| Author | Message | ||
     Sarodude |
Instead of starting a flame-a-rama conversation on broad engine configurations, I'd like to hear some educated discussions on the pros & cons of the common crankpin. -Saro (crickets chirp away) | ||
| Benm2 |
Pro: no side-to-side shakey-shakey, as both cylinders in same plane Con: one rod heavier than the other IF OF SAME STRENGTH AND MADE THE WAY THEY ARE NOW, harder to make | ||
| Bomber |
er, not to pick those nits, but you can have common crankin engines WITHOUT having the cylinders line up . . . .ya need not only a common crankpin, but a knife and fork con-rod setup for them to be in the same plane . . . . | ||
| Benm2 |
Er, yes. Sorry. Ducati's use common crank pins. I was referring to the knife-and-fork setup. I stand corrected. | ||
| Bomber |
siddown, Ben . . . .just trying to stop the flame war before it started (grin) | ||
| Mikej |
spoilsport.   | ||
| Bomber |
that's me ;-} | ||
| Rick_A |
Pro Makes a nice sound  Pro One-piece rods Pro Easily rebuildable Con Roller bearings not as well suited to high rpm operation as plain bearings. Con Limited to a fixed crank timing Con Must be trued after assembly | ||
| Mikej |
           (heh heh heh, it's like heiroglyphics heh heh heh) | ||
| Sarodude |
Regarding the One Piece Rods and Crank Must Be Trued comments... These attributes can apply to any crank / rod combo where the crank pin and crank sections must be assembled. -Saro | ||
| Hootowl |
Pro: The motor can be made narrower, as the front and rear cylinders line up with each other. Con: This shrouds the rear cylinder, and makes it harder to cool. | ||
| Bomber |
Rick . . .one-piece rods are a function of a specific design, but not necessary to have a single crankpin setup, I think (although I don't know of anyone with a multi-piece rod on a single pin crank . . . . . .phew, that's hard to say) | ||
| Mikej |
What do the Honda twins have (I think it was Honda), one main journal with side-by-side rods. I thought they were bolted on on one I saw a few years ago, but I could be wrong. What's coming down the pike, if anything, should be interesting, if not revolutionary. | ||
| Bomber |
yep, side by side, like a Duke . . .. . or, the crankpin on one model was offset to make a better sound . . . . . . lovely excersize in CNC programming (I'd like to see the first couple of runs, thoguh) | ||
| Dynarider |
Mike, I recall seeing a Honda engine that had the rods bolted to each other. Kinda a weird looking design & concept but it worked. | ||
| Benm2 |
I thought that the honda offset-crankpin design was done for the opposite reason than better sound. I thought they made a 45-degree v-twin with a 45-degree offset crank, to allow it to fire (and shake) like a 90-degree engine. | ||
| Bomber |
Ben . . .you could very well be right . .. my memoery of that design is sketchy, at best | ||
| Rick_A |
Well, I was speaking in the context of our engines. Trying to come up with the pro's+cons of all single crankpin designs is more than I can tackle. | ||
| Rick_A |
...and Saro...2 strokes and some singles are mainly the only other engines that that'd apply to. Most manufacturers tend to avoid a multi-piece crank if they can. | ||
| Jrh |
mid-usa.com has 114" air-cooled v-twin with side by side rods.Falicon crank | ||
| Rick_A |
I took a look at the site...certainly nothing revolutionary. The POWER HOUSE cam that is used in the production engine makes great horsepower and torque from about 1800 RPM all the way to 7250. Torque measures at 100 ft. lbs. from 1800 RPM to a peak of 120 ft. lbs. around 3000 RPM and stays to 7000 RPM. The POWER HOUSE 114 makes 120 HP from just off idle. It provides 120 horsepower and 120 ft. lbs. torque in a super reliable package. Whether you're a long distance touring rider or blasting around town is more your style, a POWER HOUSE 114 makes reliable power that you can use. 120 HP from just off idle???...it's also a big bitch...and people are exceeding those power figures with 88" Sportster/Buell motor and a hell of a lot less than $10,000! | ||
| Buellnuts |
Pro- Uh..........um............uh.......well if ran at a reasonably low rpm, they are acceptable. Con- more complicated than a normal rod having a rod cap. Con- Rod and Yoke having two different types of roller bearings. Con- Crankshaft spinning in tapered roller bearings instead of insert style bearing. Con- Ywo piece Crank Shaft (truing stand needed) Con- Configuration does not allow the engine to spin up thus not being able to compete with allmost every other brand of Motorcycle. (Oh, I'm gunna get it for that one) Why is it that Buell puts a Somewhat improved Air cooled (ya I know Ducati has one) engine in there XB,s and Harley used a state of the art liquid cooled engine in a chassis that in my opinion isn't worthy of an engine with true sport potential!! I guess I'm tired of the same ole HD dictation to the flegling company. It's like inviting company over and telling them, Here's the hot dogs, were havin Steak! In The Rain Forest, Bob | ||
| Rick_A |
