oil-gas ratio

[Choreboy]

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?

[cowboy]

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

[Vic Dura]

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.

I've done that often with no noticed problems.

[barry]

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

[m Ransley]

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.

[Tony Hwang]

Hi, I just use 30:1 mix on weed eater, chain saw, snow blower. Experienced no problem. I use only name brand good quality oil. Tony

[barry]

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 replacement available.)

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 full-power.

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 slightest oiling.

Is less-polluting bad? I don't think so, if it means I get to suck down less oil-smoke.

Less is more, here.

HTH, J

[Steve B.]

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.

Steve B.

[TPutmann]

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.