Will Strato charged motors be less reliable long term?

[walexa07]

The subjects being argued about here are tantamount to arguing the earth is round. Pretty simple stuff.
And do realised a traditional two stroke deposits it's the vast majority of its oil in the crankcase as soon as the fuel air mix enters. You are not considering this, nor.oil.migration times and what effects them.in your argument.

Ok this response from you is more informative than most of your other posts in this thread - elaborate more. Clearly you have had some deep thoughts on it all. Rather than just say 20% less fuel through the saw means less lubrication.

Waylan

 

[Franny K]

It's not my job to be your educator

Seems like there are folks that want to trick others to take on that role and often it seems they are doing it for amusement.

 

[blsnelling]

Most of the saws I build are new.

 

[walexa07]

Most of the saws I build are new.

The 441 that had been used for milling - did the crankcase and piston seem dryer than normal? Or when you've tried a saw out for several cuts and gone back in for tweaking did you notice anything then? Just wondering.

Thanks,

Waylan

 

[blsnelling]

That was 6 years ago. I don't remember.

 

[svk]

Alright gents, there have been some complaints about this thread. Lets keep things cordial in here. Thanks.

Apparently some couldn't keep it cordial. If this thread gets flagged again there's going to be trips to camp for the offending parties and the thread is getting zapped. I don't like to lay it out that bluntly but apparently my first request was ignored.

Carry on men.

 

[windthrown]

The emissions limits thus far are mainly intended to prevent puking raw fuel out the exhaust, which mainly comes from two sources: The scavenging losses inherent to 2-strokes, and the poor mixture control of the carbs which go rich enough to cause misfire with only a small increase in air velocity. On top of that there is an emission credit scheme, so not every saw must meet the same limits. It looks to me like addressing one of these main sources gets one pretty close, and there are many strato saws with conventional carbs.

The cooling kickup was always the best evidence that there was something to the claims of exhaust delayed scavenging, but the fact that they are putting fresh air strato systems on their high volume saws says it may not be enough across the product line. The purpose of delayed scavenging is simply to reduce the time that fuel is in the combustion chamber while the exhaust port is open, and I suspect that the exhaust delayed scavenging may create some delay, but shorter than that of a full fresh air strato system (this is indicated by the attached document which describes an attempt to model the transfer flow in a Husqvarna strato). It may be enough when combined with a feedback carb on some of their saws, given that the high volume units are now fresh air strato, often combined with a feedback carb. So you are correct that the effect is "subtle" - perhaps "minimal" would likely be a better term.

As for "all the crap required to make a fresh air stratified saw work" - a fresh air strato requires no moving parts. It is an elegant design. A separate air valve is not required, rather it is a performance enhancement that allows the strato function to be shut off at idle, and effectively gives variable intake port timing. Many newer Stihl and Husky saws use a carb with a split flow and single throttle plate (thanks to yet another Zenoah patent).

Last, a fresh air strato pulls cool air across the piston and down the transfers during intake, and then air and mix flows up the transfers as in a conventional engine. That is a much more appealing approach than pushing hot exhaust down the transfers. Also the gas that is used to delay the charge is going to be used in the next combustion, unlike exhaust which must be expelled.

Well, for one I have tossed Brad into my ignore list, at the request of management. STD is also in my ignore list, as he is reminiscent of the Ape (who's more recent renditions have also been sent to band camp, along with STD it appears). I am used to controversy, as I am constantly challenged on my ideas by marketing, competitive engineering departments, and other engineering 'gurus'. I actually have used this to great benefit in the my career. I invite all my enemies to my design reviews, because they have a keen interest in finding flaws in my designs. Better for me to find flaws early than to have them go into production and fail. My designs and methods have been for the most part highly successful. Here on this debate however these are not my designs, and I have nothing to gain or lose by Stihl having the 461 work one way or the other. I have no horse in this race. However, I believe what I believe, like it or not.

At any rate, for simplicity I will label Stihl Pre-EPA non-scavenged saws as "N-S", air scavenged strato saws as "A-S" and exhaust or delayed scavenged saws here as "E-S." You say that the A-S saws have no more moving parts, but in the carb and linkage assembly they actually do. At least on my 441 and my 211 they do where they have a separate air valve for the air intake below the fuel air intake. They also have more complex porting in the castings. Both drive up costs and make the design more complex. They are also bulkier and heavier, both of which are critical factors in chainsaws. Another drawback of A-S saws is that (at least on A-S that I own and have run) they are cold blooded pigs and require a lot of feathering when they are cold started. The E-S saws remove the added linkage and carb complexity, remove the requirement for fresh air ports in the castings, are lighter, less bulky, and they start and run a hell of a lot better when they are cold. Advantage: E-S saws.

