Dont all OHC engines have OHV as well?
I mean - its not as tho they are anywhere else. (the valves that is)
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You mean overhead valve operated by rockers and pushrods instead overhead operated directly by the camshaft?
AFAIK the last production side-valve engine was over 50 years ago, apart from I think Rolls Royce who used a hybrid overhead inlet and side exhaust.
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All current production cars have OHV engines! They just are not called as such any more, thats all.
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Cliff - I meant OHV as in a (old!) Mini 998cc. Camshaft in block/tappets/pushrods/rocker shaft arrangement...
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I don't think any OHC engine has ever had side valves, so it's implicit OHV.
I recall an ex-motoring journo who'd refer to 4WD as FWD but would also use the abbreviation RWD. I forget how he'd describe a Land Rover.
Don't get me started on nearside and offside. ;>)
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The last car I drove with OHV was a 1997 Fiat Cinquecento 899cc.
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Are you sure that wasn't an OHC?
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Definitely not, it had proper pushrods and not a whiff of a cam belt or camchain.
It wasn't the high-falutin FIRE engine, you know.
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I believe a lot of the American V8s still use pushrods/OHV
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Yes I believe the engine in the Corvette is still pushrod and dates back to the original Chevy smallblock of the 50s. Holden fit this engine to their fancy HSV and GM have manages to develop a 7litre version in the Corvette ZO6 that produces over 500 BHP and revs to over 7000 rpm.
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The odd thing is that as most people seem oddly averse to revving the engine (quotes like screaming at 3800rpm!), then, there's no real point in engines being OHC.
Of course, pushrod engines wouldn't produce such healthy performance figures to print in glossy magazines.
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Didn't Chysler introduce a new pushrod Hemi V8 last year?
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Well I'm blessed! I've just looked on C-b-C and it says pushrod.
>>not a whiff of a cam belt or camchain
It would need something to turn the camshaft!
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Gears - the old Bristol/BMW 2 litre for one had a gear driven camshaft in the block, 6 cyl, 12 valves and 18 pushrods. Seem to remember some Ford 1172 cc side valves had a gear drive made of some sort of fibre?
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Well I'm blessed! I've just looked on C-b-C and it says pushrod. >>not a whiff of a cam belt or camchain It would need something to turn the camshaft!
>>
Ah yes, but it's called a timing chain on this engine.
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Drifting somewhat OT now, but doesn't the big VAG V10 diesel have gear driven camshafts?
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Ford mass-produced cars with sidevalve engines up until 1961, if my memory serves.
Garden machinery shops are still full of lawn mowers, etc, with American Briggs and Stratton sidevalve engines, while Honda, Kawasaki, etc-powered machinery has at least OHV and often OHC.
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One of the current Rolls Royce or Bentleys still has a pushrod V8. I forget which. They managed somehow to get it through the latest emissions tests.
Regarding Ford side-valve engines, I believe the 100E was the one with a chain driven camshaft and adjustable tappets. The old engines required the valve stems grinding down in order to set the clearances.
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>>They managed somehow to get it through the latest emissions tests.
I can't imagine it makes too much difference to emissions whether the cam is below or above the head gasket.
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Referring back to Cliff's comment about side valve engines not being made for 50 yrs, the Velocette LE, one of which I have, continued with side valves until 1971.
Possibly the last application ?
Ted
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Why did OHV come first? No not a chicken and egg question!
But what were the advances that allowed OHC to happen? I can't see how having pushrods and rockers running from the bottom is simpler than having the cam just over the valves? :-S
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Was the original Skoda Favorit OHV?
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Yes the 1.3 was, and i think it may even have made it into the Felicia !
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I know they're not cars, but all of the new MAN and Iveco 7.5 tonners I work on have pushrods and adjustable tappets.
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Regarding motorcycles; all Harley-Davidsons with the exception of the V-Rod (which is a Porsche design) still use push-rod engines.
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Regarding motorcycles; all Harley-Davidsons with the exception of the V-Rod (which is a >> Porsche design) still use push-rod engines.
What do other tractors use nowadays?
:-p
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What do other tractors use nowadays? :-p
Not sure, but judging by the noise they make the Japanese have moved on to chainsaw engines; still a tenuous link with agriculture though! ;-)
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Yes the 1.3 was and i think it may even have made it into the Felicia !
I think it even made its way into the Fabia as the 1.4 mtp engine
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Why did OHV come first? No not a chicken and egg question! But what were the advances that allowed OHC to happen? I can't see how having pushrods and rockers running from the bottom is simpler than having the cam just over the valves? :-S
Easier development from side-valve?
Shorter timing chain - OHC needed long chains, or lots of gears, or even a vertical shaft with bevel gears, I think.
No need for additional shaft to drive oil pump or distributor.
Easier valve adjustment?
There were notable early OHC engines, single or double.
But I believe most "OHC" engines now are not true direct-acting cams? Haven't they reverted to rockers again, instead of shims under the tappets?
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the Velocette LE one of which I have continued with side valves until 1971.Possibly the last application ? Ted
Close, Ted, but once again Harley beat you to it!
The Servi-Car, a tricycle powered by the old "45" engine, ceased production in 1973.
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Number Cruncher wrote...I can't imagine it makes too much difference to emissions whether the cam is below or above the head gasket...
NC,
I always understood long 'knitting needle' pushrods were deemed to flex and bend, therefore making exact control of valve opening difficult.
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Yes, pushrods and rockers can have their own dynamics at speed, which was why I mentioned engine speed higher up in the thread. But, if you can keep the revs low during emissions testing, which mandates vehicle speed, not engine speed, then you would be hard pressed to see a difference.
Desmodromic valves, are IMO a bit of a problem to define. The valve cannot be closed absolutely solidly. As soon as there's any wear, you would either end up with the valve not closing, or shut so tightly that the stem would snap. In practice, there would always be a very stiff spring in series with the mechanism to allow for tolerances, thermal expnsion and normal wear. So, in my book, a true desmodromic valve system wouldn't work, and what would be needed is actually an approximation of it.
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>>> In practicethere would always be a very stiff spring in series with the mechanism to allow for tolerances thermal expnsion and normal wear.
Which is what Ducati use in their Desmodromic system. A torsion spring acts on the closing rocker arm "to take up slack" according to Ducati.
Interesting concept though.
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no ones mentioned desmodronics, ducati use them in the bikes and im sure i read somewhere rolls royce used them....
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I've thought of a pushrod engined car in current production!!
The Vauxhall VXR500 - uses a Chevy LS2 6.0 OHV V8, more commonly found in the Corvette. And very lovely it is too.
Edited by DP on 17/04/2009 at 10:13
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