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SuzukiSavage.com
/cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> Ran across this... /cgi-bin/YaBB.pl?num=1141424405 Message started by 911radioman on 03/03/06 at 14:20:05 |
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Title: Ran across this... Post by 911radioman on 03/03/06 at 14:20:05 This was copied from another forum with a theory on the engine failures talked about here recently. I figured it would be good for much banter... :D ______________________________ Hi. This Mr. CrankyPants come to talk to you about engine failure and our tendency to monkey see, monkey do. I notice that on this group, and others, there is a typical American idea that any guy with a screwdriver is a better designer than a bunch of highly paid Japanese engineers, despite the fact that these engineers can design a 190 mph 12,000 rpm crotch rocket and race it internationally. Actually, the LS650 isn't that conservative a design. It's pushing the limits of large single rpm and horsepower output for a production bike. Little cylinders can put out inherently more horsepower, because you can spin them faster, because their parts are little and easy to reverse. The flamefront ignited by the spark plug has to travel all the way across the monster piston bore to burn instead of explode. To minimize this, the spark plug should be in the middle. This flame front speed limits the rpm also, because the time to do the job at high rpm gets smaller than the time needed to propagate the flame. In a big single, you can get shock wave explosions from hot spots, also, especially if there are carbon deposits from running too rich. More later on rich. The Savage is carbureted, not fuel injected. This gives rich and lean spots in the compression space because the carburetion stops and starts, and there isn't enough length in the manifold to thoroughly mix the droplets and let them vaporize. More uneven burning. In any lean burn area, the temperature rises. The engine is already running lean due to smog regulations, and backfiring. So the would-be motorcycle engineer decides to solve this lean burn problem with a 152.5 main jet, which brute force floods the cylinder with raw unburned gasoline, which is an excellent oil solvent, which removes the oil film on the top piston rings. This causes scuffing and perhaps even deposition of piston aluminum on the cylinder walls which generates a lot of friction, which overloads the connecting rod big end bearing, which fails, overheating the conrod, which breaks and goes through the case. (Big end bearings tend to flash out the oil due to high linear speeds between the big piston pin and the bearing surface on the conrod. But you need a big bearing because that big piston and rod generate relatively large riciprocating forces that require large bearing surface. More limitation on rpm and thus horsepower. All of this just to get that lovely thump.) This ain't rocket science, but if you don't know this, and many other things, you are asking for trouble dropping a low-back pressure (loud) muffler on the bike, which makes it run lean at some rpm and rich at others. I have no doubt those engineers sweated blood designing this sweet-running big single, getting the spark advance curve right, the carburetion smooth and powerful, and the clearances just right. Then we go at it with our limited engineering knowledge, and convince each other that anything that anyone else has done must be OK because the bike hasn't blown up yet. I'm sure this sounds awful conceited and arrogant. My apologies, but I've run hundreds of thousands of miles on stock BMW's including the 250cc single, British, Japanese and Italian bikes. I've only driven a Harley 250 cc Sprint, which is Italian, and an FLH brand new, for about fifty miles, which was long enough. I know in my bones, from years of reading technical design manuals and talking to dozens of shop managers that if an engine fails, the first question is "Was it modified by the owner?" People just don't seem to understand how exquisite a balance of design features must be maintained to get performance AND reliability in any aircooled engine. Tinker at your own risk. You might not blow it up. Ten for fifteen thousand miles is just about the right failure point for a miscarbureted big single. BSA Gold Star, Matchless GS80 and 600 Typhoon, all easy to blow up by carb and muffler tinkering. Things that make you go fast and make noise decrease reliability. Have a nice ride. The Savage is already a VERY nice bike with a hard seat. Change the seat. Change the handlebars. Add saddlebags and GPS devices. Get an iPod. Goop up the squeaky speedometer. Don't overload the alternator. Leave the carburetion and the exhaust stock. Don't be greedy. The fairy tales are right. Ormond Otvos Richmond California FSU Physics, 1961. Do the math. |
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Title: Re: Ran across this... Post by torque on 03/03/06 at 14:27:47 makes perfect sense to me. |
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Title: Re: Ran across this... Post by 911radioman on 03/03/06 at 14:28:07 So, what do you guys think? Food for thought, or blowing smoke? It was an interesting read, but I want more opinions on his theories... |
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Title: Re: Ran across this... Post by pgolden on 03/03/06 at 14:39:53 That's his opinion, and we all know what opinions are like! |
