Clutch slippage in a race application.

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Jul 13, 2009
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East Lansing, Michigan
I am a member of a collegiate racing team where we design and build a formula style race car. Our power plant for our car is a Honda 600 F4i, that's why I'm posting this question here. Our problems began when during testing our clutch began slipping quite a bit under moderate throttle. We pulled the engine and went to change out the clutch pack, expecting to have to replace a toasted clutch. To our surprise the plates looked fine, minimal wear, only one plate showed even the slightest sign of overheating/discoloring. This raised a question, what was causing our slippage? At the time of the testing we were using Castrol Syntec 10w-40 which we've run for a couple of years without any issue. It seems a little unlikely but could the frictionless modifiers have been our issue? Our intake is restricted to a 10mm opening, so our little F4i is only cranking out 80hp. Which leads to part two of my question. After speaking to a Castrol rep we switched our oil to Rotella 5w-40 but I'm not convinced this is the best choice for our car. It spends most of it's races in the upper range of the rpm somewhere between 9k and 12k and isn't exactly the typical "motorcycle" application that this engine was designed for. In addition to a dry sump our car is also outfitted with an oil cooler, even with that we've seen some very high oil temps, (220+), but that's not typical. I just want to hear your guys' opinions on what kind of oil would be best suited for our application. Any information would be great, thanks!
 
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Interesting application you have there. Did you guys check the spring tension on the clutch springs? Maybe you have a spring(s) loosing tension. As far as the oil goes, I'm sure you're going to get the dutifull song proclaiming the Rotella you're using is the best for your application, happens all the time around here. I'd like you to take a look at Maxima 530RR, here , or one of the other(thicker) Maxima products. Stay with the ester synthetics and you're engine will love you for it. Good luck with your race season.
 
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Does the clutch slip with the Rotella? I assume it does not, but that you don't know if it's the new clutch plates or the oil. And I can't tell you either. The Rotella is good oil, I'm not sure why you don't think it's a good fit for your application, or why Syntec would be any better. 220 degrees is fine. Is running a lighter oil for performance out of the question? If you're getting a new engine every year or two, why not ring out all the performance you can get?
 
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If possible get some Barnett springs or shim the stock springs if you can't replace the clutch.(Barnetts should be about 10% stiffer than stock) I'd look for a thin 40wt or a 30wt that is Jaso MA2 rated(higher clutch spec) 220deg is fine 9,000-12,000 rpms is fine and FUN!!
 
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+1 on checking the clutch springs, my old dirtbike just needed those replaced and the clutch quit slipping. What's your final drive like? Maybe 1st is so tall you are overheating it launching or your driver is slipping the clutch on the shifts a bit? I'd think the rotella 5W40 is fine for you, its made for turbo diesels which requires some pretty good additives to prevent foaming problems. I run the old 0W40 in my atv which seems to be fine, I have not had the oil analyzed though. Like ccdhowell says though there are better oils for your extreme use but is the extra money going to matter for your amount of usage? 20 hours even?
 
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 Originally Posted By: bepperb
Does the clutch slip with the Rotella? I assume it does not, but that you don't know if it's the new clutch plates or the oil. And I can't tell you either. The Rotella is good oil, I'm not sure why you don't think it's a good fit for your application, or why Syntec would be any better. 220 degrees is fine. Is running a lighter oil for performance out of the question? If you're getting a new engine every year or two, why not ring out all the performance you can get?
You aren't running a lot of power for that engine and 220F oil temp is downright cool for a 4 cyl 600cc MC engine. You should consider an xW-30 weight formulated for wet clutch motorcycles. It only takes about 15F to thing an oil the equivalent of one SAE grade, so at 220F, a 30 weight would be about the viscosity of a 40 weight at 245F which is a reasonable temperature for a 600cc 4 banger MC engine. You can also go to stiffer clutch springs to avoid slippage, but stay away from oils with high CAFE mystery friction reducing formulations.
 

Number2

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The clutch hasn't slipped with Rotella, but it hasn't been through any real testing since we made the change. Just some fooling around to make sure that everything was in good working condition after dropping the engine back in. There is a little question about the clutch plates being new but they were cleaned off with acetone b/f being used. The springs should have been torqued down to spec, but there is always the chance of a human error in reassembly. They only take 9ft/lbs of torque though and none seemed loose when we disassembled. No oil is out of the question. I guess I should clarify about my earlier post too, I don't think Rotella is a bad oil. I just want to make sure that we're using the best possible oil for our situation. The shifting is pneumatic with an ignition cut on the upshift, so no chance of a driver slipping the clutch. I don't know the gear ratios right off the top of my head, but I do know that first is a little steep. However I don't think that its over the top especially with our restricted Hp. Granted our launches are a lot more aggressive than you would have with a bike since we don't have to worry about lifting the front end. But as I recall the clutch was still slipping in 2nd gear when accelerating out of corners.
 
