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Over head cam
8

Over head cam

Over head cam

(OP)
I am having difficulty seeing the logic in using that tech for average everyday cars, especially in the past before the advent of VVT tech. It is such an expensive way to accomplish the task. Expensive to manufacture and when needing repairs due to warped heads, worn cam drive systems and the like. But in this day of disposable engines it makes things a bit more logical. Problem is these all seem to be over priced inexpensively built engines, so that makes the disposability a bit hard to take in the pocket book. For racing and performance its a go, not for grocery store cars.

RE: Over head cam

enginesrus,

Personally, I don't feel overhead cams are a big cost adder, especially in the four cylinder engines that dominate the market these days. By eliminating pushrods and lifters, overhead cams keep everything tighter which helps high RPM performance valuable in short stroke engines (which are popular to keep vehicle weight down and frontal profile small). Fuel economy relates directly to both economy and emissions, so keeping frontal area (drag) low and fuel efficiency high has direct impact on the marketability of a car these days. Bring back $1/gal gas and eliminate emissions/economy requirements, and pushrods/lifters would likely still be with us.

Rod

RE: Over head cam

Nobody wants a 2.0l four with less than ~200HP these days.
At that power level, the engine has to breathe really deep.
With big ports, there's no room for pushrods.

Mike Halloran
Pembroke Pines, FL, USA

RE: Over head cam

What happened "in the past" is no longer relevant aside from many of today's engines being descendents of that past.

The engine in my car is a Fiat 1.4 MultiAir. This is 16-valve SOHC with Fiat's MultiAir variable valve timing and lift system. (MultiAir takes the place of the intake camshaft)

It's a descendent of the 1.4 DOHC 16-valve with a different cylinder head for the MultiAir components.

That's a descendent of the entire FIRE engine range that Fiat developed in the 1980s. FIRE = "Fully Integrated Robotised Engine" = designed for automated machining and assembly. Now, everyone does that, but it was revolutionary back then. The original engines in the FIRE range were 4 cylinder SOHC 8-valve, and some of those continued in production long after the 16-valve and MultiAir variations were developed.

The FIRE engine range replaced an assortment of older designs, some SOHC 8-valve, some pushrod. The original architecture for some of the engines it replaced dated back to the 1950s if not before.

Among other manufacturers, I don't think Honda has ever built a pushrod engine for automotive or motorcycle applications.

The only VW pushrod engine that I can think of is the old air-cooled flat-four. Pushrod made sense with that layout, but the inline engines (which started in the early 1970s with the VW Golf Mk1), OHC makes sense. It's an understatement to say that the VW air-cooled flat-four is obsolete in today's world.

RE: Over head cam

maybe enginesrus wants us to go back to simpler engines like the three cylinder two strokes that were built by Saab, DKW, Wartburg etc. Very simple, cheap, dirty and unreliable, but usable as a grocery car.

RE: Over head cam

Honda actually made a 4 valve push rod transverse V twin motorcycle back in the late 70's and early 80's. Just throwing that out as a historical anachronism. They even turbo'd it back when people thought that was a good idea.



I know Honda made a claim that they could build a 4 valve engine for the same price as a two valve because the smaller lighter valves were lower stressed and thus could be made from lower cost material.

I'm a big fan of DOHC 4 valve engines in my motorcycles but at the moment all my vehicles have push rod V8's. Chevy continues to develop the LS series and they are great in terms of packaging efficiency. You would never get a big V8 DOHC engine under the hood of my C6. I'm pretty pleased with the 28 mpg highway it gets too, the best of any car I've ever owned.