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Title: Re: Ran across this... Post by Dynobob on 03/03/06 at 15:18:31 911radioman wrote:
Total nonsense. A bike that's jetted correctly or on the rich side will last longer and run cooler than a stock bike that's jetted too lean due to EPA regulations. The rod failures had nothing to do with either a free flowing muffler or rich jetting. When I get more time I'll disect this guys rambling post. |
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Title: Re: Ran across this... Post by Paladin on 03/03/06 at 15:22:45 Whenever someone blathers on about a subject I want to know what makes him an authority to be listened to. This gentleman is an old fart who rides stock bikes. Lancer rides a test bed. I'll take Lancer as an authority as to modifying the carb/exhaust over some yahoo that writes: People just don't seem to understand how exquisite a balance of design features must be maintained to get performance AND reliability in any aircooled engine. *SIGH* Millions of modified Air-Cooled VWs that have been pushed past any reasonable limit prove that statement to be stupid at best. Which also places exactly how much of an authority he is. My Jack Russel is an equivalent authority. |
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Title: Re: Ran across this... Post by PerrydaSavage on 03/03/06 at 15:22:57 I know diddley about the engineering of internal combustion engines ... but I must say this eases my mind a bit after all of the horror stories of LS engine failure of late .... |
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Title: Re: Ran across this... Post by 911radioman on 03/03/06 at 15:24:53 Here's my take on it thus far... I can understand what he is saying about the fuel mitigating the effect of the oil and causing a lubrication issue -- IF the proper steps are not taken (i.e. - proper rejetting, balancing of air/fuel supply, etc.). Now, what I've learned in my crash course on carburetion is this. It is a two sided affair, what you do to one you have to do to the other. If you rejet, you have to adjust your air intake accordingly to maintain balance. From what I understand from you guys here, it appears that the 1/2 spacer mod, pilot screw enrichment, 152.5 main jet, coupled with a free flowing exhaust and a high flow air filter makes this a balanced tuning. If one were to do the muffler and nothing else, then a lean condition exists. If one were to do the muffler, spacer and rejet but nothing else, then a rich condition exists. I'm really hoping this all prompts an honest (not flaming) discussion based on what this guy wrote, because to me it stresses the need to balance the entire system. Granted, most here know this, but new folks (myself included), didn't know all of this coming in and it could save them engine problems down the road. I see a few merits in what he says, but then again, I see failures to identify the proper ways of tuning, which we all know exist. The Savage probably is pushing the envelope of big displacement, single cylinder engines. BUT, virtually any bike out there has rejet kits and exhaust systems waiting on them. Given this guys premise, this should be an all-encompassing problem on any motorcycle, not just a thumper, the way I see it. |
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Title: Re: Ran across this... Post by 911radioman on 03/03/06 at 15:28:47 Good replies so far! This is what I was hoping to get, was for everybody to just cut loose and let's get the world of knowledge that I know is out there going on this thing. :) |
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Title: Re: Ran across this... Post by 911radioman on 03/03/06 at 15:29:40 Dynobob wrote:
And that squares with everything I've ever read or been told too. It is far better on the engine to run it rich than to run it lean. |
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Title: Re: Ran across this... Post by 911radioman on 03/03/06 at 15:33:26 torque wrote:
I guess my question would be what makes sense? Here is where my quandry lies in this thing -- if this IS true, then why isn't every bike out there that has been rejetted and aftermarket exhausts applied having this problem? Carburetion is carburetion (the way I see it), and it shouldn't matter if it is a thumper or a twin, if what he is advancing is true, then there is a scad of bikes waiting to throw rods and everything else. I might could see his point if the bike wasn't rejetted properly to begin with (for instance, if a 157 was used where a 152.5 was called for), then maybe raw fuel is heading into the oil and mitigating its effectiveness. But I do have trouble seeing where just enough jetting to balance out the free flow of the exhaust could be the culprit here. |
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Title: Re: Ran across this... Post by Paladin on 03/03/06 at 15:36:39 The Savage, while a big single for a motorcycle, is not a big single. The LANZ Bulldog (http://suzukisavage.com/cgi-bin/YaBB.pl?board=cafe;action=display;num=1139236008) has a big TEN LITER single. It is not even large for a motorcycle cylinder as any twin over 1300cc has larger cylinders. |
