Valves suck

[2strokebloke]

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.

[ivymike1031]

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.

[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)

[flylwsi]

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...

[454Casull]

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.

[FYRHWK1]

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.

[SaabJohan]

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.

[ivymike1031]

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...

[2strokebloke]

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?

[ivymike1031]

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.

[2strokebloke]

"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)

[2strokebloke]

Here's a webpage that explains burned valves better than I did:
burned valves

[ivymike1031]

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?

[2strokebloke]

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
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
Willys used sleeve valve engines, and there's some information about them here.

[Gregore]

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.