Fuel Oil Ratio

[Dennis]

one more wrench

Ok, obviously the temperature in the combustion chamber is a serious factor...and whether or not 100:1 burns cooler than 50:1, is an argument that I cannot fight...I do however run 32:1 myself...

But when fighting which is better...are we taking into consideration the lubrication factors of the said mixes?? wear factor on rings...cylinder walls....the bearings...etc..obviously (in my mind) the 32:1 is going to lubricate better...Are there no tests that have been done on wear factors perhaps over a certain number of hours with certain mixes??
If 100:1 is working great for keeping the combustion chamber cooler....how is it affecting ring wear?...bearings? Same for 32:1...how is it affecting each?

Maybe I am out to lunch here?? Maybe this is part of the argument you are debating and I dont understand the big words..

-I live in my own little world...but I am well known here.

 

[Dagger]

Great questions Dennis......
As I stated previously..the bearings that quality manufacturers use are sufficiently lubricated at much lower levels of oil in the mix than we use.
The crank mains need the less than the rod ends...but both need less than what it takes to keep the oil barrier between the skirt /cylinder wall. This is what dictates the oil needed.
As far as the rings...the only lubrication that the rings gets is what is in the porosity of the cylinder wall material...because they are a friction fit, and generally scrape off the .003 to .006 (or whatever clearance is) oil film anyway. Ring wear becomes a function of how good the lubrication qualities of the oil are..not how much, and of course the quality of the ring material. Thats another factor in favor of synthetics.

 

[Fish]

So with your thermocouple tests, you do not change
the carb mixtures? Would this have an effect on the
temperatures as well? A tiny bit can make a large
difference on the temperature. I am not trying to
argue, but I do not think piston damage can be
attributed to using 32:1 mix. The carbon buildup
that causes the damage that I see is mainly in
concrete saws, saws with leaky impulse driven
oiling systems, or a chronic rich fuel/air problem.
But the seizures are of lean air/fuel type, or low
/no oil type. I see bearing failures in the 029/039
Stihls, but that can be attributed to the fact that
they are kind of cheap junk.
The use of 32:1 or 40:1 or 50:1 isn't that
big of a deal. Why would the manufacturers
say"if you use our oil use it 50:1, any other brand
40:1"? The topic must not really be that hot of an issue.
I use 32:1 out of convenience, because I repair all
types of equipment, but in my own stuff, I keep using
the 32:1{regular octane} and have no catastrophic
failures at all.
Dagger,
where do you see these piston failures at? Do you look at what
has been sent in for warranty? Do you ever go to the Lawn
and Garden Expo in Louisville?

We have a lot of problems around here with folks using any plastic jug they can find for
an oilfuel mix container, and the plastic cooks inside the unit
totally rendering it repairless.

I am not trying to be antagonistic,
but I am curious. Since you are the first from the industry to
venture here, I am curious.
I am glad to be here at this forum, since I know nothing of
saw modifications either. It is good to have such an informative
and lively discussion

 

[thacket]

Tolerances

Hi All,

One more time.... When the oil mix recommendations were changed by the manufacturers, were the engine tolerances changed as well? Anybody?

John

 

[Dagger]

Thacket...
tolerances were changed 1st..to acheive piston stabilization at higher rpms that were design goals..then oil mix recommendations, as well as oil formulas, as they became available from oil venders. You see NO manufacturer of equip makes oil..they spec mix oil from an oil mix producer..and since the manufacturer must back the equipment under the warranty period, they usually dont cut corners on the formula requested.
Simply not worth the risk of choosing a cheaper oil formula vs having failure rates go up.
Oil mix is a low margin product for us anyhow. Dang bottles and inventory cost and labels and freight and such cost us more than the product inside! So usually the spec will be the best available from vendor
(read that highest bright stock content)

Fish...
Right..in the demonstration , simply to prove the point that fuel mix cools better with lower oil content, the carb must not be adjusted, so as to keep air/fuel ratio same, for as you state, this will change the temps dramatically.
And..you bring in a great varible to the equation also..cut-off saws..much different here...lower rpms..fuel richening governer systems...terrible operating conditions...Whew..that should start a whole new thread.
029/039 bearings..consumer/price oriented designs..made with bearings from a different bearing vendor..in a different country than the high quality stuff...im sure they probably need more oil than a bearing in ..say..an 066.. you words say it well enuf..
( but i have had suspicions about the torsional vibes in that designs reduced counter weight crank)...so oil might not be the main culprit..

