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Pushrodpete
| | Posted on Friday, July 29, 2005 - 12:30 am: | 
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It seems like the weight of the counterbalancers and associated acooterments could easily be offset by not having to beef up every other part on the bike to withstand the vibes.
Discuss... |
M2me
| | Posted on Friday, July 29, 2005 - 12:54 am: |
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Pushrodpete, that's a very good point.
I'm guessing that the reason the XB/Sportster motor was not fitted with counterbalancers is because of the integrated transmission. I'm guessing that would make it more difficult, but not impossible, to counterbalance. Plus the whole "business" decisions. It would cost a lot to retool, etc. for not as much profit as the TwinCam 88B platform provides. So they decided to leave the XB/Sportster mill the way it is and rubber mount the Sportsters. |
Blake
| | Posted on Friday, July 29, 2005 - 01:09 am: |
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More mass and angular inertia in the drivetrain hurts acceleration and robs HP.
I agree that the way to do it is to built the engine from scratch with that in mind from the start. BMW and Ducati have done so, probably Moto Guzzi too.
We Americans are just too much the rough and tumble pioneer type. A little vibration, we like.
I rode a counterbalanced twin-cam on a couple occasions. I did not like how smooth it was at idle. Just wasn't right.  |
José_quiñones
| | Posted on Friday, July 29, 2005 - 07:41 am: |
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Bottom end design is much more fundamental than intake or fuel delivery systems, which get bolted on to the engines at the end of the line, not at the beginning like counterbalancers would be. Apples and oranges.
Counterbalancing would affect other components of the bottom end to the point that they would hardly share parts any more.
I don't think they could have two very different sets of engine cases, one with counterbalancers and one without, on a line that builds 5 xl's to every one xb/blast engine that goes down the line and be as efficient as they would be if all the engines get the counterbalancers.
The current XL/XB/Blast engine cases are different as it is, but not so much they can't go down the same assembly line using the same tooling.
You would probably need a separate line for the XB Buell line because the motor would be so different compared to a counterbalanced XL, not in the cards at this stage.
However the Twincam 88 and 88B are built on the same assembly line so maybe they could do it had they decided to produce a counterbalanced XL and unbalanced XB.
Whichever is the case the counterbalanced engine was shot down because it did not look right. Which caused the XL frame to gain 50 pounds because it had to "look" like the old frame while being stiffer. So instead of making the frame out of bigger diameter tubes, they kept the tube diameter the same but made them thicker.
(Message edited by josé_quiñones on July 29, 2005) |
Road_thing
| | Posted on Friday, July 29, 2005 - 08:29 am: |
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Grounder--does the BDB have a windshield? I've noticed it more on bikes with windshields--I think the sound is reflected off the backside of the shield toward the rider.
rt |
Impulse_101
| | Posted on Friday, July 29, 2005 - 10:07 am: |
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Full,
I was just wondering about you. I'm headed back up to the great white north next summer to visit friends and hang with my old roomie at the Paralyzed Vet's games, which will be in Anchorage next year. I'll certainly make it to Seward but I don't know if I'll make it as far as Homer
I've seen but never ridden the monster. Duc's are great and totally idiosyncratic in their own right. I'd love to put one through it's paces but the opportunity is unlikely to present itself.
Blake & Jose,
It seems that you're correct Buell would have to scrap everything to build a counterbalanced XB motor. Economy of scale dictates that there is no cost effective way to build a new motor when your present motor is built in tandem with another related product. Yet another reason to just deal with it.
If doubt that you would lose much weight by dumping the stronger mounting and going C/B and since the engine is a stressed member of the frame would you lose rigidity and structural integrity?
JT |
Benm2
| | Posted on Friday, July 29, 2005 - 10:36 am: |
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The Aprilia RSV / Rotax engine is counterbalanced, and did not seem to have great difficulty in keeping up with Ducatis when they were in WSB together.
I can't see how they would affect steady-state power, as they wouldn't be accelerating then. The additional weight could affect acceleration.
The new vette is two-valve, not four. |
Blake
| | Posted on Friday, July 29, 2005 - 10:54 am: |
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I'm thinking that Aprilia's was a rather small counterbalancer compared to what would be required in a 45 deg common crank pin Buell engine.
JQ, You may be right, but I doubt that Buell would have ever accepted a heavier counterbalanced engine for the XB. Apparently they turned down the Revo engine due to its excessive weight and size. |
Jlnance
| | Posted on Friday, July 29, 2005 - 11:21 am: |
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required in a 45 deg common crank pin Buell engine.
I'm not well versed in engine technology, so I'd like to think aloud (in type?) and you all point out my mistakes.
