such a way that it can be removed in the future and easily reattached without damaging the bike, which is quite a nice bike. So please keep that in mind.

Upon browsing almighty eBay I came across a so called "31cc Ryobi Conversion Engine." It would seem that some RC plane enthusiast refurbishes these engines with machining flywheels, replacing bearings and seals, and adding new carbs with fancy names. For $30 shipped, I'm tempted to buy it except for one little " - Only A Standard 12VDC Starter Required." I confess I'm a total noob when it comes to engines, having never owned one myself (yet), so naturally this leaves me a bit confused. It would seem that there's no pull start, and one of the pictures shows what looks like a spot for an electrical connection. I'm a tightwad with my cash and I dont want to drop another $80 on a fancy brandname dc engine starter. So is there any way around this? A homemade pull start maybe, or cant I just wire a couple lantern batteries with a switch myself?

Theres only 2 days 22 hours left on the auction, and I dont want to lose this seemingly miracle deal. If anyone knows more about these 'conversion kits' and has actually started an engine mroe than once, any help on the matter would be greatly appreciated.

More questions to come - getting yelled at to shower and go to bed. :rolleyes:
 

deacon

minor bike philosopher
Jan 15, 2008
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How about giving me the addy of the ebay item and I'll see what they are selling. I'm not familiar with it.

What do you plan to do with the engine once you have it. I am pretty sure it won't come set up for a bike motor. At least I have never heard of a bike kit for a ryobi even though there should be one.

What kind of drive are you planning.
 
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deacon

minor bike philosopher
Jan 15, 2008
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I went over and took a look at the ebay items. i think your engine has a reserve on the bidding. That engine will probably go for about one to two hundred dollars. It is way overkill for a bike.

You need to go to craigs list and find a ryobi that you can hear run before you buy it and then build your own frame for the bike. My frames are all for permenant mounting but Comfortable shoes had a removeable engine mount I think. If she doesn't answer this then send her a message or email.
 

comfortableshoes

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Jul 22, 2008
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Beverly, MA USA
I agree w/ D here. There is no need to get an RC converted engine it way overkill. Additionally those RC engines are converted to run for short fast runs. Most are expected to run for 10 to 15 minutes at a time and then shut off, cooled off and then fueled up again.

Because the flywheel on them is ground down flat to have a shaft of some soft attached to it you will find that it will need some sort of cooling system- either a water cooling radiator attached, running in the $100 range or a air cooled system that will run you $50 and up.

D is right att eh end of that auction that engine will hit well over $100 possibly up to $200.

A 31cc ryobi is easy to come by on Craigslist as well as eBay. There are a lot of good models for bike motoring, mine is a Ryobi 790r. Do a search on eBay for weed whacker or trimmer power head. That way you can get just the power head. THAT you will find in the $30 or less range. This is a great time of year to find cheap weed whackers n Clist- people are getting rid of them left and right because they don't want to store them for winter. I got my 790r for $20, a homelite 25cc for $15 and a craftsman 32cc for free. If you are handy and willing to do a carb tune up you can find just about anything at any price.

They are very easy to rip down to just the power head and retro fit for motoring your bike.

I made my engine what I call quick release. To remove it:
undo spring
unplug kill switch (Wire to a 3.5 head phone plug from handle bars and to a jack on the engine)
unscrew throttle cable, remove it
remove 3 bolts holding engine to frame, engine then lifts off frame.
frame can then be removed from bike with 3 bolts and snipping a few zipties and disconnecting the clutch cable But I can ride the bike without engine by holding it the clutch handle

I installed the quick release remote kill switch after I had to remove the engine a couple of times and holding the engine in one hand while attempting to remove the bolts holding the covers is not fun.... The jack simple connects to the main kill switch on the engine. A small hole in the covering allowed me to put in the jack. I used some speaker cable and hooked it to a momentary push switch from Radio Shack and a 3.5 headphone jack on the other end. It works well.

A word on those fancy Walbro and Zama carbs- yeah they are nice but you can get one for $30 or less on eBay. I'd like a nice walbro or 2, butt hey are just another WW carb- not a whole lot of range idle or wide open.
 

deacon

minor bike philosopher
Jan 15, 2008
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Now if we haven't confused you enough there is the backward mount I just did where the only bolts are the axle bolt to hold a u bracket over the tire, and two pipe clamps that wrap around your supports from the wishbone in the rear. you could wrap an old inner tube under those to keep them from scratching the paint.

