Valves suck

I hate poppet valves, for nearly it's entire existence, it has been these stupid valves that have been the 4-stroke engines weak point.
Burnt valves, pitted valves, sticking valves, noisy valves, valve jobs (ewww!)

Until somebody comes out with a workable rotary valves I'm going to continue viewing the 4-stroke-cycle as far from perfect.
My two favorite types of engine, 2-stroke, and wankel, do not have need for poppet valves, nor should any engine!
But I look back and revere those designs that sought to eliminate these horrible things, inventions like the sleeve valve engine, and the rotary valve.
Inventors have been working on rotary valves, and yet the rotary valve is not in any car being produced today. My question is why? It's been decades in development, and can potentially solve most problems we associate with poppet valves.
Has anybody heard of any recent developments in engines with unconventional valves?

you have 3 choices, a 4 stroke with poppet valves, a 2 stroke without them or a rotary. The first makes less power then the 2 stroke but a 2 stroke is about as dirty as an engine gets, there's also the problem with no change in "valve" timing because the ports dont move, then theres the rotary, a torqueless wonder with little reliability. It's up to you but poppet valves seem to be the best choice around, rotary valves have unacceptable sealing, I believe ducati had a valve that rocked back & forth but that had reliability problems too, rotaries have their ports without any variable timing so they're stuck too, the only advancement is using poppet valves and solenoid control. Maybe one day rotary valves will work, but they havent yet.

hey, you left out the two-strokes with poppet valves.

Turbo rotaries have low reliabilities.

The new ones (RX-8) should have excellent reliabilities with 12A durability and 13B turbo power. Only time will tell though.

Actually, the Aspen rotary valve seemed very promising, but I've haven't heard anything about it in the past decade! And it looked to be very neat design.
2-stoke engines, can have variable exhaust timing, controlled by a butterfly type valve in the exhaust port which increase or decreases exhaust backpressure depending on engine speed. However, in a 4-stroke there really isn't any change in valve timing.
Rotary engines aren't very unreliable, that's just the reputation they got from the Ro-80, which was one of the earliest rotary engined cars, and therefore can't really be jugded (as in, you can't say a piston engine is unreliable just because a 1899 Panhard was!)

Originally posted by 2strokebloke
2-stoke engines, can have variable exhaust timing, controlled by a butterfly type valve in the exhaust port which increase or decreases exhaust backpressure depending on engine speed. However, in a 4-stroke there really isn't any change in valve timing.

You might want to look around online a bit for info about variable valve timing. I assure you that such a thing exists, and is becoming increasingly popular (for four-stroke engines).

The butterfly valve you're referring to doesn't change the "valve timing" of the two-stroke engine any more than a variable geometry helmholtz resonator changes the valve timing of a four stroke engine. Both devices influence scavenging, not valve timing.

Using the "butterfly valve" reasoning introduced above, everybody who ever put a header on his car influenced "valve timing" in the process. Sounds a bit silly to me.

you guys might wanna read this:
http://www.automotiveforums.com/vbulletin/t94233.html

Actually Ivy, I could argue that because a 2-stroke engine does not have a dedicated exhaust stroke, the the backpressure in the exhaust system not only controls how the exhaust gasses can leave, but also when they can leave.
The effects of putting a different exhaust on a 4-stroke are different than the effects of putting different exhausts on a 2-stroke (a 2-stroke relies on the exhaust system to make power, put on a muffler made for a 4-stroker and you'll barely have enough power to move along a level surface)

And about variable valve timing, none of my 4-stroke cars have it, so I don't really see valveless engines at a disadvantage there. In fact, valved engines have many disadvantages! (most of them caused by the valves themselves)

Actually Ivy, I could argue that because a 2-stroke engine does not have a dedicated exhaust stroke, the the backpressure in the exhaust system not only controls how the exhaust gasses can leave, but also when they can leave

You could, but you'd sound pretty silly. Exhaust and intake tuning work in pretty much the same way in both cases; the two stroke is just more sensitive to them. Valve timing on a four stroke is similar to port position on a two stroke. You wouldn't say that your butterfly valve can do exactly the same things that moving the port can do, would you?

And about variable valve timing, none of my 4-stroke cars have it, so I don't really see valveless engines at a disadvantage there.

Talk about the silly things one could say... Here, let me match you one-for-one on that. "About valveless engines, none of my cars are like that, so as far as I'm concerned they don't exist."

Originally posted by 2strokebloke
In fact, valved engines have many disadvantages! (most of them caused by the valves themselves)

Luckily for the four-stroke poppet-valve fans out there, the advantages of this configuration at this point in time far outweigh the disadvantages, making it the most popular configuration currently in use. Better driveability, less harmful emissions, lower noise levels, and better fuel economy, to name a few advantages...

"Better driveability, less harmful emissions, lower noise levels, and better fuel economy, to name a few advantages..."

