# Blow up one piston, shame on Stihl. Blow up two pistons, shame on me. Blow up three pistons...?



## pepe_silvia (Apr 9, 2016)

After two it was obvious I was doing something wrong, now I know I am.

I bought the saw second hand to use while my other one is getting repaired. The piston (and some other parts) looked brand spanking new.

It made it through a couple hundred bd. ft. of pecan, and then I set to work on the big log I've had laying around, a 3' x 12' elm.

I was cutting 2.5" slabs, so there were 8 or 9 cuts total. She gave out about halfway through the last cut. I'm attaching a picture, but beware, it's ugly.

New meteor piston and cylinder are already ordered.

My mix is about 30:1. I ran probably 10 tanks of that through it. For the last couple of tanks before it gave out, I used my buddy's mix, which he says was 50:1. Went through about a tank and a half of that before she went.

I run it at WOT and let it idle to cool down for around 30 seconds after I finish cutting before switching it off. 

I run it for probably, on average, 10 minutes in the cut. My money is on this, I'm just running it too wide open for too long of a period of time.

Any thoughts?


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## Quietfly (Apr 9, 2016)

Yikes ,that sucks!
sorry to see that happen.


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## big mog (Apr 9, 2016)

at 30:1 your running far to lean, I'm surprised you got as long as you did........stihl should be run at 50:1 and properly tuned for the usage


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## moondoggie (Apr 9, 2016)

big mog said:


> at 30:1 your running far to lean, I'm surprised you got as long as you did........stihl should be run at 50:1 and properly tuned for the usage


30:1 is rich..... 50:1 is leaner.....


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## big mog (Apr 9, 2016)

someone else who doesnt understand fuel mixes.............30 parts fuel to 1 part oil is leaner than 50 parts fuel to one part oil, the more oil you mix, the leaner the fuel air mixture becomes and the hotter the saw runs, why do backyard "experts" rhink they are cleverer than the people who design the saws and produce the oils to run on specific mixes, if you dont know how to do a basic two stroke mix, perhaps you should take up a new hobby, like crochet or knitting


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## pepe_silvia (Apr 9, 2016)

big mog said:


> someone else who doesnt understand fuel mixes.............30 parts fuel to 1 part oil is leaner than 50 parts fuel to one part oil, the more oil you mix, the leaner the fuel air mixture becomes and the hotter the saw runs, why do backyard "experts" rhink they are cleverer than the people who design the saws and produce the oils to run on specific mixes, if you dont know how to do a basic two stroke mix, perhaps you should take up a new hobby, like crochet or knitting



That seems a little harsh, but point taken.

I've read quite a bit on here about guys running with more oil because it keeps things more lubricated and cooler when running wide open.


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## lone wolf (Apr 9, 2016)

What size saw is it?


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## moondoggie (Apr 9, 2016)

big mog said:


> someone else who doesnt understand fuel mixes.............30 parts fuel to 1 part oil is leaner than 50 parts fuel to one part oil, the more oil you mix, the leaner the fuel air mixture becomes and the hotter the saw runs, why do backyard "experts" rhink they are cleverer than the people who design the saws and produce the oils to run on specific mixes, if you dont know how to do a basic two stroke mix, perhaps you should take up a new hobby, like crochet or knitting


Dont be a ****


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## pepe_silvia (Apr 9, 2016)

lone wolf said:


> What size saw is it?



MS660. Was running a 42" bar on it this time.


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## moondoggie (Apr 9, 2016)

I understand 30 parts fuel to 1 part oil...30:1 would be richer in oil.....


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## big mog (Apr 9, 2016)

chain type and size, and timber type, type of chain oil, and if running auxillary oiler. and on a 660, good quality fuel and two stroke mix at 50:1 will NOT give problems, I have thousands of hours milling with a 660 on an M7 setup


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## crzybowhntr (Apr 9, 2016)

moondoggie said:


> I understand 30 parts fuel to 1 part oil...30:1 would be richer in oil.....


I hope so. Cause if not I'm losing my mind.


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## big mog (Apr 9, 2016)

the oil fuel ratio is missunderstood by almost everybody, optimun fuel air ratio is around 14:1 to 15:1, this is calculated with a 50:1 fuel oil mix, if you run more oil this fuel air ratio changes, and the burn becomes hotter, this caues the clearances on piston barrel to decrease and seizure to take place, screw around with mixtures at your own cost


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## big mog (Apr 9, 2016)

and for those still confused fuel/air ratios are what are called richer or leaner, not fuel oil ratios.......8 parts airparts air 1 part fuel....rich( typical when choke is on full) 20 parts air 1 part fuel lean....typical when mixed at 30:1 fuel oil mixes


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## pepe_silvia (Apr 9, 2016)

big mog said:


> chain type and size, and timber type, type of chain oil, and if running auxillary oiler. and on a 660, good quality fuel and two stroke mix at 50:1 will NOT give problems, I have thousands of hours milling with a 660 on an M7 setup



3/8" pitch, 0.063 gauge, 8 tooth sprocket. Not sure the brand on the chain I was using with the 42" bar. It came in a package deal with the bar. Started with pecan and did some elm as well. No aux oiler, though I had someone pooling some oil on the tip of the bar every couple minutes. Using the generic bar oil from Northern Tool.


