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History (or introductory) part is somewhat incorrectly written. Peugeot developed four valve DOHC engine in 1910-1911. Engine was powering, winning Peugeot L76 racecar, at the ACF Grand Prix in 1912. It was the first four valve headed DOHC engined car (so it was not Fiat nor the Pugatti). Four valve equipped Peugeot's won in the USA at the Indianapolis in 1912, 1913 and 1916. Peugeot was using 'some Harry Miller' services at the States (L76 and/or L45 car's were stored there during the war years). There (at the Harry Miller's shop) worked 'some Fred Offenhauser', who was one of the 'Offy' engine originators (which is derived and 'somewhat a copy' from the L76 race engine).
http://www.ddavid.com/formula1/boillot_bio.htm http://books.google.fi/books?id=CJ5-LC67ZX8C&pg=PA12&lpg=PA12&dq=Les+Charlatans+Peugeot&source=bl&ots=OJNY2_GGUM&sig=Bjlw-KzVlhIbq0TSt6BA7Hdvh14&hl=en&ei=aNwNS6yfDdWPsAbExOSOAw&sa=X&oi=book_result&ct=result&resnum=6&ved=0CBgQ6AEwBQ http://www.supercars.net/cars/1435.html http://peugeot.mainspot.net/hist08.shtml http://www.europeancarweb.com/features/0209ec_twin_cam_analysis/index.html http://www.conceptcarz.com/vehicle/z13561/Peugeot-L45.aspx http://www.kolumbus.fi/leif.snellman/gpw1.htm http://philippe.boursin.perso.sfr.fr/autohi3c.htm http://en.wikipedia.org/wiki/Fred_Offenhauser http://www.milleroffy.com/Racing%20History.htm http://forums.autosport.com/index.php?showtopic=90310 http://en.wikipedia.org/wiki/Peugeot
In 1922 Peugeot introduced 5-valve head race engine, with three camshafts, but the idea was abandoned, as the engine was failure. Late 20's and early 30's Henry Ford sold power adding kit's to their engine, which was known as the 'Peugeot Head'.
So, may I succest, some corrective edit. Regards BR —Preceding unsigned comment added by 88.112.142.9 ( talk) 01:52, 26 November 2009 (UTC)
Removed the following (speculative and subjective without references):
"This arrangement is less complex, usually has fewer parts and requires less engine power to operate. It relies on a timing belt or chain to drive the cam(s), and allows for greater valvetrain flexibility."
Discuss? CJ DUB 16:34, 8 May 2006 (UTC)
When compared directly between two valve cam in block engines (OHV) and two valve overhead cam (OHC) engines the OHC system will be less complex. An OHC system only requires a drive system such as a belt, chain, or gear drive, a cam shaft and some type of cam follower. An OHV system requires all of the components of the OHC system but would also require the addition of pushrods and tappets. The same can also be said for four valve OHV systems compared to four valve OHC systems. In engines with more than one bank of cylinders the OHC system becomes slightly more complex but still requires fewer parts. An edit was made to include those instances. IJB TA
I have not read through the pushrod page but if it is written by the same person it is also very likely wrong. I understand the capabilities of pushrod engines but the maximum speed of the engine does nothing to determine the number of parts in the valve system. If you want to argue the engine speed capabilities consider that the rotational speeds of an OHC F1 engine approach 20,000 rpm. If you consider what I have said to be speculation then you are clearly not qualified to edit these pages. IJB TA
This article is NOT a discussion. I am listing fact only. Do the research yourself, I will not be teaching you things you should already know if you are going to be editing these articles. Concerning the number of RECIPROCATING parts, just look at any OHC engine and OHV engine and count the number of major reciprocating parts. As far as references, here are some links I happen to have already. I am getting a second opinion on the "less power to operate" subject, I did not include that statement in my last edit. http://www.hondaracingf1.com/loband/car_engine.php - Most if not all F1 teams have engines that rev to the 18,0000 rpm to 19,0000+ rpm range. http://www.exvitermini.com/r33specs.htm - Here is a Skyline GTR that can rev to 13,000+ rpm. Just about all OHC Super Sport motorcycles will rev to 12,000+ rpm. IJB TA
There is nothing to discuss, these are the facts and nothing more. I am not responsible for your ignorance on this subject, it is your responsibility to make sure YOUR facts are correct. If you question the facts that I have given then it is your responsibility to do the research to determine the validity of the statements I have made. THIS IS NOT AN OPINION PAGE, so keep them to yourself. Also this site does not require me to register, that is my choice. Lastly I am not going to dig up every book I have ever read just because one person has an OPINION about this subject. Like I said before, do the research yourself, I have done mine. IJB TA
I have not said "more power" anywhere in this article, this is the last time I will say that. The cam-in-block page does not have any credible reference either, how can you say with any certainty that it is correct? IJB TA
“Fiat is credited as the first car company to use a belt-driven DOHC engine across their complete product line, in the mid-1960s.”
