| Author | Message | ||
     Hybridmomentspass |
So I recall reading on here that on the 1125R (and assuming the CR) the 'shift light'/needle glowing brighter comes on early while in neutral/clutch in due to valve float, that its not good to rev to the moon in neutral on the bike. This is something I remember stated on here a decade ago. But today I thought about it more as I had to deal with the noise pollution which was a GSXR rider acting like an A hole and just bouncing off the revlimiter while looking at my bike. For, like, 10 seconds. Does this do no damage after repeated times? Was false information stated on here regarding the early rev warning on the 1125? I really wanted to see this little piss ant pop his motor right then and there. Seen him around town a few times, hes the squid who I once saw riding with NO SHOES. Not even flip flops...NOTHING. He sits at lights in town and just revs and annoys everyone. | ||
| Torquehd |
It's hard on everything that moves reciprocally (is that a word?) and on crank bearings. Just like releasing a bow string with no arrow, or punching hard and just hitting air, or dry-firing certain guns. Without any load to transfer the power to, all of that kinetic energy goes into the limbs of the bow, or your elbow, or into everything that goes up and down in the motor. | ||
| Sifo |
I've never understood how the valve train could possibly "know" if the engine is under load or not. I can see where the bottom end would experience some different stresses loaded vs. unloaded, but loaded seems to be far worse IMO. It's nothing like dry firing a bow, where the arrow greatly reduces the speed at which the bow will flex, kind of like a load limiting RPM. But we have RPM limiters on our newer computer controlled engines. I would guess that this "knowledge" is a carry over from when it was easy to over rev an engine when not under load. IMO, things have changed. | ||
| Torquehd |
That's what I was taught at MMI back in 2002/2003. Maybe the teacher was wrong and I've been wrong all this time. But it makes sense to me. | ||
| Nillaice |
maybe the loaded combustion/compression helps close the valves faster than just the springs alone? or keeps them from bouncing? it also might be a rate of change thing with valve train lash/timing being the concern. i know the fastest way to find out.... any body want to donate a crate engine in the name of knowledge? | ||
| Aesquire |
Without load, the accelerating engine can easily rev well over red line. The valve train is always under a variable but limited range of load, independent of crank loading, so it's simply revving very high that's an issue. The no load issues are with cranks & connecting rods. The probability of zooming up to higher than red line revs will affect the valve train, but be aware of cause & effect. As to loaded stresses being worse? Not necessarily. Pure logic says yes, but piston pin offset and planned side loads on piston skirts are different with a much smaller load. That might not apply to any given engine. Over revving with the clutch pulled in or in neutral, OTOH, that's real pretty much across the board. | ||
| Aesquire |
True anecdote. A guy right down the street bought a Honda V-65 Magna. The 500's had crank issues, rather famously a bike magazine broke 2 in a row. "Solved" by hand picking bearings to perfectly match each journal. But the whole line was marginal on the cranks. This Yahoo ride the bike home from the dealer, about 15 miles, and went to do a burn out in front of his house. Broke the crank and embedded a rod into the asphalt in a puddle of oil & shattered Aluminum. Feel free to snicker. | ||
| Sifo |
So if no load is bad, it must be really bad to roll off the throttle for a corner at race speed. Yes? True that side loads on pistons will be different with low loads. It will be much less. They built it to take the side load under power, but with no load, it simply won't have the same side load. It will be fine. I'm certainly not saying running against the limiter is good for anything. It's hard on an engine, loaded or not. Stress eventually takes it's toll. I've seen an old chevy 350 run in neutral with a brick on the accelerator just to watch it splode. Patience ran out, and the float of the hydraulic lifters prevented the hoped for dramatic effect. No doubt you would eventually see valve train failure doing this, but things are typically over built to the point of it taking a lot of time. Over shooting the red line with no load? Might be a problem depending on the lag involved in sensing RPM and the chosen means of cutting power. That would be momentary though, and similar to a missed shift. Is that the problem it once was? We are talking stock engines (or reasonably close to stock) I presume. There's a lot of safety margin in most engines. I'm still back to the valve train not knowing load. Wrist pins change direction of pistons regardless of load. Adding load after that direction change shouldn't reduce stress. Adding load prior to direction change would be pre-ignition, but that's off topic. Certainly the bearings are happier at low loads. I'd like to hear exactly what is getting hurt with no load. Again, going down the straight away, is it normal to pull the clutch as you slow for the corner to prevent engine damage? | ||
| Fast1075 |
There is less cylinder pressure with no load. Cylinder pressure helps load the valve train. Even more so with power adders like supercharging or nitrous. In pure terms, "valve float" is when the valve train loses control of the valve. Many factors involved. Cam lift, profile, valve train component weight, tuning of the valve springs. When Honda first came out with the CB/CL,SL 100 engine, they were sucking intake valves left and right. Straight wound single valve spring. The little engines could turn over 12K rpm. High order harmonics causes the valve spring to lose tension at high rpm. Honda fixed the problem by going to a progressively wound spring and adding a damper spring. Get a Ducati, they can rev to mechanical failure because the valves cannot "float". As far as the 1125/1190 motors go. I saw 11 of them die at Daytona in one weekend from "valve float" even with titanium valves and the best springs available. Danny Eslick came as close as you can get from destruction without a valve actually breaking. He revved it high enough for the retainers to kill the guide seals, and got black flagged for the resulting exhaust smoke. | ||
