Easy Rider 116cc chopper

[galloping rigadoon]

Hey all,

I'm a mechanical engineering student and I wanted to get some more hands on experience with engines, as well as build a machine to tear around campus in style.

I bought an old 116cc chainsaw, and I'm going to weld a steel tube frame to make a bike that's a tribute to Peter Fonda's motorcycle from the movie Easy Rider.

Do you have any advice on using a chainsaw engine?

What I'm concerned about at the moment is gear reduction; the saw runs at 2500 rpm and I need to get that down, obviously. I have access to a full machine shop and water jet saw, so I figure I can make my own gears. How much do I need to reduce it? Doing the math, 10:1 on a 26 inch tire will give me 20mph, so I obviously want more than that.

Would 4:1 with a speed of 48 mph be feasible?

What's the biggest gear ratio I could get with two gears? I'm thinking I'll need to have two stages of gear reduction, because a 10:1 gear isn't likely.

Anyone know the best way of attaching a gear to the driveshaft of the chainsaw engine?

As for other components, I'd like to make my own rear tire out of a car tire. I'm planning on buying a front wheel and maybe a seat. I've got a pair of Trek cruiser forks but I'm going to try to build my own later, and I've got twin 800 lb/in shocks over the rear wheel.

Any idea what kind of HP should I expect from this engine? It's got a bore of 2.5 inches and a 1.44 inch stroke. I figure I should use a stronger chain than a bike chain, but is a motorcycle roller chain overkill?

 

[Buzzerbiker]

That sounds to me like a very old saw. 116ccs and 2500 RPM is not going to produce much horsepower. Does it have a centrifugal clutch? It sounds to me much like an old David Bradley saw like I use for lawn art, or maybe a Titan? I recommend something newer and smaller with a centrifugal clutch. You can weld a sprocket for # 415 chain on the clutch drum with ease, and use a double reduction with a jackshaft. Look on Craigs list for a saw. I just sold a 62cc Homelite for $35 myself, which I had bought at a yard sale for $5. Even an old Homelite or McCullough will turn 8000 rpm and get you going much quicker than any giant antique motor. Good luck to you, rigadoon

 

[2door]

First let me welcome you to the forum. You've found the right place for help with your project.

I'll be watching this for progress on your build. I did a Captain America chopper using a Chinese 2 stroke, in-frame engine. http://motorbicycling.com/showthread.php?t=35675

Hope you have as much fun on yours as I do on mine.
Please keep us informed on your progress.

Tom

 

[maniac57]

What brand chainsaw is it? Some brands were MONSTERS! Any 116cc saw motor should be pretty awesome...Picture it putting out 20-25hp with a tuned pipe. Just a guess from the few big saws I've messed with. The brand matters a lot.

 

[galloping rigadoon]

The saw is 50 years old, I'll give you that Buzzerbiker.

But it does have a centrifugal clutch, and looking at the spec sheet here
( http://www.acresinternet.com/cscc.n...40b2be5ebf32615d88256afc001f1b7f?OpenDocument )
it says the clutch engages at 2500rpm. So I would guess the max rpm is significantly higher than that.

The thing (other than the big displacement) that made this guy attractive to me is that all of the engine casing is metal, which will let me retain it as much as possible. Also, if I can get it running there's a certain glamor to running on a relic.

Thanks for the chain tip. #415 chain is just a normal bicycle chain, right? It looks like most of these bikes use bicycle chains, but it sort of gives me the creeps.

Thanks 2door. I'm in the middle of a semester now, so I won't have a ton of free time in the immediate future, but you'll definitely hear more from me as I run into problems. In the meantime-- I'd already found the Captain America 3/4 helmet, but where did you get that seat? Great bike. Was thinking about painting mine black, but yours looks amazing. What kind of paint did you use? I've painted bikes before with enamel paint, but even that chips off bad.

Until I find a front and back wheel, I'm not going to be able to get beyond sketches because the frame design depends on them so much. I'm looking for a car wheel for the rear wheel, and a motorcycle/scooter front wheel. Hopefully the actual (not rim) wheel diameters will be the same, and I'm not looking for a spoke front wheel but a cast metal one (don't ever want to true this thing, despite the departure from the Captain America chopper).

In the meantime, I'm trying to amass all the parts (easy to do while on the computer at school). What's a good source for used (cheap) motorcycle wheels?

If anyone can give me an estimate of the hp I should expect, it will help with calculations.