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Title: Re: Ran across this... Post by Reelthing on 03/03/06 at 15:45:55 There's some meirt to what he says -washing out the cylinder to the extent he describes is a problem - but seems to be anti-tuning - in the end had he insisted we use an exhaust gas analyzer to measure the fuel:air instead of what some consider to be primative - the plug chop - it would have had more - since he spoke to neither.... he likes um stock so he should keep um stock. |
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Title: Re: Ran across this... Post by thehoghunter on 03/03/06 at 16:31:34 Quote:
I would say that makes sense - I don't know what I'm doing but then again, I'm having fun doing it. Quote:
Which must be why they never got around to putting in a tripmeter - and after all that hard work, they had to change it so it would meet EPA standards - what a pity. Quote:
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Title: Re: Ran across this... Post by USCG Cremeans on 03/03/06 at 17:42:27 all i have to ask is this... if these japanese engineers spent years and a lot of effort desiging a perfect "stock" bike.. then why do we all have to fix the plug cap leak... (of course some of this is do to service from mechanics later on in the bikes life) but still... |
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Title: Re: Ran across this... Post by Dynobob on 03/03/06 at 17:56:09 Ok brief and to the point. 1. the Savage engine is very conservative. Low compression, small valves, mild cam timing, low horsepower @ low rpms 2. our rejetting is correct for power, long life, and smooth running - the stock jetting is way too lean. 3. There's no uneven burning, "rich and lean spots", fuel dumping, or excessive oil washing from either the rings or cylinder. 4. adding a "low-back pressure (loud)" muffler on a bike DOES NOT "make it run lean at some rpm and rich at others." Our rejetting regimen corrects all 3 carb circuits and I can assure you my bike is jetted correctly and will last. The reasons for these two engine failures are in no way related to what Mr. Engineer has posted. I've been modifying internal combustion engines for many years. I can assure you that free flowing exhaust and jetting for performance will only increase longevity. |
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Title: Re: Ran across this... Post by Starlifter on 03/03/06 at 21:34:32 Radioman's point is well taken. Any modification that increases power, speed, acceleration, etc. puts increased stress, friction, and heat on internal components. While this rather benign and modest modification will not result in a catostrophic engine failure 99.999 % of the time, it just might explain the two recent engine failures discused here in the forum of late. (Especally if the bike is riden hard and fast.) I have always been leary of making the aforementioned modification, and so far have not done so. It is at the very least something to consider. :-/ |
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Title: Re: Ran across this... Post by bentwheel on 03/03/06 at 21:39:28 911radioman wrote:
That's a wonderful story, but too improbable as to the cause of rod failures. If the raw gas has diminished the lubricity of the cylinder wall causing aluminum microns to be scrubbed from the piston, a more likely result will be particles escaping out the exhaust. Anyways the steel piston rings are the first contact with the cylinder liner and any buildup of the wall causing excessive friction would more likely lead to a piston/ring seizure as opposed to transferring this heat down to the connecting rod in its oil bath. |
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Title: Re: Ran across this... Post by WD on 03/03/06 at 22:10:42 Well, at least it was a mildly amusing read... My bike is probably one of the leanest running on the board. Stock spacer and jetting, modified airbox, and insanely long, low back pressure exhaust. Mainly because I've been entirely too lazy to pull and open up the carb. I have a couple jets, somewhere in the living room. Runs fine. My Vulcan, though liquid cooled, has been insanely modded in the motor dept. Low restriction exhaust. Modified air box. Stage 3 jet kit. Polished intake tracts. An online dyno shows it to make 60 hp at the rear wheel ( I kinda doubt it), stock was 46-48hp at the crank... Pops, snarls, shoots flames, and only turns the fan on in group riding at low speeds. If one of my bikes was gonna blow up from modding the fuel system, it would have done so by now. I'd lay even money that the failed con rods had manufacturing defects. No company can catch every glitch. -WD |
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Title: Re: Ran across this... Post by Jim_R on 03/03/06 at 22:53:04 Its funny how this guy can switch sides of the savage's design in the same breath. I guess his engine design experience is based on riding different motorcycles thousands of miles. Since when has that ever made anyone more qualified to make improvements to a motor? I wonder if he is Japanese? haha First praising the Japanese engineers "is a typical American idea that any guy with a screwdriver is a better designer than a bunch of highly paid Japanese engineers" and inserting his typical American idea to improve this engine that has been designed by highly paid Japanese engineers he praised earlier ;) "The flamefront ignited by the spark plug has to travel all the way across the monster piston bore to burn instead of explode. To minimize this, the spark plug should be in the middle". I am highly doubting this statement too there isn't enough length in the manifold to thoroughly mix the droplets and let them vaporize Im pretty sure if it wasnt vaporizing, it wouldnt be firing. 