Fuel Oil Ratio

[DDM]

Okay if i understand correctly the 50:1 mixture was forced upon the saw industry for emission reasons correct?But the Engine i.e. Jug piston ect
are the same correct? which would mean the saw manufactures Stretched the amount need to lube the saw to near the limit.is this a correct assumption?If i wanted to run my saws all 50:1 at 40:1 what adjustments would i need to make?

 

[Methoss084]

Whenever we set up a new saw for the customer we always tell them to run their saws at 40:1 mix. In some areas the fuel is so crappy in the Northeast, They oxygenate the fuel so much and put in 15% MTBE, not to mention the waterborn content of the fuel especially from the cheap gas stations. I recommend that customers mix at 40:1 with 89 Octane at Mobile if possible. Do you guys run 93 Octane in your saws? And if so do they get to hot?

A fouled plug is cheaper than a top end.

Thanks Josh.

 

[tony marks]

fish im not arguing, cause these guys say this works for them.
am i going to run out an change the mix for all my equipment. no way. what im doing now works good 50-1an high test.
no 2 cycle problems as i had many in the past.
i might play with the 32-1 mix in a machine for a while an see what happens. later now

 

[sawracr]

Josh, recomending the highest octain is what we do in our shop, as higher octain burns cooler,with a more even flame front, actually with less B.T.U.s. I.E. cooler burn, cooler saw.
Jon

 

[Dagger]

OH man....

Oh MAN...you guys..you are scaring the hell out of me!
As an genuine sheepskinned engineer( I know that will really help my creds in here!) Let me tell you a couple a things from an engine developers view...
first..the wrongs...
NO the 50:1 was not forced upon us by EPA regs!
HEAT WAS THE CULPRIT..
JEEZ,... and air-cooled 2 stroke saw engine is NOT really aircooled..75 to 80 %of the cooling is effected by the fuel,,the remainder by air.
As we were struggling to get our RPMs up higher than the other guy..but still having to give a warrenty as demanded by the sales dept, alot of things came in to consideration..
keep down the heat...a cooler engine last longer!
FACT: GAS cools BETTER than oil
FACT: GAS burns better and cleaner than oil (no dummy, we didnt care about smoke)it was unburned deposits in the combustion chamber, ending up in the ring grooves and on the piston walls causing siezures...and oh man..we had alot a that in the early days
we found nika-sil helped keep the heat that was building up in the walls from transferring to the piston...which we could keep cool by the fuel on BOTH sides of better than we could keep the jug cool. (*** below)..( no , it wasnt to make the bore slicker!)

FACT: the design CLEARANCE TOLERANCES and rpm level and side load factor dictate how much oil is needed..tighter tolerances...LESS OIL FILM THICKNESS..meaning less required in the ratio..we can caculate a volume requirement from this...
in other words % air/fuel (about 28 to one for highest cylinder pressure) X CFM's( that engine is just an air pump right?)
convert that to a volumetric measurement of your choice and we know how much fuel we have going thru the engine...now.in that much fuel, we put in the amount of oil need for lubrication..as dictated by above criteria..add a certain safety factor..(industry standard of 1.25 to 1.5 ) to help us get thru the warranty period whilst all them "EXPERTS" were fooling with the carb adjustments to make em run faster.
that is how manufacturers determine the recommended ratio
NOW..convince the public that MORE is NOT BETTER!
we have been trying to do that for years!
RULE..
a leaner oil mix ratio has better cooling properties than a heavier ratio. DUE to higher volatility (evaporative properities) of gas than oil.
unburned oil looks like varnish and gets "painted" on the piston skirt/sides..this in effect makes the piston "bigger" in the bore and decreases the thickness of the oil film.
This will lead to premature failure..get it!
TEST TO PROVE IT TO YA!
take 2 cans of fuel..32 : 1 and 50 : 1
take any newer high performance stock saw
get a thermocouple that fits under the spark plug( looks like a washer withe a wire attached) and a digital monitering device.
probably have a 50 :1 recommendation if it a new saw..so put that gas in and adjust carb,,if applicable, to correct RPM's..
run till heat readings are as high as it will go...3-4 or minutes is plenty. ok...shut off and pour out fuel and replace with 32 :1
repeat test and BECOME EDUCATED!
Do this same test in your HOT-SAW..you will run the rpms you want by the carb adjustment,,,then use the HEAT MONITERING test to decide the oil mix ratio..and you will have a COOLER HOT SAW!
If anyone finds that it needs more oil to stay cool...please let me know so I can throw away 25 years of engineering expierience in these areas!

