OHC in 4.0?

[5-90]

5-90: From working on vw's I have seen both solid lifter and hydraulic lifter heads. They don't look a lot different size wise to me. The hydraulic lifters don't (read: shouldn't) need any maintenance.

Not "larger" in diameter - you can make a metal slug that will replace a hydraulic lifter (which is all a solid lifter really is.) However, you do have to have a bit more length in a hydraulic lifter than you do in a mechanical lifter - to accommodate the "hydraulic" part. A mechanical bucket follower can be a simple stamped bucket with a recess to accept a shim ("mechanical lash adjustment") - while a hydraulic follower/lifter needs to be (probably) at least a half-inch long to have room to pump up and to move oil.

I'm not trying to shoot down your idea - or belittle your experience - at all! I'm just bringing to mind something that will need to be thought about for something like this. I'm thinking it will be rather easier to have an overhead cam with rockers (with or without a ratio involved - anywhere from 1.0:1.0 to 2.0:1.0) and make for a bit shorter package than having the camshaft actuate the valves directly - and I know I'd sooner have a single overhead camshaft (fewer moving parts) than a double - even though you can get more valve curtain area and more "area under the curve" for engine breathing with a double and three or four valves per cylinder (the DOHC/multi-valve setup tends to shine at higher RPM, which isn't what we're interested in here. Low-RPM would probably respond to a more aggressive lobe profile, opening the valves sooner, and reliability would be served by having fewer moving parts (at least, IMO.)

If we're going to talk about redesigned heads, I'd really like to see a cross-draft head design using Coates Spherical Rotary Valves - significantly reducing moving parts, lubrication demands, eliminating valve float, and all that sort of thing (plus making for a shorter package than an OHC and nearly eliminating valve "hot spots" like you get with poppet valves... Look them up.)

 

[Comanchedude]

Like you I wish that the American car companies were always building on the latest technology. But that’s not the case for many years and we know its due largely to corporate greed and overpaid bosses and “maybe line workers as well” that keep them from making to many changes and falling behind the other countries in that respect.
The old (if it aint broke don’t fix it mentality) that kills advancements sometimes.
I don’t know that the OHC would have made the 4.L a better engine though simply due to the fact it stands out as the most reliable longest lasting engine of any type put into service. It is a big engine and its day had to end.
To your question:
I think it was just that it would have added cost to the new engine.
Not that a OHC engine would cost more to build from the start but they used all the same molds they had from the 258 and they used most all the same engine parts just making small changes and of course new intake with FI.
If they went OHC they could have done it in the same space I think.
There is room on the current head to mount cam and followers just like most imports I worked on. IMO . They would have to make substantial changes to the block like moving the distributor and making changes to the front of the engine to run the chain or gears to the head. That would require new engine molds ect. Also they would have to prove out the new engine that would have taken time.
So I really think that its only cheaper due to those reasons, all the new parts, molds ect.
They had all the parts just had to make small changes here and there to get the 4.L
If they had the time and thought it would make them more money they may have changed to an OHC design but I think car companies are just looking at cost and profit and how long they can milk any design, to make a big change like that when they had a solid working design would not provide any long term profit gain that could have justified the effort.
But we should think about the next engine to put in our jeeps.
(Gasoline is well outdated technology) as gas keeps getting more expensive we need a fuel cell or electric engine swap to keep these awesome Jeeps wheeling .I hope we get that upgrade path available very very soon. I want to wheel my old Jeeps till I’m too old to do it 

Before you flame me, understand I am just asking a couple of theoretical questions out of general curiosity.

I understand why a v8 would have pushrods. That way you can minimize the number of camshafts you need. By why use pushrods in an inline engine? Really, doesn't using pushrods just add rotating mass, complexity, and cost? While we are on the topic of head design, why not use a crossflow head? Or more than two valves per cylinder? None of these design concepts are new; they were around long before the 4.0 (or AMC's first I6 in '58 for that matter). With an inline engine couldn't you make an engine that incorporates all of these design elements while using only one camshaft?

Don't get me wrong, I know that an OHC, crossflow head, and multiple valves only really make a difference in a high RPM engine. But why did AMC/Jeep/ChyCo make a less efficient than they had to?

I am sure the engineers that designed this engine did so for a good reason... I just don't know what it is.

I am done now, flame away.

 

[j99xj]

I don’t know that the OHC would have made the 4.L a better engine though simply due to the fact it stands out as the most reliable longest lasting engine of any type put into service.

I agree. It was and is an outstanding engine, even if the basic design is old.

And back in 1987, it kinda was the best of both worlds.....a cheap (but tough) engine that was easy to work on, yet had the modern advancements such as fuel injection added.

This should boost everyone's spirits on the engine, it still gives me pride to know that I own a part automotive history.

http://youtube.com/watch?v=I5Q5HVbNb8Q

 

[5-90]

I agree. It was and is an outstanding engine, even if the basic design is old.

And back in 1987, it kinda was the best of both worlds.....a cheap (but tough) engine that was easy to work on, yet had the modern advancements such as fuel injection added.

This should boost everyone's spirits on the engine, it still gives me pride to know that I own a part automotive history.

http://youtube.com/watch?v=I5Q5HVbNb8Q

That was AMC. They weren't on the bleeding edge of tech or advancement, but they took "tried and proven" tech and ran with it rather more than everyone else would have. As as for-instance, all of the Gen-II and Gen-III AMC V8s had forged cranks. From the factory. There was no real "small block" or "big block" AMC V8 - as I recall (and I'd have to check...) a Gen-II block could make any Gen-II engine, and a Gen-III block could make any Gen-III engine. They used a high-nickel alloy to cast their blocks (V8 and I6,) which made them tough and durable - and reduced cylinder wear.