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How does the weight of the car compare to the weight of the original motorcycle? I'm thinking it's significantly higher... If so it's not surprising for the clutch to slip in the lower gears. That original clutch was designed for the torque handling requirements imposed by the mass of the bike. You should need a stronger clutch if the same engine is trying to accelerate a heavier vehicle... Could be just stronger clutch springs will do it, or maybe the bike clutch isn't man enough for its new job? It's torque, not horsepower, that is the issue...
 
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On my dirt bike you checked the clutch springs by measuring their free length, but your clutch maybe different. I am always amazed that a simple ignition cut lets a tranny survive upshifts without the clutch, especially that your car has so much more traction and rotating mass at the axle. I guess making the final drive a higher ratio(bigger rear sprocket) should help the clutch off the starts, do you ever get courses fast enough to use the upper gears now?
 

Number2

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The car weighs a little over 400lbs. I've got to be honest I don't know the original weight of a Honda 600 but yeah I would say it's very safe to assume it's less. You're right it is the torque that's the issue, I don't remember off the top of my head what the peak torque was, we haven't dyno'd it in a while and the numbers escape me. We modify the shifting barrel and I believe remove the fork for 5th and 6th gears since we never use them during our races. The only time we ever see 4th is during one of the straight acceleration runs most of what we do is either skidpad or more of an autocross type race so average speed is much lower. The ignition cut is quite impressive, I agree. When we first enacted our pneumatic shifting system we had the car shifting so fast the driver couldn't feel the shift, so he would inadvertantly hit the paddle again thinking it hadn't shifted in the first place and wind up in the wrong gear. We wound up having to program a split second delay so that he could feel and register the shift. If you want to check it out our website is http://www.msuformularacing.com unfortunately it hasn't been updated in a little while so it seems a little stale, but there should be some of the most recent updates in the blog and the forum for anyone who's interested.
 
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A carbon fibre monocoque is impressive too as getting a car as light as the bike is quite the accomplishment. I worked a little bit on the University of Waterloo SAE car when I was there in my first year, but then I switched schools. I made the rad guards! That was a while ago but I think the tube frame car was more like 600+lbs. The car was turbo charged though if I remember correctly... Anyways, good luck with your clutch issue, I checked the waterloo site and they remove 1st gear too so maybe their steeper final drive reduces the strain on the clutch in the rest of the gears?
 

Number2

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Yeah, the carbon fiber chassis should lighten the car about 40lbs less than the tube frame, and stiffen the whole chassis both laterally and horizontally. We don't run a turbo on our car, the problem with that is that the turbo intake has to be behind the 10mm intake (per SAE regulations), so the gain would be minimal since we would still be breathing through a straw, plus then our exhaust would have to be routed near the intake, not to mention the added weight of the turbo. There's talk of sometime in the next year or two making the switch to a V-Twin and supercharge that. That would allow us to run a higher octane fuel as well. It would be much easier to tune the V-twin to a new fuel, as opposed to the F4i.
 
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Did you always run the syntec on the same honda Honda sport motorcycles are the only sport bikes ive heard of rejecting non mc oil, rotella to be exact.... were these newer bottles of syntec?
 
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My buddy had a similar issue running car oil in the GSX-R600. While it did not say energy conserving on the label as that is a rad flag for clutch slippage issue the oil still caused clutch slip coming out of corners at higher RPM under load. The clutch was setup spot on so we narrowed it down to the oil. He ended up running ester based Motul motorcycle oil and the problem went away. I run Amsoil or Maxima motorcycle oil in my track bikes and so far no issues.
 
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springs, they are chosen by the factory to be as light as possible for the the vehicle weight gearing and load etc. Keeps the pull at the lever lighter. Aslo be sure your running some freeplay in the cable, or if hydralic a line isn't too close to a heat source. I'd get the heaviest spring you can find, you don't even have to run all six, you could run 2 , 3 or 4 as long as you keep them symetrical in the basket. If you try and shim your stockers spark plug gaskets are an old trick.
 
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