How can this be? Fiat X1/9 mid-engined sports car (1972-1980) came stock with a single overhead cam 1290 cc. engine. GT —Preceding undated comment was added at 06:34, 2 August 2008 (UTC)
The first statement is correct. FIAT utilized a belt driven DOHC engine beginning in the mid 1960s beginning with the 124 Spider and 124 Coupe. The X1/9 utilized a SOHC engine, and was built from 1973-1988. —Preceding unsigned comment added by 66.15.18.136 ( talk) 00:14, 9 December 2008 (UTC)
I call bullshit on this one. The Fiat 500 was in production in the mid-60's and had a pushrod OHV engine. (I know because I stripped one.) Fiat may have used DOHC engines in the mid-60's but certainly not across their complete product line Rocknrollsuicide ( talk) 04:21, 6 September 2009 (UTC)
The Fiat 500 started was produced from 1957-1975. It is a carry over product and not within the scope of this discussion. ([[User talk:Turnsix])) —Preceding unsigned comment added by 66.15.18.136 ( talk) 21:18, 21 October 2009 (UTC)
Several obvious faults in this article, and I don't know where to start correcting them.
"I-head" was only used to differentiate between those and "L-head" engines. Since the flathead is no longer around, I don't see the point. "OHV" is the standard terminology, it's what magazines use when listing specifications. It matches with "DOHC" and "SOHC". "Pushrod engine" is an informal way of saying "OHV". Most people are not going to have a clue what "I-head" means. .45Colt 14:39, 4 January 2014 (UTC) — Preceding unsigned comment added by .45Colt ( talk • contribs)
I noticed all the "limitations" listed under the pushrod article, but that section wasn't listed. There really are no limitations? I always figured more complexity would render a better chance for wear and tear, at least I always thought cams wore down over time. Huh, guess I was wrong, there isn't such a thing as "cam wear". Oh well. Zchris87v 15:37, 29 May 2007 (UTC)
OHC engines are less complex, they almost always have fewer moving parts. OHC engines do not have to run at higher rpm to produce optimal power, but most are tuned to produce peak power at a high rpm. There are plenty of OHC engines that produce more power at lower rpm than many pushrod engines. Cam lobe wear? From what? Pushrod engines have greater loads on the cam lobes due to the much greater mass of the valvetrain. I drive an OHC vehicle and the engine very rarely exceeds 2500-3000 rpm under normal driving. Comparing two vehicles simply does not provide nearly enough information to back up what you are implying. Please read the discussion here. IJB TA 21:35, 1 June 2007 (UTC)
is there any difference at all between twin cam and DOHC engine configurations? or are those merely two different names for the exact same thing? Cirilobeto ( talk • contribs) 15:14, 3 April 2008 (UTC)
As far as the difference between the cams themselves, it's extremely uncommon to see any two engines using different configurations to have identical cams (sorry I don't have any references on hand ATM), but then it's also rare to have interchangeable camshafts between one marquee and another. -- 208.46.106.5 ( talk) 03:44, 14 August 2008 (UTC)
Please pardon my ignorance, but isn`t that picture claiming to show an SOHC head really a DOHC? Aren´t there two cams visible? If I am mistaken, please correct me. -- 328cia ( talk) 18:27, 15 April 2008 (UTC)
This article treats OHV as if it's an inferior competitor of OHC - which is historically nonsense and must rate as a basic fault of article writing. It's particularly misleading to the reader in this case when OHC = OHV! Let's have every mention of OHV out of the lead, and a section on "Development" explain how the OHC builds on what went before. TomRawlinson ( talk) 14:42, 13 December 2008 (UTC)
The first picture is a double overhead camshaft cylinder head. Those are hydraulic tappets, in place of the more common shim and bucket. Those are in fact cam lobes. An engine with over head cams and a rocker shaft does not have tappets on the valve springs.
An overhead cam can have almost as many parts. The minimum missing is pushrods. Many are as shown, with very few moving parts, and less complexity. Some over head cams even have roller followers on the rocker shaft.
The hydraulic tappet takes up valve lash. The shim and bucket style found on high performance engines requires check and adjustment, such as a high performance solid lifter cam. OHV engines do not wear the camshaft more. Engines with one intake an one exhaust valve require more lift and duration to get the same airflow as an engine with multiple intake and exhaust valves, and subsequently more spring tension to close the valve as a result, Something a multi-valve engine isn’t faced with. The engine gets more airflow at lower lift, from more total valve area. Being OHC or OHV has nothing to do with it.
