| Author | Message | ||
     Manufromparis |
Hello everybody, I've been reading the badweb but did not find a topic about hypothesis for this premature worn on oil pump drive gear. Maybe I haven't search enough... (please read my recent post in "guest-book") Recently I met this guy who rides tube framed Buells on race-tracks, not for competition but for fun. As everyone, he noticed excessive and premature worn of his "oil pump drive gear" and have an interesting theory : He thinks the main reason for unexpected worn is due to the oil pump that is backed-off at high RPM because the pressure that the oil pump puts in the oiling system can't be evacuated fast enough. An other way of saying it is : the oil route through engine is too small to drive that much oil at high RPM. Then, he thinks the pump is slowed because of excessive pressure. Then, he thinks the pump gear "brakes" on the Drive Gear, causing the worn (and in a way, slowing the engine...) As everyone, he's experiencing regular Drive Gear excessive worn when using his bike on tracks, even with the bronze oil pump drive gear that replaced the previous "chewing-gum" (usual) one. When I heard that theory for the first time, I said to myself : it can't be ! We all are worrying that not enough oil goes in the engine routes to lubricates cams, rockers, flywheel, and so on... And this guy says that there is too much oil pressure !!! But, thinking about it, I thought it made sens : those sportster engines were designed for a gentle use, not the high-level performance we're used to with those crazy Buell-prepared engines. It means HD designed the oil routes for a certain oil pressure, when engine is used at "normal" RPM, under "normal" conditions. And probably not under racing conditions... (even though the Sportster have "sport" in it's name...) I don't know the figures, but I'm pretty sure the "standard-high" oil pressure at high RPM is reached pretty early (around 3 or 4000 rpm, maybe even earlier), meaning when the engine goes faster, the pressure rises. Anyway, the interesting part is here : Then, he tried to lower the pressure at high RPM, introducing a "pressure-valve" between pump and filter (like when adding an external oil cooling system), and re-routing excessive oil in crankcase, letting the Oil Pump send it back to the oil tank with standard features. Since he added this "pressure-valve", his Drive Gears doesn't get worn earlier than the rest of gears... which, in a way, confirmed his earlier theory ! Again, I don't know the pressure-figures he used to set this valve, but I guess he used the high-pressure he noticed around 3-4000 RPM. I'll try to ask him next time I see him. I think it is a very "brave" adjustment for a race-oriented-engine and I would be very anxious adding it on my bike, but we don't have the same use, so his "adjustment" doesn't concern "standard users" as much as racers... Anyway, I wanted to share this experience and get your feedback. Have fun and ride safe ! | ||
| Blake |
So he's basically saying that at high rpm the load on the gears is excessive and causes the lubricating film to break down thus allowing metal to metal contact and excessive wear. That does seem like a valid concern. Not sure if it will bear out in all cases. A lower viscosity oil would also reduce oil pumping pressure. Hal's used to run a W30 grade synthetic in their ProThunder racing machines. They also ran a different oil pump too. Excessive shaft runout may also be a valid concern. | ||
| Reepicheep |
WhiteBuell (I think) had a pretty convincing hypothesis and some very good empirical evidence that the problem was a tolerance stack problem. That seems backed up by the fact that some bikes eat them, some don't, and how hard they are ridden didn't seem to correlate. He took a gear eating bike, found a tolerance problem, machined his oil pump to fix it, hardened a stock gear, and ran it for a while with no evidence of wear. It was enough to convince me... He posted here with pictures, do a search for him... | ||
| Aptbldr |
Similar excessive wear issues would seem likely at cold start/rev-it-up, too. No relief valve when oil pump relocated on XB's? FWIW, other four-stroke motorcycles in my garage do have oil-pressure relief valves. | ||
| Bigdaddy |
Reepi, and Whitebuell by proxy, are correct. When the oil pump design was finalized the tolerances were set for a 'tractor engine' putting down 55 hp...tight tolerances were not really a requirement. As the folks at Buell squeezed more performance from the antiquated (I still love my tuber FWIW) ICE the associated parts didn't evolve in parallel. If you were to take one that is eating gears and your micrometer you'd find that the setup that is eating gears is measurably off from a setup that leaves the gear in pristine condition. | ||
| Kalali |
How difficult is it to do a visual inspection to to rule out or confirm a gear eater beast? | ||
| Manufromparis |
Reepicheep : I also heard (or read) about this theory but never found a mesurement method to ckeck if, yes or no, a specific bike is a "gear-eater". Nevertheless, adding this guy's oil-pressure relief valve seems to be a good option, if the bike he put it on was indeed a gear-eater, which remains to be confirmed. I'll ask that too. Thanx for your answers anyway.  | ||
| Manufromparis |
kalali : the easier way is to take the oil-pump off, during an oil-change service. Then you can see (and touch) the gear's teeth. | ||
| Jramsey |
Easy as draining the oil,disconnecting the oil lines and removing 2 bolts and dropping the oil pump. Inspect the driven gear on the pump for wear then use a small flashlight and look up through the hole where the pump mounts to check the drive"worm" gear. New gasket runs about $1.50 | ||
| Reepicheep |
I think you have to drop the exhaust can on an XB as well, but c'mon, we both know you need to paint it anyway.  Make sure you check it, rotate the engine and check it again a few times. The bad wear is often asymmetrical. | ||
| Court |
>>>>The bad wear is often asymmetrical. In addition, it occurs differently about the perimeter of the gear.  | ||
| Reepicheep |
Another data point.... Having seen this thing worn on my M2 and replacing it, I have been watching it on my XB9SX. 30k miles, ridden normally (moderate aggressive street use), two track days. On the 2000 M2, at about 22k miles, I replaced the gear. A few of the teeth were getting pretty thin, but nowhere near knife edged. The thinnest point of the thinnest gear was still probably 1mm, which is about half gone at the ridge. Enough to replace it for sure. At 10k miles on the 9sx, I dropped the oil pump, and did see wear, but not a lot. Now, at about 30k miles, I dropped the pump again and saw enough wear that I wouldn't be comfortable selling the bike to a friend, and I had a new oil pump and new style gear on the shelf, so I decided to just replace it. Now that I have it apart, I don't think the gear is much more worn then it was at 10k, and I suspect the gear would easily go another 20k miles before getting really scary (for a 50k motor). So the XB's seem to have really made a lot of progress on the issue. Oh well, whoever buys my 9sx will get a bike good to go to 100k on the motor. Of if nobody offers enough for it, I'll have two bikes that'll go to 100k miles. I'll post comparison pictures later. And boy, is that new style gear a nice looking part... Makes me want to frame it. |
