My Refinements

I've been busy refining the controls of this bike. I have primed and painted all the raw steel. I have also repositioned the clutch lever to the top bar. The lever is attached using a bolt welded to the lever. The bolt threads into a coupling nut welded to a mount made from a 5" piece of 1 1/2 inch wide steel channel.  I could have used a piece of steel tubing and solid round bar for a pivot point but I wanted to minimize the width of that pivot point and didn't want the hassle/danger of a cotter pin to keep the rod from sliding out and the chance it could snag clothing or open skin.  The threads of the coupling nut hold the bolt in place while still allowing the lever to pivot because it isn't threaded all the way in.

Closeup of pivot point w/bolt welded to lever and
coupling nut welded to mount

The steel channel is placed with the channel upside down, which creates a tunnel for the brake and shifter cables routed across the top of the top tube. This assembly is attached to the top tube with hose clamps. Bicycle inner tube is wrapped around the top tube before hose clamping the lever assembly to keep everything in place and protect the finish.

The lever and spring now pull to engage the clutch rather than push to disengage it. With this new set-up, the pivot point of the clutch lever acts as a fulcrum in conjunction with the spring tension, keeping the clutch engaged until the rider flips it back. I also wrapped a folded section of bicycle inner tube at each attachment point of the engine mount to the frame to minimize engine vibration.

Clutch engaged

Clutch disengaged

The throttle control was cannibalized off another bike and works well with a compression spring on the engine side to reduce speed when the rider let's off the lever.

Throttle lever (under handlebar)

Engine mount for throttle cable with return spring

The v-belt was slipping a bit on the driven pulley.  I used three pieces of one foot long 3M anti-slip tape and applied it to the surface of the driven pulley.  Great traction now!  I'm still breaking in the engine but was able to hit 33 mph with this set up, measured by my GPS.

3M non-slip tape

Last thing I did was install a bottle holder to keep a stainless steel bottle of gasoline as my reserve tank.  The tank on the engine is rated at 1/3 a gallon.  I've yet to figure my mileage, so I'm not sure how far I can go before I'll need more fuel.  

Gasoline reserves (bottle donated by my daughter)

Shake down cruise - 29 mph



Throttle cable coiled up by rear wheel, yet to be connected.

It's been a little while since I've posted a blog entry but that doesn't mean that I haven't been working on this project. I was able to find a way to mount the engine closer to the seat.  The belt just barely clears the brake calipers but it handles much better.  Here's a pic of the set-up so far.  I'm using a 69 inch 4L v-belt.  I tried a number of different ways to put tension on the belt with a rollerblade wheel as an idler pulley, but without flanges the belt would wander off the idler pulley and start climbing the drive pulley.  I found a Snapper idler pulley that fit perfectly and have been delighted with the result.  With that, everything stayed in alignment regardless of the belt tension.  

Dishwasher door spring pulls idler pulley into belt.

I attached a dishwasher door spring to the tensioning mechanism and put some linkage on the other end so I could have tension controls up front.  In this close up, you can see the black idler pulley attached to a chrome piece of square tubing, nested inside a larger piece of square tubing.  I canibalized this tubing from a retail store clothing display stand I bought for pennies a few years ago, it came in handy.  Up front, the linkage is attached to a lever made of steel flat bar and affixed to the bike frame using a 1 5/8" muffler clamp from O'Reily (a.k.a. Checker) Auto Parts.  When released, the spring pulls the idler pulley into the belt and engages the drive pulley.  I used a hose clamp to attach an "L" shaped stop to the bike that the tension lever can rest against when the belt is disengaged.  I got it to this point at 10:30p Saturday evening.  It was far enough along that I felt it was ready for a little test drive.  I added oil and fuel to the engine (it was brand new and shipped with no oil) and started it up.  It's sure a nice running little engine.  I then peddeled out to my street at about 6-7 mph.  I released the tension lever and engaged the belt and the engine took over without a hitch.  I didn't have a way to measure speed but it felt like 12-15 mph with the engine at it's lowest throttle setting.  Since all was going well, I kept going, about two miles over all.  No problems.  I opened it up for small section just to get a sense for the top end.  It's not yet broken in so I didn't want to overdo it.



Tension lever attached to bike frame with muffler clamp.

It was also pretty late so I shut it down to keep the neigbors happy, although it isn't very loud.  Sure nice to have the option to pedal.  On Monday after work, I took it out again.  This time I had my GPS with me so I could measure speed.  I opened it up again for a short distance and got up to 29 mph.  Not too bad, and quite a bit faster than my calculations, which I had set for around 20 mph at 3600 engine rpm.  Either my math is off or the engine is turning faster than 3600. Probably a little of both.  I also found I was also able to start the engine by putting tension on the belt while peddling.  This engaged the drive pulley and turned the engine over, starting it up.  Nice.  I'd still like to attach the throttle cable (I was reaching behind me to control the throttle) and put the kill switch up by the handle bars.  I'll probably rework the tension linkage so I'm pulling to put tension on rather than pushing to take it off.  Should be easier on the linkage components.  There's a bit of engine vibration through the frame but managable.  I'll explore the idea of vibration dampening. And it would be nice to have some front suspension.  I have a slightly larger drive pulley if I wanted to increase top end, but that was back when all I thought I'd get was 20 mph.  I think 29 mph is just fine for now.  We'll keep working on the refinements!