| Torquehd |
Desmo valvetrains are a cool idea but I have no experience with them. I wish other manufacturers used them. | ||
| Aesquire |
Mechanically complex and thus more expensive. But I'd rather sit down with feeler guages and little wrenches than be swapping shims. The GS750 & GS1000 Suzukis used shim over bucket valve adjustments. I have the tool to depress the bucket to change shims. ( like small hockey pucks ) Downside is valve float can spit a shim through the valve cover casting. Happened to a buddy racing his GS1000. Kawasaki used shim under bucket, which could not spit shims, but you had to remove the cams and valve buckets to change shims, a Lot more work. Lot More. My GS1100 used screw adjusters, and I have an old Mikuni carb tool that made it a breeze. It's a box end wrench with a captive screw driver, so stubby it's just a knurled knob with a flat head protrusion. You dial the clearance with the knob, then hold the knob while you tighten the lock nut. Easy. Desmo Ducati has twice the adjusters. Once you learn the tricks, mostly eliminating lash in the train, it's just fiddly, but not hard. If you can't get zen and patient on that kind of work, get someone who can. | ||
| Aesquire |
Cylinder pressure load the valve train? Not as much as you'd think, except the tiny fraction of a second just before it closes all the way & the same as it un-seats. Sudden reversals on the drive line and engine can be huge stress. Pounds per second, per second, rate of change. Some load directions are reversed, others are not, peaks get erratic. I USED to be able to quote the math of Davis Mechanics, but haven't used it this century. http://www.halexandria.org/dward137.htm Ignore the "connective physics" bits if you like, that's verging on hippie stoner territory, or Tao of Pooh. Not "wrong" per se, but unconventional. The "stardriver" link is about a novel, unfortunately. But the REAL physics behind it is TODAY finally being put into hardware experimental form, with the EM drive. And remarkable how close the hardware is. The Davis Mechanics part, though, that is more real than quantum physics. Originally developed to explain anomalies in felt production, it's useful in valve spring bounce analysis, etc. Yeah..... Rev limiters to Cosmic Fundamentals. Ain't Science Great? | ||
| Crusty |
Desmo valvetrains are a cool idea but I have no experience with them. I wish other manufacturers used them. Mechanically complex and thus more expensive. Desmodromic valve actuation was inspired by a fan of Rube Goldberg, IMO. It may have been a good idea before improved valve spring metallurgy caught up with the idea of making a sh*tload more parts do the job a simple coil spring can do. Back when Troy Corser and Colin Edwards were beating on each other for the WSBK championship, both the Honda and the Duck were very evenly matched, showing that there really isn't any tangible evidence that a desmo valve train is any more efficient. It's just more complex and has lots more parts that can break and cost you a fortune. Harley has to build a pushrod V-twin and Ducati has to build a Desmo. As far as street bikes go, I really like hydraulic lifters. I never had to adjust a valve in 240,000 miles on my Buells or in 330,000 miles on my Harleys. | ||
| Aesquire |
I have the original 1962 publication of "The Fourth Law of Physics" by David & Stine, but didn't read it until 1974, and didn't use it until...um. '82? "hit it with a bigger hammer, faster". Which worked. (Message edited by aesquire on June 16, 2018) | ||
| Natexlh1000 |
+900000 on the hydraulic lifters. Why in the 21st century won't the Japanese accept that they work? I understand if it's revving past 8000 but in this day and age, why no civic or corolla has modern lifters? | ||
| Ourdee |
I actually like adjusting the valves on my Yamyhaul. | ||
| Fast1075 |
The exhaust valve particularly is beginning to open while there is a lot of cylinder pressure left except maybe on a tractor motor. This pressure adds slightly to spring pressure. If load does not change cylinder pressure, try this. Adjust the waste gate on your turbo by revving the engine with no load. Then run it under full throttle, full load. If you don't lift a head, it's a miracle. The motor cannot build full cylinder pressure without load. Add a heavy nitrous load and you are likely to bend pushrods or break rockers for the same reason. The reason the morons that rev the sport bikes to the moon and (mostly) get away with it, is the valvetrain is very light, the springs are very good, and the rev limiter keeps the valvesprings out of second order harmonics. | ||
| Rick_a |
All other things being equal, internal engine stress is proportional to the square of RPM. Of course there's many variables. The downside to self adjusting hydraulic devices is typically RPM limitations, weight, and complexity. The shim under bucket, DOHC has been the defacto option for performance applications for years due to simplicity, reliability, and low mass in reciprocating valve components. The desmo drives only suffer from complexity, cost, higher maintenance requirements, and more difficult maintenance. But, yeah...the people that rev the crap out of their engines as a form of douche to douche communication and to hear their own screaming engines are not cool. If you find internal combustion engines blowing up satisfying... https://www.youtube.com/watch?v=QTLqmSGwkcM | ||
| Crusty |
The desmo drives only suffer from complexity, cost, higher maintenance requirements, and more difficult maintenance. Yeah. Only. | ||
| Rick_a |
Totally depends on the purpose. Everything is a compromise. Some sporty bikes, particularly from Yamaha, have 24k valve adjustment intervals. They sacrifice some engine speed for a more street biased power delivery. The cams have to come out to make those adjustments, but that's the price people are willing to pay. Oddly enough, most people tend to sell their sportbikes at the first major service interval, if it lasts that long. |