The RENIX fuel injection may not have been as heavily advanced as other systems, but it was simple, rugged, and durable. The engine block was tougher than the hinges of Hell. The crank may not have been forged (just the V8 cranks were,) but the casting was solid and used a good alloy. Just put a later head and intake on it, and you're solid (AMC could have used a little help with their I6 heads - but their V8 heads weren't bad at all.)

AMC had some good designs, and I'd really like to see what they could have done if they were still around for the last 20 years...

 

[heyhar]

Interesting talk of OHC engines. My dad bought a new Pontiac Tempest in 1966 that had the 230 ci OHC six. It was a strong runner, supposedly equal in HP to Chevy's 283. By the time I learned to drive on this car in 1971, at less than 30k, it had almost no power. It seems the camshafts were soft, and I remember it developing a nasty tap. A co-worker of his ground out the flat, but warned him about even less power. A valve job and new cam soon put things right, but now it was blowing smoke, leading to a new short block, at 36k. My dad was meticulous about maintenance, so it wasn't neglect. Pontiac, I believe gave up on this engine by 1970, and this was about the time GM started fooling with alloys, as anyone around in the mid '70s may remember the soft cams in Chevys of the day. I later owned a '69 Firebird with the OHC six, and it seemed to run better, although leaky valve guides caused wet plugs alot. If they had stuck with this engine and developed it more, I think it would have been one of the greats. As with everything else, though, the beancounters can't see past the next quarter profits, and GM tucks it's tail between it's legs, and instead of refining some great ideas they've already got, turn around and pay good money to buy back the rough little beast they dumped years ago, the Buick V-6. I hope AMC had a good laugh!

 

[TiRod]

OHC engines have issues. Ford is looking at replacing the mod 4.6 with a Cleveland head pushrod motor with cross bolt mains. Rumors have it that the cams are expensive - so says every engine designer the past 50 years - and the power output is virtually the same in street use. So they may be making an accounting decision, but it sure won't hurt the hot rod industry.

The crossflow head part is probably accurate - a redesign should have included it, but of course, changing what side the intake or exhaust comes off affects a lot of other stuff, and packaging the total engine module for assembly line installation has more bearing than our wish list. The whole concept of OHC is really a high performance, high rpm, horsepower thing that pushrod motors are easily capable of achieving with typical American ingenuity - more displacement. If an OHC motor could make as much horse as a stroker for the price, Chrysler would've gone that route rather than dumping it. And since the OHC is principally for higher RPM, it's not the best application for a 1/4 ton 4WD utility station wagon.

I hauled home three 80# sacks of cement Sunday, and 600# of steel angle iron for my fireplace Friday. It's got over 175K on it, and will go at least another 75K with no problem. Few OHC motors in my experience will do that as they are always spinning higher and wearing faster for the same horsepower. It's all about the torque curve and where it's located. Pushrod motors rev lower and last longer. So for Jeep, it's a better decision. And for Ford, the Mustang in particular, it will probably sell better with the customer base.

 

[darjevon]

The problem with OHC is that most people are going to drive the damn thing with a belt - which, y'ask me, is a mistake. If you've got to take an engine down to get to a belt, use a chain. Belts are for pants...

As long as its a non-interference engine, I don't see anything wrong with belt drive - are there any real advantages to chain rather than belt other than low maint?

 

[5-90]

As long as its a non-interference engine, I don't see anything wrong with belt drive - are there any real advantages to chain rather than belt other than low maint?

Primarily low maintenance and overall reliability. "Interference engines" strike me as a bad design as well - you design the valvetrain around a component that is more likely to fail (the belt,) and then further fail to design it such that if the component does fail, the engine is shot. Bad idea, y'ask me.

And, for a vehicle that could spend any significant time away from civilisation, a key component that requires more frequent maintenance and can be subject to total and instant failure is just stupid. That's why military field vehicles are chain-driven. Diesels are chain-driven or gear-driven. Little toy cars are belt-driven - while most light trucks are chain-driven.

 

[darjevon]

Primarily low maintenance and overall reliability. "Interference engines" strike me as a bad design as well - you design the valvetrain around a component that is more likely to fail (the belt,) and then further fail to design it such that if the component does fail, the engine is shot. Bad idea, y'ask me.

And, for a vehicle that could spend any significant time away from civilisation, a key component that requires more frequent maintenance and can be subject to total and instant failure is just stupid. That's why military field vehicles are chain-driven. Diesels are chain-driven or gear-driven. Little toy cars are belt-driven - while most light trucks are chain-driven.

I agree 100% that interference with belt is a bad idea.

Why isn't helical gear drive more common? Seems like a good option for cam drive to me...

 

[Matthew Currie]

I agree 100% that interference with belt is a bad idea.

Why isn't helical gear drive more common? Seems like a good option for cam drive to me...

Too much space between the crank and the cam. You need either a multi-gear train, or a vertical shaft, and that gets pretty complicated, expensive, subject to wear, and noisy too. Pretty elegant when done right, though, as anyone who's had an old Ducati motorcycle can attest. They used vertical tower shafts, with spiral helical gears, to drive overhead cams and desmodromic valves. They got away with it partly, I think, because there were no valve springs, so the gears weren't so heavily stressed. The gears looked like something out of a sewing machine. Complex as hell, and all adjusted with countless unobtainable shims. But it was a beautiful piece of machinery, and the castings were a work of art.