The unrestricted intake ports of certain OHC engines do in fact yield higher performance with out the pushrod interference. The valve layout can be the same in an OHC or OHV engine. Both can have canted or angled valves, for better airflow, as turning 90 degrees to enter the cylinder inhibits airflow. An example of that would be what Chrysler calls the "Hemi", for hemispherical combustion chamber. DOHC engines of the same layout are usually called pent roof, but have the same cross flow layout. Japanese especially call it a pent roof combustion chamber, as the chamber is not as rounded as the Chrysler design.
Push rods have no effect on engine torque. Cam timing, manifold design, and bore and stroke effect engine torque. Horsepower is a function of engine torque and rpm. A small Honda engine will have less torque from less displacement compared to a larger displacement engine. If you need an explanation on variable cam timing, let me know. I am sure others can write that article also.
I have a degree in Automotive Technology, am ASE Master Certified in Automotive, and in Medium and Heavy Trucks. I work as a Field Service Representative for Navistar (International Truck and Engine Company).
The other comment is correct. This is not an opinion page.
'DOHC' is an official abbreviation for Double Overhead Camshaft and NOT Dual Overhead Camshaft. "Double Overhead Camshaft" is a well-established term, and is clearly referenced in the following academic/professional textbook - "Hiller's Fundamentals of Motor Vehicle Technology, 5th Ed, ISBN: 0-7487-8082-3, page 79". Please respect offical terminology for encyclopaedic content, and not some wrongly-informed myth from some unregulated internet forum. 78.32.143.113 ( talk) 17:31, 1 April 2009 (UTC)
Just wondered everybody's thoughts on splitting article into two articles Cam-in-head and Overhead camshaft. The difference being how the valves are actuated; indirectly actuated valves vs directly actuated valves, respectively. VX1NG ( talk) 14:02, 20 November 2013 (UTC)
What's with the second-to-last paragraph in the middle section?
It says: "SOHC designs offer reduced complexity compared to overhead valve designs — when used for multivalve cylinder heads, in which each cylinder has more than two valves. An example of an SOHC design using shim and bucket valve adjustment was the engine installed in the Hillman Imp (four cylinder, eight valve); a small, early 1960s two-door saloon car (sedan) with a rear mounted aluminium-alloy engine based on the Coventry Climax FWMA race engines. Exhaust and inlet manifolds were both on the same side of the engine block (thus not a crossflow cylinder head design). This did, however, offer excellent access to the spark plugs."
First sentence is about reduced complexity on engines with more than two valves. Why does the next sentence give us an example of a two-valve engine, and why does it mention that it's a bucket-and-shim engine? No one said anything about bucket-and-shims. It doesn't explain what that even means or what it has to do with a OHC engine. Then, although I'm sure the Hillman Imp was a very interesting car and all, I'm not sure we all need to know so much about it. I'm also not sure what the fact that it was not a crossflow engine has to do with it's being an OHC engine, and the fact that the sparkplugs are easily accessible is irrelevant. That is true of most non-crossflow engines, which can be either OHV or OHC. This is information that belongs on the page about crossflow engines, not OHC engines.
It seems like there is several entire sentences missing from this paragraph, ones that would make these different topics blend together better. — Preceding unsigned comment added by .45Colt ( talk • contribs) 15:01, 4 January 2014 (UTC)
WHEREAS the use of timing belts to operate engine camshafts is restricted, with perhaps very obscure exceptions, to overhead camshaft engines, and is therefore relevant only to overhead camshaft engines,
AND WHEREAS the overall combined size of the articles Overhead camshaft and Timing belt (camshaft) at this time is slightly more than 37 kB, far less than the suggested 60 kB limit for readable prose (overall size includes tables, thumbnails, references, etc. and is allowed to be larger), without considering the duplicated material therein,
BE IT RESOLVED THAT the article Timing belt (camshaft) should be merged into the article Overhead camshaft.
Sincerely, SamBlob ( talk) 12:34, 4 January 2015 (UTC)
____________________
Support, as proposer.
