Poulan Chainsaw Build

NormO · Oct 10, 2011

Hi everyone.

Here's my attempt at making a chainsaw bike. I'm not 100% finished, but are these things ever really finished anyway? Still need rear brakes and to shut the exhaust up a little more. I am not going to fart around with pedals because i can't take this thing on public roadways anyway. At least not without jumping through flaming hoops. First picture is after i actually got the thing to produce forward motion. The others are as it is now. If you have any ideas, i would love to hear them.

kev1n · Oct 13, 2011

I like your build. Do you have any pictures of what you did to the clutch to run the chain, also how is the clutch holdin up and if it's not burnt up yet what is your weight? What tooth sprocket are you running on the clutch?
Thanks Kevin

NormO · Oct 13, 2011

I'll get some pictures up of the clutch and drum shortly. I'll tell you what i did in the meantime. I haven't burnt it up yet. I weigh about 225lbs so i'm not a featherweight.
The first thing i did to the clutch was install a stiffer clutch spring to raise the stall speed somewhat. It was from a Jonsered RS45 clearing saw clutch. I cut a crosshatch diamond pattern into the shoes so it grabbed better, but didn't cut it very deep. I then put it back on.
Next i ran a hone on the inside of the clutch drum, again so things grabbed better. It was just a small brake cylinder hone. I drilled 2 1/8" holes in the drum to help remove heat. Then came the interesting part.
I then cut the existing sprocket on the drum so a standard bicycle chain would fit. Very tricky work but i got it done. It's 6 tooth BTW. I used a bench grinder with a small grinding wheel for the rough work then a dremel for the fine adjustments. Had no idea if anything would work or not until i first tested.
I also clean and re-grease the drum bearing about every third ride. Better safe then sorry. I don't want to give all my secrets away. Gearing in first is 24.89:1. It needs to be just a bit more for me as acceleration is a bit on the lazy side. Look out when the engine hits midrange and topend though. Things happen in a hurry.

Mannhouse51 · Oct 13, 2011

Very cool , a bike with a powerband !

kev1n · Oct 14, 2011

Wow, that's some innovative work you did to the clutch. It must've been hard work cutting that sprocket into that drum. I've been thinking of useing a rim/drum setup and welding a sprocket to the rim. A machinist could easily make a sprocket to fit on a drum setup for a rim, that would be sweet. Can't wait for the pics or a vid.

NormO · Oct 14, 2011

Here's some pics. A video is pretty much out of the question though, My camera can take both pictures and video, but it just plain stinks. as you will probably be able to tell. Plus i'm only on satellite high speed right now, that translates to just a little faster than dial-up. When the weather is good.
It wasn't hard work cutting just tricky. If i cut in too far i would have wrecked the bearing, if i cut too much off the teeth i would have had to either get another drum or think of something else. It isn't pretty but it works.
Oops forgot the actual clutch. Doesn't look like i did anything to it but i did.

killercanuck · Oct 14, 2011

Woo, looks like good fun! Nice work on the clutch gears. If that metal's hard enough to cut down thousands of trees, it'll haul your butt around for a good while.

Stay out of trouble out there

NormO · Oct 15, 2011

Thanks for everyone's comments. kev1n i don't quite understand what you are planning to do. Are you planning to do a chaindrive or belt drive? If your thinking of just a sprocket from the clutch drum and a sprocket to the rear wheel, that won't really work that well unless you plan to have a huge rear sprocket and a micro sprocket on the drum. It's best to run some sort of jackshaft in between the two. Doesn't have to be what i did. I did it that way because i was lazy and didn't want to spent a lot of money on this. I broke the bank when i spent $220 on the saw. I figured i could get something to work with what spare parts i had lying around and cluttering up the garage.

5-7HEAVEN · Oct 15, 2011

I love your chainsaw build!
JMO, these engines produce lots of hp DEPENDABLY. Reliability is what counts.

Your project's come a long way, but gearing it even lower would REALLY REALLY wake up that engine! I mean no disrespect when I say this, but I don't think your gear ratio is 24.89:1. It is EXTREMELY difficult to gear down an engine without a reducing gearbox, or three jackshafts. I have a pocket bike 5:1 transmission on my engine. I use an 11t engine sprocket and a 72t chainring gear. The bike chainring is 30t, which drives the 34t first gear on the cassette. Without the gearbox, my overall ratio would be unusable @ 7.42:1. With the tranny, it's 37.09:1. This is an excellent gear combination, and my eighth gear is usable at 12:1. Without the tranny, gearing @ eighth gear would be unusable @ 2.4:1.

What sizes are your sprockets? I know your engine sprocket is 6-tooth. I can help you develop a lower gear ratio, which will make a HUGE difference in overall performance.

For more fun factor and better standing start performance, Consider reinstalling the pedals and installing a freewheel. You will also make your clutch last MUCH longer. Also, pedalling while shifting gears will ensure a silky smooth transition between gears.

If you install an expansion pipe, you'll produce more power. In your case, it would REALLY quieten down your chainsaw engine.

Good luck. my friend. I like your chainsaw project. It has the potential to be a VERY powerful MB.

