[what do you prefer]two stroke vs four stroke

[axy]

I ride a 4T, but would like to get into the 2T realm next scoot.  That Aprilia Ditech direct injection engine sounds like it is incredible, runs fast and clean because it is so efficient.

Hope other manufactures were follow suit.

Piaggio's direct injection 2 stroke small engines are a failure of the decade. In the same time, around 2002-2003, other manufacturers also tried switching to that technology (Peugeot for example) and they all had incredible problems, engines were weaker than "regular" predecessors, the spark plug costs a lot and has to be replaced in very short intervals. Online forums are full of very disgruntled owners.

My gf has almost OEM  2 stroke Piaggio NRG 50 mc2 2 stroke from summer 2003 with 26.000 kms on it, not direct injection but normal 2 stroke engine, it drives like crazy, fully stock except lighter roller weights and clutch spring, the thing goes almost 100 km/h according to tacho and it is only a tad slower than Agility 125 in regular usage... 5.5 vs 10 hp.

[axy]

Two stroke is my preference -- all else being equal.  There used to be plenty of big displacement two strokes available and, believe me, they were wonderful to ride.  Too bad, not any more. Smooth and extremely powerful!  Some people don't like the fact there is no engine braking with a two stroke but I think it's a plus.  You don't get the diving of the front end when you let off the throttle.  

Once you get the two stroke bug, you start to love all their qualities.

We've discussed the reasons there are no more of the big two strokes here before.  It boils down to political lobbying by HD in the 1970's.    

Kawasaki was known for their 2 stroke engines, 250 and 500 cc and they used to make them throughout 80s.
They were not deathbeds, but "deathboards". They developed the power near the top and were hard to drive. A lot of dead people driving them.
In 70s they had also 750 cc 2 stroke motorcycles.

In Europe we had many 2 stroke motorcycles, for example, Italian 125 cc engine was in a number of small off road bikes and sports bikes, it developed around 34 hp.
There was also famous Honda NSR 125 with 34 hp.

They are hard to drive because they rev very high, usually had to have 6 or even 7 gears in order to use the developed power and it is a constant struggle to drive them.
They are great if you are 15 years old and live for the thrills, as you get older, you tend to like more balanced vehicles/engines.

For that reason I do not like big thumpers or 2 cylinder engines and prefer 4 cylinder engines in motorcycles.

However, my 2000 Piaggio NRG 2 stroke with 72 cc kit that developed 10 hp is still my favourite scoot from the past.
It did 115+ km/h on flat road and I used to overtake cars with it on the road between cities.

[axy]

Did you know that there were large diesel two stroke engines used in freight hauling trucks?Set up properly they were absolute screamers.Engines were made by Detroit Diesel, and were used in trucks,marine applications, and generators.

WooHooooo! I did not know that...but if I had... I would have HAD to drive one!

Ships and trains also use 2 stroke engines.

[grantourismo]

If you're talking about the need to mix oil and gas, plus the added pollution and noise, then it's 4 stroke all the way.

-Wolf

well most new carburettor has got automatic mix why do you need to mix it yourself?

[Hoolander2]

Not all two strokes are/were "peaky".  Many examples of moderately tuned ones which were a pure pleasure to ride and operate.  Yamaha RD 350 or 400,  Suzuki GT 380[edit] and 750 just to name four. 

Kawasaki and some others tuned their two stroke street bikes for near maximum hp to get people buying them.  In later years those models were detuned substantially and were not so dangerous.

It could be done because two strokes are easily tuned to maximum hp without much expense.  Not so for a four stroke with all the valves, seats, cams, sprokets, gears, rockers, etc. 

On another point, in the USA, two strokes never presented a polution problem because they never were a significant percentage of the overall number of vehicles on the road.  However, when congress was legislating them away, their alleged higher polution was used as an argument. It was BS -- only reason it was done was for US govt to give HD competing power which they had totally lost. 

I can understand that in countries where scooters and motorcycles are present in high percent, polution should be considered.

By the way, if multi-cylinder two strokes were in production today, they'd surely have cdi instead of points -- some did even back in the day. 

[Hoolander2]

Yes, Axy, you are right.  I did not mean that one cannot use engine braking on a two stroke.  Of course one can.  I only refer to the fact that there is no momentary sudden diving of the front end when letting off the two stroke throttle.     This is one thing that buggs me about four stroke performance, though it can be corrected somewhat by the inclusion of a "throttle follower".  Some four stroke engines have them and must be adjusted properly or else the bike or car won't slow down as quickly as the driver expects.  Edit to add:  Also, I suppose fuel injection or cdi programming can reduce or eliminate this effect.  My Xciting is carburated, though.   

