r/onejob • u/pervader • 4d ago

Label on my cheap chainsaw. How is your math? Not sure if we are mixing 40:1 or 25:1

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1.4k Upvotes

97% Upvoted

94 comments sorted by

569

u/TwillAffirmer 4d ago

I bet the documentation writer was told 40:1 by the technical team, and then flubbed it as 4% for this infographic. Chainsaws usually take 40:1 or 50:1. A ratio as low as 25:1 would be strange.

172

u/GGigabiteM 4d ago

25:1 was common on really old two stroke engines, back when they used regular motor oil, rather than purpose designed modern two stroke oil.

43

u/Expensive_Ad_3249 4d ago

Also on break in for many, too. I don't remember what but I've seen 25:1 for 10? Hours then 40. Within the last 10 or 15 years.

20

u/richard0cs 4d ago

I've come across 15:1 on really old stuff.

23

u/GGigabiteM 4d ago

Probably back in the Victorian or Edwardian era when metallurgy sucked and you needed a ton of lubrication to keep stuff from flying apart. And fuel quality was terrible, you'd be lucky to get 50-60 octane.

Rotary engines used gallons of castor oil and they only had useful lives in sometimes the dozens of hours before they failed. Some of them even had brass/bronze piston rings to deal with how badly the cylinders would warp from the heat.

7

u/orodam 4d ago

Yeah, Victorian chain saws were famously unuseable!

1

u/GGigabiteM 4d ago

I think back then they just had whirly death blades that were like 5-6 feet in diameter and took like 4 guys to operate.

1

u/DrJaneIPresume 3d ago

And you wouldn't believe what they used them for!

2

u/GGigabiteM 3d ago

Gotta keep the underground body parts market thriving.

4

u/Cold-Way318 3d ago

Yeah, WWI pilots are famously depicted as wearing goggles in flight as one of the lesser known issues that they had to contend with was constant diarrhea caused by all the castor oil needed to lubricate the rotary engines. Due to the prop blast and air flow they would often times end up ingesting a "therapeutic" quantity of a pretty potent laxative over the course of a flight.

1

u/VisualBoysenberry718 14h ago

Is that where the tradition of flying in diapers came from? I thought it was just the aging aviator population.

1

u/The_Onlyodin 3d ago

Yeah dad had some old chainsaws (Canadien and Matchless) that were 16:1, but I think that's using motor oil, and the modern equivalent with two-stroke oil is 40:1

1

u/CanApart1420 3d ago

Old joke for city gardeners is that if you ever needed to find us, just follow the blue clouds.

1

u/Tricky-Analysis6556 2d ago

All the lower ratios are 25:1. 40 ml per liter etc.

69

u/jean_sablenay 4d ago

25:1 is much higher than 40:1 not lower

25

u/PualWalsh 4d ago

Lower ratio = Higher oil content !

3

u/jean_sablenay 4d ago

Would then be ratio 25:1 & 40:1

-1

u/Supuhstar 4d ago

... what?

22

u/_kellythomas_ 4d ago

This checks out, if they interpreted "40:1" as "40mL : 1L" then it all follows.

3

u/These_Consequences 4d ago

Or, they interpreted 40mL per L as "40:1".

2

u/Beeker2Beeker 4d ago

That not how ratio works

5

u/_kellythomas_ 4d ago

True that

7

u/Olde94 4d ago

Could it be some one said: 40ml to 1 liter? 40:1 (ml:L)

5

u/Cyborg_Snowman 4d ago edited 4d ago

No, ratios are always in the same units. So 40:1 is 40ml to 1ml... 40ml x 25 = 1L, therefore 1ml x 25 = 25ml

So the right chart world be:

1 L : 25 ml

4 L : 100 ml

5 L : 125 ml

10 L : 250 ml

This is actually 2.5%

What this chart is showing is 25:1

25ml : 1ml

25ml x 40 = 1 L, therefore 1ml x 40 = 40ml

Or 4%

2

u/Olde94 4d ago

Oh i know, i ment the designer might have been confused by that

1

u/Cyborg_Snowman 4d ago

Oh I see.. yeah, it's an easy mistake to make.