BUT LOOK at this literature...this sure is a light saw!..LOL!!!

Policy of most manufacturers that says 50:1 with ours...40:1 with anyone elses..simply a catch all policy in case oil chosen by user has lower bright stock content than factory spec.
Anybody remember the lawsuit that Stihl LOST ...denying warranties because the user was not using Stihl brand oil???
courts decided that because the oil used was of the same American petro institute spec, that warranty responsibility CANNOT be abandoned, regardless of label on bottle!
(lesson here...dont fool with the turf of the oil companies in the USA)

I have been at every Expo in Louisville for last 22 years!
Yes I have seen hundreds..no...thousands of cylinders called in for warranty..and looked at that many more on dealers benchs in their shops...looked at several dozens failed purposely in lab conditions... and looked at a couple on my own hotsaws that were not failed purposely!..
yea used to race too!
If you have old copies of Chainsaw age...you saw me on the cover once!...AND NO..I aint McCormick!...Grrrrrrrr...(reply to offline email)

And you say Im the first from the industry to Venture here????..really..."GULP"!...
Well..i guess that the "anyominity" possible here lets us in the industry sort of vent our frustrations without fear of repromand from our employers! I will tell you all, that certain subjects have caused me to loose sleep over sometimes..not so honorable.. policies in our industry, and I guess that venting them here kind of..helps my concience.
I also get higher quality converations in here as anywhere else, for all here share similiar interests, and, there is much more knowledge/expierience I believe!

Heck, at work, most of em dont even know what a Llama is!

 

[Dennis]

hmm...so Dagger...maybe we met at the wood Expo in Elmia, Sweden in 1997...in the Jonsered tent where the free beer was..

 

[thacket]

Hi All,

Dagger, thank you very much for the information. One more question; When the tolerances were changed, did the saws get different model numbers? If not, that could contribute to some confusion on oil mixes. Thanks.

John

 

[TonyM]

"Right..in the demonstration , simply to prove the point that fuel mix cools better with lower oil content, the carb must not be adjusted, so as to keep air/fuel ratio same, for as you state, this will change the temps dramatically."

This is the whole problem with your experiment. Adding more oil to the fuel in and of itself leans the air/fuel ratio. The carburetor will only meter so much liquid fuel, and if that amount of liquid has more oil, then it must also have less gasoline. (32:1 = 3% oil 97% gas, 50:1 = 2% oil and 98% gas) Not to mention the effect that changes in the mixture viscosity have on carburation.

I'd like to see your test repeated with an air/fuel ratio sensor added, so that the carb CAN BE ADJUSTED to mantain the same air/fuel ratio.

 

[dbabcock]

Maybe it's not possible on chainsaws, but could one go to a direct crankcase oil injection like they do on some snowmobiles?

 

[Dennis]

once again I take the thread off topic..

and if we can go oil injection..why not run a supercharger off the flywheel with a belt...like on some snowmobiles??

*mumbling* "hmm....a few carb mods here....weld a pulley here...remove the starter cover..."

This is insane..I love it...

 

[Fish]

The reason for the carb adjust question is that it
has been contended here that the difference in oil/fuel mix
would drastically change the air/fuel mix, due to the
fact that there is less fuel{gasoline} in a rich oil/fuel mix.


I thought that was you in Louisville. You are the guy
that spritzes Miss Sweden with the mist bottle for
photos. She looks good when you do that. Of course you
probably double as her personal masseur, as you are the
one in mirror shades with the silly looking grin.
I will be there in Louisville this year too. I will be the
friend of Walt with Llama spit on his sleeve.

But what do you mean by bright stock content?

At least I know which booth to find you in now.

 

[tree monkey]

i find this all very interesting. we have always told the customer to use premium gas, no alcohol, manufacturer's oil, at reccomended ratio. we've seen some 046 066 main bearings go bad but only those using 404 chain. lower rod and main bearings seem to be the weak point on the 372's. we started using schaefers oil about 3 years ago at 32 to 1. no failures of any kind using it.

schaefers is a petroleum synthetic blend with micron moly. micron moly is like graphite.

these are just observations. not blaming the oil.

i've tore down saws, using high test gas mixed at 50 to 1, that were jet black inside. and saws using regular gas mixed at 32 to 1 that looked like new inside. why? brand of oil? mix ratio?

if our saws didn't wear out, the manufacturers would'nt sell as many saws. maybe there not telling us the whole story.


keeping an open mind scott

 

[Methoss084]

Back to the oil holding heat

Dagger I totally agree with the theory of the oil holding heat the combustion process, but in todays engines is this such a critical make or break point? Considering that todays alloys are so good at transfering and disapating heat. I also wonder why the 2 cycle industry hasn't adopted teflon skirted pistons similar to those in automotive applications and more closely related Tecumseh engines. Where did you used to work Dagger?

