| Author | Message | ||
     Benm2 |
The torque applied to a multi-piece con-rod is there to preload the rod bolts for increase in fatigue resistance. The "hole" in the big-end is machined with the rod assembled to ensure that distortion from the tightening process does not produce bearing issues. A huge rotating flywheel would not produce any significant load on a bearing other than that associated with its static weight (unless you try to turn it, then the right hand rule thing kicks in). A balanced rotating flywheel, that is. Its the amount of IMBALANCE that loads the bearings. So, heavy flywheels alone do not require larger bearings. Lastly, Ducati and others use common crankpins & plain bearings, just no knife-and-fork. For a plain bearing/one-piece-crank setup, the "fork" rod would have two bearing caps instead of one. And, its relative bearing surface area would have to be larger to support its (presumed) additional weight. | ||
| Mikej |
Uh, yeah, hmmm, I think I'll just wander back over to the bicycle stuff and keep myself out of trouble and bulletholefree. Say, did you know it's a small world afterall? And you can find the darndest things in the most out of the way places.  | ||
| Steve_A |
>>A huge rotating flywheel would not produce any significant load on a bearing other than that associated with its static weight (unless you try to turn it, then the right hand rule thing kicks in). A balanced rotating flywheel, that is. Its the amount of IMBALANCE that loads the bearings. So, heavy flywheels alone do not require larger bearings.<< Agreed. And even then, the flywheel imbalance forces and gyroscopic forces load the main bearings, not the big-end bearings. Piston (and rod) weight and speed are what loads the big end bearings. That's why high-speed four-strokes have slipper pistons and skinny rods. Harley and Buell haven't spent as much money as some makers going for minimal weight pistons and tapered bore piston pins. Harley in particular has been far more concerned that the pistons hold shape and clearance well for 100,000 miles, keeping social noise low and performance consistent for a very long engine life. Certainly lighter pistons could increase the rev limit of the XB reciprocating components. But the valve train in an XB engine sets the main speed limit. Substantial power increases from these engines can't come from big rpm increases without sacrificing reliability, but will instead have to come from displacement increases or non-natural induction. | ||
| Mikej |
"But the valve train in an XB engine sets the main speed limit. " You sure? Not piston speed? I've seen a 9-10,000rpm V8 in a boat before and the valvetrain was keeping up just fine. Lap after lap after lap, carb'd, normally aspirated. Maybe I'm mistaken due to the years that have passed since then. Not doubting you, just checking. I just put them together back then and let someone else figure out what to use. | ||
| Benm2 |
supernatural induction? | ||
| Mikej |
Nope. Proper configuration. 'course I had to sit on the dock and take their word for it. | ||
| Benm2 |
automotive pushrod configurations are lighter than harley's. Shorter rods & rockers that only support bending, no torsional section in the middle. | ||
| Mikej |
What torsional section? In the pushrod, the rocker arm, or the rocker arm shaft? A foot's a foot, car or bike. I think I'll just go back to lurk mode and my memories ... "just back the trailer down the middle of the ramp, too many idiot's here today. Mike, when I run the boat up onto the trailer get that clip onto the boweye. Fred, as soon as I hit the trailer rollers just hit the gas and get us out of here before any of these yahoos hit this thing. Frickin' weekend cruisers, this is the last time we test run on a Saturday morning, all right get ready..." This was followed by a circle boat making a rooster tail in a crowded ramp area at the south end of Lake Washington from a dead stop at the end of the dock, barely preceded by Fred backing the truck down the ramp at between 5-50mph and slamming on the brakes, all the while with me hanging on for dear life with my right hand hanging onto the truck's tailgate lip and one foot on the bumper and the other foot on the trailer with about two feet of slack on the winch line and the clip in my left hand (the monkey job sucked at times) hoping he hit drive before I got skewered by the fast approaching boat and hoping I got it hooked before Fred got going again and thereby leaving the raceboat sitting on the pavement. It worked, probably about the fastest boat loading that ramp ever saw, and I learned I could hang on with one hand while Fred chicanned around and between the Saturday beachgoers and out of the park area before the city police arrived. Sometimes something only works once. I think I calmed down around Tuesday, and Fred2 (the boat driver/pilot) was still talking about it a year later. Some memories are best remembered than recreated. g'night | ||