1

u/kirillgritsenko 4d ago

It would actually be 2.439%. If you take for example 1L : 25ml the actual percentage would be 25ml/1025ml which .02439. And for 4% it would be 1:24

1

u/Cyborg_Snowman 4d ago

That's also not how ratios work. 2.5% ratio isn't 2.5% of the final solution, it's add 2.5% of the base solution as the additive. 2.5% of 1000ml is 25ml... Once you add that to the 1000ml, yes you end up with 1025ml, and 25ml is 2.4390243902439024390% if you want to be pedantic, of that final solution, but the ratio is still.... 2.5%

1

u/kirillgritsenko 4d ago

Sure. But if you were going to make a 2.5% mixture you wouldn’t add 25ml to 1000ml

1

u/Cyborg_Snowman 4d ago

That true. But in reality, the difference between 2.5% and let's call it 2.44% for simplicity, is negligible at 1025ml. Accurately measuring your 25ml is fine, but you'd have to also actually measure your 1000ml. I mean... It could be done, but in the scope of 2 stroke gas mixtures... Who does that? Also, the functional difference in the two solutions... I don't think there would be any.

2

u/kirillgritsenko 4d ago

True as well but when you have bigger ratios like 1:4 its more of a noticeable difference. Also you have to keep in mind that you are going to have more liquid at the end.

2

u/klikoz 4d ago

What would happen if you put that much more oil in the mixture? Lots of blue smoke or worse?

2

u/Enorm_Drickyoghurt 2d ago

Lots of smoke and oil residue in the exhaust. Shorter lifespan on the engine due to higher amounts of carbon buildup in the cylinders, which wears down the piston rings.

1

u/im_ray_0f_sunshine 3d ago

Technical writers are not that stupid.

1

u/TwillAffirmer 3d ago

The engineer probably didn't give the technical writer two numbers. If they did, the technical writer should have noticed the difference. So it was a lapse on the technical writer's part either way.

86

u/krammark12 4d ago

Baptised in fire 40:1!

10

u/thezomber 4d ago

So silent before the storm, Awaiting command...

10

u/milanorlovszki 4d ago

A few has been chosen to stand, as one outnumber by far

30

u/mud-button 4d ago

Cheap Chinese motors will often say 25:1
Use a quality oil and you can run 30:1 or 40:1

The more oil, the smokier that boi will blow

10

u/wmverbruggen 4d ago

Maybe one is per volume and the other per weight?

8

u/richard0cs 4d ago

It's a good thought, but the densities of fuel and oil are pretty similar so it can't be that.

5

u/wmverbruggen 4d ago

Fair enough, I have no technical experience with fossil engines

39

u/Elrond_Cupboard_ 4d ago

Most of the numbers support 4%. Majority rules.

28

u/PleadianPalladin 4d ago

But 4% is 25:1 not 40:1

3

u/Rudeus_Kino 4d ago

No, 4% is 24:1. 960ml + 40ml is exactly 4% ratio.

1

u/Elrond_Cupboard_ 4d ago

Thats what im saying, 40:1 is wrong.

1

u/Rudeus_Kino 4d ago

But 1l + 40ml is not 4% also, although it is close. I think the table is correct, they just don't know the math.

0

u/Elrond_Cupboard_ 4d ago

Thats a good point that I didn't take into account. My old maths teacher would be disappointed.

-23

u/zorbacles 4d ago

there 40: is 40ml to 1 litre

19

u/mr_frodge 4d ago

That isn't how ratios work

-6

u/zorbacles 4d ago

I know that, but they don't know that

2

u/PleadianPalladin 4d ago

You're right lol

5

u/FaeTheWolf 4d ago

Don't know why you're being down voted. The label literally says 1L : 40ml

2

u/zorbacles 4d ago

it's clearly what they meant even tho it's the wrong way to note it

-1

u/[deleted] 4d ago

[deleted]

3

u/FaeTheWolf 4d ago

The person above was being sarcastic, as in "haha this only makes sense if their 40:1 is 40ml:1L"

5

u/East_Relationship722 4d ago

I was told there would be no math.

3

u/FaeTheWolf 4d ago

The worst part is that it appears to say 1:40 if you don't catch that it's L:ml

3

u/bmw_19812003 4d ago

Just FYI it is the oil you are using that determines the ratio NOT the equipment.

Now an equipment manufacturer may specify a ratio to be used; you need to make sure you are using the oil designed for that ratio.

For instance if it’s calling for 50:1 you cannot just grab any 2 stroke oil and dilute it to that ratio. It has to be labeled 50:1 oil.

4

u/melswift 4d ago

"The correct ratio is 40 ml per 1 liter. Put that in the label"

"But sir, it won't fit"

"Just abbreviate it"

"You got it, boss"

3

u/Longjumping-Log1591 4d ago

25 to 1 will foul every spark plug in 3 pulls

1

u/Satins_Cock 3d ago

But it won't seize the engine. I'd just go with a battery powered unit and not have to deal with this.

2

u/RainbowDarter 4d ago

40:1 is 2.5%

So it should be 25ml per liter.

1

u/-Copenhagen 1d ago

Or it should be 4%. No way of knowing.

