New here, with a DIY Chainsaw Bike

[Lightning Boy]

Thank you very much, RC! It's quite a head turner around the neighborhood.

I just got back from a particularly enjoyable cruise in the sunshine. There was a mild headwind at times, but I just crouched down into the handlebars "racing style" to decrease my wind drag to compensate. It's obvious I'm getting much better fuel economy with the peg method compared to the original clutch. No way to know for sure how much, because I haven't mounted a speedo/odometer yet. I know it is sizable. I used roughly a half of the saw tank to go the distance roughly a full tank would take me before- NICE! It doesn't hold much more than a typical weed whacker/ blower tank, but that is a serious and notable increase in efficiency. With the saw and reserve tanks full, I should be able to get about anywhere I would normally go around here. Every change thus far has been for the better. I think I'm finally ready to call the bike completed. I almost want a front suspension fork now, because one left over from my little bro's first dirt bike has been staring at me from the start of this build... That would be the perfect ending. However, I know when to leave well enough alone. If I end up doing it, that's all. I'd hate to screw it up by getting greedy with the amenities.

 

[Lightning Boy]

Nope, not gonna do it. I've just decided the forks will go on the upcoming Homelite XL build. The heavier saw will likely benefit more from them, anyway. Unless something fails on it, Diesel is fine as is.

 

[Dan]

A really cool thing about our crazy is nothing need be a permanent decision and as you have built it with truly interchangeable parts, can mix an match later. "Bolt on, bolt off Grass Hopper"

The one your riding. (MB) The one your building and the one your planing. But #4 gets all the cool parts, snork.


hehe, I wanna print that as a bumpers sticker; "Bolt on, bolt off, Grass Hopper" But would get some strange looks.

 

[Lightning Boy]

Very true, Dan. If I don't care for the look or the ride with them, I could always change back. It would be such a no-brainer to let it be if the fork wasn't laying right there... I'm having way too much fun riding around on the bike now to tear it apart again. Telling myself I have no good reason to swap is a lie, and I know it.

 

[Lightning Boy]

The 9V battery clip got replaced today. Got tired of taping it down to the battery, so I attached some small crimped clips on the wires. Now, I just clip them on and off. Saves a lot of extra messing around during my pre-ride checklist.

 

[Lightning Boy]

A couple quick afterthoughts of improvement:
A spark plug cover, made from the same stovepipe I made the front fender from. Just enough to keep the water and dirt away from it. Haven't had a problem with that yet, and I hope to prevent it before I do.

Also folded up another bracket at the bottoms of each side of the front fender for more stability. It did an okay job of staying out of the way of the tire, but I found myself being extra careful with it. If it happened to smack something accidentally going in and out the door, I'd have a big alignment problem. Much more solid now.

 

[Lightning Boy]

I considered making an odometer (simple counter) from calculator guts, a reed relay, and a magnet, and going full-on DIY cool with it. The extra math involved after every ride, the time it would take to construct mounts, and cost of components wouldn't be an efficient trade for a real speedometer.

So, I went and bought the first brand new thing this bike has (other than the original tube I replaced recently): A spiffy new bike computer. I know the Bell models have mixed reviews, but the Schwinn was out of stock everywhere; and this one was only $13. Being a tinkerer of all sorts, I figured any problems that may arise could be resolved. Some say the vibration of motor bicycling makes them useless, but I haven't had any problems with mine at all. I noticed a bit of wiggle between the mounts and the handlebars when I first attached it, so I placed some thin folded cardboard squares between the gaps. It doesn't lose signal, cut in and out, or move around like I've read of them. It wouldn't have been nearly as solid without something filling those gaps. This has worked well for my bike, anyway.

If you have one of these particular bike computers, try this before you toss it. Mine has worked for a mile and a half so today, at speeds up to 21 mph.

After doing some fast calculations, I've put no less than 10 miles on this bike doing my daily rounds since I built it. This doesn't include the distance run across town, either. I'd estimate that was at least another 3 each way. That's a good indication of longevity if I treat it right.

 

[Lightning Boy]

Quick update: I reached a new top speed of 26.3mph yesterday. Backed off the tension bolt a couple turns, for less low torque and more top. It took a few minutes of fine tuning on the U-bolt, but the extra 5mph was worth it. Now I know how many turns from there it takes for pulling myself and a full backpack, should I need to adjust again later. I'm marking notches on each set of threads with a sharpie for now.

 

[Lightning Boy]

Here's the latest: I made a new header from plate steel to replace the soup can properly. It's the first welding I've done in ten years, so it's far from a pretty bead; but strong and functional. Same steel as the muffler cap, welded together with it. The open end is bolted through the spark arrestor holes on the exhaust flange from the motor. It's a slightly longer rectangular chamber, as opposed to the short wide style of the old. The volume/capacity is similar, and it clears the tire well.

I noticed an improvement of at least 2mph on top end and less 4-stroking at low throttle on the test run. It only chugs when starting now, and "gets the flow" much sooner on takeoff.

Between the miles ridden and the goose chase it endured around town in the trunk, that can never stood a chance. I couldn't see the hole in the underside at all until I removed it to mount the new header. Glad I had something at the ready to replace it. Can't claim to have planned it out that way.