That's because Harley saw a big opportunity in the growing power cruiser market and wanted a piece of it. Roller bearings and multi piece cranks are used in just about every two stroke motorcycle engine built...they hold up well in high rpm (though not as well as precision inserts), but the main factor limiting rpm is the valvetrain. In pre-XB Buells piston speeds are also a factor. The flywheel mass may be a problem, too. Later Buells (I think it was 2000 and up) use straight roller bearings instead of tapered in the crank bearings. I guess another plus would be low friction and less losses to drag due to the lower lubrication needs of the roller bearings. The V-rod engine is tremendous in comparison to just about any other sportbike mill I know of. I think it's well suited to its intended use...not a sportbike. I guess it would look cool if a sportbike could be made out of it...a big engine with wheels bolted to it... ...and I'd still rather have my S1. | ||
| Blake |
LOTs of prior discussion on this very topic at... http://www.badweatherbikers.com/buell/messages/3842/7717.html | ||
| Steve_A |
Hi guys, There are lots of misconceptions on this thread. First, engine speed capabilities of Buell/Sportster engines are not particularly limited because of the crank configuration/bearing/rod design. The speed limitations are far more imposed by the relatively long strokes (even on the XB9; compare its 3-1/8-inch stroke with the sub-2-inch strokes of Japanese 600s and 750s) and the two-valve, pushrod valve train. The pressed together crank design with roller bearing main bearings is still used on many, many four-stroke singles, such as the Rotax that still dominates short-track and TT racing. These, btw, spin to 9000 rpm reliably in racing with a stroke longer than an XB9, and with a 600 to 660cc cylinder displacement. The new four-stroke Japanese motocross engines, with roller mains and needle piston pin bearings, rev to well past 10,000. These days, the best plain bearings (perhaps Honda's; no company spends more money on basic engine research) probably have an absolute speed/load advantage over typical roller bearings, but the difference is not huge. Nor are the best roller bearing designs necessarily used in production engines; I suspect that you could make the same type of silicon nitride rollers work (at least in racing) that have been used in some fairly exotic gas turbines. The one big advantage of the common crankpin/inline cylinder configuration of the Buell engine is that it produces no rocking couple, allowing Buell's uniplanar mounting design to be extremely effective at minimizing the vibration that reaches the rider. But, then again, a different crank/cylinder configuration could reduce vibration inherently (even opening the V-angle up to 55-60 degrees would make a big difference), so minimizing the need for rubber engine mounts. There are essentially two ways to design connecting rods for a V-Twin with cylinders all in plane. You either use Harley's knife-and-fork design, or you use a master-rod/slave-rod system as used in aircraft radial engines. Harley filed some patents on the latter, but has never put it in production. Such a design would allow a one-piece crank and plain bearing mains, but to this point, any advantages of cost, reliability, or ruggedness have not been enticing enough (if they exist) for Harley to put such a design into production. Finally, even the XB9 engine has relatively heavy flywheel mass. This doesn't effect peak rev capability; it just makes the engine respond a little more slowly, as when you snap the throttle open with the clutch pulled in. It does make the bike feel less zingy than a Japanese Four, but it also means it does fewer bad things if you're a bit rough with throttle on/off transitions. I might like it a little lighter, but not to the extent of Suzuki's TL1000R. Take too much crank weight off a Twin, and it ends up feeling not all that different than a Four. | ||
| Sarodude |
Now that Steve has started to skirt the types of points / perspectives I was fishing for, I'm going to ask another question... What aspect of a common crankpin mandates the use of roller bearings? Or one piece rods / multi piece cranks? -Saro | ||
| Court |
Steve: I feel duty bound to caution you that there may be servere consequnces for introducing facts into one of these "snowbound in the cabin" inpassioned discussions. Are you familiar with the "Patch fine?"  Thanks you for shedding some light... Court | ||
| Benm2 |
I can't see any that do. As long as the crank were drilled to allow oil flow to plain bearings, the rods could be two-piece with split plain-bearing inserts, and bolt-on caps. The crank could then be forged in one piece. Roller bearings GENERALLY dictate that an assembly be built in such a way as to allow the bearing to slide on/off the shaft. Some people do make split roller bearings, but these are generally for more industrial applications. | ||
| Rick_A |
It seems logical to me Steve, that a huge rotating flywheel mass would put more stress on bearings than a flyweight flywheel, wouldn't it?...at least if they spun at the same rpm and both used the same size bearings. Those motocross 4-strokes have lightweight engine components throughout to help achieve that performance. I've seen their innards. It's pretty wild. It's simple, Saro...single piece cranks need to have the multi piece rods torqued down...which doesn't make the use of rollers practical, and necessitating the need for precision fit bearings to get the proper clearances. With a common crankpin the opposite holds true. It's not practical to accurately fit/gauge/install a plain bearing...so a roller is used. Something like that... | ||
| Blake |
Thank you Steve! MikeJ, What are you trying not to say? |