Also, anyone have any idea what strength and dimensions of steel pipe I should use to construct the frame? Looks like steel is labeled in "schedules" and though I can convert that into more familiar units, I don't have a good feeling what it means in practice.

Thanks for the replies!

 

[Buzzerbiker]

Hi again,"rig".That mill may have some potential after all if it isn't dusted or galled. You are probably looking at an easy 5HP at 6000-7000 rpm. To go 45mph you need overall gearing of approx 12:1, give or take. Final tire circumference will determine ratio. With the clutch engagement @2500rpm, you would be a little over 15mph to start using your saw. Excess clutch slippage will build heat that destroys stuff. Knowing that going in, you'll be OK. Also now that we know that you've got a fair rpm potential, I would definitely use a belt primary drive off that clutch. If you go to the motorized mountain bike forum, you can see my latest belt primary on a Honda 4 stroke with centrifugal clutch. It's at "chassis for second bike". Don't try to hop up that old saw much, a relatively small expansion chamber is enough to add a lot of extra torque, and I wouldn't advise any more rpm. These engines ran on a 16:1 fuel/oil mix with standard motor oil. Leaded gas, of course, provided a little extra lube. I have run smaller, slightly newer saws at 50:1 with GOOD synthetic oil, and NO ethanol premium. Go ahead and get it running a couple tanks with a 32:1 mix, and if it sounds good, rock on and build a bike! Best of luck to you. Can't wait to see photos, but take your time rig.

 

[Buzzerbiker]

OH! I forgot, 1/2 inch bike chain= # 43. 415 is much heavier, perfect for your secondary drive.

 

[Buzzerbiker]

Hi rig, after logging out, I realized I overlooked your link to the saw, very nice. I am quite sure that the engine is made by Tecumseh. They supplied various displacement engines for many saw companies. The 77cc motors were most common, and the 116cc a little rarer, and hard to come by info. The 77's put out 4HP@ 4500 rpm, the 131cc produced an advertised 8HP@ 5000rpm. There are a lot of conflicting numbers. I think you could count on 6HP easily enough, but, I believe 5500rpm is going to be your ceiling, use the best oil you can find. Also since I finished my latest belt drive, here's a photo. I have used Subaru power steering pulleys, but 80's to 90's vintage Ford PS pulleys might be a better choice for the jack shaft at about 4.75" OD. If you can find a 2" OD 5 rib alternator pulley, it would make a 2.6:1 primary drive simple to construct. Note how I cut notches every 3/8" across the ribs. This does two things, reduces the amount of tension needed, and reduces kinetic loss from turning over a small pulley. Hope this helps, again, good luck!

 

[galloping rigadoon]

Engine rehab update: I'm not getting a spark.

I took the spark plug out and checked to see if I could see a spark, but got nothing. I replaced the spark plug and tried again and it still didn't work. So it's not the spark plug, which means the problem has to be upstream of the spark plug connection somewhere. I figure there's either a problem with the magneto or with the connecting wires.

I know the voltage is way too high to read with a multimeter, but I tried measuring it anyway. It did read a voltage when I drew the cord, so there must be at least a little bit of potential getting to the spark plug.

Any thoughts?

 

[Buzzerbiker]

That oldie uses points and condenser. You'll have to pull the flywheel and clean them. Don't use an abrasive. Ask any OLD mechanic buddies if they still have a points file. If they're not trashed, even a business card will do. Clean everything up, check for shorted/frayed wires, set max opening .017-.020 inch. The coils were not terribly prone to failure, but check resistance. As a pure guesstimate, look for approx 1 ohm. primary, and 7K secondary. Best to you man.

 

[galloping rigadoon]

Wow, time flies.

I finally managed to get the flywheel off today. By that, I mean I took it to someone who knew what they were doing and they did it for me. Turns out I had the right technique (screwdriver + hammer on crankshaft bolt) but I wasn't hitting it hard enough. Timid.

So I blew out the dirt from under the flywheel, and then opened up the points case. It looks like they're not opening enough and are asynchronous, so this weekend I'll adjust them.

Buzzer, on the spec sheet for the C70 it says that the point gap is 0.015", so I'd assume I should go with that rather than making it 0.017" or more?