| Davegess |
Mike, Harley's have very long pushrods compared to say a small block Chevy. The small block cam is way up in the V not down near the bottom. Believe that has a negative effect on the revolutions. | ||
| Benm2 |
Mike: Take a look at a crane rocker for a 350 chevy, then look at a crane rocker for a hd. You can see it all at their website, as they make products for both. The 350 rockers work like a seesaw thats a little longer on one end than the other. An HD rocker arm is the two sides of the see-saw with one side offset over the pivot. (ie if you were sitting on the seesaw, your partner on the other side would be a few feet to the right or left) There is a tubular section between the arms to tranmit the motion, and this adds to the valvetrain mass. Great story, though. Sounds like a real pants-filling experience.  I've got a story similar to that. Once, when I was seventeen, I got a ride home from a wera endurance race at Pocono, on the racebike. I put on my uncles leathers, and climbed on the back of a 1983 CB1100F, behind my dad. We were both in red/white/blue racing leathers, full face helmets, etc, on a bike with NO lights and a full set of number plates, running an ontario 4-1 pipe with NO baffle. The ride was about 30 miles, we got home in somewhat less than 1/2 hour. Did I mention there was NO passenger footpegs? That's my best racing story. | ||
| Mikej |
Dave and Ben, Got it and got it. Somehow I was thinking of the internally ribbed pushrods and thought they would overcome any flexing. Ben, Got my feet wet from time to time, but never filled my pants. Course I never got a ride in the drag boat either.  It seems that no matter what the vehicle, when things get to the extreme ends of the envelope some rules tend to get a little, shall we say, bent slightly. Getting slightly back on topic, didn't someone once come up with a cam or something in the bottom of the "V", or has my imagination taken off again? I know some have played with converting a H-D engine to overhead cams, but I thought there were some other avenues explored as well. Oh well, time for sleep. | ||
| Blake |
Rick, "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." If you are thinking of the loads imparted by the weight of the flywheel, you would be correct. If you are thinking about the loads imparted by the flywheel when you dump the clutch you would be correct. But those loads are small compared to the peak loads generated by combustion (controlled explosions after all) that are transferred by the pistons to the rods through the flywheel to the crankshaft and on through the entire powertrain. To give you a feel for the loads... Yes the engine *only* puts out 80 LB*FT of torque which amounts to 40 LB*FT per cylinder, but when you consider that the 40 LB*FT of continuous torque output that each cylinder contributes is effectively generated within approximately 60 or less degrees of crank rotation, you can see how high the peak torque comprising each power stroke can get. There are 720 degrees of crank rotation between each power stroke. Dividing 720/60 gives us a factor of 12 which means that the average torque during the effective portion of the power stroke is not 40 LB*FT, but 12*40=480 LB*FT. That's torque though, a twisting force, which is something that by design the bearings cannot transfer. Radial roller bearings can only transfer plain old force. So, what about the loads on the bearings? Glad you asked... A high performance engine can generate a 2,000 psi peak combustion pressure. Acting over a 3.5" bore, 2,000 psi generates a load transmitted through the connecting rod that is near 20,000 pounds (p*3.52/4*1,000=19,242 LB). Yes, I neglected the angle of the rod and the ensuing kick load generated, but I also neglected friction between piston and cylinder which tends to cancel that. Anyway, 20,000 pounds is fairly close and certainly good enough to illustrate the point. How does that compare to a The negative aspect is that when accelerating aggressively, the flywheel also absorbs some of the energy that would otherwise be transferred to the rear wheel. A bigger flywheel