The kill switch is a light switch mounted to the engine frame. the clutch is a lever which lifts the motor from the front. This mount would probably be pretty easy to remove but not on a daily basis. The throttle is the worst part. On that particular bike I use an old brake lever. I snipped the handle of the lever off a bit so I wouldn't get it confused with a brake lever. It works pretty well.

Also there is a front mount. I prefer to drill holes in the frame for it so you probably don't want to do that. By the by you are old enough to ride one of these aren't you.
 

Zippster

New Member
Oct 8, 2008
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Austin Texas
Wow.

Okay then.

There were also used WW's going for about $20 to $30 on eBay, surprisingly far better than my local craigslist, with a Ryobi going for about $60. Is buying a used engine off of eBay a really bad idea? Without ever seeing it run before hand, or even knowing that it matches up with the pictures, you can see why I'd be a bit skeptical. If that fails I can always go for craigslist, but I'd prefer to not spend twice the alternative if at all possible.

What I meant by 'removable' was more along the lines of 'wont permenantly damage bike,' ie. no drilling or dremeling, etc. I've pretty much made up my mind to go for a chain drive, and I've thought of a relatively easy way to do it: mount a sprocket on the rear wheel opposite the derailer assembly, and just run a normal bike chain from this to an engine mounted where the water bottle cage used to be. There are numerous threaded spots to mount stuff toward the front so I think I can pull it off, and short of that there's always hose clamps. The problem I can foresee with this though would be the lack of a clutch. Correct me if I'm wrong, but with the setup I just described I could never stop without lifting the rear wheel off the ground when the engine was idling. That would be a problem.

Assuming I didnt leave something out of that, or even if I did, how would I prevent this? If I should acquire a centrifugal clutch would that work? And even with a centrifugal clutch would I still get some resistance when I pedal alone?

I know deacon is a master of the friction-drive gospel, but they just dont appeal to me. I get enough flats as it is and I'd hate having to replace the drivewheel and tires all the time. If I'm in hopelessly too far above my head with the chain drive by all means point out the fatal flaw - regardless, I implore you to grace a mere mortal with your omniscient and infinite wisdom about these motorized contraptions.

PS: How much oil does a Ryobi 31cc need anyways? Everyone I ask gives me a different answer.
 

comfortableshoes

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Jul 22, 2008
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Beverly, MA USA
OIl mix depends on teh ryobi, older engines ask for more mix, mine is 32:1 but some of the newer models I've seen ask for 50:1

The only issue with center mounting the engine on a bike is that it will be hard to do- the WW engines don't have the same ease of attachment as a kit, you will need to fabricate a mount. I recomend that when you are doing this part of your build that you wrap you bike in couple of layers of masking tape to protect it from scratching, some nice painters tape will do the trick.

However it is not out of the question to attach a new clutch to a WW. The clutch that comes stock on the Ryobi is junk. Really junk. You would be able to drive a 65lb child on a 10 inch bike with it. SpiderSpartan has a thread about center mounting a WW and getting a new clutch on it and building a jackshaft. Good stuff. I'm working on a similar build.

Here's the rub, the WW come with a drive shaft that is small than most clutch shafts, meaning you have to find some way to retrofit the clutch to the drive shaft, sometimes it's a new drive shaft, sometimes it's fitting something over it sometimes.... You get the picture. SpiderSpartan milled his own drive shaft. Dave's Farm on youtube machines his own clutch and uses the stock clutch bell as a guide for the interior. (Darn I wish I had the tools for this.)
 

Motormaker

New Member
Aug 6, 2008
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North Central Indiana
You can chain drive a bike with no clutch. However it has some limitations. Number one being you will have to kill the engine to stop. Which works on friction-drive bikes. So that shouldn't be a problem. Number two you can not ride/pedal with the engine off. It will seize the piston in the cylinder from lack of oil (remember the lube is in the fuel on 2-strokes). Also no idling down hills (if your not giving it gas your not giving it oil) With no clutch the forward motion of the bike acts like a giant flywheel loaded all to h*ll with stored energy. Now with all that being said it has been done and it does work. (Quite well) When I was a kid my father talked about a motored bike he had as a kid. It had a "blip button" kill switch on the bars. His description was that the bike had a throttle-less carburetor so the engine ran wide open all the time. The blip button was used to control speed. You would tap the button to slow down and use longer and longer taps to slow down more and more. Until you hold the button all the way in and mash the brakes at stop signs. Then you would crank the pedals a time or two and the engine would snap to life and carry you down the road. I do not know if the kill switch was rigged dead man style or regular. I would love to build one like that. However in this day and age of $30 trimmer engines running a simple throttle cable is more practical.
 