 

[sedanman]

What I'd like to see is this, have a test where saw operators are given two identical saws, one which will always be run using 32:1 and the other which will always get 50:1. The operators would have to switch saws every time they ran out of fuel to keep the hours on the saws equal (this could be by the gallon not the tankful). The test would have to be large enough to be able to weed out the freak saw failures and have a variety of saw brands/types, bucket saws, mid-size, and big felling saws. Oh yeah, the saws would all have to operate on the same brand and octane fuel to minimize variables.

 

[Dagger]

thacket...lessee..some models numbers were changed..for instance...2100 became 2101.....just slight changes like that..infact that particular saw was one of the few ...and the changes internally were simply a lighter weight..slighty larger..cam ground piston..I dont believe any consumer model numbers were changed...but really back then...there was not near as much difference in consumer models and pro models as far as design theory...nuttin like today!

Dennis...nope...i was not there pard..in 97! besides...I always had a real hard time with that warm beer over there!
I like my brew cold!

Tony...Excellent anyalsis pard! but you are not the first to think of it!..viscosity tests on fuel mix ratios from 2o:1 to 100:1 were undertaken long ago..difference extremly low...and the only reason we went to such extremes was because we could detect no change at 1 %..we already knew that we could get 3% change in viscosity in a heavy oil ratio (24:1 I think) if we changed the temp of fuel AND AIR..50 degrees..but couldnt get that at light ratios. That came from vapor lock studies in fact.
a real problem in south american market.
Now..about changing the adjustment..you didnt say it..but i see your thinking and you are in fact correct. However the difference is smaller than you are assuming.
1st ..we never used air/fuel mixture ratio moniters,,dont know if such a thing exists that woud work in this scenario..but how we do it is caculate. we know that in our test saw it takes a particular BMEP for instance, to get say 13,000 rpms, and we know that with a *test fuel* that it takes say...28:1 air/fuel to achieve burn rate and combustion temp to achieve this...so
by adjusting to 13,000...we have the air/fuel ratio we want..ok..so when we change the mix...THEN re-adjust the carb back to 13,000 we will have 28 :1 again. so YOU CAN do this yourself...and the washer configured thermo-couples and digital moniters are readily available today, at very reasonable prices, about than you will pay for a piston/cylinder assembly. so you dont have to take my word here men..as i can feel that many dont want to!...just DO the test...you will find that you will only change the temp difference by 15..maybe 20 percent...so if you get 50 degrees difference without re-adjusting...then it will be 40 after you re-adjust!....
*Test Fuel* is simply a certified fuel of known properties, IEctane,burn rates,volatility, reed vapor press..etc. ALL carb testing and heat testing and so done when developing a saw design has no worth if test fuel is not used,,because results cannot be duplicated when fuel standards are not kept to close standards.
Somehow...many here are really missing my point, I am simply trying to help you guys achieve a better way to find what ratio you should be using with your saw..weather stock or modified..all designs will respond slightly different to this because of cooling effiency of particular design. I have given you the results of my experiences..I have told you how manufacturers do it..thats all..use them to add to your knowledge, or disregard them...at your convenience.

Fish...You aint payin attention bro!! ..hehe I will not be in that booth...unless visiting an old friend or 2..left that outfit 8 years ago for previously mentioned reasons!.and they have had about 99% turnover in help since then!..But when I find you...the brews on me pard! just cause your posts make me laugh, and I know we gonna get along well! (got a better expense account now too!)
Bright stock... the lubricating additive found in mix oil that determines its lubricating quality...pure bright stock is similar to STP. When specifiying a mix formula to an oil vendor,,,this is main additive on the list..others include viscosity reducers..dye, stabilizers, etc..

Tree monkey, I like the idea of a moly additive, for reduced ring wear particularly..but it doesnt burn worth a dang...never heard of schaefers..but I also like synthetic/petro blends..just a small amount of moly will go a long way too! if its not causing any extra buildup of "unburned crap" on the top of piston..they probably have it just right!

