50:1 vs 40:1

[paccity]

50:1 for me. haven't lost a saw due to running that ratio. . ya bob, that would be a great sig.

 

[Johny Utah]

for the blokes in aus ,if u go down the street to your local husky or stihl dealership ask them what the number 1 cause of a chainsawsaw blowing up is" he will tell you its becouse people are running the 50:1 ratio that is in the manuals, i hounstly dont know anyone that usses this mixture here its well known not to. and from experience i blew up a mates 088 3 cuts threw a big messmate and shes seized like a ##### = tested his fuel and what did we find !!!!!!!!!!!

Then you guys got different fuel down there or it's because of your climate. The factory specs have been rigorously tested and they would not publish false recommendations. Reputation is everything in this industry.

 

[edisto]

Okay if I steal that line for a signature?

I'd do anything for 15 min of fame...

And just to drag us all, kicking and screaming, back to the original topic...are we using 40:1 or 50:1...just thought I'd ask. Politely.

I run 40:1 because my can only holds 2 gallons, and I'm bad at math.

 

[splitpost]

Then you guys got different fuel down there or it's because of your climate. The factory specs have been rigorously tested and they would not publish false recommendations. Reputation is everything in this industry.

This is my take on it,Dad always mixed at 25:1 for his saws and mowers and thats what i followed with, but when i bought a new ms390 in 2005 the dealer said 50:1 as does the book unless using another brand oil,so thats what i used,

when i bought a used 310 it was running on 25:1,i automatically switched to 50:1 after all its basically the same saw, not long after she picked up a piston but not from the mix ,it had another issue,

it was around that time i needed a larger saw so i went to the dealer and picked up a spankin new 660 ,immediatly i was told to run 25:1,i questioned this thinking he thought i was using another brand oil ,his reply was stihl Australia will not warrant the saw on anything but 25:1...................OK i thought ,so 25:1 it is even though the stihl users manual states otherwise i did run it on 40:1 for a bit but didn't like the near light brown colour of the exhaust ,it just played on me ,specially when working the fark out of it,

when the 880 was purchased in 2010 i was told the same thing 25:1
now when the 880 took a dump at 12months old that was the first thing i was asked and thankfully they covered parts and labour(new P&C)
so now it just makes sense to run the same mix in all my 2strokes with the stihl badged/castrol oil,apart from the odd fouled plug and the higher oil usage i'me sticking to 25:1,Dad must know something after all Thats my reason for running oil rich ,:smile2eace of mind

 

[Terry Syd]

These 'oil threads' are getting better.

I'm still thinking about some of the heat/power issues. There were some interesting charts in that PDF that OMB posted. I wish I knew how to cut and paste them into this thread for discussion.

It appears the initial drop in power on a two-stroke is quite rapid for the first 30 seconds (probably with the piston getting hot), with further loss out to about 3 minutes (probably related to the cylinder coming up to temp). A richer mixture will then stabilise the power, however a leaner mixture will continue to drop. I suspect that the leaner mixture allows more heat soak into the crankcase as the cylinder is already up to temperature by about 3 minutes.

That's information for the racers/cookie cutting members of the forum, the first 10 seconds or so will be faster with the lean mixture and for testing of field conditions the richer mixture moves ahead in power. Its also something that might be considered during 'shoot outs' where the cutting may be less than 3 minutes.

In regards to Blair's comments about most of the atomisation occurring in the cylinder, perhaps the bulk of the atomisation does occur in the cylinder because the mixture is blown across and in contact with the hot piston crown. Whereas, beneath the piston very little mixture comes in contact with the bottom of the crown. Further, in regards to the radiation of heat from the crown, the crankcase has a large volume compared to the small surface under the crown. However, the mixture in the cylinder is confined in a small area above the hot piston crown.