Going back to the Ford Modular V8 DOHC in the video, I'm not aware of any egregious problems with that engine. When they are made in the millions, every engine family has some that break. Every engine has to be produced to a cost that consumers can stand. Every car company has to sell products in a very competitive environment. If there are bad failure modes people stop buying the products. Fords F150 is the best selling vehicle in the country and has been for a long time. Statistically, vehicles are getting more reliable every year. I don't think toysrus has a leg to stand on.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: Over head cam

(OP)
Greg I see the answers. And something else I have seen in my time, is some engineers that have no time behind a wrench, or a machine tool. OHC especially the higher end DOHC's not the geo metro's is very labor intensive to work on as far as timing chain and head R n R, overly complex on some brands. I am not complaining about power potential of the design, its the lack of durability (material choice and design), and difficulty to repair. The LS and the Hemi are great examples of not choosing the OHC design.

This is quoted from above.
""" What happened "in the past" is no longer relevant aside from many of today's engines being descendents of that past.
"""
I think this is a problem in engineering these days, no one has learned from what the old guys toiled to improve back in the days of slide rules and rotary calculators. And is why there has been such a rash of problems that have cost some owners of the new age cars thousands. Things learned years ago seem to have been forgotten in some cases. And some things thought as new ideas are really old ideas.

RE: Over head cam

Lack of durability (material choice and design) is not a pushrod-vs-OHC issue. Difficulty to repair is not a pushrod-vs-OHC issue, either.

Vehicles nowadays are designed to go down the assembly line easily, they are not designed to be serviced afterwards easily, and they are ALL like that. The engine is designed to go together in automated and semi-automated fixtures on its own without anything else around it, then it gets mounted on a subframe together with accessories and transmission and steering and suspension parts, then the whole thing gets plonked into the bodyshell as a single unit. The fact that you now can't reach parts of the engine for access without dropping the subframe ... is not their concern. And they are ALL like this and it doesn't matter if the engine is pushrod or OHC.

Fortunately, stuff generally needs less fiddling than it did in the old days. The days of needing periodic valve clearance adjustments are gone. The days of needing to fiddle with breaker points and condensers are gone. Spark plug replacement intervals are often 100,000 km or more. It's not common to need to remove a cylinder head any more. (I've never had to have the cylinder head removed on any car or truck that I've owned, and I've taken a couple of vehicles past 400,000 km.)

The Chrysler Hemi perhaps is a good design but so is the Pentastar V6, and those are DOHC 4-valve with VVT. Changing spark plugs on those is a bear ... part of the intake manifold has to come off. But that's not the DOHC's fault. Fortunately, it isn't specified until 160,000 km.

Would the Pentastar be a better engine if it were a pushrod design? Well, considering that the single Pentastar engine design replaced a raft of prior designs, some SOHC, some pushrod, and it makes more power and is lighter and is more efficient than any of them ... probably not.

Would the Hemi be a better engine if it were DOHC 4-valve with VVT? It wouldn't have the same marketing, that's for sure. One thing of note is that if it kept a 90-degree layout, it would be wider (the Pentastar is a 60-degree V6 and this is not an issue). Yes, pushrod cylinder heads are more compact. But this is mostly only a 90-degree V8 issue. For an in-line or a 60-degree V6 ... The DOHC heads fit in all the applications that matter.

I think Chrysler make the right choices for both of these.

RE: Over head cam

Do you have any proof of this widespread lack of durability in OHC engines?

RE: Over head cam

The way these threads usually seem to go is that any request for data to back up the OP's wild assertions about engineering are met with bluster followed by a rapid and permanent exit from the thread.

Then two weeks later there's a new thread about some other way that every engine designer in the world is doing it wrong.

RE: Over head cam

Ah yes, but it's sometimes good to question whether we are here (i.e. at today's implementations) by evolution or by design.

Steve

RE: Over head cam

We're here by both- the evolution of design.

RE: Over head cam

I don't think people appreciate the extent to which evolution in simulation and manufacturing technology combined with the evolution of emissions standards has influenced engine design. Engines aren't the way they are because designers are stupid!

RE: Over head cam

Quote (RodRico)

Engines aren't the way they are because designers are stupid!


Well put.