The only reason we still have poppet valves is because for most engineers they they were simply "good enough" not because they were the best.
With rotary vavles, better volumetric efficiency can be gained, valve noise can practically be eliminated becacause the valve rotates instead of clapping open and shut, and no matter how fast the engine revs, valve float would be totally impossible.

As to 2-stroke exhaust, no the port itself will not move, therefore port timing itself is not actually changed, but the backpressure causes a huge change in performance, I guess I worded it badly, I did not mean to write that 2-strokes have variable port timing, but that essentially the same effects of such can be had with this valve.

Let's just say this, my 2-stroke car's engine has five moving parts, produces 1.19hp per cubic inch @ 5500rpm (better than most muscle cars, and better than a Viper) is ultra reliable, I've never had to deal with valves, because it doesn't have any. This means, I've never had to change a timing belt (or gears, or chain) never had to set valve clearance, never had the engine eat a valve, or burn a valve either, never had a sticking valve etc. etc. And I certainly can not write all of that about that about my 4-strokers.

Also, if you're literate, you'll never see that I debated the existence variable valve timing, I just stated that it wasn't on any of my 4-strokers and it wasn't on my 2-stroke either.

The poppet valve is old and outdated (and has been for more than half a century now) is it not time we look to a better alternative?

However, in a 4-stroke there really isn't any change in valve timing

And about variable valve timing, none of my 4-stroke cars have it, so I don't really see valveless engines at a disadvantage there.

Also, if you're literate, you'll never see that I debated the existence variable valve timing, I just stated that it wasn't on any of my 4-strokers and it wasn't on my 2-stroke either

yawn... You'll never see that I debated the existence proper grammar. Also, if you're literate, you'll never see that I didn't say you did.

Perhaps you should re-read the thread. All I said was that the logic you used in the second statement listed above was very similar to "if I don't have it, it doesn't exist." To be more precise, perhaps I should have said "if I don't have it, I don't see it as an advantage." Oh well. Your literacy is helpful lesson me.

my 2-stroke car's engine has five moving parts

can you name them?

"You'll never see that I debated the existence proper grammar. " :lol:

Five moving parts: Two pistons, two con rods, and one crankshaft.
2+2+1=5 :)

Originally posted by ivymike1031
hey, you left out the two-strokes with poppet valves.

didn't even know they had those :o but yeah i suppose you could have them, and the valve timing could be changed, unless they just stuck a valve in a port to allow them to retard the "timing"

Turbo rotaries may be less reliable then the NA counterparts, but i've seen more then 1 NA blow it's front seal because of a hot summer day and semi low oil level (meaning he didn't add a quart every half hour) the oil temp shot through the roof and pop, 1 blown rotary. Now i'm a fan of being in touch with my car, but anything that regularly eats oil and has to be watched or else it'll blow is too much for me. I can set my valve lash every week or 2 in a short amount of time, and maybe the new one will be more reliable, but i suppose i'm just going to stick with my personal preference.

As to rotary valves. . .
911GT2 put it perfectly, to create a perfect seal you would have to have alot of contact, you have 150-200+ psi in the chamber, sealing a circular ball valve without actually covering the edge leading to the intake/exhaust ports requires an extreme amount of pressure, ESPECIALLY since the pressure will be forced away from the ball valve and directly to that hairline seal around the valve. Because of the amount of forc e needed to keep the valve sealed you'd have alot of wear and alot of friction, which requires oil, oil that would be burnt up on the seal and cause carbon deposits to build up.

They would score the seal and eventually create a leak, meaning the valve and seal would be under constant watch of wear & tear. The oil would also create terrible emissions, something that will never be allowed again by the damn tree huggers, even for very small production run cars. Sounds alot like another motors big problem doesnt it? these are the reasons rotaries go as well, and i dont think adding the rotaries biggest weakness to a piston engine would help many people.

Now what i want to know is this, since theres no forces testing it's tensile strength (that i can imagine anyway) would Si be possible? it would require no lubrication and doesn't absorb heat like a metal rotary valve and seal would. I'd definitly be all over a system like that, I believe Si can hold quite a bit of compression force (my professor has compared it to concrete, extremely strong in certain areas, but just the inverse in others) so the pressure need to keep a seal would be doable, but i haven't done a ton of research in the area either.

re two-stroke w/ poppet - one example that I'm 100% sure of is the 710 engine from GM/EMD: http://www.gmemd.com/en/locomotive/innovations/engine/710engine/

I believe the configuration is also found on some tractor engines, and some ship engines. Dunno about smaller vehicles.


Five moving parts: Two pistons, two con rods, and one crankshaft

So I suppose it has journal bearings, not roller bearings, and you're counting the piston pins as parts of the conrods, and the piston rings as parts of the piston. No oil pump, fuel pump is not counted, TV damper is not counted (or not present), and the engine is air cooled (or water pump is not counted)?