I'm thinking common crank pin means that both pistons are connected to the same pin on the crank shaft. This means that both pistons are moving in pretty much the same direction (the 45 degree seperation is the only reason they are not moving in exactly the same direction.) It seems like the first step in reducing vibration would be to alter the crankshaft so that one piston is going up as the other is going down? This would make the crank shaft more difficult to machine, but it shouldn't make it significantly larger. Perhaps it would fit in the same engine case? |
M1combat
| | Posted on Friday, July 29, 2005 - 11:26 am: |
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But then they have to be side by sideso the engine gets wider. |
Kenb
| | Posted on Friday, July 29, 2005 - 11:30 am: |
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my mistake I thought the LS2 was 4 valve.
it is a pushrod engine though, i got that right. |
Whodom
| | Posted on Friday, July 29, 2005 - 11:45 am: |
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Jlhance,
Basically the problem is the pistons are moving up and down (reciprocating), while the balance weights are going around in a circle (rotating). You can partially compensate for the reciprocating weight by adding rotating weights to the crankshaft; how much is part art and part science. A 90 degree V-twin can be balanced perfectly because the rotating weight is always opposed by one or the other piston.
Along the lines of what you mention in your post, Honda and others have made V-twins like my VT500 Ascot that have narrow angle cylinders with a "split" crank pin. This makes the engine look like a ~45 degree V-twin on the outside, but work (more-or-less) like a 90 degree V-twin on the inside. This makes the balance better, but induces another smaller imbalance because the two connecting rods are no longer in the same plane. The exhaust note doesn't sound nearly as good as a true 45 degree V-twin either (listen to a VTX1800 some time).
If you really want to get into it, check out this page:
http://pdmec4.mecc.unipd.it/~cos/DINAMOTO/twin%20motors/twin.html
which has detailed technical discussions on all 2-cylinder engine configurations. |
Benm2
| | Posted on Friday, July 29, 2005 - 11:51 am: |
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Honda's 45-degree Shadows when first introduced had a single offset crankpin. The rods were side by side, not knife & fork. But the offset was even larger than what was required just from the rod arrangement, the rod journals were separated by 45-degrees ON THE CRANKPIN. They so wanted the engine to LOOK like a harley (45-degree cylinders) but didn't want it to shake. So... cylinders are maybe 1.5-2" apart side to side. Which, of course, produces a differnt vibration, but not as bad. With the 45-degree cylinders and the 45 degree crank they got 90-degree PRIMARY balance. The Buell with the knifenfork (KNF) has perfect secondary balance, as the cylinders are directly in line.
If you've ever looked at the KNF rods, one rod is cut away so the other can move through it, as they follow slightly different rotation paths as the engine turns. If you kept KNF rods AND offset the crankpins, the cutouts in one rod would be much larger to allow the other rod to pass through it. Plus, the crank would get wider, as the pin offset couldn't be "instant". And, it would be a real job to put the crank bearings on the center journal, unless you changed to a plain bearing crank.
A 55 degree motor would be neat, though. |
Whodom
| | Posted on Friday, July 29, 2005 - 12:25 pm: |
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If you've ever looked at the KNF rods, one rod is cut away so the other can move through it, as they follow slightly different rotation paths as the engine turns. If you kept KNF rods AND offset the crankpins, the cutouts in one rod would be much larger to allow the other rod to pass through it. Plus, the crank would get wider, as the pin offset couldn't be "instant". And, it would be a real job to put the crank bearings on the center journal, unless you changed to a plain bearing crank.
Ben, you couldn't, nor would there be any reason to use KNF (cool acronym by the way) rods on a split crank pin. The KNF rods allow both cylinders to be exactly in line and use a single crankpin. For comparison, Vincent used a single crankpin in their V-twins, but slightly offset the cylinders so that two conventional connecting rods could be used. Both of these arrangements use roller bearings on the crankpin, but require a 3-piece (minimum) crankshaft to allow for assembly.
The Honda v-twins with split crank pins use a one-piece forged crankshaft, plain rod bearings, and the rod ends are split like those in an auto engine to allow assembly. |
Blake
| | Posted on Friday, July 29, 2005 - 03:49 pm: |
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Ben,
Yer makin' my head hurt! 
Not sure what you mean by "different rotational paths." Pretty sure that each conrod follows the exact same circular path. Pictures are good. I like pictures...
1997 Buell Conrods and Crank Assembly |
Benm2
| | Posted on Friday, July 29, 2005 - 04:10 pm: |
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quote:Ben, you couldn't,
The engineering throwdown!