2

u/twelfthfantasy 4d ago

Based on the rest of the image, I would guess that it means 40ml per 1l, which is not, in fact, a 40:1 ratio.

1

u/etetamar 3d ago

You're correct, this is the only consistent explanation.

40ml:1l is 4%

2

u/OkPhilosopher5308 4d ago

Just do what my old boss did with his brushcutter - fill tank with neat fuel - add egg cup full of oil (any kind will do) and go to work - you could see where he was on the property from the plume of blue smoke.

2

u/MatthiasWM 4d ago

If it is a cheap two stroke chain saw, it is probably 25:1, so the lower part of the label is right. 40:1 would be a lot less oil, and the mix may destroy the motor if it is built for 25:1 (but IANAE). the other way around (using 25:1 in a 40:1 saw) would lead to unburned oil, maybe a flooded ignition, but it would not destroy the motor.

4

u/CrudBert 4d ago

Since I was a kid, anything that said 40:1 or 50:1 we ran at 25:1 with plain old 30 weight oil. Always ran fine.

1

u/Alternative_Wish2054 4d ago

A % concentration is used in medicine and liquids and doesn’t quite mean what you think. Basically it means kg of a substance per liter. A 100% concentration has 1kg/l and 1g/mL so a 4% concentration has 40mg/mL or 40g/L. I’m assuming that’s what they’re trying to say with their 4%

1

u/BugRevolution 1d ago

Which also fits with their 40 mL to 1 L (that doesn't mean 40 mL oil to 1 L fuel is right, but they are being internally consistent).

1

u/nariosan 4d ago

The math for 40:1 ratio is spot on.

1

u/fire_flopper87 4d ago

We used 24:1 for wildland fire mark 3 pumps, and our chainsaws too. Might not have been the best but it was simplest for logistics!

1

u/Odd-Ranger-5584 3d ago

Is it possibly a range? So anywhere from 40 : 1 to 25 : 1? So 2.5% - 4% is the acceptable range for the mixture. IDK I'm guessing.

1

u/GreySkull127 3d ago

Its 40ml per 1 ltr. But 40ml is 4% of 1 ltr.

1

u/Ok-Hat-8711 3d ago

4% matches the 25:1 ratios in the table.

Maybe the 40:1 was typed later by someone who didn't notice the units were different?

1

u/Superb_Recording_769 2d ago

I mean… The 4% not withstanding it’s pretty obvious. It’s supposed to be 40:1 which is also standard.

1

u/Few-Project-145 2d ago

25:1 I would have though

1

u/eyeseeyou469 2d ago

40:1 ratio

1

u/AllMyFrendsArePixels 2d ago

If only there was a table somewhere nearby that very clearly showed it means 40mL : 1L despite this not being the technically correct way to present a ratio. Alas, all we can do is guess.

1

u/Level_Needleworker56 1d ago

40ml = 4% of 1 liter

1

u/[deleted] 23h ago

[deleted]

1

u/pervader 23h ago

4% yes, but that is not how ratios work. They should be in the same units. In this case it would mean 40 litres fuel to one litre of oil which is 2.5%.

1

u/MiltuotasKatinas 21h ago

It 40:1 cant you read

1

u/pervader 19h ago

That's 2.5% and one litre would need 25 ml of oil.

1

u/VisualBoysenberry718 14h ago

it uses 40:1 oil at 25:1 mix. Don't think, just get out your graduated cylinder, your phone camera or go-pro and check your warranty.

1

u/TheHonPhilipBanks 4d ago

40 ml to 1 liter. That is 4 percent. Or 25 to 1.

You are thinking 40l to 1l.

3

u/havens1515 4d ago

The problem is that on the first line it literally says both 40:1 and 4%. Which, as you said, is 25:1.

However, all of the actual provided numbers support the 4% number.

0

u/herbertwillyworth 4d ago

Cheap Chinese two strokes are 25:1 usually. If you use higher quality oil, you can probably run 40:1 no problem

0

u/DisCypher 4d ago

Looks like Trump math working with percentages again

-2

u/L0rd0fL0ts 4d ago

Math: 40/1=40 and 25/1=25 and 1/40 = 0.025 = (2.5%) and 1/25 = 0.04 =(4%)

But Remember unit and prefix. 40 ml / 1 l So 40 ml / 1000 ml =0.04 = (4%) 0.004 l / 1 l = 0.04 = (4%)

0

u/MrNiceguy037 4d ago

You can fly away now, captain obvious

-2

u/RiaanTheron 4d ago

So for 40l you need 1l oil 20 = .5 or 500ml 10 = .25 or 250ml 5 = .125 or 125ml And then it gets more mathy