better mitigates/reduces the peak loads on the main bearings and other powertrain components downstream from the flywheel (primary drive, tranny, final drive). The flywheel does not help mitigate the loads on the rod bearings or wrist pins since they see the loads of combustion thrust before they make it through the flywheel. Are you familiar with basic electrical circuits? If so, consider that a flywheel is to a mechanical system as a capacitor is to an electrical system. They are analogous. As the voltage in an electrical circuit fluctuates, a capacitor absorbs or discharges electrical energy in the form of stored charge. If the capacitor is properly sized, voltages in the circuit downstream from the capacitor are thus smoothed out; any sharp voltage peaks and valleys are significantly reduced. In an engine, torque is analogous to voltage and rpm is analogous to electrical current. A flywheel absorbs/stores in the form of angular momentum (arpm*inertia) some of the peak positive torque during each combustion stroke then gives it back during the peak negative torque during the compression stroke. If you have a four cylinder and a twin each producing the same torque, the torque pulses produced by each cylinder in the twin will be twice as great as those of the four cylinder mill (assuming that no two cylinders fire concurrently). So you can see why an engine with a few big cylinders and lots of torque might need a larger flywheel. Of course if you rev the engine and pop the clutch, the flywheel releases it's stored energy and so in that case would be increasing the loads on the main bearings, but reduces the loads on the rod bearings and wrist pins. If you did not have the flywheel in that case the engine would tend to stall much more easily. Are you confused yet?  | ||
| Bomber |
Mike Vincents had the cam placed pretty high up the V, if memory serves, but it's been a month or three since they've been built . .. you're likely thinking of something else? | ||
| Joey |
Blake! If Voltage~Torque and Current~RPM, what is Horsepower? I think I knew once, but that was decades ago... | ||
| Sarodude |
Watts! | ||
| Joey |
I just read that on another thread. Thanks anyway! | ||
| Mikej |
Watts | ||
| Rick_A |
Wouldn't the extra resistance when accelerating put more stress on main bearings with a big flywheel too, then? I know the aim is to smooth power pulses...but is it more to change the running characteristics of the motor or to better control loads? I'm sure it's both, but on the other side of the coin, a single puts out the widest torque pulses...yet a majority...even the "big bore" singles...have fairly tiny, lightweight flywheels. | ||
| Davegess |
Rick that is true for most modern singles but not for the old british bikes. The classic big torque big single did not actually have loads of torque just really heavy flywheels that gave the big singles there classic "feel". | ||
| Blake |
Rick, "Wouldn't the extra resistance when accelerating put more stress on main bearings with a big flywheel too, then?" No. The flywheel is absorbing the peak loads keeping them from being transmitted as harsh spike-like shocks to the rest of the drivetrain. Higher revving, shorter stroke, lower torque engines generally need smaller flywheels, like the ones you mentioned. Low revving, long stroke, high torque engines need larger flywheels to protect the drivetrain and attenuate vibration problems. Without a flywheel to absorb peak rod input load/torque, all the torque gets transmitted directly to the drive sprocket and into chain tension which causes a reaction at the main bearings with the output shaft bearing taking the the severe hit. With a flywheel the peak primary chain load is reduced and thus so is the reaction at the output bearing. Pictures might help...  A flywheel attenuates/diminishes peak power pulse loads as seen by drivetrain.  Lack of flywheel allows peak power pulse loads to transfer on through drive train. The lengths of the load vectors (arrows) are proportional to the magnitude of the loads. Notice how much more load the output shaft bearing and primary chain must sustain for the "without flywheel" case in the bottom pic. I didn't show the actual flywheels in the top pic since they would obstruct the illustration. You know what they look like right? | ||
| Davegess |
My understanding, and this is often wrong, is that the Classic British "big single" had oversized flywheels to make them suitable for pulling a sidecar. Something to do with smoothing out the power pulses to allow lugging. These bike did not make a lot of power and often carried very heavy loads. Blake does this make any sense? | ||