RE: Over head cam

RodRico - exactly, even though some people still insist the high point of engine design was the end of the '60's.

I'd also like to know what in the newer engines can't be fixed which makes them a throw away item.

At any rate, mistakes can still happen (design and build) and not every single engine built will run 500,000 miles trouble free. But, some of that can be attributed to usage and maintenance. The hard work of the design engineers have produced MUCH better products then we had even 15 or 20 years ago and engine reliability today is way superior then anything produced 20+ years ago. Engines today easily go 100,000 miles before requiring any maintenance beyond oil changes. That would be the point where the plugs had been replaced 10 times and the engine was needing a rebuild 30-40 years ago.

RE: Over head cam

Quote (LionelHutz)

At any rate, mistakes can still happen (design and build) and not every single engine built will run 500,000 miles trouble free.

Right on.

The other thing that I think a lot of the worshippers of the past fail to understand (or just ignore altogether) is that failures today get public attention they way they couldn't 50, 30, or even 15 years ago.

In 1980, if Ford released a bad batch of Mustang engines out into the world and they all blew head gaskets, there was no Jalopnik trolling MustangForums.com and then writing articles about it.

The much-lauded Focus RS head gasket debacle got a ton of press, but it's a problem that cropped up on less than 150 cars. And Ford is replacing probably 15,000 head gaskets because of it. In 1980 (or 70 or 60) an issue that grenaded 100 engines out of 100,000 wasn't even a blip on the radar. Now it's cause for picketing in the streets.

RE: Over head cam

(OP)
The lack of durability comes from the need for the long snaked timing chain and the plastic guides it rides on to support and guide on its path up to the heads and back down to the crankshaft. There are plenty of stories about the various engines that need this timing chain drive system fixed at very low mileage figures. And in some cases there is enough destruction to require total engine replacement.
Pentastar ? Is the exhaust manifold still an integral part of the aluminum head on those engines? They have done so many redesigns on that engine and had to increase the warranty mileage to help sell them.
I guess not many here have turned a wrench on push rod vs DOHC engines since there seems to be a lack of knowledge of what is required to say remove a head from one or the other.

RE: Over head cam

(OP)
That's like asking me for data of airbag problems before it became so widespread that the manufacture finally had to admit there was a problem. That is pretty much how problems with cars are dealt with. Like the BMW failures of the past.
Or the Porsche problems, or the Toyota problems, many just swept under the rug.
It is not like extracting data from a dyno run.

RE: Over head cam

[ I don't think Honda has ever built a pushrod engine for automotive or motorcycle applications.]

Ooops....The first C50 was a pushrod engine, the CG110 and 125 were very popular, and of course the CX already mentioned. They also made a high cam engine in quads, similar to BMW, where the cam is in the head, but opperates pushrods. Engines converted from pushrod to OHC (Volvo, Ford Falcon) are much taller engines...that's not exactly going to get frontal area down.

RE: Over head cam

Quote (enginesrus)

That's like asking me for data of airbag problems before it became so widespread that the manufacture finally had to admit there was a problem.

Do you realize that cars have been on the road with overhead cams for more than a century?

I mean... did you know that? Seriously? This isn't new.

RE: Over head cam

(OP)
I've got 4 that do have OHC. They are great for repair shops, a head pull means dealing with cam drive and timing along with the normal things needed on a push rod engine. Cam drive was never an issue on say an old chevy 6, and they out lasted many modern engines of now days. Just so many 10,000 to 20,000 dollar disposable auto engines now. Has anyone here ever worked on a W8 VW engine? I have, and how much fun is dealing with the cam drive system on that engine?
https://www.youtube.com/watch?v=slQ9E1s1FuQ W8 is very similar to this cam drive at about 4:00.

Disposable
https://www.youtube.com/watch?v=c2g6H3u9B8o

RE: Over head cam

Quote (enginesrus)

an old chevy 6, and they out lasted many modern engines of now days.