Yes, you could, but you'd have to do it on both sides of the center pin. There would be a single center pin connected to two outer pins by some "transition area". The rods would have an awful lot of "overlap", where one rod would be crossing the other like scissors, but it WOULD be possible. Just IMMENSELY ugly (from an engineering point of view), and really kind of pointless.
But possible. 
Seems my post was practically identical to yours. Must have been typing at the same time! Always thought it was odd the lengths that Honda (and others) would go through to copy "a look" while missing "the point". |
Bomber
| | Posted on Friday, July 29, 2005 - 04:17 pm: |
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Grounder and Thang -- the Black Death Barge doesn't make any weird noises I've heard (except the somewhat disturbing cackle issuing from the operator) -- no windshield either, which may subtract from the grinding and add to the cackling
good thread -- thanks for the engineering types for sharing their knowledge |
Benm2
| | Posted on Friday, July 29, 2005 - 04:21 pm: |
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Blake, depends where your measuring the rods rotation. The rods actually rotate very little while their ends follow either a straight or circular path. I like pictures too, but didn't have any.
From your picture, you can see the rod labeled "3" is inside the other rod. The angle between the rods doesn't stay the same as they rotate, so the other rod has a cutout in it so the "3" rod doesn't bang into it.
Clear as mud now? Technical writin' not really a strong point... |
Bob_thompson
| | Posted on Friday, July 29, 2005 - 04:24 pm: |
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Anybody remember the KISS (not the band) principal. (keep it simple, stupid) I think our engines along with BMW boxers are a fine example of this, and seem to have worked well for a very long time. Bob |
Whodom
| | Posted on Friday, July 29, 2005 - 04:29 pm: |
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Benm2:
The engineering throwdown!
Hehe- not intentional, I should have checked your profile before posting. There's nothing an ME hates worse than being told something can't be done!
Yes, you could, but you'd have to do it on both sides of the center pin. There would be a single center pin connected to two outer pins by some "transition area". The rods would have an awful lot of "overlap", where one rod would be crossing the other like scissors, but it WOULD be possible. Just IMMENSELY ugly (from an engineering point of view), and really kind of pointless.
But possible. : )
I can't quite visualize that. ME's can't talk without drawing (or looking at drawings) either...
Seems my post was practically identical to yours. Must have been typing at the same time! Always thought it was odd the lengths that Honda (and others) would go through to copy "a look" while missing "the point".
I thought the VT500 was a neat idea when it came out; maybe a step forward from what Harley had done. Looking at it now, it's kind of a clumsy solution to the problem, but it was pretty innovative at the time. That said, my Ascot vibrates worse at high speed (55 MPH and up) than my S3.
Here's a pic of the Honda internals from my Ascot parts fiche:
 |
Panic
| | Posted on Wednesday, August 03, 2005 - 11:09 pm: |
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"A 90 degree V-twin can be balanced perfectly because the rotating weight is always opposed by one or the other piston."
Well... no.
Read my article:
http://victorylibrary.com/mopar/crank-bal.htm |
Blake
| | Posted on Thursday, August 04, 2005 - 12:38 am: |
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Ben,
"Blake, depends where your measuring the rods rotation."
At bearing center on the big end, the ONLY point which follows a purely "rotational" (your word) path.
I see what you are trying to say though, that the rods rotate about the big end bearing-center back and forth relative to each other. Easy for me to say.
I agree with Whodom, your statement that "If you kept KNF rods AND offset the crankpins, the cutouts in one rod would be much larger to allow the other rod to pass through it. Plus, the crank would get wider, as the pin offset couldn't be "instant"." does not make any sense. Offset cylinders do not use KNF rods. |
Jlnance
| | Posted on Thursday, August 04, 2005 - 06:58 am: |
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does not make any sense. Offset cylinders do not use KNF rods
I think he is suggesting not offsetting the cylinders, but rather having a crankping that looks something like a W. One cylinder would be connected to the high poing in the center of the W and the other would be split and connected to the two low points in the W. |
Whodom
| | Posted on Thursday, August 04, 2005 - 10:09 am: |
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Well... no.
Read my article:
http://victorylibrary.com/mopar/crank-bal.htm
Panic,
OK, that's a very interesting article, but it's a bit deep for the laymen here. Admittedly my statement regarding 90 degree V-twin engine balance is drastically over-simplified, but I was trying to come up with something the non-technical types among us could understand. |
Frausty12r
| | Posted on Thursday, August 04, 2005 - 05:37 pm: |
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Bill00,
you read my mind (was just a little late in the post)
Coates Engine heads are revolutionary. I called and got a quote for my nissan I was going to put a turbo on, (know how much they cost?) get this..