Sincerely, SamBlob (
talk)
12:34, 4 January 2015 (UTC)
Just from a note raised above, a few engines used the rare system of coupling rods to drive an OHC, not terribly dissimilar to a steam engine! I think the first of these was the unique 1923 Maudslay, which used a Y shaped rod to drive both camshafts from a single large eccentric. A similar system was used for the 3 litre Vauxhall, as covered in such depth in Ricardo's book. It's best known as a system though through either Parry-Thomas and the Leyland Eight or else the Bentleys. These didn't use large eccentrics though – to avoid such a device (I think the Maudslay got away with it by using ball races) they went for smaller and smaller eccentrics, almost a three-throw crankshaft rather than eccentrics - with of course needing three rods to connect them. The cost of these small journals was needing to use a three-throw system, to deal with the off-axis loads. Strictly these were still eccentrics, as they were just large enough to encompass the central axis of the crankshaft. The rods were an abomination mechanically as they made introduced a substantial reciprocating mass into the cam drive (just what were these supposedly expert engineers thinking?) Parry-Thomas did his inevitable of perforating the rods into Meccano and W O used what appeared to be a bag of knitting needles, having confused a reduction in parts count with elegance of structural design. Even more so than R-R, Bentleys were awful cars, looked after by surgeons. The whole sorry idea had its last fling in the 1950s with the NSU Prinz. By using a moderate size of eccentric, counterweighting and teaching dynamics in German high schools rather than Latin, the Germans managed to make a reliable design with only two rods.
All of these rod-drive designs used a reduction gear from the crankshaft before (obviously) the cam drive. So they weren't even any quieter than a geared drive. Andy Dingley ( talk) 12:09, 1 February 2015 (UTC)
{{
cite journal}}
: Invalid |ref=harv
(
help)
Sincerely, SamBlob (
talk)
02:47, 8 February 2015 (UTC)Something needs to be done about the "History" section. It is disorganized and haphazard. It needs to be either rewritten with some proper structure or dispersed into the relevant sections. There is quite a bit of SOHC history in the "Single overhead camshaft" section. This seems to be a good solution and I have copied that with the "Timing belt" section, moving some info out of "History" and into "Timing belt".
So which way should we go? Improve the "History" section? Dissipate it among the technical sections? A bit of both?
Sincerely, SamBlob ( talk) 13:16, 5 March 2015 (UTC)
I have disrupted the order of the article, and possibly not for the better. I had split off the section "Camshaft drive systems" from the "Overview" section and expanded it somewhat. Because I split it off from "Overview" I put it directly after that section, which puts it before the sections on SOHC and DOHC. It has just dawned on me that this might not be where this section belongs. Should I move "Camshaft drive systems" further down the article, between "Double overhead camshafts" and "History"? Sincerely, SamBlob ( talk) 18:08, 5 March 2015 (UTC)
Information about the Ford 427 "Cammer" engine was placed in a passage in the section Overhead camshaft#Single overhead camshaft dealing with the simplicity of SOHC when compared with DOHC. It is not clear from the passage how the "Cammer" engine illustrates the point being made by the Hillman Imp engine before it and the Toyota and Volkswagen engines after it. It is also unclear how the Cammer advanced the development of the overhead camshaft engine in general or the single overhead camshaft engine in particular, or what feature of the SOHC engine it is supposed to be illustrating. If the "Cammer" is just another example, should it not be put in the "History" section instead? Sincerely, SamBlob ( talk) 15:43, 12 March 2015 (UTC)
Can we get an accurate definition of "Unicam" please.
The idea of a single camshaft working both inlet and exhaust valves is inherent in SOHC. It's the use of a single cam lobe that matters.
Sharing a cam between inlet and exhaust is almost as old as SOHC. Not for mass-volume production cars, but for a number of engines, both car and aircraft. Particularly for V12s, which are otherwise a great many lobes to provide.
The Dolomite Sprint innovation was to use a single camshaft for 4 valve heads (with a single cam for each inlet/exhaust pair, ie still 8 lobes). This is not technically a particularly revolutionary design: it combines the shared inlet/exhaust cam lobe with 4 valve heads; but it's not as great an innovation as either of its components indivudally. I think this may have been novel (although I wouldn't be surprised to see an obscure early example), it was certainly novel for mass production cars.
The Dolomite 1850 engine was a "conventional" [ sic] SOHC with 8 lobes and 8 valves. This is the base engine used as the Saab derivative. Only the Dolomite Sprint engine had 16 valves. I can't think of another use made of it (the TR7 Sprint didn't go into production).
