2 stroke and 4 stroke history

[Noelm]

OK, first off this is not to defend or discredit either system, but there has been a thousand threads of late, all comparing or asking advice on the two different principals of operation, opinion and advice varied from good to sheer stupidity, it is often remarked that if 2 strokes are so good, then why are there no 2 stroke cars, so here goes a little history lesson on 2 and 4 strokes. Take this as you will, toast me if something is not right, I don’t care and welcome any constructive comments, but no bull crap or mines better than yours, OK!
Way way back (in the late 1800’s and early 1900’s) when engines were being refined, almost every one made was a 2 stroke, why? they were easy and cheap to make. So lets look at the advantages of an early 2 stroke (forget e-tec and opti for a while) they are mechanically simple, (a single cylinder uses only 3 moving parts), very light for their size, and quality could be high because of so few parts, but the disadvantages were very bad for use in cars, difficult to muffle and a smoky exhaust, fuel/oil costs kept HP low, and needed to be under load to run smoothly, but, when that’s all they had, all cars were 2 stroke powered and were smoky noisy things. Some time later a couple of guys started work on a new system and the 4 stroke was born, some advantages made it an instant hit with “horseless carriages” such as smooth idle, even without load, no smoke and no oil in the fuel costs, remember the old 2 stokes used to run at 15:1 fuel/oil ratio, so cost was an issue, being such a suitable engine for Automobiles, all research and development went into 4 stroke technology, hence why they are in cars today, it had nothing to do with longevity, or more power or anything else, but, a few engineers of the time still thought 2 strokes were the way to go, and persisted with the system. Marine and motor bike engineers were the most persistent of them all and all sorts of ideas came into being, auto oil systems, far better engineering that allowed for very lean fuel oil ratios and a host of other refinements.
Enter electronic fuel injection, and a whole new world was opened up for both 2 and 4 strokes, but it meant a whole lot more for 2 strokes, (enter the e-tec and opti and a group of others) from then on they idled smooth with no load, made no more noise than the same HP 4 stroke, oil ratios were now getting on towards 200:1 at idle, so smoke and smell was almost a non event , but the 2 stroke simplicity had just about disappeared, both systems now had complicated electronics, EMM/ECU technology and weight grew in time with output and technology until today there is really no reason to not buy either operating system. Just to clear something up, a 4 stroke still has a lot more parts, valves, camshafts and other gear, but they are very high quality and there is absolutely no reason they should fail just because there is more of them, but there is a weight penalty. So there you go, a fairly simple explanation as to why 4 strokes are in cars, I really doubt any of the major Auto players would look into developing any 2 stroke technology, whether it would be better (or worse). There is no reason a 2 stroke will last longer or less than a 4 stroke (or the other way around) purchase costs are almost the same, but usually still favour the 2 stroke, simplicity is a thing of the past for both engines, unless we are talking lawn mowers and brush cutters and so on, I doubt we will ever see a modern 2 stroke powered car, but then who knows what is lurking around the corner, people like Sarich and his orbital engine and others like him might just turn things around with their “outside the box” thinking.

[Chimo]

Interesting stuff

Two stroke lawn mowers have the advantage of lubrication if your mowing steeper slopes. Theres only one 4 stroke lawn motor mower with an oil pump that I am currently aware of. Starts with T.

Being one whos not very keen on the super complicated electronics of the newer motors (2 stroke) I think I'll stick with the old carby machine for a while longer. Also correct me if I'm wrong but aren't the old carby machines a bit more tollerant of the iffy ULP we seem to be forced to use these days?

Car wise, I certainly feel the difference with the higher octane brews in the Ford and we get considerably more KMs too.

In the mean time I'm waitng for diesel outboards to come back, I reckon I could hang one big muther on the back of the Vag and it wouldn' be any heavier than the two 115s on there at present.

Cheers
Chimo

[cormorant]

Several who are car manufacturers are looking at 2 stroke combustion ( power every stroke using) sump and both direct air and fuel injection ( no oil) as lightweight motors in eco cars as they are more effecient and higher torque without gears to run genset under a bonnet. This method gets rid of the rquirement to have large expansion chamber exhausts etc

Sort of a combination of both technologies as the head contains valves and injectors.

The other reason for transition in early cars was that a 2 stroke had big issues of heat if you leaned them off in oil and fuel to make them run cleaner as they didn't have the metal knowledge to cope with higher thermal load.


It is a real mixed bag out there and people shouldn't mistake the naming of the combustion process with all the other bits of lubrication , exhaust etc.

Won't even go near the discussion of turbines and rotary or newer lobe motors

[Noelm]

almost everything in the early days was air cooled, so heat was a major problem, as the HP grew, so did the heat, but as usual the inventors of the time came up with water cooling, the very early systems did not have a water pump, they had a convection system, and most had a thermometer sticking out the top of the radiator that the driver could see, but as HP started to get larger, water pumps, fans and all sorts of things came into being.

[wrxhoon]

Another reason why outboards stuck with 2 stroke is because you can run a 2 stroke in any position even upside down ( fuel injected).
4 strokes are ideal for cars because you have the crank paralel to the the cars position so you have a wet sump under it , another reason its easy to run the exhaust and the other, 4 strokes are perfect for running at various RPM not constant . All in all perfect for cars not so perfect for a boat though , crank is the wrong way around in an outboard, you realy need a semi dry sump because you lean the outboard and then what about the exhaust very hard to fit in the cowling , some of them run it through the sump.
4 strokes last longer if you vary the speed ( a lot longer than 2 strokes) if you run a 4 stroke at full revs she won't last long, look at how long they last in a race car .
2 Strokes you can run at full revs and they still last, the killer of old 2 strokes was very low rpm running, they use to stuff up the plugs very quick and carbon the pistons .