Zippster

New Member
Oct 8, 2008
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Austin Texas
I've been doing some thinking and some eBay searching, and have begun to consider changing my angle on this project.

Having read a few of SpiderSpartan's posts, I noticed that on his rig he simply removed the pedals altogether. For me thats a problem. Not only will I be *screwed* if something happens to the engine, but where I live, not having the human-power aspect would get it designated as a moped, subject to registration - which ain't going to happen. Therefore the only feasible way for me to mount this thing would be on the rear wheel assembly itself. Should it come to it, I'll gladly use a friction drive to get this thing working, but I'd like to avoid that possibility if I can.

Seeing as Austin is an extremely hilly place, with barely a flat area anywhere around my house, I'm going to need some serious torque to get me anywhere without peddling like crazy. Motor-assisted bicycles, by state law, may not exceed 40cc engine displacement without legally becoming mopeds, so instead of the 31cc WW I've been looking at 38cc and 40cc chainsaw engines, which may just end up making the whole build a lot easier for me.

Given their nature, chainsaws ought to have built in clutches, or there'd be a few more orphaned digits and apendages in the world. Not only that, but the drive system is already conveneiently a chain, and should be easily converted to drive a sprocket. The question is whether these stock clutches are worth their salt, and if so, what kind of gear ratio can I expect to get out of one of them? I've heard of people using chain drives on a rear tire mount and I dont see why it wouldnt work. On top of that, how much more power would a 38cc chainsaw give me over a 31cc WW? Given a 20% increase in displacement I'd think it'd be significant, but I've been wrong many times before.

I know I've been asking a lot of questions lately, but I'm getting closer to this one I can feel it, and simply cant wait to order an engine.

I hope I havent scared you guys away already - I have a bad habit of doing that on other forums I visit.
 

deacon

minor bike philosopher
Jan 15, 2008
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I build with chainsaw engines. The chain they have is for cutting logs not running bikes. it is a different animal all together. They do have a more robust clutch than a weed eater but it has the wrong end on it. You would need a sprocket or at least a pully to make it work.

You can ask around I did a lot of that before I decided to go friction drive but do look into it. I would hate to see you settle for something you don't want.
 

Motormaker

New Member
Aug 6, 2008
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North Central Indiana
The chain saw clutch may be robust enough if it is geared right. The problem with the one I have is that the clutch sprocket needs to have an internal spline. Not the easiest thing to find or make. You could possibly weld the sprocket to the chain saw chain spur. It would need to be centered very well. There are many clutch/spur types. Here are 2 common ones. Trimmer clutches are different. As Shoes said earlier the cheap Weed Whackers don't have grippy enough clutches for bikes.

Two types of chain-saw spurs

Check out this video it might help you
YouTube - weedwhacker, motorized bicycle
Same Bike more Detail
YouTube - how to build a weedeater motorized bicycle
 
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deacon

minor bike philosopher
Jan 15, 2008
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yes mine looked like that. I had thought about having a sprocket welded to the gear on the clutch but then the whole line up thing came into it. Just the least bit out of line and you have a chain whipping around.

then two like shoes said, WW and chainsaw carbs are mostly wot and idle. not a lot of setting inbetween some but not a lot
 
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comfortableshoes

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Jul 22, 2008
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Beverly, MA USA
here's something else, if you can find a really old weedwhacker, i'm talking from the mid 80's, like the craftsman I got for free, the clutch is good enough to use. BUT here again you need to figure out how to attach a sprocket to it. The shaft on the craftsman was 3/8th with a 1/4in square hole in it. It was plenty robust for a friction drive and worked quite well until my own stupidity screwed it up.

Most sprockets have a 5/8th center....

It seems to me that if someone were able to devise a threaded sleeve that slipped over a WW shaft, taking it from 3/8th 26 threaded to 5/8 and give you a key for attaching either a go cart clutch or a sprocket that people might buy it.

I know I would, being able to go take a cheap WW and turn it into a sprocketed or pulley driven bike motor that would be pretty awesome. Imagine taking a $30 WW you got at a yard sale, stripping it down ordering a $10- $15 part and all of a sudden the possibilities are endless. From there, go kart parts, motored bike parts, go ped parts, etc are all attachable and usable.