 

[aussie2]

Come on Aussie 2, admit it, you're not really an Aussie, you're some Yank that is pretending to be an Australian.

hahaha i wish i was sometimes you guys have some whopa tree's .i got to check out those redwoods oneday

 

[aussie2]

no disrespect but the few dealers I have chatted to, including Husky construction reps and Hire store mechanics dont really know the depth of what they talk about. I have heard that 50-1 will blow up saws and to run at 30 or 25-1, when I ask about re tuning to suit the new ratio they ask what am I talking about. Tell a concreter to run at 25-1 in his Construction saw and how the hell is he going to tune it when they are spline drive needles and the tools arent readily avialable here. Will he even know how to tune the saw?? I don't run my saws at 50-1, but that is not becuase I think my saw will blow up at that ratio.....and FWIW, I have had Stihl dealers tell me I absolutely have to run my Stihl string trimmer at 50-1 as the whole engine is designed to run at that AND the STihl oil is ONLY designed to run at 50-1. (I said Castrol make their oil and have no problems with different ratio's in other aplications, his response was it is formulated for Stihl and specific to 50-1....I got the feeling that if I changed the ratio the world would end)

I have also been told by a different dealer that I can not run Stihl chain on my husky as it is different, wont fit and wont work. Even when I said that if I had a 0.63 gauge bar (which is common Stihl gauge in 3/8) he said wont work......If you are running fresh non-ethonal fuel, good quality oil, clean filters, zero air leaks, sharp chain and correct tune I doubt running at 50-1 is going to kill a saw. JMO

your right mate the smaller tsaws and pole saws are a little more safe to be running that mixture thats just my opinion.my husky dealer im good mates with has a 40 foot container full of blown up saws lol a good way to know where a good spot your saw should be running is to work up from 25:1 noticing the wear of your plug + oil is being burnt pritty clean.i think the test for a saw running 50:1 would be on a 45degree day cutting tank for tank .is it going to last?i dont persanly think it will .but others will say it will so where not getting anywhere hahah

 

[edisto]

It appears the initial drop in power on a two-stroke is quite rapid for the first 30 seconds (probably with the piston getting hot), with further loss out to about 3 minutes (probably related to the cylinder coming up to temp). A richer mixture will then stabilise the power, however a leaner mixture will continue to drop. I suspect that the leaner mixture allows more heat soak into the crankcase as the cylinder is already up to temperature by about 3 minutes.

Yup. I wish they had redone figure 14 using different mix ratios so you could separate the effects of more oil from a more dense mixture of fuel.

In regards to Blair's comments about most of the atomisation occurring in the cylinder, perhaps the bulk of the atomisation does occur in the cylinder because the mixture is blown across and in contact with the hot piston crown. Whereas, beneath the piston very little mixture comes in contact with the bottom of the crown. Further, in regards to the radiation of heat from the crown, the crankcase has a large volume compared to the small surface under the crown. However, the mixture in the cylinder is confined in a small area above the hot piston crown.

I don't think that expansion necessarily equates with atomization. I'm sure Blair is right about the atomization, I just don't think it means you don't get expansion from heating in the crankcase that lowers the effective charge density in terms of filling...especially with no reed or rotary valve.

 

[aussie2]

Then you guys got different fuel down there or it's because of your climate. The factory specs have been rigorously tested and they would not publish false recommendations. Reputation is everything in this industry.

yeah i think the climate may be a factor ,i use 95octane premium and always use husky oil.what fuel/gas do you use ?

 

[redheadwoodshed]

Jesus H. Tapdancing Christ.

Why is there always a direct correlation between the stupidity of the question, and the degree of snottiness with which it is asked?

Now Professor, don't be unkind.Here I am trying to learn something for free and you go and make me blow ice water through my nose!
Anyway,I will never stop by the gas station and just "get some gas" again.
I buy my oil from the sawshop in the 6 pack, I like 6 packs you know, and they make 50:1 when mixed with a gallon.But I like to stop the pump on .90, just to be on the safe side.Now that can is for my "modern" saws Stihls, Husky and newer Poulans and my weedeater.I put 2 bottles of oil in my other gas can for my old Macs.I figure they are old and have cast iron cylinders, they may need that extra oil.But then I ran out of the 25:1 old Mac gas the other day due to needing to start up a brush pile and used the 48.397:1 "modern" gas in one of the old Macs and it seemed to run a little better.I do tune on them once and a while, not because I know what I'm doing, but just to see what will happen, you know.But over all they ran better, so I'll just stick to my secret mix.Now that I have revealed the methods of my science I will continue reading yours.
Maybe my head won't explode next time I gas up.Carry on.:smile2:

 

[Terry Syd]

Opps, my bad, I should have written 'vapourisation' not 'atomisation'. Obviously, when a liquid moves to the vapour state there is an increase in volume - steam engines come to mind. In any case, whether the charge is expanded primarily above or below the piston, a cooler running piston crown is preferred for power.

