Talk:Overhead camshaft engine

message: 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)
thread_title: Peugeot history

message: 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)
thread_title: OHV vs OHC

message: “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)
replies: text: That sentence is speaking mid 60s, not 70s.... but eg Alfa Romeo has been using dohc engines since 20s....  --— Typ932T | C  07:15, 2 August 2008 (UTC)
thread_title:  Fiat Dohc 

message: 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)
replies: text: Yes there can be difference, twin cam doesnt tell where the camshafts are and dohc tells they are overhead. --— Typ932T | C  15:23, 3 April 2008 (UTC)
replies: text: Ok, so location could be different.  how about the cam themselves?  is there any difference in them as to size, valve opening or anything like that? Cirilobeto (talk) 17:12, 3 April 2008 (UTC)
replies: text: While the terms DOHC and Twin-Cam are commonly used interchangeably, as said previously, Twin-Cams are not necessarily overhead. Additionally, in any engine with two banks (like a V-engine or a Boxer) a DOHC will actually have four camshafts. For an inline engine with two overhead cams, both terms apply. 
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)

text: For a long time, all twin cylinder Triumph motorcycles used twin camshafts. They were still OHV engines, not OHC. They ranged between 350cc and 650cc and that was the only design used (by one of the world's very biggest manufacturers?) from the mid 1950s to the 70s. (1970s three-cylinders models the same). Both camshafts remained in the crankcase, with pushrods etc and for all purposes were regular OHV engines, just slightly more complex. TomRawlinson (talk) 23:54, 28 October 2008 (UTC)
thread_title:  twin cam and dohc 

message: 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)
replies: text: No, the photo is in fact of a 12 valve SOHC head. The 2 shafts which you are mistaking for camshafts are rocker shafts. The camshaft is connected to the centre of the cam sprocket, and is obscured and not visible in the photo. Also notice there is only a single cam sprocket, meaning there is only a single cam.219.90.153.215 (talk) 10:46, 23 April 2008 (UTC)
replies: text: Apologizing for the delay, I do thank you ever so much for correcting my errors. --328cia (talk) 02:50, 26 October 2008 (UTC)
replies: text: I think you've just pointed out something very useful - all the photographs are useful - except this one. I'm almost tempted to say it should come out and replaced with a better example when we've got one. In fact, I'd go further, photographs of multi-cylinder engines simply confuse people. TomRawlinson (talk) 18:00, 1 November 2008 (UTC)
replies: text: How is the photo not useful? How do photos of mutli-cylinder engines confuse people? Please explain. IJB TA (talk) 01:56, 20 January 2009 (UTC)
replies: text: people can easily confuse the visible shafts on multi-cylinder heads with the cam shaft which in turn makes the engine appear to be DOHC. Besides which (and correct me if I am wrong) isn't this a 6 cylinder engine? If so then it is not from a Honda CRX as can be varified easily at the Wikipedia article on the CRX.  — Preceding unsigned comment added by Kingfrito 5005 (talk • contribs) 19:36, 15 May 2013 (UTC)
thread_title: Honda CRX picture

message: 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)
thread_title:  Stop rabbiting about OHV 

message: 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.
:Corrections for the corrections. The question concerning the picture of the SOHC head was directed at the second picture, the CRX head is in fact a SOHC. OHC engines always have fewer parts when comparing systems with the same number of valves and cylinders (4 cylinder 2 valve OHC engine to 4 cylinder 2 valve OHV engine). Though it is true that some OHC engines do come close to the high moving part count of an OHV engine it is very rare. The Honda SOHC C series V6 engines for example had a pushrod and two rockers just for the exhaust valve. Yes OHV designs can have some of the same configurations as OHC engines but OHV engines simply do not have the same versatility. There are some SOHC engines that have true hemispherical combustion chambers (LOM and Ranger inline 6 aircraft engines are two examples). Hemispherical heads are different from pent-roof heads, it's not just a different name for the same thing. There are no automotive engines with true hemispherical heads in production today, they simply wouldn't meet the current emissions or fuel economy requirements. Your point about a 2 valve engine being able to match the airflow of a 4 valve doesn't make much sense, at similar lifts the 4 valve will always have superior airflow. This is why at the very best 2 valve engines can only achieve volumetric efficiencies around 100% and 4 valve engines near 140%. The pushrod itself does not affect torque but it does affect the basic design of the engine including port design and valve area, both of which effect torque, and both suffer as a result of that design. 4 valve engines almost always make more torque for their specific displacement so a smaller 4 valve engine can match the torque output of a larger 2 valve engine. Also, I wrote much of the VVT article. IJB TA (talk) 02:37, 28 February 2009 (UTC)
thread_title:  Corrections 

message: '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)
replies: text: Looks like someone still can't read - they reversed the above IP editors corrections.  Now re-instated correct encyclopaedic terminology, alon with inline academic text-book citations. 194.75.238.4 (talk) 10:41, 29 August 2012 (UTC)
thread_title:  DOHC - correct terminology 

message: 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)
thread_title:  Article Split? 

message: 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)
thread_title:  Confused paragraph. 

message: 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)
replies: text: Sincerely, SamBlob (talk) 14:03, 1 February 2015 (UTC)

text: Looking at this further, it is interesting that you mention the 1923 Maudslay as the first when Parry-Thomas's engine was shown at Olympia in 1920 and, unlike the two prototypes of the  Maudslay, a few Leyland Eights were actually sold to customers. Sincerely, SamBlob (talk) 04:21, 6 February 2015 (UTC)

text: For future (use as a) reference:  Sincerely, SamBlob (talk) 02:47, 8 February 2015 (UTC)
thread_title:  Crankshaft or eccentric drive to OHC 

message: 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)
thread_title:  History section 

message: 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)
replies: text: I have moved the sections as as I had suggested above. Sincerely, SamBlob (talk) 18:12, 9 March 2015 (UTC)
thread_title:  Order of sections 

message: Nobody calls it that.  Dual Overhead Camshaft.   139.138.6.121 (talk) 07:46, 15 January 2021 (UTC)
replies: text: Sorry I don't make sense I was a kid 174.240.176.209 (talk) 03:59, 28 April 2023 (UTC)
thread_title:  "Double Overhead Camshaft"