They lasted longer?

You sure?

Have any data that says so?

Something other than a youtube video?

Something other than your opinion?

RE: Over head cam

2
Don't cite a VW engine as an example of engine design. Just don't.

and, "or the Toyota problems, many just swept under the rug. " Hunh? Toyota has run so many voluntary recalls on their products it makes your head swim. Voluntary recalls are a sign of a healthy company, willing to fix things so their customer base stays loyal and happy.

RE: Over head cam

The W8's maintenance nightmare (which it was), wasn't the fault of it being OHC.

I've had the cylinder head off a few motorcycle engines, all OHC, and the fact that you have to disconnect the timing chain tensioner and remove the camshafts as part of the procedure is a relatively trivial part of the overall job.

RE: Over head cam

(OP)
Brian, then just use the Mercedes as a OHC maintenance nightmare, or maybe the subarus, or BMW's. And when the cam drive system goes out, its most always a front cover removal to access the plastic chain guides. Except for the rear timing chain engines like the W8.
Data on the old chev 6's out lasting the newer engines? Data? Where would you even begin to find such data?
The OEM's for all the failed modern engines will not release such info, and they will be the only source for it, because even when out of warranty they will still be the number one point of first contact in hopes of help. Maybe attorneys would have the info. And to be fair the data would have to only compare the number of failed engines with in 1 year when the warranty runs out. There would be little if any data available beyond that.
jgKRI if you trust the other sources on the net there is data of the modern engine failures, in the form of consumer complaints, there will be none on the old stuff.

RE: Over head cam

3

Quote (enginesrus)

Data on the old chev 6's out lasting the newer engines? Data? Where would you even begin to find such data?

I have no idea where you would find this data. And....

That's my point exactly. You're making a baseless claim.

If there's no data available, where did your opinion that the old 'chevy 6' is the paragon of gasoline engine reliability come from??

I can tell you one data point that doesn't support your case- look at the history of automotive warranties offered by Big 3 OEMs.

In the 60's there was a 'warranty war' as all three major players added years and mileage to their warranty programs, in an effort to outmarket each other and boost sales. Lincoln's BIG PLAY early on was to offer a 2 year, 24,000 mile warranty. If that was the 'halo' warranty offering from any major non-luxury manufacturer now, they likely wouldn't sell very many cars.

By the early 70s, these warranty programs had sank back down to single year with low mileage limits- because the cars of the late 60s were built with such varied quality that the warranty war cost the big 3 massive amounts of money.

Engines today are categorically better that the 'chevy 6' you reference and it is not close. They are lighter, they last longer on average by a large multiple, they produce a LOT more power from smaller packages, they are much less expensive to own over the long term, they are made in larger numbers with much better manufacturing consistency, they are better for the environment... they are literally better in every single conceivable way. The fact that they use technology that you don't understand or don't like is not a valid argument for much of anything, let alone for why we should all be pining for slant sixes iron heads and single barrel carbs.

You're worshiping an era that no one wants back, and making a wild claim that you, by your own admission, can't support. And you do this same routine in seemingly every thread you start... I'm not sure why.

RE: Over head cam

(OP)
Thank you for the help.

RE: Over head cam

Seems to me there are lots of interesting tradeoffs. (initial cost, bulk vs weight vs power per liter, etc...)
If emissions standards weren't mandated, cat converters wouldn't be needed, and priorities of engine development would have been quite different.
However - seems to me that power and economy would still have driven fuel injection and related developments.
I sure don't have the answers - don't even have all the questions!
It certainly would be fun to know more about statistical reliability of various engines. Consumer Reports ratings of new and used cars offers some clues, perhaps.
Two of the cars I had in the past were downrated (by CR) for fuel injector problems - Buick 3300 V6 pushrod motors.
I put lots of miles on the cars I had (two 3300s, one older 3.8, and a 3800) with never a hint of FI issues.
But three vehicles out of millions - not statistically meaningful.
Another data point re repairability - most 3800 enthusiasts consider the motor not worth rebuilding, as it is easier to find a good used motor with only 100k miles or so, and run it!
And that is an iron block, iron head pushrod motor.
Yeah, the Ford spark plugs are a bit scary - need to have some care getting them out to avoid a cyl head R&R.