Except for milling, a chainsaw spends most of its time cycling back and forth between WOT and idling. The build up of heat in the crown is therefore not as great as one would find in other two-strokes. Perhaps that is a reason why one-ring pistons are often used.

Have you ever run into any research on the differences in temps between one and two-ring pistons? I can see an argument for using two-ring pistons in a saw for milling, but I wonder how much greater the heat transfer is from the crown with two rings.

 

[husq2100]

yeah i think the climate may be a factor ,i use 95octane premium and always use husky oil.what fuel/gas do you use ?

Aussie2, our octane ratings are different to the USA, we both use numbers that sound the same, but it is a different rating system. AFAIK there is ethonal in all our unleadeds, both normal and premium. The one I am fairly sure doesnt have ethonal is BP Ultimate 98 octane. I have been told by Kart racing guys that the Shell Optimax 98 (or what ever it is) does have ethonal. They had problems with it at a race meet and when engines were stripped done they could trace the problem back to moisture in the carb.

Now I recokon ethonal would be worse than running at 40-50-1.....Nothing wrong with changing the fuel oil ratio for what ever a person wants, that is their choice. But it must be retuned to that new mix.

Are all your dealers telling you to retune with the new mix or is that just taken for granted?

what blown huskies does he have haha :hmm3grin2orange:

BTW I run BP Ultimate 98 and a blend of maxima 927 with Husky xp oil (50/50) @ 40-1 in all my saws, blower and string trimmer. By the sounds of it, I would not do any where near the work on my stuff as you, nor in your heat...

 

[edisto]

Now Professor, don't be unkind.Here I am trying to learn something for free and you go and make me blow ice water through my nose!

Sorry Red...hard to believe I didn't get enough coffee in me by 11 am, but my wife left me and my 4-year old boy on our own this weekend. It's fun, but he does run me ragged!

Can't take it out on the boy, so I had to vent somewhere!

 

[edisto]

Opps, my bad, I should have written 'vapourisation' not 'atomisation'. Obviously, when a liquid moves to the vapour state there is an increase in volume - steam engines come to mind. In any case, whether the charge is expanded primarily above or below the piston, a cooler running piston crown is preferred for power.

Right up until the transfers close!

Maybe a mercury-filled piston, so the mercury would stay at the top collecting heat on the down-stroke, and then shift it into the skirts on the upstroke. Wait...that would heat the charge...damned 2-strokes!

Have you ever run into any research on the differences in temps between one and two-ring pistons? I can see an argument for using two-ring pistons in a saw for milling, but I wonder how much greater the heat transfer is from the crown with two rings.

Research...no, but I know you can get plenty of opinion if you ask on the forum! It's the equivalent of flinging a shovel-full of crap into a very large, very fast fan.

I'll have to dig up the heat transfer paper I looked at when I get back to work on Monday. I don't think they varied ring number, but I might be wrong.