These sorts of ideas make me wish that I had #1 a larger garage #2 I had the skills and tools to make these things I have ideas for. #3 I worked less...
 

comfortableshoes

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Jul 22, 2008
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Beverly, MA USA
I know I've been asking a lot of questions lately, but I'm getting closer to this one I can feel it, and simply cant wait to order an engine.

I hope I havent scared you guys away already - I have a bad habit of doing that on other forums I visit.
If there is one thing you will find on THIS forum is that we all ask questions and we all give answers this is the BEST forum for DIY motored bikes. There is more info here than anywhere else on these fabulous home brew bikes.

Given the above statement I wonder what you've done or what other forums you've been too. Personally if I think your being a d**k I'll PM you and let you know.

As for getting flamed here, I've only seen one troll here in this forum in the last few months I've been posting here so Hopefully if you don't feed 'em they go away.

In shorts, ask the questions, throw your ideas up onto the screen and somone will respond, we've all got ideas and we all like to share them. In fact when we see pictures of your build we'll all be happy and excited for you and share in the sense of accomplishment, and we all learn from each other. That's what this is all about educating ourselves and making it easier and better for the next person who tries one of these builds!
 

Zippster

New Member
Oct 8, 2008
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Austin Texas
I just found a chainsaw off of eBay, 38cc McCulloch Super Pro 40, model year 1977. Would a 31 year old chainsaw be a really bad idea? I dont know how these engines would wear or lose power over time, but if the older models have better clutches then would this be the way to go?

I may have more in there somewhere but I'm out of time atm.

What I meant by my last line was just that on any other forum, the replies would have just stopped without reason. No trolling, flaming, or generic being a dick, but they simply wouldnt reply at this point. Weird huh.
 

comfortableshoes

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Jul 22, 2008
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I just found a chainsaw off of eBay, 38cc McCulloch Super Pro 40, model year 1977. Would a 31 year old chainsaw be a really bad idea? I dont know how these engines would wear or lose power over time, but if the older models have better clutches then would this be the way to go?
.
Honestly I don't know if older CS have better clutch, older WW do.... that being said. I dunno man, 30 years without testing it? yeash... The real question is how much is it? If it's like $20 why not, you can always use the carb and parts on another build if it doesn't run... but then what kind of shape is the thing in?

I think if I were buying that I'd want to see it in person and meet the owner....

I'm sending you a PM....
 

deacon

minor bike philosopher
Jan 15, 2008
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From the weedwhackers I have heard about I would avoid mac anything.

There are a ton of poulan and craftsmen on there usually. You cant afford stihl and some of the newer japanese ones. I have a poulan and a craftsman and I like both just fine.

33cc is the smallest I've seen and I think I saw one over 50cc once. I wouldn't want one under 33cc.

If they say it runs when you pour gas in the carb or in the cylinder you probably have a bad carb. You might or might not be able to save it. Rotted gas lines usually means the carb diaphragm is gone as well. You want one that runs but is missing the blade and chain for the best deal. I doubt they are going to tell you the lbs of compression that is the best indication of how it was run.

It should definitely have a spark. If not you are looking at replacing the pick up at least and they ain't cheap. I broke my poulan carb because I'm stupid, but I put a carb from a ryobi 31cc WW and it runs just fine. So you can do a lot with them, but for best results at least get one from a seller with a good rep and one who tells you what kind of shape the thing is in.

My 42cc craftsman came from ebay for 35 including shipping and it works fine. It's a crap shoot though
 
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Sep 4, 2008
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zippster, a few years ago i built my daughter in law a chainsaw bike.48cc remington if i remember right. i knocked the center out of an idler pulley off of a mower deck [bearing] welded the outer pulley to the chainsaw clutch drum, mounted to bike fork, welded two 26'' rims together , mounted tire on left one and used right one for pulley. i had to notch the right side of the fork to clear the right rim [pulley]. it was pretty low geared but with 2 cycle it did run about 20 mph. she rode it till my grandson came along, sold it, now that he's 3 she wants me to build her another one. just another idea for you to think about, good luck with your build vernon
 

Caus-I-Can

New Member
Sep 15, 2008
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hi been reading your posts, and a bit confused how much where you willing to spend and what max size engine r u wanting. the company that i get my motors off sell them for$79.95 aus. with the the way the American v's Aussie dollar is at the mom(fallen 30%) you could get one for 50-55 American and sorry thats a 49cc 2 stroke high performance pit bike motor. i also get chains and sprokets for $5-8 (aus) each if you want to know more get back to me....