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Posted by Choreboy on June 29, 2005, 12:22 am
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?
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Posted by cowboy on June 29, 2005, 12:43 am
> 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?
No
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
oil mix
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.
cheers!
cowboy
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Posted by Vic Dura on June 29, 2005, 8:02 am
On Wed, 29 Jun 2005 00:22:37 -0400, in alt.home.repair RE: oil-gas
>How do manufacturers of two-cycle power tools arrive at their
>recommendations for oil-gas ratios?
Dart boards.
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
board.
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
new-employee orientation.
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.
>If the ratio recommended for one tool is higher than for another, could
>one mix be okay for both tools?
I've done that often with no noticed problems.
--
To reply to me directly, remove the CLUTTER from my email address.
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Posted by on June 29, 2005, 10:28 am
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
piston.
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.
HTH,
J
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Posted by m Ransley on June 29, 2005, 10:46 am
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.
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