Both have good and bad, I prefer 2 st for amature usage because you can leave them there for a long time and nothing happens to them. If I was using them everyday , doing lots of hours I would use 4 strokes with much bigger HP than needed so you can tun them at mid range RPM . Diesels are perfect for that aplication.
Who ever said they don't use for strokes on cars , GM have 2 stroke diesels they use on trucks!!
Old Ralph tried very hard to sell his invention to carmakers but none took it up .
Optimax and other DFI engines are very close to his original invention .
The worlds most powerfull diesel is a 2 stroke, turbo of course, it powers huge supertankers and max revs at about 100-120 rpm .

[Noelm]

just on the 4 stroke exhaust thing, there has been quite a few big HP Yamahas (200 to 250) have been having major drama with the exhaust sytem corroding out and causing the oil to leak into the lower leg and causing major problems, and it is not a warranty issue! might start another thread about it and hope the owners don't flame me too much!

[Noelm]

back to the topic, that is true, the car engines the motors are based on are highly modified to allow for the vertical crank, including new oil pumps and of course sumps.

[Malcolm W]

http://people.bath.ac.uk/ccsshb/12cyl/

The worlds most powerfull diesel is a 2 sroke.
My old man had a Galion Grader with a 2 stroke diesel 30 years ago. There seems to be a few different diesel 2 strokes still around after doing a search.

[black runner]

2 stroke diesel configuration is quite a bit different to small 2 stroke petrol motors. The diesel has inlet ports in the piston bore where supercharged air is forced in prior to compression to scavenge the exhaust gas out of a traditional four stroke style exhaust valve/s.

Cheers

[suzygs1000]

Two points to this:

Two strokes by their nature, wear pistons, rings, and bores much faster than a four stroke, all other things being equal... two strokes are under load on the way down on every stroke, while fours basically are coasting down every second stroke, hence less wear on that stroke.

High performance two strokes are extremely intolerant of wear, just ask any of the motocrossers who race two strokes...new rings every meeting, and a rebore every second meeting!

Dry sumps aren't new.. British bikes had them for 80 years! (except royal enfields).

Sorry , guys, two strokes are on the way out!!

Dave

[Noelm]

no one is arguing whether 2 strokes are on the way out, on the way up, or not even any good, the topic is whether a 4 stroke outboard is so much better than a 2 stroke (or the other way around), for fuel, noise, servicing, emmissions and a host of other stuff, I claim that for almost any plus of either principal, there is a minus.

[ozscott]

The old 2 strokes seem more tolerant at being locked away and started once in a blue moon (probably because there are no potential valve train issues with lack of use)...for me thats perfect. But if I used my boat more I would love a Yammy 150hp 4 stroke. I understand now that hole shot is very comparable on 4stroke versus DI 2 stroke. If you had to re-build a 4stroke then it would be dearer, but lets face it it is wear that is causing the need for a re-build, you might as well toss the motor out cause its probably 20 years old plus and therefore corroded on the inside water galleys...I did a set of rings and honed the bores once in an old Merc 650 at home and it made a big difference until it sprung a leak in the port on number 1 a moment later and was ingesting water..bugger...nice clean plug though! So we can rule out re-build costs I reckon. So now we are down to weight and power to weight and then really for smoothness and noise the good 4 strokes have the later, but the former is still a problem...but getting better all the time.

Good thread Noelm.

Cheers

[Noelm]

OH and Suzygs1000, we are not talking about racing engines, if we were then 4 stroke outboards are almost non existant in the trophy department, and the same could be said for racing 4 stroke autos, do you think the (say) V8 supercars or F1 cars do not rebuild their engines after every event? they are (as are race bikes) the very top of the mechanical limit as far as RPM and output goes, almost anything gets a bit "loose" valuable tenths of a second is lost. So, as you can see, every plus has a minus, if you think your 4 stoke outboard is the best ever made (you must 'cause you bough it) then so be it, if (say) Jabba thinks his e-tec is the best ever made, then so be it, it's your cash, spend it how you like, but facts are facts, and they always need to be sorted from the emotional fiction! and by the way, sorry Jabba, you were the first one I though of that has an e-tec.

[suzygs1000]

Hi, Noelm,

I was referring to the statement by WRXhoon as below. This implies that two strokes can run flat out all day, while four strokes can't.

"4 strokes last longer if you vary the speed ( a lot longer than 2 strokes) if you run a 4 stroke at full revs she won't last long, look at how long they last in a race car .
2 Strokes you can run at full revs and they still last, the killer of old 2 strokes was very low rpm running, they use to stuff up the plugs very quick and carbon the pistons ."

He is implying that four stroke race engines don't last long (as they don't) but two strokes do. This is incorrect and this is the point I was trying to make.

Dave.

[STUIE63]

I just think that you have to look at each individual hull and application to make your decision on which type of outboard to get and that DI 2 strokes should not be put in the same class as carbie 2 strokes they are a complete different kettle of fish
Stuie