I know nothing of the "Unicam" engine, or of any way it innovated beyond the Dolomite Sprint. Andy Dingley ( talk) 21:29, 29 March 2015 (UTC)
Nobody calls it that. Dual Overhead Camshaft. 139.138.6.121 ( talk) 07:46, 15 January 2021 (UTC)
Sylvia Bordeaux inventor questions 4803623675 174.240.176.209 ( talk) 03:58, 28 April 2023 (UTC)
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History (or introductory) part is somewhat incorrectly written. Peugeot developed four valve DOHC engine in 1910-1911. Engine was powering, winning Peugeot L76 racecar, at the ACF Grand Prix in 1912. It was the first four valve headed DOHC engined car (so it was not Fiat nor the Pugatti). Four valve equipped Peugeot's won in the USA at the Indianapolis in 1912, 1913 and 1916. Peugeot was using 'some Harry Miller' services at the States (L76 and/or L45 car's were stored there during the war years). There (at the Harry Miller's shop) worked 'some Fred Offenhauser', who was one of the 'Offy' engine originators (which is derived and 'somewhat a copy' from the L76 race engine).
http://www.ddavid.com/formula1/boillot_bio.htm http://books.google.fi/books?id=CJ5-LC67ZX8C&pg=PA12&lpg=PA12&dq=Les+Charlatans+Peugeot&source=bl&ots=OJNY2_GGUM&sig=Bjlw-KzVlhIbq0TSt6BA7Hdvh14&hl=en&ei=aNwNS6yfDdWPsAbExOSOAw&sa=X&oi=book_result&ct=result&resnum=6&ved=0CBgQ6AEwBQ http://www.supercars.net/cars/1435.html http://peugeot.mainspot.net/hist08.shtml http://www.europeancarweb.com/features/0209ec_twin_cam_analysis/index.html http://www.conceptcarz.com/vehicle/z13561/Peugeot-L45.aspx http://www.kolumbus.fi/leif.snellman/gpw1.htm http://philippe.boursin.perso.sfr.fr/autohi3c.htm http://en.wikipedia.org/wiki/Fred_Offenhauser http://www.milleroffy.com/Racing%20History.htm http://forums.autosport.com/index.php?showtopic=90310 http://en.wikipedia.org/wiki/Peugeot
In 1922 Peugeot introduced 5-valve head race engine, with three camshafts, but the idea was abandoned, as the engine was failure. Late 20's and early 30's Henry Ford sold power adding kit's to their engine, which was known as the 'Peugeot Head'.
So, may I succest, some corrective edit. Regards BR —Preceding unsigned comment added by 88.112.142.9 ( talk) 01:52, 26 November 2009 (UTC)
Removed the following (speculative and subjective without references):
"This arrangement is less complex, usually has fewer parts and requires less engine power to operate. It relies on a timing belt or chain to drive the cam(s), and allows for greater valvetrain flexibility."
Discuss? CJ DUB 16:34, 8 May 2006 (UTC)
When compared directly between two valve cam in block engines (OHV) and two valve overhead cam (OHC) engines the OHC system will be less complex. An OHC system only requires a drive system such as a belt, chain, or gear drive, a cam shaft and some type of cam follower. An OHV system requires all of the components of the OHC system but would also require the addition of pushrods and tappets. The same can also be said for four valve OHV systems compared to four valve OHC systems. In engines with more than one bank of cylinders the OHC system becomes slightly more complex but still requires fewer parts. An edit was made to include those instances. IJB TA
I have not read through the pushrod page but if it is written by the same person it is also very likely wrong. I understand the capabilities of pushrod engines but the maximum speed of the engine does nothing to determine the number of parts in the valve system. If you want to argue the engine speed capabilities consider that the rotational speeds of an OHC F1 engine approach 20,000 rpm. If you consider what I have said to be speculation then you are clearly not qualified to edit these pages. IJB TA
This article is NOT a discussion. I am listing fact only. Do the research yourself, I will not be teaching you things you should already know if you are going to be editing these articles. Concerning the number of RECIPROCATING parts, just look at any OHC engine and OHV engine and count the number of major reciprocating parts. As far as references, here are some links I happen to have already. I am getting a second opinion on the "less power to operate" subject, I did not include that statement in my last edit. http://www.hondaracingf1.com/loband/car_engine.php - Most if not all F1 teams have engines that rev to the 18,0000 rpm to 19,0000+ rpm range. http://www.exvitermini.com/r33specs.htm - Here is a Skyline GTR that can rev to 13,000+ rpm. Just about all OHC Super Sport motorcycles will rev to 12,000+ rpm. IJB TA
There is nothing to discuss, these are the facts and nothing more. I am not responsible for your ignorance on this subject, it is your responsibility to make sure YOUR facts are correct. If you question the facts that I have given then it is your responsibility to do the research to determine the validity of the statements I have made. THIS IS NOT AN OPINION PAGE, so keep them to yourself. Also this site does not require me to register, that is my choice. Lastly I am not going to dig up every book I have ever read just because one person has an OPINION about this subject. Like I said before, do the research yourself, I have done mine. IJB TA
I have not said "more power" anywhere in this article, this is the last time I will say that. The cam-in-block page does not have any credible reference either, how can you say with any certainty that it is correct? IJB TA
“Fiat is credited as the first car company to use a belt-driven DOHC engine across their complete product line, in the mid-1960s.”