As for the gas savings and lower smog factors on A-S saws, I believe the same applies to the E-S saws, and that the exhaust banding or buffering in E-S saws is larger than you imply. In principal, the effects are the same in either saw; a buffer layer of fresh air or a buffer layer of exhaust between fuel charges keeps raw fuel from being dumped out into the exhaust before the exhaust port closes. The builders all point to port timing, but that is not where the exhaust scavenging comes from. Exhaust scavenging comes from the pressure differential that draws exhaust into the transfers when the transfers first open. That exhaust then leads the fuel charge when the pressure flips on the later downstroke, and is dumped into the muffler instead of raw fuel. That in turn makes the E-S saws more efficient and less polluting than N-S saws. It may not be as significant as A-S saws (I do not have the smog numbers handy), but it is not trivial and it is not all smoke and mirrors as is implied here.

 

[blsnelling]

The builders all point to port timing, but that is not where the exhaust scavenging comes from. Exhaust scavenging comes from the pressure differential that draws exhaust into the transfers when the transfers first open. That then leads the fuel charge and thus exhaust is dumped into the muffler instead of raw fuel.

Please explain how the 461 or 661 can do this if port timing is relatively unchanged from a 460 and 660. If it's happening in the prior, then it's happening on the later. That's all I ask.

 

[bwalker]

Seems like there are folks that want to trick others to take on that role and often it seems they are doing it for amusement.

Or just intellectually lazy.

 

[bwalker]

Please explain how the 461 or 661 can do this if port timing is relatively unchanged from a 460 and 660. If it's happening in the prior, then it's happening on the later. That's all I ask.

Haven't owned the Stihls in question. Do they actually run cleaner than previous versions? Strato saws don't even smell like a two stroke once they are warmed up so it should be apparent.

 

[bwalker]

Well, for one I have tossed Brad into my ignore list, at the request of management. STD is also in my ignore list, as he is reminiscent of the Ape (who's more recent renditions have also been sent to band camp, along with STD it appears). I am used to controversy, as I am constantly challenged on my ideas by marketing, competitive engineering departments, and other engineering 'gurus'. I actually have used this to great benefit in the my career. I invite all my enemies to my design reviews, because they have a keen interest in finding flaws in my designs. Better for me to find flaws early than to have them go into production and fail. My designs and methods have been for the most part highly successful. Here on this debate however these are not my designs, and I have nothing to gain or lose by Stihl having the 461 work one way or the other. I have no horse in this race. However, I believe what I believe, like it or not.

At any rate, for simplicity I will label Stihl Pre-EPA non-scavenged saws as "N-S", air scavenged strato saws as "A-S" and exhaust or delayed scavenged saws here as "E-S." You say that the A-S saws have no more moving parts, but in the carb and linkage assembly they actually do. At least on my 441 and my 211 they do where they have a separate air valve for the air intake below the fuel air intake. They also have more complex porting in the castings. Both drive up costs and make the design more complex. They are also bulkier and heavier, both of which are critical factors in chainsaws. Another drawback of A-S saws is that (at least on A-S that I own and have run) they are cold blooded pigs and require a lot of feathering when they are cold started. The E-S saws remove the added linkage and carb complexity, remove the requirement for fresh air ports in the castings, are lighter, less bulky, and they start and run a hell of a lot better when they are cold. Advantage: E-S saws.

As for the gas savings and lower smog factors on A-S saws, I believe the same applies to the E-S saws, and that the exhaust banding or buffering in E-S saws is larger than you imply. In principal, the effects are the same in either saw; a buffer layer of fresh air or a buffer layer of exhaust between fuel charges keeps raw fuel from being dumped out into the exhaust before the exhaust port closes. The builders all point to port timing, but that is not where the exhaust scavenging comes from. Exhaust scavenging comes from the pressure differential that draws exhaust into the transfers when the transfers first open. That exhaust then leads the fuel charge when the pressure flips on the later downstroke, and is dumped into the muffler instead of raw fuel. That in turn makes the E-S saws more efficient and less polluting than N-S saws. It may not be as significant as A-S saws (I do not have the smog numbers handy), but it is not trivial and it is not all smoke and mirrors as is implied here.