25,000$ for one 4/cyl head, AND I had to ship TWO long heads to them.. But, from their approximation, normally aspirated, would be 170-180 hp, at 10,000 rpm. not enough hp for the cost, and unfortunately it will probably remain that high of a cost until more companies see the benefit, no lubrication, no reciprocating mass in the heads, no need for adjustment... EVER. [edit] Sorry forgot to mention 10k miles between oil changes as it wouldn't absorb nearly the carbon poppet valvetrains do. Can you say WOW?! [edit]
Mmmmm But if we got them on our buells, the exhaust note would change as it's not so much the crank/pistons that make the final note, it's timing/duration of the valves.
(Message edited by frausty12r on August 04, 2005) |
Bill00
| | Posted on Thursday, August 04, 2005 - 07:15 pm: |
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I read some were that a guy that works at Coates, said they put a set of heads on a 5.0 Mustang and was making about 900hp, supposedly running 14to1 compression and a stock short block.(don't know if I believe that)
Coates already makes motorcycle heads. I think it would be wild if Buell used their heads. |
Benm2
| | Posted on Thursday, August 04, 2005 - 08:04 pm: |
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Jl, that's exactly what I meant. The cylinders wouldn't be offset. I expect that such an engine, especially with a 45-degree offset at the crank, would be a really crappy engine. If it were 5 degrees or so, on a plain bearing crank, you could gain a little clearance down at the piston skirts and still maintain a narrow vee. |
M1combat
| | Posted on Thursday, August 04, 2005 - 10:07 pm: |
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By doing that you would need to have a deeper "notch" in the fork conrod. Down at the bottom of the stroke the offset would be backwards. The conrods would be crossed.
What exactly were you trying to solve by doing that?
It wouldn't reduce side loading at all. It would only make both pistons hit TDC at the same time.
Keep in mind that we aren't running a twingle setup.
I probably just missed it... What are we trying to solve for? Are you saying we should weaken the journal and one conrod for reduced vibration? |
M1combat
| | Posted on Thursday, August 04, 2005 - 10:09 pm: |
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Uless you are trying to cross them up at the top so the engine would act somewhat like a 90 degree engine? |
Benm2
| | Posted on Thursday, August 04, 2005 - 10:30 pm: |
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M1, wouldn't be trying to solve a damn thing. As I said, I think it would be a crappy engine.
At the lower end of the range, like 5 degrees, it might allow for some mods. At BDC, the 45-degree pistons come close to touching. The longer the rods are, the better this gets.
While there are some who say that longer rods mean better power, there are others that say reducing reciprocating mass is the way to go. So...
If you can reduce the piston-to-piston interference at BDC by offsetting the crank pins, you could use shorter (lighter) rods and reduce loadings on the crank bearings, and potentially increase HP.
That would have to be balanced against the benefits of longer rods, in that the piston spends more time at TDC during the burn cycle, which raises peak combustion pressures (if I remember my thermo right). Buell on the XB9 went with longer rods, there's got to be a reason. |
M1combat
| | Posted on Friday, August 05, 2005 - 02:44 am: |
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"M1, wouldn't be trying to solve a damn thing."
Sorry... I thought you were trying to get a balance issue straightened out.
"Buell on the XB9 went with longer rods, there's got to be a reason."
Yeah... I would guess that was so they didn't need to use shorter jugs or move the wrist pin location. I could be wrong though. Keep in mind that when you use shorter rods you also increase side loading. This hurts reliability and with a rod length/stroke ratio greater than ~1.7/1 you can use slipper pistons. Do the XB's use slipper pistons?
"If you can reduce the piston-to-piston interference at BDC by offsetting the crank pins, you could use shorter (lighter) rods and reduce loadings on the crank bearings, and potentially increase HP. "
I assume you mean by going to a larger bore? Why not JUST use longer rods (to get the pistons farther up the jugs at BDC) and a little shorter stroke (to get them to not bash the valves at TDC)? This would also reduce side loading. I think it would also be a less expensive crank to produce. One more thing... I don't think our power limitation is based on the crank bearings. I hear the stock cases/bearings are good for about 115lbs of torque reliably. To get more, you need to machine the cases to install a timken bearing. I don't know how much those are good for, but I think a lot  .
I'm not trying to rain on your parade at all... Just learning. |
Blake
| | Posted on Friday, August 05, 2005 - 02:50 am: |
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I think I get it! Like having two parallel rods driven by one piston with the other piston's rod situated between them. Would be configured kinda like a triple with the two outer cylinders having identical crank and valve/ignition timing.
You were right and I was wrongly dongly, again.  It's good to learn new stuff. |
M1combat
| | Posted on Friday, August 05, 2005 - 12:24 pm: |
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I "think" you got it... |
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