It's air cooled all right, and fuel flow is by way of gravity.
Usually, the piston pin is set tight in the piston(as it is in this engine), so it doesn't move. And most people don't count piston rings as moving parts (but if you did, this engines still has far fewer parts than a 4-stroke)

There are 2-stroke diesel engines with poppet vavles for exhaust, so I guess that these could be fitted with variable valve timing, but I was hoping to keep this down to simple crankcase compression 2-strokes.

Usually, the piston pin is set tight in the piston(as it is in this engine), so it doesn't move.

Did you mean "usually in your vehicle" or did you mean that in a more general sense? It has been my experience that the above configuration is the least common of the three main piston pin retention schemes, with conrod-fixed and fully-floating being the first two, in that order.

I meant that in most engines, the piston pin is fixed. I know that in some American made cars, you even have to use a press to push it into place. And every 2-stroker I've had apart has had the piston pin stationary, I usually get them out with a dowel and a hammer (and in that way too)

hmm...
rotaries are not reliable... why... b/c mazda designed them with inadequate cooling systems...

beef it up, and you've got less problems...

also, the cooling system does less of the cooling, it's more in the oil, so you have to cool that more than anything, b/c that's what takes the heat. then you've got a reliable motor.

they can be done correctly and reliably, so it's not really fair to hear that rotaries are unreliable b/c someone worked one past it's stock limits...

just my .02...

Originally posted by flylwsi
hmm...
rotaries are not reliable... why... b/c mazda designed them with inadequate cooling systems...

Really.

Pretty much most diesel two-strokes use exhaust valves.

fuel flow is by way of gravity
Fuel drops into your engine? :o

FYRHWK1... silicon itself isn't pretty useful. I assume you're speaking about Si3N4? Si3N4 has a compressive strength of 3-500ksi, and a flexural strength of 100-150ksi (IIRC).

Si3N4 also has a pretty low thermal conductivity, so I imagine that a Si3N4 block/heads would function in a compression-ignited engine quite well. Would raise diesel efficiencies up past 60-70%, one would hope.

I'm fairly sure thats it' i couldnt remember the entire formula itself so i figured Si alone would get the point across. they were, and probably still are, testing the idea of making certain engine components out of it, namely pistons, heads & block being it's not very good at taking tensile loads, andlike you said a very low thermal conductivity, i'm curious as to why more bearings and races arent being made of this material, no oil is needed and it's extremely resistent to scratching, no oil means less clearance necessary and that alone would keep most debris out.

Originally posted by 2strokebloke
I meant that in most engines, the piston pin is fixed. I know that in some American made cars, you even have to use a press to push it into place. And every 2-stroker I've had apart has had the piston pin stationary, I usually get them out with a dowel and a hammer (and in that way too)

In all engines that I've seen have had floating piston pins and I think this is most common.

Usually the pins are fixed in the axial direction with some sort of clip. The pin can otherwise move around. However, they can sometimes be hard to remove or assemble.

partially fixed piston pins (conrod- or piston- fixed) are not uncommon in low-bmep applications, especially where durability is not the highest concern (cost far outweighs it). It has been my experience (as I said earlier) that conrod-fixed pins are more common than piston-fixed pins.

Fully-floating pins are very common in high load or long life applications, because of their improved load carrying capability and better durability.

Perhaps I should start a thread called "I hate fixed piston pins," and cite them as the Achilles' heel of the engines that use them? Nah... that would be silly. Almost like calling poppet valves the bane of four stroke engines...

Hmmm, I've never heard of a burned piston pin, or had an engine eat a piston pin, or ever had to adjust a piston pin, I still think that poppet valves are the weakest part of the 4-stroke engine.

So what engines have you had apart that have had floating piston pins?

The Cummins ISB, for one (I6 in dodge pickups). Honestly, I can't think of a single pickup-truck size or larger diesel engine that doesn't have a fully-floating piston pin, but there may be some out there.

You've never had piston rings wear out either, I guess? Never had a "spun" bearing? No fuel control or ignition problems? Blow head gasket? Warped head? Shattered piston? Worn out injectors? Clogged carburetor? Scuffed piston skirt? Siezed-up piston? I'm beginning to suspect that your (apparently quite limited) experience with engines doesn't qualify you to make an accurate assessment of their common failure modes. Heck, your previous posts suggest that you've never even heard of hydraulic lash adjustment... Is that the case, or did you just ignore their existence because it made your "adjustment" argument work better?

Out of curiousity, just what the heck IS a "burned" valve? I've heard plenty of "experts" refer to them, but I've never actually heard anyone explain what one is. Is that a funny name that "tech" people give to worn or deformed valves? Is it a catch-all name for valves that don't seat properly? Is it something to do with carbon buildup or other contamination? Seat recession?

