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Jimidan
| | Posted on Thursday, March 23, 2006 - 12:19 pm: | 
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Let me say at the onset, that this is my first post on Badweb in a long time, and that it is good to be back!
We have been having a discussion on another board regarding what happened to at least two of the XBRR's at Daytona, and I thought it would be interesting to hear what the knowledgable folks on here have to say on the subject.
As has been reported, at least two Buells suffered premature clutch basket failures during the race. I understand from talking to folks in the pits during the week that clutch failure had occured during practice and in CCS racing the previous weekend.
Specifically, these failures were blamed on excessive porosity in the castings of the clutch hubs, made in Japan no less. Notwithstanding the irony here, I am not conviced that the porosity of the clutch hub is really the whole problem, but maybe just a symptom. It may have been just the weakest link in a solid chain drive system. If they patch up this symptom with billet hubs we may just find out where the next weakest link is.
The thing I noticed when I was looking at the XBRR rear wheel was that the sprocket was directly bolted to the wheel, which is the typical method of converting to chain drive on a Buell. It is the easiest way to do it. However, in the past, we were not dealing with 150+ HP and the very high torque (the torque was so high that it was literally tearing the tires apart in practice). In other words, there was no shock absorbing hub, or so-called "cush-drive", as is standard equipement on ALL bikes with chains.
Without a shock absorbing hub, all of the hammering impacts of say wheel hop, for instance, is directly transferred to the primary drive. That is a hell of a lot of hammering considering the speeds at Daytona, or any race track for that matter.
The good thing about a chain is that it is so strong. The bad thing about a chain is that it is so strong...as there is really no give to them. Belts on the other hand have all kinds of give in them, which is why stock Buells do not need to have shock absorbing hubs. Try towing a car with a chain instead of a strap or rope and you will see what I mean. The chain is bone jarring.
Since Buell recast the stock wheels in Magnesium for the XBRR, why didn't they cast in a shock absorbing hub? With all of that torque and compression, it seems logical that the cast aluminum clutch hubs could fail, excessive porosity or not. Until they develop cush drives in their hubs, I fear that the problems will persist.
I think there is a reason why every modern chain driven bike has the cush drive rear hub...it was put in there to protect the drive line and engine. If it didn't need it those engineers would not have spent the money to build it.
At Daytona during practice and CCS racing, I was watching the Buells come off the straight away out of the International Horseshoe and try to get slowed down for that tight single track righthander (the one that 25 Supersport riders missed during the qualifying...and Matt Mladin too). The Buells rear wheel was hopping all over the place, especially while the riders were trying to learn how to ride the thing. There was some serious hammering going on and it sounded terrible.
Where did all of that hammering force go...right back up the chain secondary drive and into the primary. What is the weakest link in the primary...not that triple row steel chain or the steel sprockets, but rather the aluminum clutch basket.
On a chain drive bike, a cush drive is an integral part of the total design. It allows lighter weight components to be used, which is what Buell does with its front brake system in relation to the wheel weight. It is a lot easier and cheaper to replace a broken cush drive than drive line parts...although I have never had one break. What is to break, the rubber inserts?
I have heard that developement of a slipper clutch was in the works to try and fix this problem. I am not convinced this is the solution. True, most every superbike and probably the factory FX bikes have slipper clutches. But these bikes have a completely different kind of engine, nearly devoid of a flywheel. Slipper clutches are certainly a lot more expensive than a cush drive and they are easy to fry on these motorcyles with a lot less torque than the XBRR...just ask Eric Bostrum. They are generally good for about one or two starts on a racebike...and then it is pushing it.
Since the XBRR has a much more substantial flywheel than the IL4, it probably doesn't even need a slipper clutch to prevent excessive engine braking. Given this, why install a fragile slipper clutch to protect driveline parts? Plus, considering the engine configuration of the Buell, changing out a fried clutch is not a quick operation.
Why not have a really strong clutch with a cheap light weight cush drive and be done with it? It is less expensive, much more durable than a slipper clutch, simple, lightweight, and will do the job. Then our racers can really drill the start for the hole-shot without worrying about not having a clutch for the rest of the race. The KISS rule seems to apply here.