How can this be? Fiat X1/9 mid-engined sports car (1972-1980) came stock with a single overhead cam 1290 cc. engine. GT —Preceding undated comment was added at 06:34, 2 August 2008 (UTC)
The first statement is correct. FIAT utilized a belt driven DOHC engine beginning in the mid 1960s beginning with the 124 Spider and 124 Coupe. The X1/9 utilized a SOHC engine, and was built from 1973-1988. —Preceding unsigned comment added by 66.15.18.136 ( talk) 00:14, 9 December 2008 (UTC)
I call bullshit on this one. The Fiat 500 was in production in the mid-60's and had a pushrod OHV engine. (I know because I stripped one.) Fiat may have used DOHC engines in the mid-60's but certainly not across their complete product line Rocknrollsuicide ( talk) 04:21, 6 September 2009 (UTC)
The Fiat 500 started was produced from 1957-1975. It is a carry over product and not within the scope of this discussion. ([[User talk:Turnsix])) —Preceding unsigned comment added by 66.15.18.136 ( talk) 21:18, 21 October 2009 (UTC)
Several obvious faults in this article, and I don't know where to start correcting them.
"I-head" was only used to differentiate between those and "L-head" engines. Since the flathead is no longer around, I don't see the point. "OHV" is the standard terminology, it's what magazines use when listing specifications. It matches with "DOHC" and "SOHC". "Pushrod engine" is an informal way of saying "OHV". Most people are not going to have a clue what "I-head" means. .45Colt 14:39, 4 January 2014 (UTC) — Preceding unsigned comment added by .45Colt ( talk • contribs)
I noticed all the "limitations" listed under the pushrod article, but that section wasn't listed. There really are no limitations? I always figured more complexity would render a better chance for wear and tear, at least I always thought cams wore down over time. Huh, guess I was wrong, there isn't such a thing as "cam wear". Oh well. Zchris87v 15:37, 29 May 2007 (UTC)
OHC engines are less complex, they almost always have fewer moving parts. OHC engines do not have to run at higher rpm to produce optimal power, but most are tuned to produce peak power at a high rpm. There are plenty of OHC engines that produce more power at lower rpm than many pushrod engines. Cam lobe wear? From what? Pushrod engines have greater loads on the cam lobes due to the much greater mass of the valvetrain. I drive an OHC vehicle and the engine very rarely exceeds 2500-3000 rpm under normal driving. Comparing two vehicles simply does not provide nearly enough information to back up what you are implying. Please read the discussion here. IJB TA 21:35, 1 June 2007 (UTC)
is there any difference at all between twin cam and DOHC engine configurations? or are those merely two different names for the exact same thing? Cirilobeto ( talk • contribs) 15:14, 3 April 2008 (UTC)
As far as the difference between the cams themselves, it's extremely uncommon to see any two engines using different configurations to have identical cams (sorry I don't have any references on hand ATM), but then it's also rare to have interchangeable camshafts between one marquee and another. -- 208.46.106.5 ( talk) 03:44, 14 August 2008 (UTC)
Please pardon my ignorance, but isn`t that picture claiming to show an SOHC head really a DOHC? Aren´t there two cams visible? If I am mistaken, please correct me. -- 328cia ( talk) 18:27, 15 April 2008 (UTC)
This article treats OHV as if it's an inferior competitor of OHC - which is historically nonsense and must rate as a basic fault of article writing. It's particularly misleading to the reader in this case when OHC = OHV! Let's have every mention of OHV out of the lead, and a section on "Development" explain how the OHC builds on what went before. TomRawlinson ( talk) 14:42, 13 December 2008 (UTC)
The first picture is a double overhead camshaft cylinder head. Those are hydraulic tappets, in place of the more common shim and bucket. Those are in fact cam lobes. An engine with over head cams and a rocker shaft does not have tappets on the valve springs.
An overhead cam can have almost as many parts. The minimum missing is pushrods. Many are as shown, with very few moving parts, and less complexity. Some over head cams even have roller followers on the rocker shaft.