Now that I've started welding again, I'm ready for anything. Once I get some more practice in to get the feel back, the fun will be endless.

 

[Lightning Boy]

Diesel had its first major meltdown situation today. The stock exhaust flange connecting to the newly constructed header gave way, ripping the studs through the mounts. The studs are still torqued down tightly, but that stock flange for the spark arrestor screen is a goner. Mounted support beams to help hold the extra weight of the new exhaust, and all. Still, I chalked this up to work hardening and vibration.

Luckily, I was a couple blocks from home when it happened. The exhaust managed to stay attached to the bike via the support structure around it. I hit the kill switch, stopped to loosen the tension bolt, and pedaled it home to avoid overheating or damaging the engine.

Then, I grabbed my other chainsaw bike and got back on the road again. Thank goodness I built another. Nice to have that around in case of a problem. Number two seriously saved the day.

The plan so far is to build a flange and weld it to a pre bent pipe to fit exactly the way I want it to. Now that I'm no longer limited by the stock flange, the design can be modified further. If that doesn't pan out, I can always make another cap flange for the header and improve the supports.

The port is too small for a kit exhaust, and I've never seen another quite this size and shape. It's got to be customized around the motor mounts and back tire anyway, so this isn't much of a problem. The muffler will be the easy part. That flange being strong and matched is the crux of the entire job.

Here goes nothing.

 

[Dan]

You will get it! And really cool to see your progress.

“I have not failed. I've just found 10,000 ways that won't work.”
― Thomas Edison

Then he made a light bulb that worked and was viable!

http://www.goodreads.com/author/quotes/3091287.Thomas_Edison

 

[Lightning Boy]

Thanks for the encouragement and fitting quote. Big fan of both Tesla and Edison.

I've got a new port flange box constructed for the header, but it still needs a bit of grinding on one corner to clear the tire properly. If that doesn't give enough clearance, I plan to chop the corner out and weld a flat plate into that gap. That will definitely give more room. I should be able to test it sometime this evening.

 

[Lightning Boy]

The new flange fit right up! I cut and bent a box shape from a recycled computer monitor brace, because I didn't have any other thin plate steel on hand. Then, I drilled the stud holes and a slot for the port. I ended up with an opening slightly smaller than stock, but it didn't decrease performance enough to bother me.
I may have to open the flange port a little wider after a few more rides, but it performs well enough to leave it be for now. I want to make sure it will hold up before taking much more material away from the plate.

The new port box slid over the header tightly and bolted together easily. I considered welding it, but that would be a real problem to remove in the event of another flange failure. Very happy it allows me to use the newly constructed header and Briggs muffler again. It took some brainstorming and a few hours of metalwork, but it should be worth it in the long run. Hopefully, this is the last exhaust project for number one.

 

[Lightning Boy]

The new exhaust system was slowly working itself loose from the head, so I went back to the drawing board for some improvements.

First, I made a spark arrestor from an old drag racing 327 gasket. (The stock screen didn't fit anymore and was decreasing performance slightly without one.) After peeling away the fiber of the gasket, I was left with a very strong screen, albeit with larger holes than the stock saw example. Clearing the holes fully with a nail and air compression finished the preparation. Then, it was easy to cut for size and drill the mounting holes. It slid right into the header easily, and bolted up in a flash.

I realize that I don't technically need the spark arrestor now, but the behavior of the bike says otherwise. The extra baffle really helps the sound level, and stopped the fluctuations in speed on the extreme top end. It's completely different riding without it.

Also, I decided it would be a good idea to make a matching gasket for the new port box. A few broken aluminum 350 gaskets worked perfectly. All I had to do was score the port and holes into the gasket to trim and drill them out.

These two things and a shot of loctite on each of the head bolts made for a much improved exhaust. There is no wiggle between them now. Volume has decreased, and performance is very close to its former self. If it stays attached, we may have a winner here.

 

[Lightning Boy]

Still riding well. I've restored enough confidence in it to go for a night ride and put a few more miles on this evening. So far, so good!

 

[Lightning Boy]

The "Diesel" is still going strong, and I haven't had to adjust or fix anything. It's pushing 50 (documented) miles now. The stock tires also show very little wear, and will likely last me a while.

This is why it's my favorite. Reliable as the sun.

 

[massdrive]

Welcome cool bike.

 

[Lightning Boy]

Did some port matching today of the exhaust gasket and DIY header box. It was riding fine, but I figured it was time for me to reclaim a couple mph. The ports are matched as closely now as I could get with a grinder and hand files.

Number one is now faster than she's ever been. I hit 29 mph for a new top speed on it, and acceleration is also improved. There was a healthy wind in my face at the time, too. The flow seems just about perfect.

It'll be hitting 80 (documented) miles sometime this weekend.

 

[Lightning Boy]

Sitting at 96.529 (documented) miles tonight. Here's what it looks like in the dark. I do ride at night a lot, but not without proper lighting. Turn signals are pretty bright too, but I didn't have a spare hand for the switch.

 

[Lightning Boy]

The odometer reads 103.78 miles tonight! Finally crossed the triple digit threshold (documented, anyway). Still a joy to ride, and no issues at all. Amazing what a bunch of old odds and ends from the garage can become with the right tools and imagination.