NormO · Oct 15, 2011

I really don't know if the gear ratio is 24.89:1. That is just what the gear ratio calculator told me after inputting the numbers. I don't have any reason to doubt the final numbers. The sprocket sizes are 6T on the drum as you know. That runs down to a 48T on the main chainring. First ratio 8:1. Then there is a 9T welded on the crank axle that cannot be easily seen. It then runs to the rear cassette, in first is 28T. It's an average cassette that is found on most bicycles.It's a 6 speed. Calculator says 3.11:1. Final drive ratio 24.89:1. I at least am going to get a megadrive rear cassette. Not right now because the bike is going to be locked up for the winter. Do you have any thoughts on a SRAM Dual Drive? These have always intrigued me but don't know if they do any good or not other than to get back the three lost gears. I didn't go with pedals because of the legality of this thing. It has to be off-road only so i didn't want to play around with freewheels, sprockets and such. My mind could be changed though. I'm also too lazy too remove the reflectors off of it. As i mentioned before i also at the beginning of the build i didn't want to sink a lot of money into this thing, it was only going to be a weekend plaything and nothing more.

5-7HEAVEN · Oct 15, 2011

Man, you can improve to MUCH better off the line performance by swapping in a 7 or 8-speed rear cassette with a 34-tooth first gear. Gear ratio will lower to 30.22, which you will feel. With 20 teeth, fourth gear would be 17.78:1, which will be an awesome highway gear. Third gear with 19.56:1 would be your cruising gear at 35-40mph.

A 7-speed cassette like this:
http://www.ebay.com/itm/SHIMANO-7-S...Cycling_Parts_Accessories&hash=item19c9bf01cc

Maybe this sprocket would fit:
http://www.ebay.com/itm/Vintage-Sch...939?pt=LH_DefaultDomain_0&hash=item2568651123

If it does, low gear with your cassette lowers to 33.7:1
If you use this 65t sprocket and a 13-34 rear cassette, first gear lowers to 45.82:1.
Your off line performance would be awesome, as well as EVERY gear in your cassette.

Your bike has awesome potential for cheap. xct2

JMO, do not powershift. Slack the throttle, slowly roll into it, then apply power.

You see, that's why you need pedals. When upshifting or downshifting, pedals allow you to shift gears, pedal for a smooth transition, then apply power. Pedals also help to downshift all the way down to first gear.

Pedalling while shifting makes for a silky smooth gear change.

NormO · Oct 16, 2011

Very nice prices. I guess my days of running to a bike shop to get parts are over.

5-7HEAVEN · Oct 16, 2011

I buy all my cassettes online. They're cheap, which is good when you're just testing stuff until you find the right combo. xct2

kev1n · Oct 16, 2011

Ahh, I now sorta see where you have a smaller sprocket on the crank. I was wondering how you got the gearing to work with that setup.
I just wanted to center mount a chainsaw in the bike like yours and run a chain for a friction drive setup, I might use your idea and try to carve a sprocket in the drum, I have to keep the pedals so the police don't hassle me because I'm in the city.

NormO · Oct 18, 2011

I like the friction drive idea. In a way i kinda wish i had done it myself. I suppose i still could. There would have been less fiddling with gears. I can still get the pedals back by way of Sick Bike Parts shift kit. Won't need the whole kit, but i will have to get the larger sprocket some other way. I thought my handlebar footpegs complete with recycled china girl handgrips was i nifty idea.
I have already parked the bike in the garage for the winter, It's a bit too cool now for riding without being bundled up.
The bike may be changed quite radically when it re-emerges this spring i don't know yet. The hardtail may be ditched in favor of a full suspension frame. Again i don't know yet.
As the engine breaks in the lazy acceleration is going away. Possibly a carb tuning may help out yet again, as it's still a bit too lean on the bottom and too rich on the top. I left it like that for break-in purposes only.
Still will need to gear it lower though.

kev1n · Oct 18, 2011

You could gain some power if you modded the muffler or better yet opening up the exhaust port some with a dremel tool. The mufflers on newer chainsaws are extremely restricted from the epa regulations and benifit greatly when opened up. Like you said these projects are never done and always evolving, good luck with the project.

NormO · Oct 18, 2011

The muffler on this engine doesn't look that restrictive, but the spark arrestor screen sure does. The muffler itself is basically a chamber without a baffle even.
I like the idea of an expansion chamber and muffler as suggested by 5-7HEAVEN.
Probably the best mod i could do would be to lay off the beer and potato chips.

5-7HEAVEN · Oct 18, 2011

Lol, If you cut your beer and chips intake by 50% this winter, you can do a WHOLE bunch of stuff on the bike.

I predict that your bike will SCREAM! in the spring! dance1

NormO · Oct 26, 2011

Just a quick update. I just nabbed a completely mangled rear wheel from my neighbors trash. The good news is that the rear cassette is fine or it looks it anyway. The tooth count is 34t-14t. 7-speed. Looks like i got lucky there.

cannonball2 · Oct 27, 2011

kev1n said:
You could gain some power if you modded the muffler or better yet opening up the exhaust port some with a dremel tool. The mufflers on newer chainsaws are extremely restricted from the epa regulations and benifit greatly when opened up. Like you said these projects are never done and always evolving, good luck with the project.

Thats true at the cost of some extra noise. I converted a Homelite 46cc chainsaw engine for a low budget R/C camera plane. Object on the engine was to use as much stock stuff as possible. First run on the engine was pretty good but it didnt really rev to suit me. It had a similar can muffler. I opend the 1/4" holes to 5/16 and added 2 more. I immediately picked up 750rpm, the engine had become a real power house! I think the OEMs limit output for longevity/warranty issues. A muffler is an easy way to do it.

Poulan Chainsaw Build

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