 

[Johny Utah]

This is my take on it,Dad always mixed at 25:1 for his saws and mowers and thats what i followed with, but when i bought a new ms390 in 2005 the dealer said 50:1 as does the book unless using another brand oil,so thats what i used,

when i bought a used 310 it was running on 25:1,i automatically switched to 50:1 after all its basically the same saw, not long after she picked up a piston but not from the mix ,it had another issue,

it was around that time i needed a larger saw so i went to the dealer and picked up a spankin new 660 ,immediatly i was told to run 25:1,i questioned this thinking he thought i was using another brand oil ,his reply was stihl Australia will not warrant the saw on anything but 25:1...................OK i thought ,so 25:1 it is even though the stihl users manual states otherwise i did run it on 40:1 for a bit but didn't like the near light brown colour of the exhaust ,it just played on me ,specially when working the fark out of it,

when the 880 was purchased in 2010 i was told the same thing 25:1
now when the 880 took a dump at 12months old that was the first thing i was asked and thankfully they covered parts and labour(new P&C)
so now it just makes sense to run the same mix in all my 2strokes with the stihl badged/castrol oil,apart from the odd fouled plug and the higher oil usage i'me sticking to 25:1,Dad must know something after all Thats my reason for running oil rich ,:smile2eace of mind

I believe what your sayen, it just seems funny that the saws won't run on 50:1 over there even though it's Stihl recommended. Interesting:msp_thumbup:

 

[Johny Utah]

your right mate the smaller tsaws and pole saws are a little more safe to be running that mixture thats just my opinion.my husky dealer im good mates with has a 40 foot container full of blown up saws lol a good way to know where a good spot your saw should be running is to work up from 25:1 noticing the wear of your plug + oil is being burnt pritty clean.i think the test for a saw running 50:1 would be on a 45degree day cutting tank for tank .is it going to last?i dont persanly think it will .but others will say it will so where not getting anywhere hahah

+45 that's hot for humans let alone saws. I'll take -40 any day over +40.:hmm3grin2orange:

 

[Johny Utah]

yeah i think the climate may be a factor ,i use 95octane premium and always use husky oil.what fuel/gas do you use ?

Up here I use premium ethanol free gas with a little octane boost. Never had any 2-stroke ever burn down on me from oil issues. I've run 50:1 in everything from dirt bikes and snowmobiles to trimmers and saws. Our premium fuels in Canada so far are ethanol free.:msp_thumbup:

 

[fir]

Up here I use premium ethanol free gas with a little octane boost. Never had any 2-stroke ever burn down on me from oil issues. I've run 50:1 in everything from dirt bikes and snowmobiles to trimmers and saws. Our premium fuels in Canada so far are ethanol free.:msp_thumbup:[/QUOT There as been ethanol in B.C. since Jan 1st 2011.

 

[redheadwoodshed]

Sorry Red...hard to believe I didn't get enough coffee in me by 11 am, but my wife left me and my 4-year old boy on our own this weekend. It's fun, but he does run me ragged!

Can't take it out on the boy, so I had to vent somewhere!

I understand completely, I have a 3 1/2 year old who has to go treasure hunting pretty much every day when I'm at home.That usally means I end up carrying her back from where ever she finally found her treasure.(gold covered chocolate, she could care less about the gold, chocolate is another story altogether, that's serious treasure!)
Your comments about the mercury made me think of something.I freely admit I'm fairly ignorant about mechanics in general, although I am learning.But metals and heat transfer I know a little about.That's why I was wondering if anyone had ever experimented with a copper alloy (bronze or other) cylinder head?I would think it would be more efficient at heat transfer out of the cylinder, and run cooler altogether.I would think it would handle the pressures and other stresses as well as or better than aluminium.A little heavier, yes, but not much.
Just a random thought early in the morning....I really don't like the time change!

 

[edisto]

Your comments about the mercury made me think of something.I freely admit I'm fairly ignorant about mechanics in general, although I am learning.But metals and heat transfer I know a little about.That's why I was wondering if anyone had ever experimented with a copper alloy (bronze or other) cylinder head?I would think it would be more efficient at heat transfer out of the cylinder, and run cooler altogether.I would think it would handle the pressures and other stresses as well as or better than aluminium.A little heavier, yes, but not much.
Just a random thought early in the morning....I really don't like the time change!

Found some British bikes in the 30's that had bronze cylinder heads (just the heads).

Just took a quick look, but it seems that the copper alloys are not in the same league as pure copper (or aluminum) for heat transfer?

I know copper head gaskets get brittle, and need to be annealed to be reused, would that be an issue? Seems like roughly 3 times the mass too, so that's probably why they stick with aluminum.