*** this is why you see the motorcycle/snowmobile world of 2 cycles evolving to liquid-cooled designs..to reduce the share of the fuels cooling duties so air/fuel ratio's can be adjusted to give higher combustion pressures

 

[Keener]

Thanks to Dagger! Thats what I think the forum should do, maybe with more diplomacy but thanks none the less.
I'm just a guy who feeds his family by making chips and the longer the saw,chain,bar ect ect last on the job the more money I have to feed my family so I'm" Keener" to learn what I can.
I'm sure others will want to disagree with you but the great thing about that is it forces me to think more about what I know or think I know, let the debate begin

 

[TonyM]

What you're saying about running hotter is true, all other things being equal. You can do the same damage by adjusting the carb too lean, that's why I said mixing to lower ratios causes a leaner condition, and you have to adjust the carb to compensate for it. Once the carb is adjusted, the amount of fuel entering the engine should be the same, and the amount of oil will increase. Do the same temperature test but allow the carb to be properly tuned and I'd be surprised if the temperature will rise at 32:1. I have seen dyno charts of the same engine (all be it water cooled) run at several progressively lower mix ratios, and the lower the ratio, the higher the Hp. There is a limit to how much oil can be run through the engine before it starts to deposit on the plug and the rings as you said, and from the evidence I've seen, 32:1 is still relatively safe. I really wish I could remember the test I'd seen, but I'd have to dig through ten years worth of magazines to find it.

 

[rosshuber43]

Stihl says to run 50:1, Hill City mechanic says 50:1, the wyoming guys are going to stick with 50:1.

 

[DDM]

So ummm Dagger,Me being a Dummy and all Would you explain what effects if any Running an older saw with a 32:1 Ratio with 50:1 Mix would have.

 

[ricksvar]

As I said earlier in this threat I use a 50:1 fuel mix.
However,as a saw wears and those "tighter tolerances" diminish, would it extend the life and power a saw has to change to 40:1 or even 32:1 on a saw with several hours of use?If less oil coating is needed with a new saw it would seem more is needed (oil film)on a older worn saw.Sorta like STP in a old car engine!

 

[Dagger]

First,I must say honestly, that i have never done any testing to determine the if a older saw would benefit from a higher content of lubricant in the fuel mixture, and am not aware of any professionally reported data.

However, I have participated in many conversations that considered this possibility. I am aware of so many examinations on this that I couldnt decide for myself without doing such a test myself. And i never have. But, just consider this, if you consider the industry standard 1.5 percent factor, your 50:1 saw is designed for perfect lubrication at a 75:1 ratio, and I can tell you that i am aware of several pro swede models that are on the 100:1 standard, (*** see below)... then you are have already alot more lubricant passing thru than you need.
Our bearing venders also have contributed greatly to this and with the higher quality ball bearings we have today, already the quality stuff on the market has bearings that will run on 1/10th the oil we put thru them. A design team of engineers 30 years ago did not have these available. So the last thing we have really been concerned with in some time is skirt/cylinder clearances and keeping that aluminium piston from melting.
so cooling vs lube needed....thats the question.. dunno the answer for a "worn saw"..and it would hard to be conclusive, and if I did perform the testing, with many heat monitoring points, including EGT. I would be hard pressed to say that they represented the charcteristics of any other make and model!
But Its possible!


