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Engineering/Technical Ask technical questions about cars. Do you know how a car engine works? |
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01-26-2004, 04:58 PM | #46 | |||
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Re: Re: Re: Re: Pushrod vs. SOHC vs. DOHC
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Score: xOHC motors have cam driving mechanisms that require inspection, service and replacement on a frequent basis over the life of the car. OHV motors have cam driving mechanisms that require nothing and last the life of motor. Advantage OHV as originally stated. These "frequent" replacements of the timing belt that you keep harping on still amount to a single replacement in the entire life of the vehicle, in the vast majority of cases. Well, managing editor of C&D Csaba Csere has an engineering degree which is more than you do, and he himself has conducted such tests AND he has an online presence - feel free to contact him and inform him how useless his findings are. Its not all that hard to measure the noise output from the engine bay at any RPM. Why, I even hear the measuring devices are simple enough be used by high school students such as yourself! Aint modern progress grand? How about if you post a link to a site where this guy actually makes the claims that you attribute to him (belts are noisier than chains, in case you forgot what you're talking about). Alternatively, since you insist that he's making these claims, you contact him, then tell us what he says. That's the responsibility of the person making the ridiculous claims (you), not the person who says that something smells (me). You clearly haven't a clue about NVH measurement practice, nor about the equipment required. Not surprisingly, you have no idea what my credentials are either... Quote:
You are so funny mikey....you want me to do what you have not...but suffice to say, I am satisfied with my college education and degrees earned. Perhaps you should reassess that level of satisfaction. I think that my college education and present field of work put me on pretty firm ground here... and I can tell you don't have a clue. I think I'll stand pat...however, when you do graduate high school, I highly recommend a college education if you can swing it. Very beneficial. ...or so you've heard, right? btw - that fact that you do have a chilton book for your car is admirable, many people fly blind. btw, it's not a chilton book, and it's not for my car. It's a factory service manual for a Honda Civic, which I keep on my desk for the occasional reference or diagram. It's great for occasional client questions like "can you give me any examples of a lost-motion device that is used in the valvetrain of a current production engine?" take if from someone much older and more experienced You may be older, but based on your statements thus far, you're clearly not more experienced in the field of automotive design.
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01-26-2004, 05:06 PM | #47 | ||
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Re: Re: Re: Re: Re: Re: Re: Pushrod vs. SOHC vs. DOHC
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eh, sorta....OHV motors really only need a smidgen of oil to lube the ball/rocker assembly, pushrod end and cool the springs. since the cams in an xOHC motor are held in aluminum, in most cases without benefit of a bearing shell, forming a hydrodynamic wedge is critical - and maintaining same across the cam. On a DOHC V, there are 4 steel cams that can wipe out the aluminum bosses in MINUTES, not miles. In the old days, OHV engine had a simple 'x lbs per y rpm' oil pressure requirement...today, the xOHC motors tend to require much more oil rpessure at much lower rpms to ensure all the cams are oiled at idle. Im not sure what you mean by size, do you mean physical size or displacement? displacement wise, you can have equal displacements with either method of valve actuation, however in terms of physical size - use the example I gave you, the 4.6L SOHC ford pickup motor is LARGER in physical dimensions than the 7.3L diesel!!! and note, a DOHC motor makes it worse. As for your valvetrain comments....you're all wet. Hydraulic cam followers are what EVERY manu has went to. Now note, save geometry, the parts and use of are the same - with a solid setup, you must set the clearance correctly - just having said clearance leads to a LOT of noise (just ask anyone with an older honda ;car or bike; or toyota) and it accelerates wear. with hydraulic lash, the tension on the plunger is measured in inch-lbs, whereas the seat pressure on the valve is measured in ft-lbs. In solid designs, the lobe must whack the follower which deforms the iron or in some cases steel slowly but surely. In hydraulic designs, the cams are offset ground (in OHV applicatins) to rotate the follower/lifter - wear is negligible. whereas solid deisgns require readjustment every 15Kish miles due to wear, hydraulic designs last forever. but please note, the loss of oil pressure on either will cause negative results. I have seen cam lobes wiped clean, but the vast majority as any professional will tell you will be incorrectly set solid designs - once the clearance is gone, the cam lobe is ALWAYS against seat pressure, (as opposed to plunger pressure in a hydraulic setup) Do hydraulic lifters collapse? yep, but it is so rare as to not require mention. Of note is the use of roller followers today, I and many others have taken roller lifters out of 200K mile motors and reused them after inspection on a fresh cam. they just dont wear out. |