Jay Maechtlen
http://www.laserpubs.com/techcomm

RE: Over head cam

Wasn't the push towards OHCs vs pushrods more to do with weight reduction and fuel economy, as it was easier to design light, small capacity, high power engines with DOHC at the time? That's not to say that in retrospect it was the right decision, compare the DOHC LT5 Corvette engine and its pushrod successors, LS1 and LS6.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Over head cam

The Ford plugs were a perfect storm - neck down the plug to a tiny section; make it from a low-expansion material and drop it into a close-fit hole made with high expansion metal; then introduce fuel which won't combust well in the narrow gap, depositing carbon; tell people they don't have to mess with the plugs for 60 or 80 thousand miles and, finally, tell people they have to change the plugs when the heads are cold, so that differential expansion gets the tightest grip the head can possibly have on the carbon coated plug.

If they had changed any of those things there would have been few to no problems.

RE: Over head cam

Quote (3DDave)

The Ford plugs were a perfect storm... finally, tell people they have to change the plugs when the heads are cold, so that differential expansion gets the tightest grip the head can possibly have on the carbon coated plug.
That is interesting. I just acquired a 2003 Grand Marquis, and was warned by my mechanic brother to R&R the plugs sooner rather than later. But the hot vs cold, I get the differential thermal expansion, so is there also data supporting that removal hot is better than removal cold?

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

RE: Over head cam

I'm not sure that hot/cold matters, because by the time you get the first one out, the engine will be cold anyway.

My mechanic friend suggests applying PB Blaster (or Kroil if you have it) to each plug for several days in a row, then working slowly and carefully to ease them out.

Mike Halloran
Pembroke Pines, FL, USA

RE: Over head cam

lol
I meant to include in my post, only 50,000 original miles, so the assumption is the plugs are original (undisturbed) also.
@MikeHalloran, I was thinking along those lines myself.
Does anyone know a maximum safe removal torque?

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

RE: Over head cam

How long does it take to remove a plug? Anyway, if the engine cools before they are all out, put in the new ones and toast it up again, just don't over torque the replacements; wait for the engine to cool before setting the final torque. Differential thermal expansion is one of the things a person can count on. It looks like the eventual recommendation was to use impact tools on the spark plugs; maybe it fractures the carbon.

Not sure how the Kroil gets past the threads to where the interference is. This isn't the threads binding in the head, it's the probe that feeds into a tight passage that breaks off because of jamming with carbon. http://www.fordproblems.com/trends/spark-plug-stuc... That probe is swaged to the threaded body, so it twists off and then breaks the ceramic and electrode off.

I think the rate for changing plugs was between $50 and $100 each for labor to make up the cost of removing the stub, but if it got bad it seems some were charging closer to $5000 per head to remove the fragments. Obviously better to avoid injury lawsuits from mechanics getting burned on hot engine components than worry that changing a set of plugs might cost the the customer a thousand dollars or more.

I found the original recommendation was 100k miles interval, but the class action settlement prevented anyone from claiming if they had more than 80k. Most of the checks were under $100. It is now 65k, but I think most owners are going for 35k to be safe.

RE: Over head cam

Popularity/beauty contest for engines? No mention of serviceability or reliability there...

RE: Over head cam

Quote (3DDave)

How long does it take to remove a plug?

Spark plugs at least in the early 3-valve Ford modular engines are notorious for breaking during removal, so it's apt to involve more than simply removing the coil-on-plug assembly and unscrewing the plug. There are special "broken spark plug remover" tools available from a number of sources, as it's apparently that common.


