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Engineering/Technical Ask technical questions about cars. Do you know how a car engine works? |
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01-22-2004, 09:02 PM | #31 | ||
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Re: Re: Pushrod vs. SOHC vs. DOHC
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I say "blame canada!"
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01-23-2004, 10:20 AM | #32 | |
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Re: Pushrod vs. SOHC vs. DOHC
f1 uses pneumatic valves with success.
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01-23-2004, 11:14 AM | #33 | ||
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Re: Re: Pushrod vs. SOHC vs. DOHC
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01-24-2004, 01:59 PM | #34 | |
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Re: Pushrod vs. SOHC vs. DOHC
wow ivy mike that was inteligent
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01-24-2004, 06:47 PM | #35 | ||
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Re: Re: Pushrod vs. SOHC vs. DOHC
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01-25-2004, 08:27 PM | #36 | ||
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Re: Pushrod vs. SOHC vs. DOHC
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however, if you need a small engine to make the hp of a large engine, you need to force feed it, OR increase the RPMs. when you increase rpms, xOHC designs allow more consistent valve actuation at higher rpms (chevy 350s run over 9000rpm in nascar so pushrods can move quickly) the problem with xOHC designs is the increased size, noise and rotational moment of the moment. For example, a SOHC 4.6 or 5.4 ford engine, is larger than the IH 444 block diesel. Kinda interferes with aerodynamic body designs. Plus, take a cam for a V8, has 5 bearings to oil. The same v8, if only a SOHC has 10, if dOHC it has 20. This means increased demand on the oiling system to deliver high pressure oil to the very top of the motor - not an easy feat. (the most common failure of xOHC motors is in fact damage due to top end oil starvation) Also, OHV motors are usually chain driven for the cam, nice and quiet and reliable - chains RARELY break. xOHC designs use external belts, which break often if not changed often and add a lot of noise. Lastly, you now have cams and pulleys rotating at the outer extremes of the motor, making it a bear to hold still in the engine bay. So, xOHC engines have advantages, but they have disadvantages. |
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01-25-2004, 11:18 PM | #37 | ||
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Re: Re: Pushrod vs. SOHC vs. DOHC
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01-26-2004, 10:07 AM | #38 | |||
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Re: Re: Re: Pushrod vs. SOHC vs. DOHC
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01-26-2004, 11:02 AM | #39 | |||
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Re: Re: Re: Re: Pushrod vs. SOHC vs. DOHC
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some info on the subject: http://www.hse.gov.uk/pubns/top10noise.pdf "Noisy chain drives can often be replaced directly with quieter timing belts. Within the range of timing belts available, there are also quiet designs that use different tooth profiles to minimise noise. There is also a very new design of belt for applications where noise is critical which uses a chevron tooth pattern to provide very quiet running. Noise reductions in the range of 6 - 20 dB are often possible using this approach." http://www.me.ic.ac.uk/dynamics/stru...cona2000_2.pdf "Even if timing belts are generally considered as silent transmissions, when compared to mechanical chains, nevertheless a large interest is devoted to further enhancement of the vibrational behaviour under operating conditions." http://www.babcox.com/editorial/us/us70343.htm "Play in a gear or chain style cam drive can cause noise, retarded valve timing and/or ignition timing depending on the engine design and application. With rubber timing belts, noise is seldom a problem even at high mileages. Valve timing and ignition timing (if it reads off the camshaft) also remain steady because timing belts don’t stretch." http://www.powertransmission.com/fea...cdrivenews.htm "The Browning HPT synchronous drive line from Emerson EPT combines the timing action of gears with the speed and noise level of belts. "
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01-26-2004, 11:53 AM | #40 | ||
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Re: Re: Re: Re: Re: Pushrod vs. SOHC vs. DOHC
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and I notice not one of the links was from an auto manu or testing magazine (like cd, rt, MT, aw, SC, ff, mm &c) who actually measure noise with a meter and report coincidently the same findings I do ;-) PS - I defy you to stand outside a GM 3800 and find ANY xOHC engine that makes less noise. I stand on my position. You are free to argue the minority position as long as you desire. |
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01-26-2004, 01:08 PM | #41 | |
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Re: Pushrod vs. SOHC vs. DOHC
yup honda for 1 and many others recomend timing belt repacement at 60k or 100,000km how ever there are cases when they even break before this time. On an interferance engine as many ohc's are this results in at least a few bent valves.
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01-26-2004, 01:09 PM | #42 | |
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Re: Re: Re: Re: Re: Re: Pushrod vs. SOHC vs. DOHC
Chains are used in both push rod and OHC engines (BMW and Saab are examples on the latter). Chains tend to make more noise, especially when they become worn. (basic engineering)
Many high revving motorcycles use chains for the cams, but at high performance applications gears are common. This introduces however more noise. The service interval on belts have become a lot better lately, 60k is very low. But the cost of a belt is low and many people can do it theirself if they want (not that much more complex than to change waterpump/generator/servopump/AC belt). A chain lasts longer, but not until the end of engine life (unless you have a low quality engine), and it's more expensive to change. Both chains and belts are stretched somewhat during their life. Both push rod and OHC engines need oil to the top of the motor, escecially with high performance engines when valve spring cooling is important. The difference in size of a push rod and DOHC engine is very small, the increase in performance more than compensate for this. The largest valvetrain problem is probably hydraulic lifters, which can cause wear of too high pressure against the cam or start to leak and the cam to lifter clearance till be off. |
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01-26-2004, 02:34 PM | #43 | |||
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Re: Re: Pushrod vs. SOHC vs. DOHC
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If the GM 3800 is your "gold standard" of engine refinement, then I know what sort of person I'm speaking to, and that it's pointless to continue this discussion of automotive technology... I leave it to you to pursue an education in automotive design; it's not my job or desire to educate you (nor am I confident that it would be possible).
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01-26-2004, 02:37 PM | #44 | |||
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Re: Re: Pushrod vs. SOHC vs. DOHC
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90k miles is the recommended timing belt change for every Honda I've seen in the US. And I have never heard of one breaking before 90k unless someone went and screwed with it, the gears or the cover at an earlier point. Quote:
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01-26-2004, 04:30 PM | #45 | ||||||||
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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. Quote:
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btw - that fact that you do have a chilton book for your car is admirable, many people fly blind. But please tell us you didnt 'rice it out', take if from someone much older and more experienced: it does NOT look cool that way. |
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