| Mikej |
Look at a generator, relatively low power with a huge flywheel. Take forever to rev up, run very smooth (usually), and spin down slow when they run out of gas. Weight mellows out everything. | ||
| Steve_A |
>>My understanding, and this is often wrong, is that the Classic British "big single" had oversized flywheels to make them suitable for pulling a sidecar. Something to do with smoothing out the power pulses to allow lugging. These bike did not make a lot of power and often carried very heavy loads. Blake does this make any sense? << Yes. Heavy flywheels tend to smooth out drivetrain vibrations, such as the resonant jerking you get on some singles and twins if you apply full throttle while lugging. Most dual-purpose singles don't like to be lugged because -- among other factors, such as cam timing -- they have light flywheels, espicially compared to those classic English Singles you mention. That makes them much more responsive, and makes the bikes they power feel much lighter offroad because it's easier to break the rear tire loose, but at the tolerable cost of limiting the low-speed operating range/load. Needless to say, Buell and Harley flywheel requirements are different for what should be similar engines because Buells and Sportsters aren't ridden in the same way. Many Harley riders just want to get it into top gear and not shift much, and it takes a lot of flywheel to make a Twin pull smoothly from 1500-2000 rpm. BTW, when you get to the level of flywheel in a Evo Big Twin, it adds 0.2 to 0.3 seconds to quarter mile time compared to a minimally flywheeled machine with the same power. That's because some substantial energy is being stored in the flywheel rather than adding to the kinetic energy (speed) of the bike. | ||
| Rick_A |
Well, why not put on considerably lighter flywheels and a cush drive or other such damper on the primary drive sprocket?...A gear drive primary would make a lot of sense, too. Please draw me up a flywheel pic Blake...I've never seen one before. | ||
| Blake |
Rick, Sarcasm is difficult to interpret without a smily/emoticon, so for the benefit of those who truly are not familiar with the bottom end of a Buell engine... If you look at a picture in the service or parts manuals, the flywheel is integrated with the crank counterweight lobes. Two BIG heavy disks, one on either side of the crank/rod bearing. If the output sprocket were made bigger, thicker and heavier, it too could become an effective flyweel. Cush drive? We already have one. The final drive belt. A cush drive would eat power without being able to efficiently store it and return it to the drivetrain. A flywheel efficiently stores energy. A cush drive is not an efficient storage mechanism for mechanical energy. A cush drive on the primary drive would open a whole new can of worms... backlash (sloppy loose connection to the transmission and ultimately the rear wheel), resonant backlash (bad harmonic vibrations. Stiffer is better. Loose and sloppy is, well, sloppy. You do the drawing. (Picturing a bicycle wheel covered with flies)  | ||
| Imonabuss |
The XB has a cush drive. Cush drives are good for smoothing in some ways, but definitely not the same effect as flywheel mass. | ||
| S320002 |
Rick, Buell has been using progressively lighter flywheels throughout the years to allow the engine to spin up more quickly. The short stroke of the XB allows it to have the lightest crank wheels of any Buell twin to date. Greg | ||
| Rick_A |
S320002...I know. Imonabus...I didn't know Blake...I don't think the sprocket needs be any bigger, either...there's already a huge rotor attached to it. I have seen some rotors with a mercury filled tube around 'em for "active balancing." They are supposed to make huge reductions in vibration...at least by manufacturer claims. Anyway I disassembled, measured, and rebuilt two motorcycle motors this week already. I've seen enough innards for the time being. though I may do another tranny tomorrow I've seen many a Harley flywheel, too. The ones in old shovelheads make Buell flywheels look downright spindly by comparison. | ||
| Rick_A |
Your last statement brought back memories of a bicycle wheel full of bird. I was doing about 40mph on a slight downhill when this bird tried to fly right through my wheel...just imagine the outcome of that one! | ||
| Blake |
The XB has a cush drive. Learn something new every day. I'll have fun telling Keith that. |