I also ended up buying a vintage manual and parts diagram on ebay. It cost me a trivial amount of money, but it bugged me that in this day and age you have to pay for something like that. So in the spirit of free information, I will post scans of the diagrams here: keywords wright saw C70 diagrams parts list wright chainsaw exploded diagram

 

[Buzzerbiker]

.015" is dandy. This ignition system is not very powerful, so a GOOD, properly gapped spark plug means everything. Best of luck.

 

[galloping rigadoon]

I've got spark!

I'd never adjusted points before, but I've done more than my fair share of research watching youtube videos about it, and it went well.

I spent a lot of time in the shop looking for a feeler gauge, but it turns out the points cover doubles as a 0.015" feeler gauge, which I thought was pretty nifty.

The points were not opening enough, and they were also covered in this yellowy-brown powder. I cleaned that off, buffed up the points with some 600 grit sandpaper, and after I'd put everything back together I had a beautiful blue spark.

I reassembled the rest of the saw and gave it a few test pulls, but now something else happens that seems weird. Most pulls on the starter cord feel normal, but every few pulls the crankshaft seems to jam and the starter cord thing seems to turn without moving the crankshaft. Did I screw something up putting the starter assembly back together? It doesn't seem to be a huge problem, but I wonder what's going on.

Next up is to put a new fuel filter on the gas tank. The old one fell off and was pretty crummy.

It's amazing how much I've learned about engines so far in this project. Mission accomplished, and I'm learning more all the time!

 

[Buzzerbiker]

Good job man! Your recoil starter may have a weak spring. That should be a Fairbanks Morse. There are parts on ebay, but I'll bet it is also just gummed up. Before trying a disassembly which is slightly tricky. Remove the recoil starter assembly, and spray a liberal dose of WD 40 into the dogs while pulling the rope several times. Have fixed many that way. Nice that you got all that service info, and, nice job of clean up. That old mill looks like pretty low hours, Hope it runs well. Carb should be a Tillotson, parts should be easy. but do your homework before you overhaul it. Best again!

 

[Buzzerbiker]

OH! BTW also, since you used sandpaper on the points, I hoped you used alcohol or something to clean off the oxide residue. AND, there should be a very light film of lube on the cam surface.

 

[galloping rigadoon]

Well, got the saw running with a new carb and fuel filter. But now I've fallen in love with it and I'm not willing to hack-mod it into my bike.

So I got a Briggs engine instead. Made this project a lot more expensive, and now I'll have a whole host of new problems, but that's fine. Any advice on getting a clutch onto a Briggs? At the moment I'm just planning on replacing the clutch every few months, but that's not an elegant solution.

I now have my front wheel, back shocks, and engine, and jackshaft. I need to make a custom sprocket for the back wheel, which I will build out of a car wheel. Then I need to build the front forks/triple tree and weld the frame and everything onto it. Bombs away.

 

[Buzzerbiker]

Hey cool! Ya , once you get something like that running, kinda get an affection for those oldies. There are lots of places to get clutches for Briggs. vbeltsforless.com used to have a go kart section with centrifugal clutches for 1/2"and 3/4" shafts. e baY should have LOTS! Many even have interchangable weighting to change engagement RPM. Another fun option would be a CVT belt drive. They are readily available too, and would give you good low end and great top speed. Ya check ebay, and have fun man!

 

[Scary G]

Hey Easy, I noticed you mentioned a couple of times that you want to use a car tire. Bad idea, a car tire is too flat across the tread surface. You will find cornering pretty hairy. Use something made for a bike with a rounded tread surface. It should help you keep your skin where its at instead of smeared along the pavement.

 

[mat_man]

I am sure every tire engineer would agree with SG.
But for a list of the almost 700 souls that live dangerously:

Darkside Tire Info Center
http://darkside.nwff.info/?p=tires


Post on running spare tires:
Skinny Darkside?
http://mcdarksiders.forumotion.com/t2065-skinny-darkside

The narrowest spare I have been able to find:
105mm / 25.4 = 4.13" width (approx.)

 

[galloping rigadoon]

Well, I guess the 116cc in my title isn't very accurate anymore... Here's my new engine, and my wheels. Gas tank is coming in next week, and hopefully by then I will be much farther along on designing the frame. I'm going to mock it up using bamboo (cheap, easy to cut) before I go and buy steel pipe to weld.

Anyhow, some pictures. I took the covers off the engine to see what was under them, but it's a 9hp B&S snowblower engine. Made sense of everything except the gear teeth on the flywheel... thought that there wasn't ever supposed to be load on a flywheel.