Building the Rack, Phase 2

I had a little more time the other evening and put together an offset frame that mounts to the engine and also to the rack.  I cheated and welded this together because I didn't have the hardware handy to bolt it together.

I then attached it to the engine and clamped it on the rack to see how the alignment was.  The engine has to sit back there pretty far in order for the belt to clear the bike brakes.

I took the bike for a spin under pedal power to get a sense of the handling.  Hmmm, feels like a 25 lb. child on a bike seat back there.  It's okay, but we won't be bustin' any moves in a BMX competition.  I'm going to see if I can reposition it so the engine's mass is more forward.  There just might be clearance for the belt if I can get it forward enough.  More to come...

Building the Rack, Phase 1

I'm a member of a great forum called MotoredBikes.com.  There are tons of smart people there who are eager to show their work and help you with yours.  I've had many great suggestions from them regarding this project.  Earlier this week, I picked up an engine from Harbor Freight (97964).  It's a 2.5 hp.  I documented on that forum how I got this $129 engine for about $76 out the door.  You can read about it here.  When you get to the page, scroll down to comment #15.

I'd like to have had more time for this project today, but there were too many other demands.  However, I was able to un-box the engine and see if it would fit inside the bike frame.  A member of the forum has done it and told me it would fit if I were to remove the fuel tank and the exhaust system.  Assuming I was willing to go that far (I might be willing...some day), there's the added complexity of adding a jackshaft to get the power to the back wheel.  For this build, that's a little more customizing than I want to do.  So I'm going with the rack mount and I've made a little progress on the rack.

Of course there are more elegant materials that I could use, but I'm just using up my scrap pieces of steel to make this work.  I picked up some U-bolts from Fastenal because Grainger didn't have them in stock (huh?).  I held the steel pieces up against the bike frame and marked the steel where holes needed to go and drilled them out.  I then attached the steel to the bike frame with the U-bolts.  Whoa, it's sturdy!  Here are a few pics:

In the next phase, I'll be adding offset rails to the rack that will allow the engine to be positioned in alignment with the rim-pulley on the bike.

New Idea For Attaching Rim-Pulley To Bike Wheel

I was at the hardware store yesterday and came across these small plastic clips used in electrical applications to hold wire/cable in place. They are referred to as "cable P-clamps" in the hardware store. They come in a number of sizes. It got me thinking that they could also attach to the spokes of my bike wheel to hold my driven rim-pulley to the wheel. So I bought nine of the smallest at $.06 each, along with some small machine screws and nylon lock nuts. Total of $1.74 with tax. If this works, it'll be much easier than cutting slits in screws as I was doing previuosly. Furthermore, this set-up should be more forgiving. If something is going to break, my hope is that it'll be a P-clamp rather than a spoke. Another benefit is that since I'm using smaller machine screws, there is less chance of the screw heads interferring with the belt.  One downside is that these will add a little thickness, and I don't have much room, the tolerances are already pretty close.

I began swapping out the slotted screws with the P-clamps. There were only three that I'd made so it didn't take long. But after putting four P-clamps on (enough to hold the rim-pulley for evaluation), I found that they added too much thickness. This made the rim-pulley come in contact with the bike frame. Not enough to bind it, but enough to scrape and make noise. So I removed the rim-pulley and clamped it in the vise, closing the jaws to squeeze the outer edges of the rim-pulley together. I repeated this process all the way around the rim-pulley. It was enough to narrow the rim-pulley to clear the bike frame.  This is good news!

Here's how it looked when it was reattached using the P-clamps. I like how it turned out. You can see that the P-clamp is a little bigger than the spoke, but once I put all nine on, there was no play, the connection was tight.  So at this point I'm abandoning the slotted screw idea.

Now I need a Harbor Freight 15-20% off coupon to go get an engine and for the engine to be on sale at the same time. Once I do, I'm considering mounting the engine on the frame of the bike instead of a rack mount. I'll explore using the side mounts on the engine, attached to a plate, attached to the frame using some U-bolts or muffler clamps. My biggest concern with this idea is engine/pulley alignment. By the time I get it aligned with the driven rim-pulley, it may be hanging out too far to the right for me to pedal the bike.

Rack Mounted Bike Engine Project

INTRODUCTION

I've started a new project, a rack mounted engine on a bike frame.  While I have money to buy specialized parts for this build, my mission is to get it done using commonly available items, and my own limited engineering/building skills.  I have an okay shop with a few tools to help me out, including a lathe, MIG welder, drill press, and assorted hand tools.