Buellistic noted that he thought that the primary chains may have been too tight, thus causing the problems. While this may have been a contributing factor, all the slack in the world in the primary chain would not absorb the hammering that would normally be absorbed by a cush-drive or belt.
What do you think?
(Message edited by jimidan on March 23, 2006) |
Buellistic
| | Posted on Thursday, March 23, 2006 - 12:28 pm: |
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"IMPROVISE" and move on !!! |
Anonymous
| | Posted on Thursday, March 23, 2006 - 12:34 pm: |
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Thanks for your thoughts, but a rear wheel cush is not needed. The XBRR has a cush drive in the clutch instead of the rear wheel. This is more expensive and harder to do than a rear wheel cush, but it saves a bunch of unsprung weight, around three pounds. Since you can't have a force without an opposing force, putting the cush anywhere in the driveline accomplishes the same thing. |
Buellistic
| | Posted on Thursday, March 23, 2006 - 12:40 pm: |
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PRIMARY 3/4 inch on the tight spot, cold !!!
Would help the motor sprocket nut on the XB's ??? |
Imonabuss
| | Posted on Thursday, March 23, 2006 - 12:51 pm: |
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That is correct. In fact the TZ Yamahas used to have a cush drive clutch, while the street RD's did not. The street RD's used a cush rear wheel. If you put a fixed hub TZ rear wheel on an RD with all the TZ performance parts except for the clutch cush drive, the transmission would break in one weekend. |
Race_pirate
| | Posted on Thursday, March 23, 2006 - 01:01 pm: |
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It seems as engine compression figures are rising most racing V twins and even I4's are running some sorta slipper clutch set up. My first street bike VF1000R had a slipper -or- one way clutch. I am not trying to start an argument but I question the crank/flywheel comment, I would be suprised if the Buell flywheel weighed significantly more then an I4. Or let me say the whole recipricating assembly. I am about to compare apples to oranges but one of the first things I noticed when switching race bikes (250 2 stroke to XB9R) was the lack of decel engine compression. It was closer to the non existant nature of my 2 stroke, I found the XB was quite mild for an American Vtwin. Also aside from rear cushdrive weight, as the pucks get hammered it makes the secondary drive sloppy and unsafe. Racebikes are about getting as much power to the ground as possible and transferring the feel to the rider.(IMO)
Nothing that broke on the XBRR cant be resolved easily, it was minor in my opinion and the real race season starts now. |
Buellistic
| | Posted on Thursday, March 23, 2006 - 01:19 pm: |
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XL's, get the OLD PARTs books out, had a
"COMPENSATING SPROCKET" !!!
Wouldn't that work better than the "BUELLschite" in the REAR WHEEL HUB or the "CLUTCH BASKET" ???
In BUELLing
LaFayette |
M1combat
| | Posted on Thursday, March 23, 2006 - 01:48 pm: |
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I figured that the un-sprung mass would factor in there... A cush-drive in the clutch sounds like a good solution to me. Better than in the rear wheel actually (once it's made to work that is...).
I suppose though... The question now turns to something along the lines of "why isn't it cushy enough?"
Porosity? Sounds like a decent explanation. Solution to that? Quality control at the clutch manufacturers level (just plain un-likely)? Billet (more cost)? Larger clutch (more mass)?
Compensating sprocket? Unless it was mounted in a way to absorb the hammering as the opposite side of the primary chain gained tension I can't figure how that would help... Maybe one on top and bottom that would place a good deal of tension on an otherwise "somewhat" loose chain? That may work, and may be a way to solve the single row chain issue, but chains do some weird stuff when you try to make them go all sorts of different directions at high RPM... We're adding mass, friction and complexity at THAT location, but it may allow the removal of the cush drive from the clutch hub, and then maybe a "more proper" slipper could be engineered?
Any thoughts from the engineer types? |
Court
| | Posted on Thursday, March 23, 2006 - 01:52 pm: |
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Great memories. . . my first Buell was chain drive and had a cush-drive.