The hydraulic tappet takes up valve lash. The shim and bucket style found on high performance engines requires check and adjustment, such as a high performance solid lifter cam. OHV engines do not wear the camshaft more. Engines with one intake an one exhaust valve require more lift and duration to get the same airflow as an engine with multiple intake and exhaust valves, and subsequently more spring tension to close the valve as a result, Something a multi-valve engine isn’t faced with. The engine gets more airflow at lower lift, from more total valve area. Being OHC or OHV has nothing to do with it.
The unrestricted intake ports of certain OHC engines do in fact yield higher performance with out the pushrod interference. The valve layout can be the same in an OHC or OHV engine. Both can have canted or angled valves, for better airflow, as turning 90 degrees to enter the cylinder inhibits airflow. An example of that would be what Chrysler calls the "Hemi", for hemispherical combustion chamber. DOHC engines of the same layout are usually called pent roof, but have the same cross flow layout. Japanese especially call it a pent roof combustion chamber, as the chamber is not as rounded as the Chrysler design.
Push rods have no effect on engine torque. Cam timing, manifold design, and bore and stroke effect engine torque. Horsepower is a function of engine torque and rpm. A small Honda engine will have less torque from less displacement compared to a larger displacement engine. If you need an explanation on variable cam timing, let me know. I am sure others can write that article also.
I have a degree in Automotive Technology, am ASE Master Certified in Automotive, and in Medium and Heavy Trucks. I work as a Field Service Representative for Navistar (International Truck and Engine Company).
The other comment is correct. This is not an opinion page.
'DOHC' is an official abbreviation for Double Overhead Camshaft and NOT Dual Overhead Camshaft. "Double Overhead Camshaft" is a well-established term, and is clearly referenced in the following academic/professional textbook - "Hiller's Fundamentals of Motor Vehicle Technology, 5th Ed, ISBN: 0-7487-8082-3, page 79". Please respect offical terminology for encyclopaedic content, and not some wrongly-informed myth from some unregulated internet forum. 78.32.143.113 ( talk) 17:31, 1 April 2009 (UTC)
Just wondered everybody's thoughts on splitting article into two articles Cam-in-head and Overhead camshaft. The difference being how the valves are actuated; indirectly actuated valves vs directly actuated valves, respectively. VX1NG ( talk) 14:02, 20 November 2013 (UTC)
What's with the second-to-last paragraph in the middle section?
It says: "SOHC designs offer reduced complexity compared to overhead valve designs — when used for multivalve cylinder heads, in which each cylinder has more than two valves. An example of an SOHC design using shim and bucket valve adjustment was the engine installed in the Hillman Imp (four cylinder, eight valve); a small, early 1960s two-door saloon car (sedan) with a rear mounted aluminium-alloy engine based on the Coventry Climax FWMA race engines. Exhaust and inlet manifolds were both on the same side of the engine block (thus not a crossflow cylinder head design). This did, however, offer excellent access to the spark plugs."
First sentence is about reduced complexity on engines with more than two valves. Why does the next sentence give us an example of a two-valve engine, and why does it mention that it's a bucket-and-shim engine? No one said anything about bucket-and-shims. It doesn't explain what that even means or what it has to do with a OHC engine. Then, although I'm sure the Hillman Imp was a very interesting car and all, I'm not sure we all need to know so much about it. I'm also not sure what the fact that it was not a crossflow engine has to do with it's being an OHC engine, and the fact that the sparkplugs are easily accessible is irrelevant. That is true of most non-crossflow engines, which can be either OHV or OHC. This is information that belongs on the page about crossflow engines, not OHC engines.
It seems like there is several entire sentences missing from this paragraph, ones that would make these different topics blend together better. — Preceding unsigned comment added by .45Colt ( talk • contribs) 15:01, 4 January 2014 (UTC)
WHEREAS the use of timing belts to operate engine camshafts is restricted, with perhaps very obscure exceptions, to overhead camshaft engines, and is therefore relevant only to overhead camshaft engines,
AND WHEREAS the overall combined size of the articles Overhead camshaft and Timing belt (camshaft) at this time is slightly more than 37 kB, far less than the suggested 60 kB limit for readable prose (overall size includes tables, thumbnails, references, etc. and is allowed to be larger), without considering the duplicated material therein,
BE IT RESOLVED THAT the article Timing belt (camshaft) should be merged into the article Overhead camshaft.
Sincerely, SamBlob ( talk) 12:34, 4 January 2015 (UTC)
____________________
Support, as proposer.