8) Does a lean stock bike (his preferred savage) have more potential for engine failure than a properly jetted one? I would think over the long term the stock jetted one with a free flowing muffler or k&n air filter would fail sooner than a completely stock bike or a bike with 152.5 and air filter with free flowing exhaust would . I believe this is true because its extra lean condition would make the temp higher as well as other things. Even a stock bike runs extremely hot and in the summer it was almost frighteningly hot sometimes. This ain't rocket science he states. Thank god. I wouldnt let him come anywhere near my rocket ;D He could always be secretly working for the EPA and make up this propaganda hehe. |
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Title: Re: Ran across this... Post by Les on 03/04/06 at 03:14:53 :) Some thoughts- Every carb engine washes the oil every time it runs (That is the nature of a Carb) Plug placement and flame travel are affected by combustin chamber design and inlet-exhaust flow Remove weight from these little bikes. Personally if its to loud you are to old-Les |
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Title: Re: Ran across this... Post by 911radioman on 03/04/06 at 05:37:21 Starlifter wrote:
That is not my point. My point is that if this is the case, why aren't bikes of all cylinder numbers and sizes failing because it is the same principle? Heck, my bike is modified as well. I'm not against these mods, just trying to figure out this guys thinking and wanting to share what he said with the forum here. I'm not in agreement with him on it, save maybe one or two little points. |
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Title: Re: Ran across this... Post by torque on 03/04/06 at 05:41:06 911radioman wrote:
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Title: Re: Ran across this... Post by Ed_L. on 03/04/06 at 07:03:42 I think that one thing that this article didn't address is how much more perfomance is realized by the rejet and exhaust mod. After all we are only talking about a 15 to 20% increase in power, stock at around 30hp, mod at around 35hp. This power increase should be well in the safety limits built into the specs of the connecting rod no matter what they are made of. If the rods are that weak then there would be a lot more failures with nonmodified engines. After all the Savage is consitered an entry level bike and has been detuned for that reason. As to raw gas being introduced into the combustion chamber, well I haven't seem any raw gas being sprayed out of the exhaust which is where it shows up. Also everybody has been reading thier sparkplugs to insure that the fuel/air mixture is correct so the cylinder wall wash down theory really doesn't apply. I'm not going to argue the point that increasing the horsepower of an engine can decrease the overall life of that engine, I've been a firm believer in that for years. It just is a ballance between performance and engine longevity. We are not asking the big single to produce double or tripple the stock horse power, we are only bringing the engine up to power levels that have been shown to be reasonable by other engines of the same basic design. The author seems to have a problem with backyard mechanics who enjoy tinkering but without backyard mechanics we would still be riding horses and buggies. Just my .02 cents |
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Title: Re: Ran across this... Post by lancer on 03/04/06 at 08:16:15 I just spent almost an hour responding to Ormond's statement and when I went to post it the site said it was too long and I lost the whole freaking thing. I am going to have to rest up a bit before trying again. He seems to be a bit short on practical as well as theoretical experience/knowledge of the internal combustion engine. He reads and talks to others but does not mention his HANDS ON experience. He views a stock engine as being in a DELICATE BALANCE and any changes to that would upset the balance and lead to destruction. A lot of what he says is just not valid. He apparantly rides a lot though, and that is good. |
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Title: Re: Ran across this... Post by CHRIS on 03/04/06 at 15:29:14 My opinion is this is: If you don't have the knowledge or a knowlegable friend to help you with the modifications then, NO you should not be doing them. I seen people bringing in there bikes saying "this thing ain't running right" or "it's backfiring to much". You ask them if they did anything to the bike, they say "yeah, I put on a set of drag pipes". Of course when you ask the other obvious questions about jetting and the air/fuel screw they act like they didn't even know the bike had a carb. This guys opnion about leaving the bike stock I think is just his own uneducated opinion. If the modifications you're doing are done right, there should be little or no affect on the reliability of the bike, If fact, eliminating the stock lean mixture alone should improve performance and engine life. |
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