I know that not everyone has these items, so one could question my "mission" about commonly available items.  Oh well.  I might have to resort to using those items on occasion, but I'm still trying to keep it "real" and affordable.

OVERVIEW

I have a MTN TEK mountain bike that will be the host for this project.  This is the same bike I used with the push trailer (see earlier post).  This will be a belt drive to keep it simple and quiet.  The engine (Greyhound 2.5 hp from Harbor Freight) will be mounted to a platform attached to the frame of the host bike.  It'll have a lever actuated idler pulley as a form of clutch.  The clutch lever will be mounted on the handle bars, along with a throttle lever.  The belt will be a standard Goodyear or equivalent automotive 3L belt.  After running some numbers, I'm planning on about a 14:1 direct ratio.  At 3600 rpms, that should move the bike at close to 20 mph.  I think the engine has enough power for that and is good enough for starters.

LARGE DRIVEN PULLEY

With a 1.5" drive pulley on the engine at 14:1, I'd need a 21" driven pulley on the bike. To purchase a large enough pulley (a.k.a sheave) would be hundreds of dollars.  But I figured I could make one without too much trouble.  A bike rim might work, but the closest size is 20".  That's a ratio of 13.3:1 - probably still okay.  I needed a 20" bike rim that I could mount to my 26" rim as a large driven pulley for the belt drive.  The local classifieds at ksl.com had plenty of used bikes for cheap.  I bought one for $5 and disassembled it, cannibalizing all the usable parts.

When I got to the wheels, I removed the tire, tube, and cut the spokes out of the front one.

I struggled to find ways to attach this "rim-pulley" to my rear 26" rim.  I had a number of ideas, but finally decided to drill holes around the edge of one side of the rim-pulley, in-line with the spokes on my bike's 26" rim.

<=== Here's how it looked after the first hole (see the side wall of the rim at the far left of the photo):

Before I went any further, I wanted to test fit the "rim-pulley" for clearance.  There is less than 1/16" between the pulley and the bike frame - good enough!

I completed the remaining holes, nine in all.  This gives me an attachment point on every other spoke on the left side of the MTN TEK wheel.

Why every other spoke?  Not because of science or engineering, since I don't really have any.  Just seems like with that many, it "otta" hold.

Then I took a Phillips pan head screw and cut a slit in the shaft of it with a hack saw.  I kept a nut on it, threaded up to the head so that if I buggered up the threads, removing the nut could straighten them out.

Once the slit was cut, I used a belt sander to open up the slit wide enough for a spoke to nest into it.

The screws goes through the side holes I drilled in the "rim-pulley," then intersect with a spokes on the 26" rim on the host bike.  The nut threads on the back side and holds it all together. I may need to use nylon lock nuts or Loctite to keep 'em on long term.

It takes a while to cut these screws and widen the slit, probably about 5-6 minutes a piece.  I thought about using split bolt connectors but they were too expensive at four bucks a piece on the low end.  I might try using a Dremel to carve the slits in these screws to see if it speeds the process up.  I've made a total of three so far, which will allow me to mount the "rim-pulley" to the host wheel for alignment.

MOUNTING THE "RIM-PULLEY"

Placing the bike upside down, I disconnected the rear rim and slipped the "rim-pulley" next to the host rim.  I then placed the first of the three Phillips pan head screws through the opening in the side of the rim-pulley and aligned the spoke in the slot.










Here it is with the nut pinching the spoke against the rim of the pulley.  I'm not tightening this down real tight because it appears to stress the spoke.

And here's how it looks with mounting complete.  It's centered to within 1/8" total variation.  With some adjustment, I might be able to get it closer.  To find the high side, I cranked the pedals to get the wheel spinning then put a Sharpie marker close to the pulley such that only the high side would hit the Sharpie, thus marking the pulley.  I then stopped the wheel, found the Sharpie mark, and moved the pulley in the opposite direction from my mark.  And while I have a dial indicator (for use with the lathe), I don't think I'll need that level of precision.

Bike Push Trailer

In the last few years, I've become interested in engine powered bikes. After a bit of research, my son and I built a push trailer using a Harbor Freight 2.5 HP engine. We welded a frame from 1.25" angle iron and painted it blue to match the engine. The engine is fix-mounted to the frame and chain tension is maintained using an idler pulley on a bar with a spring attached.

We bought the wheel, sprocket, and chain from a local distributer and used conduit for axle bushings to get the back tire to line up with the clutch sprocket. Cannibalizing a brake lever from another bike, we attached it to the handle bars as a throttle lever and purchased an extra long cable and shield from the bike shop to connect to the engine.

I fabricated a universal joint to connect the trailer to the bike at the seat post. We got it all put together and took turns riding it around the neighborhood. I clocked my son at 23 mph. Plenty fast for him in my opinion!

Last night, I sold the set-up to a neighbor who saw us riding it.  He wanted it to drive to work. There was more I wanted to do with it but I'm also interested in another project; a bike frame mounted engine!  Watch for more on that coming soon.