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01-26-2004, 05:29 PM | #48 | ||||
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Re: Re: Re: Re: Re: Pushrod vs. SOHC vs. DOHC
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you dont have a degree in 'automotive design' you dont work for any automobile or motorcycle manufacturer you dont simply design automobiles nor any of the components. like it or not, those are the fact that you have now exposed. So you have attacked me ad hominem claiming 'expert status' why? Quote:
you are not engaged in employment in any matter dealing with anything automotive on a technical level. If you were, you would not have asked for the reference on the SAEs stance on the 3800, simply because you would have HAD it on your desk (for future reference, when you commit such blunders, especially in an online environment, your credibility is shot forever. shall we examine the other 713 posts you have made?) Furthermore, you would know who Mr Csere is and have read him quite often. I am not going to do for you the homework you should have already done. Ps - it is of light humor that we note you have not to date challenged any point in any of my posts on a technical level, merely the timing of suggested timing belt changes (all the while, on a grander level of humor noting that you skirted the issue that they in fact need changed, whereas chains do not, as I originally stated) I believe my correct stance at this point should be (in your vernacular): Bwahahahahahahah |
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01-26-2004, 08:33 PM | #49 | ||||||||
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Re: Re: Re: Re: Re: Re: Pushrod vs. SOHC vs. DOHC
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If you read this thread from the start, you might have noticed that in the fourth paragraph of my first post, I made the following statement: The advantage of a chain is that it lasts longer; belts are quieter, easier to package, and offer better high-rev performance if the drive load requirements aren't too high. I stand by that statement. I don't need to "skirt" the subject of timing belt changes. You seem to be intent on misrepresenting the frequency with which they must be performed, which is not entirely surpising, given that you seem to be prone to grandstanding and make-believe. Quote:
Honda still uses mechanical lash adjustment, with a recommended adjustment frequency of about 60k miles. Mechanical lash adjustment is also used in a number of high-perf applications, and on a very large number of heavy duty diesels. Wear is definitely not neglible at the cam-follower interface on pushrod engines. Ask a mechanic. Pressure is never measured in ft-lbs (duh). With a hydraulic lash adjuster, the expansion spring preload is not very large (say 40N or so), but the force that the lash adjuster exerts against the cam & pushrod on the base circle when the engine is running is much higher (say 150N). If you'd like, I can explain to you how a typical HLA works. There are often collase and pump-up issues with HLAs during development, usually they're sorted out by the likes of me before the likes of you get an engine. A properly adjusted mechanical system will have less force on the cam-follower interface over the base circle than a HLA valvetrain (close to zero). Roller followers are used on both overhead and in-block cam valvetrain configurations (as noted in my MUCH earlier post).
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01-26-2004, 10:04 PM | #50 | |
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quaddriver do you seriously expect anyone here to take your comments sersiously? Not only are you attacking one of the most knowledgable enginers I know, but you are doing it with no surporting evidence and incorrect use of terminology already clearly defined in this thread. You are of course welcome to give and provide your opinions in the forums, but please stick to topics you know something about, unless your asking questions, and please refrain from flaming other members. It would be a shame to have to ban you before you make a complete fool of yourself.
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01-26-2004, 10:33 PM | #51 | ||
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Re: Pushrod vs. SOHC vs. DOHC
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Ban if you must, but the attacks have only come from him. |
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01-26-2004, 11:15 PM | #52 | |
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Re: Pushrod vs. SOHC vs. DOHC
Well ivy mike they cirtianly didn't teach you any modesty or maturity at university.
