How do manufacturers of two-cycle power tools arrive at their
recommendations for oil-gas ratios?
If the ratio recommended for one tool is higher than for another, could
one mix be okay for both tools?
different two-cycle devices have reeds made of different materials as well
as different piston, ring and head materials
some are hardened with titanium and other materials and can tolerate a lower
a good example is motocross bikes, some of the racing bikes of today can run
60:1 because of new expensive metals inside and better oils, whereas 25
years ago some of the best were needing 20:1
the engineers who designed the tool know the optimum for their product
however if the two ratios are very close, you can split the difference for
convenience, such as one tool needs 20:1 and one tool needs 24:1 you could
get away with 22:1 in both, but I wouldn't split a larger gap than that.
On Wed, 29 Jun 2005 00:22:37 -0400, in alt.home.repair RE: oil-gas
Most manufactures have dart boards with pie shaped sections that say
8:1, 10:1, 12:1, 16:1, 32:1, 50:1
When the time comes to release the documentation for a new model
engine, the engineer that worked the most unpaid overtime during the
engine development gets to throw a dart over his shoulder at the
For liability reasons many manufactures are moving from dart boards to
ping-pong balls in a black hat. Too many bystander engineers in the
room during the dart ceremony were getting hit by errant darts.
By the way, because of the highly custom (and private) nature of the
ceremony, it is *not* taught in engineering school. It must be learned
at each individual manufacturer and is usually covered in the
I've never worked at an engine manufacturer, but as an engineer for
the past 35 years, I've often been invited to these ceremonies by
colleagues in that business. I've always looked forward to them.
They're really nice. In the old days, we were served bourbon and red
meat as snacks. Alas, for liability reasons that has changed to
cookies and milk during the past few years. Still, it's an exciting
ceremony and that's what counts.
There's also a *very* exciting ceremony to determine the *TYPE* of oil
to use. But that's another story.
I've done that often with no noticed problems.
To reply to me directly, remove the CLUTTER from my email address.
As others have mentioned, it's a guess. And a compromise. Whatever
the ratio chosen, if it's "right" at max power, it's much too oil-rich
at idle. But, fouling a plug is a much smaller problem than seizing a
The good news is that current 2-stroke engines survive nicely on 50:1
synthetic mix. I've used that for years in engines that mfgs said
should have 16:1 or 24:1, and they're "happy." They also don't have a
blue cloud in the area for minutes after starting, and their exhaust
ports & mufflers stay much cleaner.
Very few modern 2-strokes have reed valves- piston-port is essentiall
"it" except for some rotary-valves on bikes.
No brand-X 50:1 oils for me, thanks. Name-brand only.
With the EPA doing their job manufacturers are trying to " show" their
units as less polluting by leaning out mixtures. I feel at the expense
of engine life . 32-1 I feel safe with. 32-1 with synthetic or a bit
leaner will give you the longest life. True construction of engines
vary, but steel sleeves, rings and bearings have not changed much for
your average 2 stroke lawn and garden machine.
Nothing to do with feeling here, just empirical results. E.g. an Echo
saw that's 25+ years old, and has been run only on 50:1 after the first
couple of tankfuls. Ballpark 500 hours, all at full power. (Engine is
like-new, but half-wit son broke plastic part of starter, and no
Similar story for 3400 Poulan. Still runs like new. Never changed
plug on either.
Similar stories for other 2-strokes, that are almost constantly run at
Steel sleeves? Please show me one on any "real" 2-stroke engine with
steel sleeves. Chrome-plated bore, almost exclusively. And, ...
bearings on any serious 2-stroke are roller, and need only the
Is less-polluting bad? I don't think so, if it means I get to suck
down less oil-smoke.
Less is more, here.
I'm sure it isn't ok but I do it myself for the weedeater and lawn
mower. I mix to the lawnmowers specs and let the weed eater live with
it. Weedeater is about six years old now and still works fine.
They sell some of those two cycle oils that are supposed to be mixed
according to the directions on the container and claim they work for
ALL 2 cycle engines regardless of the recommendations. Just wanted to
mention this. I have never used them, I got rid of all devices with 2
cycle engines years ago, since they tended to piss me off more than do
their work. I only know this because of an ad I was reading at the
mower parts shop a few weeks ago while waiting for the guy to find a
part for my mower.
On Wed, 29 Jun 2005 00:22:37 -0400, Choreboy
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