Methoss..well i sure cant answer your question why teflon skirts are not with us..could be because teflon is a GOOD heat conductor, and we dont want heat transfer from cylinder wall to opiston..but i dont know...and Tecumseh..really..did know that..is it a teflon coating? which engines?
I have built several alky burning tractor pulling engines, and always drilled the skirts for teflon buttons to insure piston stabilization, plus they keep the bore from wearing really well as no matter what happens to lube...skirt never touchs cyl wall.
cold, hot, crankcase full a alky, whatever..they are really a block/bore saver!

also..yea..i know what you mean on those lower bearings...but ill tell ya...these new lightweight crankshafts are the cause of an awful lot of this...the ones you said.."only when using .404"..sounds like a lead in that direction...different vibration resonance maybe.
2 cycle bearings must have alot of clearance built in..for lubrication flow...and torsional vibration, and certain vibe frequencies can destroy em fast...and we cant really see why they seemed to just fall apart..hard to diagnose...for anybody.
when we cant find any heat indications..what do we do...just chalk it up to a bad bearing usually. if we do see heat indications..we say it was bad/lackof oil maybe...but hard to determine if heat came before...or after bearing failed sometimes.

Where did I work?..heck I aint never worked...just ask any a my emplorers...just sat around and drew pay..me ..work...nope. me an Maynard G!

 

[Harley]

I really should be stacking wood, but....

I figured out the theoretic stoichiometric mixtures assuming oil to be a long chain alkane. Just like Octane only much longer. The difference is around .4 air/fuel ratio. Now figure in that your changing from 50:1 to 32:1 and its much smaller of a difference. So, when adjusting, your only going to "bump" the needle alittle towards rich.

Second, if you burn more oil, with a higher BTU content, your temperature is going to go up. When you tested for temp difference did you take into account the BTU difference in the fuel?

Third. I know that Top Fuel engines fill the oil pan with alot of oil. Something like half the depth of the crank. They say that the added mass of the oil helps to dampen out harmful harmonics, that would otherwise cause the crank to break. If your vibration theory is true, this could be why the exprience here shows that more oil in the mix solves the bearing problems.

Dagger, its not that I don't believe you. I just like the fact that we can exchange ideas and theories here. Thank you.

BTW: Its hard to find out exact numbers reguarding important fluid properties of both oil and gas. That being said, the above is pure educated guessing.:angel:

 

[gatkeper1]

I find it hard to believe that Top Fuel engines are run with the crank submerged into the oil. Everything I have been taught says you don't want the crank touching,churning up the oil. Thats why we run crankshaft oilscrapers, windage trays and dry sump systems. all in the effort to keep the crank out of the oil. When the crank is spinning and it makes contact with the oil it will aerate it tuning it into froathe, the oil pump would pick this aerated mix up and since air doesn't lubricate thats the end of the motor. But my experience is only with engines that have to run longer that 6 seconds

 

[Dagger]

Harley. on the 1st-..right on pard... the difference is so small that it qualifies as "negligible"..!

on the second-
No the higher BTU content of oil than gas is not figured, here is why. After considerable debate I might add, it was theorized that under compression, as we know, the burn rate of gasoline accelerates much faster than the burn rate of the higher btu oil, and that at high rpms, the burn rate of the oil is slow enough that it does not contribute to higher combustion temps without increasing the compression to unacceptably high ratio's for the gasoline. (the debate BTW really centered around what rpm level this takes place at, and what effect increased BMEP has on it)

on the 3rd-
The crankcase full of oil trick on top fuel engines is past me too...I have always subscribed to the windage trays on our tractor pulling alky burners.

and AMEN bro, this exchange of ideas and theory is what makes me come back...just to hear what everyone thinks. Our individual expieriences all amass into the world of knowledge, and that world is so deep than no one can comprehend it all. what seems the greatest asset to us is the fact that when we read all these different reports, our minds will retain them , whether we think they are right at the time or not really may not matter. But when in the course of our lives, we come across a problem that we think we have the answer too, just the knowledge of this ideas will undoubtedly help keep us on the right track.

 

[Harley]

I'll have to find out where I found the info on the Fuel motor. I remembered it because I thought like you guys are saying. As little windage as possible is the best, after all smoky knows best. But did you ever notice that there aren't any dry sumps involved in top fuel?

Actually Gatkeper, the air is not a real problem. You want to keep oil off the crank so that it frees up HP. Top fuel motors make more HP than they can use, so I don't see the loss from that point of view as being a problem.

 

[Harley]

Here's the link where I found the info.

Nitro oil