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01-26-2004, 11:29 PM | #53 | ||||||||||||||||||||
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Re: Re: Re: Re: Re: Re: Re: Pushrod vs. SOHC vs. DOHC
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sidebar: I have to ask, because the answer I fear is apparent: you have never actually SEEN any of these systems in component form have you? Just ask and I will photo any of the components and upload them and explain to YOU how they work. the fact that oil travels up the pushrod is apparent. but how the flow is triggered you got wrong. way wrong. Quote:
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ps- GMs newest valve train technology, the VVT used on one of its 660 motors, hmmmm, is it mechanical or hydraulic? Not that this was ever the topic, but it shows which direction the industry continues to travel. |
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01-26-2004, 11:31 PM | #54 | ||
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Re: Re: Pushrod vs. SOHC vs. DOHC
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Ivymike's been posting here for years, dutifully answering engineering questions for the masses and without having to piss on anyone's parade. Now some people are waltzing in and after a few days on the board want to question his integrity, knowledge and honesty without even knowing who he is, what he does or where he's coming from (though some of you have made plenty of INCORRECT assumptions throughout this thread). Quit before I have to close the thread, and learn to be a little more respectful of the guys who regularly help others and just might be able to do the same for you... if you'd chill out and listen to them.
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01-27-2004, 12:20 AM | #55 | |||
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Re: Re: Re: Pushrod vs. SOHC vs. DOHC
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And texan, with all due respect, read his other posts in other threads, I took a few moments to do so after his first attack. His 'Im smarter than thou' additude is duplicated in each thread he contributes to. If that is help, then so be it, but my experience has found that people asking for help do not like smart azz answers. |
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01-27-2004, 12:39 AM | #56 | |
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seems as though i'll be spaming ivymike with questions.
Anyways what is the simpler design OHV(Cam in block?) or OHC(Cam in head?)? I'd have to say belts create less noise than chains if we consider there application to an OHC design, and a chain that long would be heavy, we also have to consider the HP of the engine and how much stronger the transfer medium to the cams has to be, which reflects the size and weigh increase. Discuss amongst your selves |
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01-27-2004, 01:19 AM | #57 | ||
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Re: Pushrod vs. SOHC vs. DOHC
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Whether or not chains or belts create the most noise isn't of much importance IMO. With either layout there is a combustion event regularly taking place just inches away that produces far more noise than either drive system, but it is also well suppressed with something as simple as a muffler. Chain driving Honda's S2000 motor doesn't seem to create any great underhood noise, and it's actually got a reasonably complex variable cam timing device thrown into this drive system. On the other hand my belt drive system seems nearly transparent underhood, but both have enclosures that are designed to supress their respective noise generating properties. In other words, it's how well you supress the noise coming off each that will matter to the end consumer, because both can be noisy or nearly silent depending upon how good a job the NVH crew does. Lastly, there's also that intangible difference between noise and sound that will always muddle this argument. For example the quitest exhaust system isn't often the best appreciated, it's the "quality" of sound that matters more than it's quantity in these types of discussions. I prefer the metallic goings on of a double roller timing chain to a cogged belt drive, but that's just me.
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01-27-2004, 09:47 AM | #58 | ||
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Re: Re: Pushrod vs. SOHC vs. DOHC
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...and the latest VVT mechanism that I've seen from GM, which is mentioned here, uses a hydraulically actuated vane-type phaser (as opposed to a spline-type phaser) on each cam (OHC). It also uses three separate chains (hydraulically tensioned) to drive the cams. more info: http://media.gm.com/division/powertr.../2004LY7A1.DOC
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01-27-2004, 01:34 PM | #59 | ||
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Re: Re: Pushrod vs. SOHC vs. DOHC
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01-27-2004, 01:35 PM | #60 | |
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Re: Pushrod vs. SOHC vs. DOHC
IM - that link says 60-deg V6 engines don't need balance shafts. True?
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