*** 100:1 Standard

complete engineering standards detailing load/lubricant tolerances in engine manufacture published by
Scott-Atwater Outboard div McCulloch Motors by
Bob McCulloch in the late 50's


P.S. for Keener...i'm trying..this better?

 

[Keener]

Much improved Dagger! Like I said I'm just a guy who makes chips for a living( bigger the better) but we all hang on to our bias with more or less determination. As for me the more I learn the more I realize I have yet to learn.
I think it is important to share Knowledge unless we want to become a third world country.
In Canada we are already headed that way, just look at what we used to manufacture in the way of chainsaw, chain ect. Now except for some subsidized businesses back east we can't figure out how to make a better slice of toast, if we did no Canadian bank or individual would finance it. It would end up in the U.S. where there are some risk takers still.
It's been suggested before, someone should put a book together with all the knowledge displayed here so those that care to can look after their saw investments properly( probably lots of $ in saws represented here).

 

[Fish]

I am not trying to argue, but the seizure failures I have
encountered have nothing to do with too much oil in the
mix, but either a no-oil mix, or a lean air/fuel mix. I have seen
the ill effects of too much oil run in a two-cycle engine[hardly
catastrophic], and units that have been run too rich on an
air/fuel mixture. The worst of the problems was piston damage
caused by a buildup of carbon in the exhaust ports, but that is
very rare. I, and am sure many others would like to discuss this
at length.

 

[dbabcock]

Hey Keener,
I make chips too. Now if only I could use a chainsaw to do it.

 

[Rotax Robert]

I am with KD. I also use 927 @ 30:1 on my Rotax and 35:1 on my other saws, Hotsaws included...I have found that my Modified Saws run good to 16:1 ratios with plug changes often of course. A bit smokey though. Hmmmm...maybe bad valves

 

[homelite360]

my old truck had bad valve seals and it fouled plugs every 2000 miles that might be a casue bad valve sealsit. it burn so much oil i was thinking about draining all the oil out of it and filling the crank case up with 2 cycle gas and seeing if it would run. i should have tried that before i got rid of it.

 

[Methoss084]

Well since my 40:1with 89 octane theory was cut down like the oh so many trees in the Rain Forest. What do all you "Engineers" recommend that I tell my customers to use in their 2 cycle hand held equipment. And as far as Squish bands , Flame fronts, Exhaust port deposits, Scavenging rates, and raw fuel through the exhaust is concerned, customers don't care about it. So Dagger, whats your take on this? Not to be sarcastic or anything. What should it be 50:1 for that lean burning grey sparkplug or 40:1 for that margin of safety?

 

[sawracr]

Dagger, I wish you could see some of the big end rod bearing falures I have incountered as of late, both major manufactures , rods blue as hell, got to be heat! at 50-1 rato. ????ed if Stihl is'nt putting little scollops on the rod to improve oiling! As the Nascar races are proving ground for the automotive sector, so to a competition saw can test the limits of any good engineer, the oil at 50-1 is not keeping the bearings from skating.

 

[Cicero]

I have been taught the same as dagger. I was told that the reason a richer mixture of oil vs gas will actually burn hotter is due to the fact that oil burns hotter than gasoline. (our Stihl regional service rep.)

I really dont see how a richer mixture can prolong life in a saw. The fact of the matter is that if the oil is keeping metal from contacting metal during operation than that is all that counts. Who cares how thick the oil film between the piston and cylinder is as long as it is there and keeping metal components apart. If 50:1 does it than why go less??

 

[Keener]

Doug, you need someone to design a T- shirt for you. A chainsaw cutting into a PC with "chips" flying.
On the ratio debate what if you don't worry about exact mix ratio as long as you mix between 40:1 and 50:1 and call it good, using high octane gas of course.
Getting it exact is (for me) too large a mental challenge at 7:45am when I have to be at the job at 8:00 and it's a 30min drive.
Since I don't race my saws and do my best to keep other maintenace variables under control I think I can afford a tolerance on the mix.
Results? I have not lost a saw to cylinder damage in 20 years, your comments( positive or negative) are invited