Long Haul Gravel Sled

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Been here a while now..
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Joined: Sun Mar 03, 2013 4:07 am
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Long Haul Gravel Sled

Post by larkout » Tue Jul 08, 2014 5:54 am

Ok, not really a building thread because its done and built, but some folks might like to hear me ramble about how I put together my diesel bike. I wish I had taken some more pictures in the build process, but I kind of get into the flow of things and forget about a camera...
There are so many nitty gritty details to talk about, but I'll go over the basic recipe that I worked with.

The rough overall scheme was to make a little diesel bike on the cheap, one thing leads to another and I decided that it would all be easier if I made a frame from scratch for the whole project. I wanted a diesel only for economy, so that meant a small diesel, and the yanclones are so wonderfully available that that just seemed like a fine idea. I was a little worried about the sub-interstate top speed capability, but then I sort of realized that that isn't where I wanted to be anyway, so having a bike that would force me on to the back roads and fire roads is actually a benefit. I wanted a bike that was maybe not a total dual sport, but certainly capable of cruising the logging and fire roads of the Western States.

The engine is a Launtop 186fa, standard 418cc yanclone stock.

The gearbox is from an old AMC type box from a pre-unit Norton Atlas. I settled on the Norton box because there is actually a pretty good used Norton/Triumph shop just 45 minutes from my house, and a big Brit bike swap meet that happened coincidentally when I had a little cash in my pocket. There are so many Norton dorks out there that I knew parts would always be in decent supply. The primary for this box would normally be running a #40 simplex roller chain in a shallow bath of oil. I knew it would be difficult to fab an oil tight chaincase. Opinions conflict on whether that chain will hold together in a 'dry' scenario, so I started looking at getting a belt drive. Belt driven clutches are predominantly available for Commando style clutches which use the same spline as the Atlas, but a slight different seat so thus a different main shaft on the transmission. I tracked down a Commando main shaft for the gear box, ordered up a Commando belt driven clutch basket, and cobbled together some standard Commando clutch internals. Generic AT10 pulleys tend to only be available with small hole, but I got lucky to find a friend that happened to have a 1" reamer and a broach for an ANSI keyway.

The wheels were scored from a parted out 1972 Honda XL 250. Perfect and cheap. Came with the forks, triple clamps, and swing arm.

I've done a little bicycle frame building, how hard could a motorcycle frame be? After a while, it all just seems like a game of connect the dots. The head tube is defined by the steering stem and forks. The engine was sort of lined up to leave enough ground clearance and enough clearance for the front wheel. The gear box follows the engine. The swing arm pivot follows the location of the output sprocket of the gear box. Figure out a peg height for good ground clearance then a seat height for good posture based off of the pegs. Once I nailed down all those locations I started to figure out what kind of a frame shape would connect them all. After a lot of looking around, the Norton Featherbed style frame seemed like the most accomodating and easiest to fabricate. I settled on 1" x .065 4130 Chrome Moly tubing for the structure. It mostly tig welded with a few fillet brazes in the ridiculously tight spots. Titling a custom bike in California requires jumping through a few hoops, but if the bike is functionally street legal then there shouldn't be any problem getting the paperwork through.

All of the lights are LED. The headlight is a generic 7" bucket that GE came out with recently. Low takes about 1.5 amps, high is about 3 amps. The light is a nice even white and brighter than the lights on my 20 year old pick up truck. The battery has been too low to crank the engine a couple of times, usually in the morning after riding into the evening before with the headlight on... I don't know how to tell if the battery is toast, if the generator putting out as much as I think, or if I have some other drain in the system.

I put about 1000 miles on the little beasty last week. About 100 miles in town shake down, then I hit the hi way. I was heading north along the coast, into a headwind most of the time, and had to shift a lot between 4th and 3rd. If it was flat and not too windy I could shift into 4th at about 50 mph and crank up to about 55 and hold it, but if there was much headwind or a slight incline then I'd be down to 3rd which seemed to provide enough leverage that I could keep on at 50 mph... on the second and third day of riding, the best pleasure I could find all day was getting behind a big square horse trailer, even with an occasional spray from some kind of dribble out the back of the trailer there is no way to beat the feeling of letting off the twist grip, sitting up, and rolling along at 65 mph. There was some air sneaking in around the filter (maybe through the filter? it is a little soggy after contact with the biodiesel) during the whole trip, due to the holiday I wasn't able to get a new filter and better clamps, but I think that it should run a little crisper and stronger as soon as that gets fixed.

My best calculation for the first two fill ups was about 80 miles per US gallon, on biodiesel. The last tank was good old dino diesel, and I didn't actually look at the volume of fuel, but based on the price and what I paid I think I got closer to 100 miles per US gallon. The first tank was straight out highway riding, the second had some puttering up and down fire roads, and the last tank was mixed slower highway riding with more slow going through towns... I can imagine that the motor was getting a little looser by the last tank.

I've been folding down the mirror, tucking in, and revving it out pretending I'm going for a land speed record... 55 mph with saddle bags and a milk crate.

It's the best riding bike I've had, and is perfect on 45 mph swoopy paved back roads and logging roads up the side of the mountain. Pretty much all the places I want to be.

I plan to put a little cafe quarter fairing on it. I think that will give it enough extra edge to hang on in 4th gear for a little longer.

Blunt Eversmoke
I luv the smell of Diesel...
Posts: 119
Joined: Thu Dec 01, 2011 6:15 pm
Location: Somewhere by Bremen

Re: Long Haul Gravel Sled

Post by Blunt Eversmoke » Tue Jul 29, 2014 8:40 pm

Beautiful in a ratty-bobberish sense :) Not a common combination to see - let alone so well executed.

I luv the smell of Diesel...
Posts: 212
Joined: Sat Aug 01, 2009 2:23 pm
Location: northwest of Calgary, Alberta, Canada

Re: Long Haul Gravel Sled

Post by albertaphil » Wed Jul 30, 2014 5:15 am

Nothing quite like the feeling of riding something you built... Congratulations!

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