Nostalgia. . . |
Anonymous
| | Posted on Thursday, March 23, 2006 - 02:02 pm: |
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Yeah, the old Buell H-D powered bikes had a cush drive because the engine didn't have one back then! The RW-750 had a clutch one though, and none in the rear wheel |
Blake
| | Posted on Thursday, March 23, 2006 - 02:54 pm: |
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My impression is that the clutch failures reported earlier in the week during the CCS/ASRA events were of the basic burned-up disk variety. If so, those would not have been indicative of the basket casting issue, would they?
Welcome and great post Jim.  |
Jens
| | Posted on Thursday, March 23, 2006 - 03:39 pm: |
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Hi,
I donīt want to comment the usability of the slipperclutch to compensate engine or driveline problems. But generally on my point of view the RR or not any other modern racebike will race in front without a slipperclutch. The differences in rearwheelchattering and drivebility of the bike are so huge that no serious racer is willing to race without it, if a working system is available. You are simple quicker with the slipperclutch than without.
Jens |
Anonymous
| | Posted on Thursday, March 23, 2006 - 03:43 pm: |
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You are right, Blake. All other failures were simply clutch burning, which is why at the start of the 200 all the Buell riders left the line so slowly. They were afraid of burning the clutch.
It gave even more credibility to the rides of the guys, because they all came around on the first lap well below their qualifying positions, then proceeded to make it up and more.
Jeremy was 12th on the first lap, for example, and proceeded to move up to 7th. he gotten a good start and the draft of the leaders, he would have been higher placed. In the end it's a moot point as far as Daytona went, because we broke, but it's great knowledge to have to apply to refinements.
Excellent discussion, Jim. Thanks for bringing the thoughts over from other boards, now we can pass the right info back to them. |
Race_pirate
| | Posted on Thursday, March 23, 2006 - 04:39 pm: |
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'Cause I'm talkin' progress, folks!"
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Court
| | Posted on Thursday, March 23, 2006 - 06:35 pm: |
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For the benefit of those who may not have ridden Buells with Cush-Drive.....
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Slaughter
| | Posted on Thursday, March 23, 2006 - 06:55 pm: |
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Jens makes a good point to my very limited way of thinking as a Buell racer:
When on the front brake hard going into a turn, the tendency is to try to slip the clutch and not let it out til I'm accelerating. I usually only try that when passing while braking going into a turn. It's VERRRY DIFFICULT to execute properly.
It has nothing to do with reducing the driveline stresses - but has EVERYTHING to do with keeping the rear wheel in contact with the pavement. |
Imonabuss
| | Posted on Thursday, March 23, 2006 - 07:04 pm: |
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Two very significant things the slipper clutch does are: first what Slaughter mentioned above, and second it keeps engines from being over-revved during downshifts. Rev limiters only work on the way up! |
Jackbequick
| | Posted on Thursday, March 23, 2006 - 08:02 pm: |
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"..All other failures were simply clutch burning..."
I'm don't understand why that happens. Is there a mandatory need to slip the clutch regularly on the XBRRs?
I'm used to thinking of a clutch as something like an on/off switch. You let go of the lever and it is engaged. The riders job is to match the RPM, stay off the throttle until it is engaged, or generally do whatever is necessary to use it right. Which should include not slipping it excessively, no?
Jack |
Sparky
| | Posted on Thursday, March 23, 2006 - 08:46 pm: |
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Jack, not being a racer myself, I'd think that throttle restraint is not what you need when trying to be the first to the corner.
Mastering the drag race start off the line is the key to clutch longevity and finishing. You don't want to bog or wheelie, so you mete out the power with the clutch. If the clutch is not up to this abuse, well, you saw what happens.
Sparky |
Jimidan
| | Posted on Thursday, March 23, 2006 - 08:52 pm: |
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Race Pirate sez:
"I am not trying to start an argument but I question the crank/flywheel comment, I would be suprised if the Buell flywheel weighed significantly more then an I4. Or let me say the whole recipricating assembly."