On the same subject, another popular "failure mode" of valves seems to be the "sucked valve." I can tell you that there is no such thing, and anyone who claims to have had a "sucked valve" probably doesn't know the proper name for what actually happened inside his engine, and very likely doesn't have a clue what the cause was either.

"On the same subject, another popular "failure mode" of valves seems to be the "sucked valve." I can tell you that there is no such thing, and anyone who claims to have had a "sucked valve" probably doesn't know the proper name for what actually happened inside his engine, and very likely doesn't have a clue what the cause was either."

If you are referring to when an engine eats a valve, then yes it does happen, most usually the cause is that the valves were set too loose, my friends Renault ate an exhaust valve once, and I've been told that this is rather common for air-cooled VWs to do as well.

Burned valves? more common for exhaust valves (in fact I've never seen a burned intake valve) If the valve doesn't seat properly, then hot gasses will be getting past it even when closed, the valve will get too hot and burn, commonly this also goes hand in hand with sticking valves, or valves that have not been adjusted properly.

Blown head gasket? yeah it has happened, but it took me three minutes to replace, so I'm not complaing (I'd like to see anybody do that with a 4-stroker)

Here's a webpage that explains burned valves better than I did:
burned valves (http://www.peebles34.freeserve.co.uk/Pages/Big%204/Valves/Burned%20Valve.htm)

the valves were set too loose Say what? Do these engines use adjustable valve retainers or something? If so, that's hardly a typical configuration. There is generally not any adjustability in the valve spring installation, excluding shimming the spring seat for hi-perf applications.

People usually say "suck a valve" in conjunction with some discussion of exhaust system backpressure or lack thereof. It's complete rubbish.

Apparently "burned valve" is a catch-all phase for valve failure caused by improper seating of the valve. I'm not surprised. The "burning" of the valve was not the failure, though, simply a leftover clue about an earlier problem.

"Eating" and "sucking" are not appropriate names for valvetrain failures. Valve retainers fail sometimes, which will allow the valve to drop into the cylinder, with dire consequences. Spring fatigue failure can cause the same thing. Piston-to-valve contact can occur without either of the above, as with lifter pump-up, poor dynamic control of the valvetrain, improper cam phasing, or failure of the cam phasing mechanisms (timing belt or chain, cam phasers (vvt)). Of the above, I would say that failure of the cam phasing mechanism (snapped timing belts) would be the most common type of valvetrain-related engine failure for daily drivers, at least when you're speaking about engines built since, say, 1991 or so. I've never known anyone who had any of the other problems on a commuter car. I've seen problems related to sticking valves on some diesel engines, but it's not nearly as common as you seem to think it is. The biggest problems that engines will run into in use, as far as I can tell, stem from improper (or lack of) maintenance, especially oil changes and coolant system maintenance.

I'd be interested to hear about any 2-stroke vehicles that can meet current US auto emission standards. Do you know of any?

Actually sticking valves are quite common, even on "new" cars, even today's fuels still leave carbon buildup, but it's not what I'd consider a big problem, there were a several cars with this problem that came into the dealer where I used to work only about a year ago.

Let's try and stay on topic here buddy, (and in case you have forgotten, the topic was for valves other than poppet, as in: rotary, sleeve, etc.)

Aspin rotory valves (http://www.lortim.demon.co.uk/aspin/)
The link above is to a site that provides some history and information about the Aspin rotary valve (but mainly early types) and some pictures too.

Willys Overland (http://clubs.hemmings.com/clubsites/wokr/gallery/wk_hist.htm)
Willys used sleeve valve engines, and there's some information about them here.

Let's just say this, my 2-stroke car's engine has five moving parts, produces 1.19hp per cubic inch @ 5500rpm (better than most muscle cars, and better than a Viper) is ultra reliable, I've never had to deal with valves, because it doesn't have any. This means, I've never had to change a timing belt (or gears, or chain) never had to set valve clearance, never had the engine eat a valve, or burn a valve either, never had a sticking valve etc. etc. And I certainly can not write all of that about that about my 4-strokers.

What car do you drive? I didn't know that there were any 2-stroke cars left on the road. I guess you might find an old Saab 3 cylinder. You folks are much more knowledgeable than I am so I will not vociferously join the debate, except to say I've always been taken with the two stroke for its simplicity and power. Of course it has disadvantages as well as advantages, many have been cited here. Regarding head gaskets, a two stroke doesn't necessarily have to have one. I know when Chrysler was working on their automotive 2-stroke some years back they were exploring single-piece castings of block and head. With no valvetrain or airways in the head it is conceivable. Anyone aware of what Bombardier is doing with direct injection (and "semi-direct injection") two strokes in the area of recreational vehicle engines? They claim better emissions in their Evinrude line of ourboards than equivalent 4-strokes.

Please!!! Don't revive old threads. This one is two years old.