31cc Ryobi Conversion Engine, and more...

Zippster · #1 (**permalink**) 10-08-2008, 11:31 PM

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.

deacon · #2 (**permalink**) 10-08-2008, 11:54 PM

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.

deacon · #3 (**permalink**) 10-09-2008, 12:08 AM

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 · #4 (**permalink**) 10-09-2008, 06:46 AM

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 · #5 (**permalink**) 10-09-2008, 07:37 AM

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 · #6 (**permalink**) 10-09-2008, 07:12 PM

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 · #7 (**permalink**) 10-09-2008, 08:24 PM

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 · #8 (**permalink**) 10-09-2008, 08:37 PM

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.

deacon · #9 (**permalink**) 10-09-2008, 09:07 PM

Good luck with the build is all I can say and that isn't sarcasm i mean it I wish you luck with it.

Zippster · #10 (**permalink**) 10-09-2008, 10:19 PM

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.