Sincerely, SamBlob (
talk)
12:34, 4 January 2015 (UTC)
Just from a note raised above, a few engines used the rare system of coupling rods to drive an OHC, not terribly dissimilar to a steam engine! I think the first of these was the unique 1923 Maudslay, which used a Y shaped rod to drive both camshafts from a single large eccentric. A similar system was used for the 3 litre Vauxhall, as covered in such depth in Ricardo's book. It's best known as a system though through either Parry-Thomas and the Leyland Eight or else the Bentleys. These didn't use large eccentrics though – to avoid such a device (I think the Maudslay got away with it by using ball races) they went for smaller and smaller eccentrics, almost a three-throw crankshaft rather than eccentrics - with of course needing three rods to connect them. The cost of these small journals was needing to use a three-throw system, to deal with the off-axis loads. Strictly these were still eccentrics, as they were just large enough to encompass the central axis of the crankshaft. The rods were an abomination mechanically as they made introduced a substantial reciprocating mass into the cam drive (just what were these supposedly expert engineers thinking?) Parry-Thomas did his inevitable of perforating the rods into Meccano and W O used what appeared to be a bag of knitting needles, having confused a reduction in parts count with elegance of structural design. Even more so than R-R, Bentleys were awful cars, looked after by surgeons. The whole sorry idea had its last fling in the 1950s with the NSU Prinz. By using a moderate size of eccentric, counterweighting and teaching dynamics in German high schools rather than Latin, the Germans managed to make a reliable design with only two rods.
All of these rod-drive designs used a reduction gear from the crankshaft before (obviously) the cam drive. So they weren't even any quieter than a geared drive. Andy Dingley ( talk) 12:09, 1 February 2015 (UTC)
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Sincerely, SamBlob (
talk)
02:47, 8 February 2015 (UTC)Something needs to be done about the "History" section. It is disorganized and haphazard. It needs to be either rewritten with some proper structure or dispersed into the relevant sections. There is quite a bit of SOHC history in the "Single overhead camshaft" section. This seems to be a good solution and I have copied that with the "Timing belt" section, moving some info out of "History" and into "Timing belt".
So which way should we go? Improve the "History" section? Dissipate it among the technical sections? A bit of both?
Sincerely, SamBlob ( talk) 13:16, 5 March 2015 (UTC)
I have disrupted the order of the article, and possibly not for the better. I had split off the section "Camshaft drive systems" from the "Overview" section and expanded it somewhat. Because I split it off from "Overview" I put it directly after that section, which puts it before the sections on SOHC and DOHC. It has just dawned on me that this might not be where this section belongs. Should I move "Camshaft drive systems" further down the article, between "Double overhead camshafts" and "History"? Sincerely, SamBlob ( talk) 18:08, 5 March 2015 (UTC)
Information about the Ford 427 "Cammer" engine was placed in a passage in the section Overhead camshaft#Single overhead camshaft dealing with the simplicity of SOHC when compared with DOHC. It is not clear from the passage how the "Cammer" engine illustrates the point being made by the Hillman Imp engine before it and the Toyota and Volkswagen engines after it. It is also unclear how the Cammer advanced the development of the overhead camshaft engine in general or the single overhead camshaft engine in particular, or what feature of the SOHC engine it is supposed to be illustrating. If the "Cammer" is just another example, should it not be put in the "History" section instead? Sincerely, SamBlob ( talk) 15:43, 12 March 2015 (UTC)
Can we get an accurate definition of "Unicam" please.
The idea of a single camshaft working both inlet and exhaust valves is inherent in SOHC. It's the use of a single cam lobe that matters.
Sharing a cam between inlet and exhaust is almost as old as SOHC. Not for mass-volume production cars, but for a number of engines, both car and aircraft. Particularly for V12s, which are otherwise a great many lobes to provide.
The Dolomite Sprint innovation was to use a single camshaft for 4 valve heads (with a single cam for each inlet/exhaust pair, ie still 8 lobes). This is not technically a particularly revolutionary design: it combines the shared inlet/exhaust cam lobe with 4 valve heads; but it's not as great an innovation as either of its components indivudally. I think this may have been novel (although I wouldn't be surprised to see an obscure early example), it was certainly novel for mass production cars.
The Dolomite 1850 engine was a "conventional" [ sic] SOHC with 8 lobes and 8 valves. This is the base engine used as the Saab derivative. Only the Dolomite Sprint engine had 16 valves. I can't think of another use made of it (the TR7 Sprint didn't go into production).
I know nothing of the "Unicam" engine, or of any way it innovated beyond the Dolomite Sprint. Andy Dingley ( talk) 21:29, 29 March 2015 (UTC)
Nobody calls it that. Dual Overhead Camshaft. 139.138.6.121 ( talk) 07:46, 15 January 2021 (UTC)
Sylvia Bordeaux inventor questions 4803623675 174.240.176.209 ( talk) 03:58, 28 April 2023 (UTC)