In would be curious if the crankcase volume has changed appreciably from previous models. Lower primary compression might cause the effect you describe. Lower primary compression also lends itself to wider power curves.

 

[Trx250r180]

Haven't owned the Stihls in question. Do they actually run cleaner than previous versions? Strato saws don't even smell like a two stroke once they are warmed up so it should be apparent.

Once modded ,the 461 is a gas hog ,not sure about stock

 

[Chris-PA]

You say that the A-S saws have no more moving parts, but in the carb and linkage assembly they actually do. At least on my 441 and my 211 they do where they have a separate air valve for the air intake below the fuel air intake.

As I said before, the separate air valve is not used on some newer fresh air stratos (like the MS241 and 543XP). Instead the carb has two flow paths, one which picks up fuel and one that does not (which is only a minor mod over a standard carb with choke plate), and a common throttle plate. There are no additional moving parts in this version, although you lose the ability to vary port timing and there is some mixing of fuel into the strato ports for throttle angles less than WOT.

 

[tree monkey]

Please explain how the 461 or 661 can do this if port timing is relatively unchanged from a 460 and 660. If it's happening in the prior, then it's happening on the later. That's all I ask.

long transfer runners hold the exhaust
short transfer runners allows it to mix
if husky would have raised the transfers on the old 372's, they would have achieved the same thing

 

[tree monkey]

The 441 that had been used for milling - did the crankcase and piston seem dryer than normal? Or when you've tried a saw out for several cuts and gone back in for tweaking did you notice anything then? Just wondering.

Thanks,

Waylan

bottom end is oily, piston is dry, from what I have seen
coking of the piston on most of them.

 

[tree monkey]

Once modded ,the 461 is a gas hog ,not sure about stock

depends on the porting

 

[tree monkey]

In would be curious if the crankcase volume has changed appreciably from previous models. Lower primary compression might cause the effect you describe. Lower primary compression also lends itself to wider power curves.

461 has a larger case then a 460

 

[blsnelling]

Thanks Scott.

 

[heyduke]

As I said before, the separate air valve is not used on some newer fresh air stratos (like the MS241 and 543XP). Instead the carb has two flow paths, one which picks up fuel and one that does not (which is only a minor mod over a standard carb with choke plate), and a common throttle plate. There are no additional moving parts in this version, although you lose the ability to vary port timing and there is some mixing of fuel into the strato ports for throttle angles less than WOT.

chris-pa-

this tread got me to looking at the "xtorq" 372. from what i can see in the ipl, it lacks the separate fresh air intakes and has an ordinary looking carb. however the carb is different from the non-strato 372 and its walbro model number has a prefix of "DP" which i assume stands for "dual path." i've never worked on one of these so i'm really just guessing.

also, if the hypothesis, "stratified charge saws don't get enuff oil" was supported by experimental data, the dumpsters would be full of smoked chainsaws. the only data shown here is that davey tree's stihl 362's have a lot of failures and early husky 575 had some crank bearing failures, a problem that was corrected. it's been more than ten years since this technology came to market. you'll have to pry my 575 from my cold, dead hands. and it may kill me because it runs so long on a tank of mix i never get a break.

 

[Stephen C.]

chris-pa-

this tread got me to looking at the "xtorq" 372. from what i can see in the ipl, it lacks the separate fresh air intakes and has an ordinary looking carb. however the carb is different from the non-strato 372 and its walbro model number has a prefix of "DP" which i assume stands for "dual path." i've never worked on one of these so i'm really just guessing.

also, if the hypothesis, "stratified charge saws don't get enuff oil" was supported by experimental data, the dumpsters would be full of smoked chainsaws. the only data shown here is that davey tree's stihl 362's have a lot of failures and early husky 575 had some crank bearing failures, a problem that was corrected. it's been more than ten years since this technology came to market. you'll have to pry my 575 from my cold, dead hands. and it may kill me because it runs so long on a tank of mix i never get a break.

If one is concerned that the strato saw is not getting enough lubrication because of the lower fuel consumption the easy fix is tune it to run on 32:1 if it is a 40:1 saw or 40:1 if it is a 50:1 saw.