I really do not have any solid info about what the XBRR flywheel weighs, but I do know that my Ducati 998 race bike's stock flywheel weighs in at 3 lbs., but that does not include the whole rotating assembly of the crankshaft. I sold my spare crankshaft so I cannot weigh it...but it was tiny compared to my Buell. I currently have the "lightened" 2 lb. race flywheel in it, along with a Bucci slipper clutch. I don't really like the lightened race flywheel as I like more torque. That bike, like my old v-twin Honda Super Hawk 998, certainly needs a slipper clutch on the track with the light flywheels, as when you let off it is like hitting the rear brake hard.
I know that one of my Buell 88" engines has the 20 lb. S1W flywheel in it (my other one has the stock XL Sporty flywheel at 22 lbs.). I have a buddy who races XL based drag bikes and his flywheel was 'cut down' to 18 lbs.
Race Pirate continues:
"I am about to compare apples to oranges but one of the first things I noticed when switching race bikes (250 2 stroke to XB9R) was the lack of decel engine compression. It was closer to the non existant nature of my 2 stroke, I found the XB was quite mild for an American Vtwin."
I would suggest that the reason that you found very little difference in the engine braking between a 250 2-stroke and the XB9 was because of the heavy flywheel. I have been told that the heavy flywheel was necessary in the HD because of the single pin and the resulting irregular power pulse delivery inherent in this design. I am sure there is a limit on how light a Buell's flywheel can be and it still run smoothly, but I haven't a clue what it is.
I know when I have had my Buell at the track, I pulled the clutch in at the same time as I am heavy breaking at a 'bus stop' kinda curve to keep the dang flywheel from pushing me through it faster than I wanted...kind of a poor man's slipper clutch, as it were.
Jimidan |
Jimidan
| | Posted on Thursday, March 23, 2006 - 09:04 pm: |
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Anony sez:
"Thanks for your thoughts, but a rear wheel cush is not needed. The XBRR has a cush drive in the clutch instead of the rear wheel. This is more expensive and harder to do than a rear wheel cush, but it saves a bunch of unsprung weight, around three pounds. Since you can't have a force without an opposing force, putting the cush anywhere in the driveline accomplishes the same thing."
Thanks for the info. I could not see the clutch and don't know if I would even recognize the clutch cush hub if it bit me on the nose. I guess you guys have figured it, but it is difficult for me to see 3 lbs. additional weight at the hub for a cush drive...that is a lot of weight.
I am wondering now like M1Combat as to..."The question now turns to something along the lines of "why isn't it cushy enough?""
jimidan
(Message edited by jimidan on March 23, 2006) |
Jimidan
| | Posted on Thursday, March 23, 2006 - 09:18 pm: |
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Anony sez:
"You are right, Blake. All other failures were simply clutch burning, which is why at the start of the 200 all the Buell riders left the line so slowly. They were afraid of burning the clutch."
Dang, those were some delicate clutches, as they burned up in just a few laps...and that was with our boys leaving the line rather easily. Maybe that + or - 3 lbs. of unsprung weight on the rear hub might start looking better as time goes on. I will bet that the Rivera clutch would last a lot longer than that, but it doesn't slip without pressure on the lever  ! |
Jimidan
| | Posted on Thursday, March 23, 2006 - 09:42 pm: |
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Jackbequick sez:
"I'm don't understand why that happens. Is there a mandatory need to slip the clutch regularly on the XBRRs?
I'm used to thinking of a clutch as something like an on/off switch. You let go of the lever and it is engaged. The riders job is to match the RPM, stay off the throttle until it is engaged, or generally do whatever is necessary to use it right. Which should include not slipping it excessively, no?"
I am not a racerboy either, but I have been taught by some. When you launch a bike in a drag race manner, it is all about the clutch. Like Sparky said, you feather the power out to just prevent wheelying, but not by much. It is not an on/off switch. You don't spin the tire either, so to keep the revs (power) up, you must slip the clutch.
Once launched, the rider then feathers the clutch in and out to make the transitions of shifting as smooth as possible. You are right that you want to match the rpms. The last thing the rider wants to do is be herky-jerky with shifts as it upsets the bike.
