Engineering: Thumpers

Your basic small car is usually an Inline 4 cylinder. The most popular one, in a Honda Civic was actually based on a motorcycle engine, with water cooling added. A 4 can get vibration at certain revs, so if you want luxury you need a V6 or V8 to smooth it back down again. However, the more cylinders you have, the more torque you're losing at Lower RPMs. In a ground vehicle that's expected to climb hills, that's a problem, which is why Jeeps tend to be big 4 cylinder engines, and Harley Davidsons are big two-cylinder engines. Lots of lower RPM torque. However, when you get to true offroad bikes and tiny engines, you get down to a single cylinder, what's called a Thumper.

It is worth mentioning that a thumper can be 2-stroke or 4-stroke. A 2 stroke has twice the power, but has issues with burning its own oil due to some particular design decisions to save weight, such as venting hot exhaust inside the crankcase, where the heat literally cooks the lubricating oil. Not only does this damage the oil, it also damages the moving parts and requires you to put oil in the fuel and to change the oil in the crankcase, as well as replace rings on a schedule based on hours, not miles. Not to say that a 2-stroke MUST vent exhaust into the crankcase, nor is it absolutely necessary to ignore oil injection instead of mixing oil and fuel, and a Master Valve solves the blowback issue the crankcase venting is doing on purpose. There are good available mechanical solutions to making a 2-stroke more reliable and efficient and cleaner running, fairly easy to do. Easy enough that I wonder why the insistence on hundreds of millions invested in Eco Motors to solve this 2-stroke air pollution problem since ignored to make truck motors at a huge profit AFTER collecting big funds from Green contributors. Ahem. I'm sure that's not breaking the law (it is called Fraud). Their alleged 2-stroke diesel would be great, if it really works and really does scale down.. however you could easily make a replacement 2-stroke scooter motor that has a regular exhaust port into a pipe with expansion chamber, like on race bikes, with a master valve sliding baffle to keep the resonance in the right value, and use oil injection and drastically cut maintenance, wear and tear, and pollution all at once. Totally the way to go with a 2-stroke. Hell, put an oil cooler on the crankcase, just to help. Why not?

The more common option, with half the horsepower of a 2-stroke of the same size, is a 4-stroke. There are a number of these on the road, though you might not notice them. Most 250cc motorcycles, all scooters (except Maxi scooter), all Enduro bikes are single cylinder thumpers. So is your lawnmower and the very pretty Enfield motorcycle, currently made in India with highly questionable reliability according to reviews I've read. The newer ones have better engines and transmissions shipped from Austria, but the rest is still Indian so is a bit... MEH? The Enfield even suffers damaging resonance due to the vibration of the thumping against the pretty cooling fins, which can actually break off. Instead of reshape the fins to avoid this problem, like a good engineer would, the Indians instead ship the bikes with black rubber inserts to damp the fins... which fall off. This is bad engineering. They make Harley look really progressive. A damn shame, too, since the Enfield really is a beautiful bike, built of metal, not plastic, and repairable for generations. Its just the machining tolerances are whatever the thing put out this week, the QA is the 2nd worst in motor sports (Tomos is worst of all), and that's a really hard thing to correct in the minds of riders who want to go places and see things, not get broken down on the side of the road. If you want to break down, ride an English bike.

Speaking of Harley, they are now going to make a 500 and 750cc model starter bike instead of the usual 800cc Sportster alone. I'm not quite sure why the Sportster gets panned so hard, being an $8500 "starter Harley" and therefore not good enough to ride with the clubs with the $19500 real hogs with 1300cc V-twin engines etc. Meh. Its a club thing. I can't possibly understand. Anyway, which the 500cc is being built in India for Indian sales, it is being built in America for American sales, so that's good. Reviews I've heard are that its narrow, and aiming for the bad boy poor biker. Rat bike scene I guess.

