Honest question: Overhead cams

hiimandy1 said:
I have a somewhat related question, not pushrod vs OHC, but OHC vs DOHC. What is the advantage of a single cam vs double cam engine? Is it just fewer parts and therefore cheaper? AIRC the -55AMG cars and SLR use a SOHC engine, as well as Acura's V6s. Not cheap cars, so it's not like they couldn't afford another camshaft or two.
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It is very hard to make a 4 valve per cylinder head with only a single cam. Usually if you are going to put in that second cam, it is for a 4v or 5v layout. Also, I'm fairly sure the AMG V8s are all DOHC. I think the SOHC Acura engines are 3 valve.
 
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Crazyjeeper said:
It is very hard to make a 4 valve per cylinder head with only a single cam. Usually if you are going to put in that second cam, it is for a 4v or 5v layout. Also, I'm fairly sure the AMG V8s are all DOHC. I think the SOHC Acura engines are 3 valve.
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Honda has a few SOHC 4v engines. The benefit to Dual cams is better control over valve timing (with VVT) and allowing for a better head design that doesn't have to deal with locating rockers going every which direction.
 
It just seems there is less to go wrong in a non-interference low compression 2V design. Car complainies these days make cars that are impossible to fix yourself because nobody bothers anymore :(

Cars are complicated disposable transportation appliances and only certified dealership employees should play with its witchcraft? What is the world coming to :(
 
My Jag has a high compression interference DOHC 4V design engine and it is rock solid.
 
MattD1zzl3 said:
It just seems there is less to go wrong in a non-interference low compression 2V design. Car complainies these days make cars that are impossible to fix yourself because nobody bothers anymore :(

Cars are complicated disposable transportation appliances and only certified dealership employees should play with its witchcraft? What is the world coming to :(
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My truck is a low compression 2 valve non interference design, it also happens to be a SOHC motor.
 
MattD1zzl3 said:
It just seems there is less to go wrong in a non-interference low compression 2V design. Car complainies these days make cars that are impossible to fix yourself because nobody bothers anymore :(
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And an SOHC version of any given engine design has less still to go wrong than a pushrod version. There will be less parts in an SOHC engine and as we all know, any parts that aren't present can't possibly break.

Cars are complicated disposable transportation appliances and only certified dealership employees should play with its witchcraft? What is the world coming to :(
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Um, no, I play with modern vehicles all the time and don't find them all that much harder to work on if you have half a brain. Often they're actually easier to service than the older designs.

You shouldn't let your experiences with the Camry (which is a terrible example of modern engineering from a servicing standpoint) be the basis for your view of every vehicle whose engine doesn't date back to the 50s. Pretty much all but one of the vehicles I own are 'modern' engine designs with several having high mileage. All of them are SOHC or DOHC and all are rock solid reliable.

The last two pushrod V8 engines I had were quite the opposite. They were the "non-interference low compression 2V design" that you wax ecstatic about, and they were complete piles of crap; only lasted 30K or so apiece.

One other thing - Toyota can't make V6s, at least not consistently. That's why if you wanted a Japanese V6, you typically went over to the Nissan store instead because their VG/VQ lineup is the closest thing to invincible in that class.
 
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Wait... you're using a Toyota as an example of something to work on? The Japanese have NEVER been known for designing cars easy to work on. This is a company who thought it was a good idea to put an oil filter UNDER an exhaust manifold.

The Japanese are fantastic at making solid & reliable engines that don't need to be worked on so can be a PITA to work on. Go work on a BMW, a lot of the normal maintenance stuff is pretty easy to get to... well except if it's a 7 series.
 
I have the impression the thread title should be "I love pushrods, try to prove me wrong".
 
thedguy said:
Wait... you're using a Toyota as an example of something to work on? The Japanese have NEVER been known for designing cars easy to work on. This is a company who thought it was a good idea to put an oil filter UNDER an exhaust manifold.
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Yeah, I got the impression he's bitching about his Camry.
 
Redliner said:
I have the impression the thread title should be "I love pushrods, try to prove me wrong".
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:(

...whatever, close the thread than.
 
thedguy said:
Wait... you're using a Toyota as an example of something to work on? The Japanese have NEVER been known for designing cars easy to work on. This is a company who thought it was a good idea to put an oil filter UNDER an exhaust manifold.

The Japanese are fantastic at making solid & reliable engines that don't need to be worked on so can be a PITA to work on. Go work on a BMW, a lot of the normal maintenance stuff is pretty easy to get to... well except if it's a 7 series.
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Miatas and Hondas aren't very difficult to work on. My old Maxima wasn't too bad, although it was no Honda. Haven't had much experience with other Japanese cars.



Redliner said:
I have the impression the thread title should be "I love pushrods, try to prove me wrong".
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He just doesn't want to take our word that OHC engines are any good. Good for him.
 
...Stupid Sepp's... :rolleyes:

1) First off we are talking about where the camshaft is in relation to the valve train, Not the number of valves

2) In a simple flow situation there is no advantage of a OHC to a cam in block when only 2 valves are involved.

3) Its not what you've got, its what you do with it...I'm a avid fan :p of bashing pushrod engines, but the Gen 3 engines prove this point...:blink: I would rather have a pushrod engine with a modern (well advanced) EFI system, low friction pistons etc than a "advanced" OHC engine without this stuff..

4) A 4 valve layout with only 1 cam overhead camshaft is quite easy, Subaru, Daihatsu, Fiat, Mitsi....hell a heap of makers do this. The main issue is the inclination and location of the spark plug. If you want to look around all SOHC Subaru EJ's are 4 valve

5) A OHC motor will generally have higher oil system requirements, both in quality and volume, you have the cam bearing up the top, the lifters (if you have hydraulic's) --> which means you need to have more oil feeds to the top of the head, get your oil drains setup correctly so at higher rpm you don't pump all up into the cam box's and run bearings (are you listening Nissan?!? Damn 4 valve crap...)

...plus when you start the thing you have to pump oil all the way up to the top of the motor (yes I know you end up with stored oil up in the cam boxes)

I think this is why OHC motors initially got a bad rap in reliability (well and OHC cars with timing belts snapping), but it simply isn't a issue these days. It really isn't.

(Oh and if you want fun to work in try a Alfa Romeo 147GTA)
 
What kind of magic engine do you have?
 
GRtak said:
What kind of magic engine do you have?
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Almost 270K on timing chain number one on the Series III; over 100K on the XJR. I had 400K+ on timing chain number one on my former Toyota pickup truck with the 22R motor.

Most OHC engines have chains that run for hundreds of thousands of miles. It helps if you don't make idiotic design decisions like "hey, let's make the timing gears out of nylon!"
 
Spectre said:
Almost 270K on timing chain number one on the Series III; over 100K on the XJR. I had 400K+ on timing chain number one on my former Toyota pickup truck with the 22R motor.

Most OHC engines have chains that run for hundreds of thousands of miles. It helps if you don't make idiotic design decisions like "hey, let's make the timing gears out of nylon!"
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Or use cheap plastic tensioners. :p
 
I blame Ford for that one. Ford was notorious for getting cheap on timing chains and then wondering why everyone got angry at them over it.
 
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