I rode on the back of Jason Pridmore at his Star School and he was so smooth in shifting and braking that it was unbelievable. The best riders are the smoothest riders...then speed just comes to them.
jd |
Jackbequick
| | Posted on Thursday, March 23, 2006 - 10:14 pm: |
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Okay, thanks for the answers. I'm not arguing about how they're doing it, I'm just not used to thinking of feathering the clutch as the way to control power at the rear wheel.
I guess with better tires, more traction, and better clutches, the control of power delivery would have to be different.
Jack |
Anonymous
| | Posted on Thursday, March 23, 2006 - 10:53 pm: |
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Jimi,
Not to be confrontational, but are you being so?
"Dang, those were some delicate clutches, as they burned up in just a few laps...and that was with our boys leaving the line rather easily. Maybe that + or - 3 lbs. of unsprung weight on the rear hub might start looking better as time goes on. I will bet that the Rivera clutch would last a lot longer than that, but it doesn't slip without pressure on the lever !"
Now, this is a mixing of issues. The guys left the line with an easy launch so they wouldn't burn the clutch. The reason for this is because at Daytona when geared for 175 mph, the tall first gear (remember, it's only a five speed) goes to about 90 mph. So when the guys earlier in the week tried to clutch their way to a drag strip start (the way you describe in another post)they smoked the clutches. So they launched gently, and none of the clutches burnt out after the easy launch. The hubs broke, and not the cush drive system. Totally different problem.
Bikes with cush drive rear wheels chatter under braking, too, especially with no slipper clutch.
BTW, if you think Jason is smooth, you oughta see Jeremy. |
Anonymous
| | Posted on Thursday, March 23, 2006 - 11:12 pm: |
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Jimi,
One more thing on the cush drive. It really does add a lot of weight, three pounds on the design that we looked at. The old Buell designs like Court showed you were an attempt to make a light system, but were not very durable at all. So what makes up the weight? Well, I'll try to describe it in words, although an exploded drawing would be better. Basically to have a durable high quality cush drive, you need to do the following: Basically you make a complete wheel, with bearings on both sides, just like a non cush drive wheel. But instead of having a flat shear plate hub area with additional material just where the five or so tapped holes that the sprocket bolts to, instead you have an area in the wheel that has a bunch of webs on top of the shear plate that the cushions push against, and an additional cylindrical extensions that enclose the cushions top and bottom. Then you add five or six large rubber cushions into the webbed cavities. Now you have to make an additional part. This part is a casting that carries another bearing, has the mount holes for the sprocket, and on the back side has matching webs that insert into the rubber cushions.
Whew. Anyhow, it really does add significant weight. Which brings us back to the question, why did the clutch hubs break? Well, we are working on that, but it won't be a cush drive rear wheel that will fix it, nor will it be different clutch plate material. When you break parts in a couple of laps that in other tests have gone hundreds of miles with no issues, it takes a lot of analysis to figure out what could be wrong.
And you can bet your butt neither this problem nor any of the other Daytona problems will surface again. |
Davegess
| | Posted on Thursday, March 23, 2006 - 11:12 pm: |
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At Daytona bikes are geared very high and it is tough to balance a good start with good clutch life. You need that clutch for 4 starts unlike anywhere else.
I think the riders were overly conservative on the start of the 200 being aware that they had been too aggressive in earlier races and being very aware of not killing the bike on lap one. |
Davegess
| | Posted on Thursday, March 23, 2006 - 11:26 pm: |
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Looks lke, while I pur my daughter to bed the boss gave a better expanantion of why clutches are an issue at Daytona than I did.
BTW I have to agreee that Jeremy was amazing. Watching him and tracking his lap times over the week does make it clear that AMA racing is clearly minor league stuff compared to MotoGP or World Superbike. |
Loki
| | Posted on Friday, March 24, 2006 - 01:19 am: |
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I need to make a call, er email.
Those pesky little drive cushions on my RS are all sorts of shriveled up and looking really hard. Kinda thinking all the extra play is not so good an idea. |
Crusty
| | Posted on Friday, March 24, 2006 - 05:08 am: |
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And you can bet your butt neither this problem nor any of the other Daytona problems will surface again.
THAT I can believe. I'm eagerly awaiting the next race. |
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