Eric Buell, one of the engineers for Harley, built a very odd and progressive series of large displacement Thumpers for street riding. They weren't very popular, due to bad vibration and other reasons, but I sometimes see them on the road (Hwy 49), though I hear them first. The bikes didn't sell well, or rather most sold several times each because riders didn't like them for long. They vibrate a LOT. So after that bankruptcy, Buell has gone into racing and is focused on that. His fans online hope that a few of those bikes will trickle down to public. For their sake and his, I hope that happens.

Thumpers are the only real engine type in offroad bikes. You get the most torque with one cylinder, and you want that at low speeds to tractor up hills, across scree slopes (loose stones), and through sand at speed. Torque is key. The big ones for torque are the KTM 450, the Kawasaki KLR-650, the Suzuki DR-650, and the Suzuki DRZ-400 (beloved of farmers). There are also smaller engine models, and many of those ATV's are running thumper engines, though some are multi-cylinder engines. I've even read of a triple designed by an Australian Cafe Racer's specifications by an American motorcycle engineering team in the Deep South, that got built by the Chinese for export and then the Housing bubble burst and who knows where the engine is now? A pity. Would make a great noise and was the ideal 375cc's instead of the typical 650 or 1300 that Triumph makes. Which is weird to me. A scaled down 375cc Triple, like a Ninja, would be a good seller.

I guess the cost of labor prevents these loss-leader bikes? A shame. I'm hoping that in time, CNC machining and makers will offer a scaled down Triple suitable for an upgrade to various bikes that aren't so great right now but could be with the right engine. Upgrade a 250cc twin road bike to a 375cc Triple and fix a problem you didn't know you had.

Not to say there aren't some dandy road thumpers. The Suzuki TU-250 is a lovely bike, for those few people who actually found one to buy. I think most stay in Thailand rather than get over here. They aren't sold in California at all, due to a feud between Suzuki and CARB, the smog agency. Suzuki changed the paint and CARB insists the new color needs a new crash test. Someone needs to get fired at CARB. This might be a consequence of bizarre legal restriction, but it smells like retaliation and some improper personal vendetta. A real shame. Its a lovely bike with fuel injection and upright seating position. Looks like something from the 1960's and will do 50 mph all day long, according to reviewers. The bike is beautiful. Like the old Triumph Lightning.

Now, compare that to Honda's Thumper, their CBR-250. Also fuel injected single cylinder with lots of usable torque, that muffler makes me feel actually sick to the stomach. What WERE they thinking?

Who is this designed for? The engineering on the engine and EFI are great, and the brakes are good and the suspension gives it a safe ride. Yet it looks awful. It's kinda like the mistakes of the Suzuki SV-650, which despite being a competent bike with a 90-degree V-twin, very smooth power band, had a high saddle difficult to swing your leg over and is famous for a fat woman's naked behind in traffic. Do your own search for that. There isn't enough brain bleach to remove that image. Ugh.

Still, the bike is solid and good, so good it was cancelled. It needed that engine in a different frame. As I understand it, the Bandit 650 was that. A small frame twin with great ergonomics for medium sized riders and excellent balance for a sport bike. I've seen them up on Donner Pass Road, old Hwy 40, and it was smooth and competent. A good bike if you must ride on freeways some of the time.

Now, compare that to the Suzuki DRZ400-SM, a supermoto (smooth tires) version of their farmer motorcycle. With all that suspension it makes for a smooth ride with the progressive shocks and having both kinds of tires means its a bike that you can go through the Apocalypse, or even Obamacare's inspired defunding of state treasuries for things like road repairs. More and more potholes out there. Yes, 4 wheels is inherently safer. And yes, you can build a kit-car from the ground up with carbon fiber and aluminum if you want, and if you're a good welder or can pay one that is. Its just that these bikes are a lot cheaper and if you don't ride like a crazy fool and keep your speeds down, you can do this safely. Its the speed insanity that leads to wrecks. If you must go really fast, consider getting a pilots license. There's neat stuff happening in that too, its just really expensive and annoyingly controlled. I don't think they use thumper engines in planes, however.