Two stroke lubrication

Picking up on a side issue from John Manders' thread, (well done, BTW!) I'd been thinking recently about two strokes (TS) & oiling. Several varieties of
our Iron Toys are two strokes and built at a time when TS oils were much poorer at their job than they are today. Bearing in mind the task presented to the oil in a modern high performance TS motorcycle, it's a wonder to me that they survive at all, let alone soldiering on for decades at a time with little but abuse and neglect for company.
For instance, thirty years ago, I was always struck by the ability of a needle roller bearing in a TS small end to do it's job without dying in the first five minutes. But they worked just fine and even though the rollers never complete a full revolution, the eye of the conn rod rarely guttered.
I owned several Suzuki 500 TS twins and these had pumped lubrication to the mains (and thence to the big ends) and also to the cylinder walls. The result was the reduction of the traditional wake of smoke behind the bike to the occasional puff upon acceleration as the oil pump was linked to the throttle. Very good idea, too.
Therefore, I grow ever more convinced that the recommended ratio of oil to petrol can be drastically reduced in older engines designed to run on bacon fat lightly cut with paraffin. This year, I'll put my engine where my mouth is and try it. My next side project is a spare Homelite engine I found at the Sortout last year, so there's summut I can practice on!
Perhaps I ought to mention that oil takes up combustion space, so less oil will mean a richer mixture, just as too much results in a weak mixture.
I'd be interested in the thoughts of the esteemed Eric Brain who has had a bit more to do with experimental automotive engines than me ;o))
regards,
Kim Siddorn
Man is just an ape that shows promise ...
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<snip>

I'm not sure I follow that bit. I suspect that more oil = less petrol, therefore a weaker mixture. The effect of the oil on the combustion space is negligible. My memory says that the normal air fuel ratio is about 14:1 by weight. Then consider the difference that the quantity of oil in even a 25:1 mixture makes and it's very small.
John
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It was a twinge of memory from my days as an occasional racing mechanic. I remember that Shell Racing made a big thing of weak mixtures caused by adding an extra splodge of oil "just for good measure". Whilst our engines are hardly stretched mechanically, one never knows who is reading stuff wot one has writ ;o))
OTOH, water injection makes a big difference to combustion temperature, flame front travel and actual compression ratio, yet is only a slow drip or fine mist spray.
Regards,
Kim Siddorn

oil
is
25:1
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or
Water injection cools the cylinder charge due to evaporation. That reduces compression pressure but cannot reduce compression ratio. That's a fixed mechanical ratio of volumes.
John
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True - pardon my confusion of terms ;o))
Regards,
Kim

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John Manders wrote:

Gentlemen, Pardon me for my igrants but I 've always thought that water injection was for perfomance, i.e. instant steam increased Volume/charge not cooling and also to improve pre ignition?
Martin P
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By cooling the incoming charge, more mixture (by weight) can be drawn in. During compression, further evaporation causes more cooling so pre-ignition is reduced. This means that higher CR can be tolerated, hence more power. The evolution of knock sensors and ECU's mean that the norm now is to simply retard the ignition timing to stop pinking.
John
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Water is also useful for de-coking. Amongst others the manual for air-cooled Wisconsins refers to slowly tipping 1/2 pint into a fast running engine. I have tried it and it does work. Sort of steam-cleaning I guess :-) regards Roland

was
and
pre-ignition
simply
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When I referred to "effective compression", I meant that as the combustion temperature rises following ignition, the steam expands rapidly, thus increasing the volumetric efficiency. The cooling effects of water injection are also valuable.
Frankly, I'm surprised that it has not been followed up in the automotive world. It was one thing when you had to remember to turn it on and off yourself, but now a chip can do it for you, things are very different.
Regards,
Kim Siddorn
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injection
I've never actually done the maths but I suspect that the heat taken to evaporate the water reduces the chamber temperature and hence volume more than is gained by the volume of steam. As I say, never really worked it out numerically. Anyone tried? Ah chips, wonderful things and you can run a diesel car on the oil used to make them.
John
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Actually it has, although AFAIK only as an after-market kit. I added a water injection kit to a Fiat 124 sport coupe 1800cc twin cam (many years ago) and was quite impressed with the extra performance. It was probably only a few percent but overall, the engine ran smoother and felt more punchy. In those days, mixing water and Fiats was not a good idea! The infinitesimal increase in humidity along with the infinitesimal increase in air flow over the bodywork was enough for it to leave a trail of rust behind it wherever it went. It was four years old when it made its last journey to the scrap yard in sky with terminal tin-worm!!!! - those were the days! :)) In it's remarkably short life, it eat 3 litre Capri's for breakfast! (Actually, I had one of those as well - sick b*****d?).
Mark
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On Mon, 6 Dec 2004 17:40:14 -0000, "Kim Siddorn"

Certain models of Saab used water injection (Just pre-GM days, IIRC)
Cheers Tim
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Tim Leech wrote:

we still use W.I. on the 5litre Kelvin , twin carb and electronic ignition as well. RPM maxu0., top speed about 8mph. :-) Bill
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Quoting from 'The Aeroshell Book':-
"It used to be commonplace for large piston engines to require special fluids to increase their take-off power. Similar injection systems are also incorporated in some turbo-jet and turbo-prop engines. The power increase is achieved by cooling the air consumed to raise its density and thereby increase the weight of air available for combustion. This effect can be obtained by using water alone but it is usual to inject a mixture of methanol and water to produce agreater cooling effect and also to provide additional fuel energy"
The book then gives spec of four power boost fluids, including Joint Service Designation 'WTA' - water!
--
NHH



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Nick H wrote:

Sort of missed this first time around. Large marine diesels are now using Direct Water Injection to reduce NOx emissions. Using a combined fuel & water injection valve with a separate needle valve for each, water injection starts first to cool down the combustion space to ensure low NOx formation before fuel ignition. Water pressure can be from 200-400 bar. NOx reduction is in the order of 50-60% with no detrimental effects. The ratio of water to fuel injected is from 0.4 to 0.7 with the power output unaffected.
Tom
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On Thu, 2 Dec 2004 23:23:29 -0000, "Kim Siddorn"

How much do they rotate ? I'd always thought they had to be small enough to get a full rotation in, or else they did collapse. Do they creep around gradually ?
--
Smert' spamionam

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A full rotation isn't necessary. It's good if the arc of movement is enough to overlap the needle contact points. ie, a 32 needle bearing should rotate more than 1/32 of a rev. I practice, the needle move around anyway, so even that isn't essential. The problem with low rotational speed is that the rollers don't develop a hydrodynamic wedge of oil so they are permanently working with boundary lubrication.
John
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bacon
mouth
our engines turn more slowly, with lots of force, compared to most bike engines. would that require a higher viscosity oil, or more oil? I wonder what the piston feet per second numbers are on various engines and if that makes a large difference in the viscosity or ratio required.
Rob Provins Sebring, Florida
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Rob Provins - Sebring, Florida Our engines turn more slowly, with lots of force, compared to most bike engines. Would that require a higher viscosity oil, or more oil? I wonder what the piston feet per second numbers are on various engines and if that makes a large difference in the viscosity or ratio required

Whilst the pistons may be bigger, they move a lot more slowly. Compressions are lower, bearing sizes huge and parts lightly loaded for their size. We could use chip fat and the things would still last for ages ;o))
Regards,
Kim Siddorn
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I must admit I'm not too fussy about exact petroil mixture. I generally have two strengths made up - 25:1 which I use in anything with plain big ends and/or mains and 50:1 for those blessed with rolling element bearings. Only for short term off/light load running though, for an engine doing a proper job of work I might think again.
--
NHH



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