Omega Owners Forum
Chat Area => General Discussion Area => Topic started by: Field Marshal Dr. Opti on 07 July 2013, 20:13:30
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Even a cretin such as myself has a rudimentary understanding of the 4 stroke cycle
1. Induction
2. Compression
3. Power
4. Exhaust
.......or suck.....squeeze.....bang ...and blow for the sniggering schoolboys amongst us.... :y :D
But what of the 2 stroke cycle? ??? ??? ??? ??? ??? ???
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Think squeeze/bang
Not having valves, but ports, it can do 2 of the cycles at once, so a bang every rev.
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Probably better than I can explain...
http://www.animatedengines.com/twostroke.html
The wikipedia animation looks good as well
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Achieved by sucking induction in through the bore/piston wall ports, then on compression a read valve closes, sited after the carb, to prevent the gasses being forced back out, until the ports close as the piston rises. Then the real compression starts.
Crank bearing are part of the crank case induction chamber, as is the bore, so the inlet mix must be lubricated. Hence two stroke oil. Either by separate mechanical pump, or mixed with the petrol.
Exhaust is a dark art iirc. Hazey on this bit, but the key to it is timing, so the height of the exhaust port needs to be set so its revealed by the piston first for gasses to escape, but closes before the incoming petrol mix escapes.
Usual reason for common seizures is tuners getting greedy with port size and the piston ring escaping slightly in the port orifice, then trapping it by the rising piston.
Oily smelly unreliable things they are. So fazed out mostly. But they produce twice as much power as the four stroke, or the same amount for half the engine size, due to twice as many firing strokes.
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Aprillia use a disc valve, as opposed to a reed valve, to control crank case pressure iirc.
Gives a more peaky delivery apparently. No idea how that works, never encountered one.
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Oily smelly unreliable things they are. So fazed out mostly.
Mostly phased out by the do-gooding, tree hugging hippies, due to poor emissions.
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Oily smelly unreliable things they are. So fazed out mostly.
Mostly phased out by the do-gooding, tree hugging hippies, due to poor emissions.
In motogp, Honda pulled the plug long before iirc. There's no future in lubricating fuel.
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But my god they where fun to ride. So light weight, hence ideal for chain saws, with at the time, better bhp than any four stroke.
Shame really.
The four stroke is such a massive waste in resources. A stroke of say 60 mm, but a total engine height of almost two feet. Valve stem height, cam gear in top, plus room for the inlet on top. Plus a big deep sump underneath. 2stroke Has none of these.
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Never fortunate enough to ride a big 2 stroke, but even a 250cc was friggin pant messingly quick, with a brutal delivery.
My eldest bro had a Fizzie, that thing would show 60mph on the clocks (not 2 up though ;D)
The flip side was I remember the chainsaw being an utter arse to start most days.
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2 strokes were my first bikes , started off with an MB 50 then went straight to the air cooled RD250 :o Mate had a KH 750 .... had a go on it then changed underpants shortly after :o
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Never fortunate enough to ride a big 2 stroke, but even a 250cc was friggin pant messing.......
Used to work on 12000 horsepower two strokes. Diesel at that!!
35 foot step ladder in the crankcase and twin Turbochargers.
Big bits for little hands..... 8)
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2 strokes were my first bikes , started off with an MB 50 then went straight to the air cooled RD250 :o Mate had a KH 750 .... had a go on it then changed underpants shortly after :o
.....neatly holed pistons were never far away. :y
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Never fortunate enough to ride a big 2 stroke, but even a 250cc was friggin pant messingly quick, with a brutal delivery.
My eldest bro had a Fizzie, that thing would show 60mph on the clocks (not 2 up though ;D)
The flip side was I remember the chainsaw being an utter arse to start most days.
<------ I've still got one if you fancy a trip down memory lane. :y
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2 strokes were my first bikes , started off with an MB 50 then went straight to the air cooled RD250 :o Mate had a KH 750 .... had a go on it then changed underpants shortly after :o
.....neatly holed pistons were never far away. :y
My mate still has a mint KH750 and a Kettle, as well as a few modern big bikes. :y
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2 strokes were my first bikes , started off with an MB 50 then went straight to the air cooled RD250 :o Mate had a KH 750 .... had a go on it then changed underpants shortly after :o
.....neatly holed pistons were never far away. :y
My mate still has a mint KH750 and a Kettle, as well as a few modern big bikes. :y
Ahh yes the kettle , still a good looking machine . Lusted after the RD500 when it first came out , then i got married :'( And divorced a year later :( ;D
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quite liked my Inchley tuned t250, you most certainly didn't wind on too fast in the lower gears for fear of chewing the bars !