This is a different phenomenon than the optional use of a compression release mechanism for engine braking which both two and four strokes can use.  Neither usually comes equiped with one, though. 

If you were raised or learned to ride on a four stroke, you come to expect this momentary dive and it's nothing. 

If two strokes is what you learned on, it's annoying.

I do remember when I was a child, there was one two stroke car in my little home town in Florida.  Could it have been a Saab? 

 

[Rianna]

I don't particularly like the way it feels when that happens on the 4 stroke. It reminds me a bit of older cars with cruise control that take that extra second to slow down when you hit the brake.

I wanna control my own cruising and stopping.

[Hoolander2]

Ha!  Rianna, then you might not like a two stroke cause when you let off, it's like nothing happend for a second!     What I'm saying is I happen to like that! 

[Rianna]

Oh, okay then. I imagine I would get used to it, though. I'd like to ride/drive/try everything out there possible. I couldn't count the number of cars/trucks/vans I've owned in my lifetime. When I was younger, Hoolander, I even wanted to fly a plane...until I learned the cost of flight school.

[grantourismo]

it seems that all you bike / scooter boys do have a thing for 2 stroke 

[ts1]

Internal friction of the engine enables engine braking and, ceteris paribus, it is determined by engine's compression ratio.
Usually Kymco's small 2 stroke engines have compression 1:7-1:8 while small 4 stroke engines have 1:8-1:9.
So, they will pretty much engine brake the same, regardless of 2 or 4 stroke composition of the engine.
Whoever drove 2 and 4 stroke motorcycles can from experience notice the same.

I noticed, that the additidonal friction of all those additional 4 stroke parts (camshaft & Co) make a signifikant difference. "ceteris paribus" isn't applicable.
My experience covers Yamaha Neos (50cc, 2 stroke) up to VEB Trabant P601 (599cc, 2 stroke). (And bigger scooters, but no 2 stroke motorcycles.)

[axy]

Not all two strokes are/were "peaky".  Many examples of moderately tuned ones which were a pure pleasure to ride and operate.  Yamaha RD 350 or 400,  Suzuki GT 380[edit] and 750 just to name four. 

Kawasaki and some others tuned their two stroke street bikes for near maximum hp to get people buying them.  In later years those models were detuned substantially and were not so dangerous.

It could be done because two strokes are easily tuned to maximum hp without much expense.  Not so for a four stroke with all the valves, seats, cams, sprokets, gears, rockers, etc. 

On another point, in the USA, two strokes never presented a polution problem because they never were a significant percentage of the overall number of vehicles on the road.  However, when congress was legislating them away, their alleged higher polution was used as an argument. It was BS -- only reason it was done was for US govt to give HD competing power which they had totally lost. 

I can understand that in countries where scooters and motorcycles are present in high percent, polution should be considered.

By the way, if multi-cylinder two strokes were in production today, they'd surely have cdi instead of points -- some did even back in the day. 

HD is Harley Davidson?

I do not think that 2 stroke engines were in the same market niche as HDs.

Japanese motorcycles killed off HD in 60s/70s, not small 2 stroke engines.

[axy]

I noticed, that the additidonal friction of all those additional 4 stroke parts (camshaft & Co) make a signifikant difference. "ceteris paribus" isn't applicable.
My experience covers Yamaha Neos (50cc, 2 stroke) up to VEB Trabant P601 (599cc, 2 stroke). (And bigger scooters, but no 2 stroke motorcycles.)

They do, in terms of somewhat higher compression ratio, as I already said in my previos message.
Both Neos and Trabi had 7.5:1, similar 4 stroke engines nowadays have 9:1 - 11:1.

Divide those numbers and you will see how much more there is engine braking with 4 strokers. 20-45 % more, in fact.

But claiming that 2 stroke engines do not brake with engine is not correct.

No special magic there.

[axy]

Yes, Axy, you are right.  I did not mean that one cannot use engine braking on a two stroke.  Of course one can.  I only refer to the fact that there is no momentary sudden diving of the front end when letting off the two stroke throttle.    

I do remember when I was a child, there was one two stroke car in my little home town in Florida.  Could it have been a Saab? 
 