Norm

RE: Over head cam

Been reading the Wards 10 best for decades, didn't know there was a wiki summary. Wards do not take serviceability or reliability into account. Frequently the engines are brand new designs so no reliability data would be available. About the only outfit I'm aware of that compiles reliability data is Consumers Report and I have my doubts about their data since I believe the vast majority comes from members and is thus skewed by the bias of what kind of cars their members buy.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: Over head cam

Quote (MikeHalloran)



I'm not sure that hot/cold matters, because by the time you get the first one


Our engine manufacturer wants us to set valve lash and injector timing on a "cold" engine. We have determined any engine that isn't running is "cold" regardless of the actual temperature.

RE: Over head cam

Quote (TugboatEng)

. We have determined any engine that isn't running is "cold" regardless of the actual temperature.

NASCAR says it's something 3 hours after shutdown. Engine builders for that series can set the bore to come down to size after 2:45 or so.
My motorcycle mechanic friends insisted on letting a Kawasaki ZL-1 sit overnight before measuring the valve clearances.
I worked on a Kawi racer warranty claim, and measured the piston bore clearance every way I could think of. After three hours, it finally settled down to just barely tight enough.
On a big marine Diesel, it might take three hours just to get the works exposed enough to begin measuring the valve lash, so I'd agree that 'not running' is practically appropriate.

Mike Halloran
Pembroke Pines, FL, USA

RE: Over head cam

Well, I found and read the TSB (08-7-6) on the Ford modular engine spark plug issue. Interestingly, it only refers to specific models and years, which do not include my vehicle. Since it is not an overhead cam specific issue, but rather a spark plug design issue, I'll discontinue the hijack.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

RE: Over head cam

''Available in the US market''....I wondered why it was so biased.

RE: Over head cam

Quote (pushrodsrus)

I guess not many here have turned a wrench on push rod vs DOHC engines since there seems to be a lack of knowledge of what is required to say remove a head from one or the other.
Actually, I have (at various times, all three - pushrod, SOHC, and DOHC), and I think you're cherry-picking particularly difficult/more involved examples with your German car and Subaru examples. The German mfrs have a reputation for taking the complex way out, and a boxer engine manages to hide most everything (especially when turbocharged and there's an intercooler sitting on top burying the engine itself under yet another layer).


Norm

RE: Over head cam

Quote (enginesrus)

I am having difficulty seeing the logic in using that tech for average everyday cars, especially in the past before the advent of VVT tech. It is such an expensive way to accomplish the task. Expensive to manufacture and when needing repairs due to warped heads, worn cam drive systems and the like. But in this day of disposable engines it makes things a bit more logical. Problem is these all seem to be over priced inexpensively built engines, so that makes the disposability a bit hard to take in the pocket book. For racing and performance its a go, not for grocery store cars.

VVT is not exclusive to DOHC engines. I believe the Dodge/RAM hemi has had it since 2009, it's definitely in my '14 RAM 1500 5.7 liter push rod hemi. GM finally got around to introducing similar technology in the 2014 LT1 6.2 liter C7 Corvette motor (not sure what they use in their pickups).

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: Over head cam

Quote (dGallup)

(not sure what they use in their pickups).

Every V8-powered GM truck sold since MY 2010 has had VVT.

RE: Over head cam

Doesn't GM's pushrod VVT affect cam phasing relative to the crank without being able to vary intake to exhaust timing? Kind of a halfway step.


Norm

RE: Over head cam

Yes, that's how VVT on the GM pushrod engines work. The entire cam is phased. Fortunately, in the circumstances where you want to run partial Atkinson cycle, delaying intake closing in order to intentionally reduce VE also delays exhaust opening so that it makes more use of the expansion stroke, and delaying exhaust closure (and valve overlap) to after TDC also produces "internal EGR" which is usually favorable in that scenario.

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