It could have been Saab, maybe this one: http://en.wikipedia.org/wiki/Saab_96

There was just one in my city when I was a child. Very rare machine (except in Sweden, probably).

Regarding nose dive... you will experience that with 4 strokes ONLY with large displacement thumpers (1 cyl, >400 cc) and especially with 2-cyl bikes.

This problem can be compounded with short first three gears. For example, if you drove any 650 cc 2-cyl bike like SV650 or even worse, Suzuki TL1000 or Aprilia Falco 1000 that all have 2 cyl, they have high compression and big pistons and tend to brake HAAAAARDDD when you back off the throttle.

The big ones also want to lock rear wheel if you are not very careful when downshifting from 4->3 and 3->2, especially on poor surfaces. Many people fell off their bikes that were 1000 cc and 2 cyl. Today similar bikes exist too, for example, Tuono 1000 series, but they are a bit more mellow.

This phenomenon is even more evident in one and 2 cyl "supermotard" bikes like KTM Duke or Husabergs that have 60-70 hp, very short gears and low top speed. I never liked those bikes.


However, you will never experience such sudden deceleration driving 4-cyl 4-stroke bikes, even on beasts with 1000 or 1400 cc. Never, ever, they are very smooth. There are drivers that like one and two cyl bikes and those that like smoothness of 4 cyl bikes, I am in the latter group.

[axy]

A few more things about 2 stroke engines.

1. They are simple, easy to performance-mod: for 50-100 EUR you can double the power just by changing the piston and cylinder and ramping up the displacement for 50 % and almost double the power; the problem is that these aftermarket parts are of low quality, tend to last less than 10.000 kms and the crankshaft usually dies too because it is not suited for 100 % more power. The crankshaft costs usually three times the price of the cyl+piston.

2. Spark plugs tend to last 5000 kms compared to 4strokers where they are great even after 10000 kms

3. 2 strokers usually have oil pump that is almost always powered by a small toothed belt that is "very OEM" and there are no alternative replacements; you already guess that these tiny belts has to be replaced when the variator belt is replaced and this doubles the maintenance cost. They are also prone to breaking, and if they do, the engine does not get oil in mixture and it locks up -> major problem. Very rarely, and in older scoots, the oil pump is sprocket powered.

4. 2 strokers are simple, but very sensitive to tweaking (carbs, air, exhaust). Exhausts tend to clog up because the engine runs much hotter than in 4 strokers and in a number of scoots, the exhaust has to be torn apart and cleaned even in intervals as short ast 3-5.000 kms. Ask any Italian 2 stroke high performance scoot owner. This also causes some major costs because mechanics usually do not want to mess with tearing apart the exhaust and welding it back and want to replace it with a new one that costs 250-300 EUR. A LOT OF MONEY.

5. 2 strokers are not that reliable when there are temperature extremes and tend to overheat more easily than 4 strokers. The only case when I saw the bike overheating was with (liquid cooled!) 2 strokers. Never with 4-strokers, regardless of outside temperature and load on the bike.

6. 2 strokers have twice as much strokes as 4 strokers in a unit of time, they tend to achieve higher revs, develop power higher. They consume TWICE AS MUCH as 4 strokers and develop TWICE AS MUCH POWER per cubic centimeter of engine. (an average 50cc 2 stroke engine has 5 hp, 4 stroke has 2.5 hp; average 50 cc 4 stroke will consume 2 l/100 km, average 50 cc 2 stroke will consume 3.5-4 l/100 km).

125 cc 2 stroke`s 35 hp average consumption is 5.5-6 liters: the same as 750 cc 4 stroke bike with 100 hp.
As you get higher with displacement and power it gets worse.

7. They are very basic and not too durable: 2 stroke engine with 30.000 kms is quite old engine and you can expect 40.000 km only with high quality brands/materials, while 4 stroke engines can last twice that without problems.

8. They do not have valves and camshaft, but have very problematic intake valve ("intake louvre") that tends to get stuck or even break and enter the cylinder freezing it and damaging it permanently.

9. There is no maintenance of engine itself, no valve adjusting, no camshaft chain to be checked or replaced, when it dies, you rebuild it, but usually everything else dies around the engine except the engine itself.



I already said that if I had to drive 50 cc for some reason, I would buy ONLY 2 stroke because I am too heavy for 4 stroke 50 cc that is too low powered (or I am too heavy, or the hills are too steep, choose yourselves...)

In all other cases - only 4 stroke engines...