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## pepe_silvia (Apr 9, 2016)

big mog said:


> and for those still confused fuel/air ratios are what are called richer or leaner, not fuel oil ratios.......8 parts airparts air 1 part fuel....rich( typical when choke is on full) 20 parts air 1 part fuel lean....typical when mixed at 30:1 fuel oil mixes



I get what you're saying. How would I refer to a mixture of more oil to avoid confusion?


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## Blisters (Apr 9, 2016)

big mog said:


> and for those still confused fuel/air ratios are what are called richer or leaner, not fuel oil ratios.......8 parts airparts air 1 part fuel....rich( typical when choke is on full) 20 parts air 1 part fuel lean....typical when mixed at 30:1 fuel oil mixes


Yeah man I get it. Lean means not enough fuel too much air... Rich means too much fuel not enough air... Don't have much to do with how much oil is in your gas.


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## big mog (Apr 9, 2016)

if your going to be doing a lot of milling on big dia hardwoods, start looking at a move to stihl pmx chain, 3/8picco, a lot smaller kerf, an 050 gauge, and match it to a GB bars milling bar, uses a lot les power for the same cuts, screw your oiler up to maxand run the thinnest best quality chain oil you can afford, your fuel tank should empty just before your oil one, and on a 3' by 12' elm, 1 cut should be about 1 tank on a 660(sharp chain....very important)


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## big mog (Apr 9, 2016)

the more oil question........doesnt happen...DONT do it, set your saw up carefully


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## Blisters (Apr 9, 2016)

Ppl I have talked to call it fuel & oil mixture. 32:1 40:1 50:1 ...


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## pepe_silvia (Apr 9, 2016)

big mog said:


> if your going to be doing a lot of milling on big dia hardwoods, start looking at a move to stihl pmx chain, 3/8picco, a lot smaller kerf, an 050 gauge, and match it to a GB bars milling bar, uses a lot les power for the same cuts, screw your oiler up to maxand run the thinnest best quality chain oil you can afford, your fuel tank should empty just before your oil one, and on a 3' by 12' elm, 1 cut should be about 1 tank on a 660(sharp chain....very important)



Thanks for the advice. I'll try it out. I've had part of it right at least, had the oiler maxed and was filling both oil and fuel after every cut.


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## big mog (Apr 9, 2016)

pepe, the best advice I can give you is get a chain grinder if your serious about milling, even after 40+ years sharpening chains, I still prefer the acuracy the grinder gives me.....every tooth is identical, every raker the same, it shows in the surface finish of the boards, I work with a 4 chain rotation, and run them equally, every time I buy a new set, I replace the sprocket, every 2nd to 3rd set, replace the bar, price your jobs appropriatly, and remember to cost in plenty of fuel and oil on the big timber jobs.....time?.....when someone gets a formula for working that out chainsaw milling, let me know...lol


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## Blisters (Apr 9, 2016)

I


big mog said:


> the more oil question........doesnt happen...DONT do it, set your saw up carefully


I've had some problems with tuneing a carb on a saw I built out of scraps leftover from 5 saws I got. its a 42cc poulan. I know a lot of ppl don't like em. I can tune nearly anything but this thing is a trip. I think I need to make smaller adjustments.


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## BobL (Apr 9, 2016)

It's pretty common to hear folks referring to using lower gas/oil ratios as "running rich" - it's a wave that sort of comes and goes but never seems to die out.

Most saws will actually run safely on any gas/oil ratios between ~ 8:1 and 100:1. 
Even the Stihl manual says if you don't use their Stihl 2 stroke lube you should run 25:1 (I won't go into why they do this here)
BUT
Whatever is used the saw MUST be re-tuned for that ratio.

Yes a saw will run and even mill quite safely on 100:1 (using a fully synthehic lube) which demonstrates how little oil is need for a modern saw.
However,r the reason the manufacturers recommend 50:1 is because it is very easy to stuff up making a 100:1 mix in small quantities - you only have to be a teeny weeny bit out and you end up mixing 150 or 200:1 and then the saw will be in trouble.

At less than 50:1 increasingly amounts of the lube just add more unburnt gunk like smoke suppressants into the air around the operator. This stuff is not good for you so will make more of it than necessary?


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## KiwiBro (Apr 9, 2016)

pepe_silvia said:


> Thanks for the advice. I'll try it out. I've had part of it right at least, had the oiler maxed and was filling both oil and fuel after every cut.


Good on you for rolling with the sanctimonious and uncalled for flaming from big mog long enough without objecting to reach a worthwhile point.


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## lone wolf (Apr 9, 2016)

pepe_silvia said:


> MS660. Was running a 42" bar on it this time.


Too lean of an air mixture or a vac leak maybe.


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## pepe_silvia (Apr 9, 2016)

big mog said:


> pepe, the best advice I can give you is get a chain grinder if your serious about milling, even after 40+ years sharpening chains, I still prefer the acuracy the grinder gives me.....every tooth is identical, every raker the same, it shows in the surface finish of the boards, I work with a 4 chain rotation, and run them equally, every time I buy a new set, I replace the sprocket, every 2nd to 3rd set, replace the bar, price your jobs appropriatly, and remember to cost in plenty of fuel and oil on the big timber jobs.....time?.....when someone gets a formula for working that out chainsaw milling, let me know...lol



I actually just picked up a grinder. It's the one here: http://www.northerntool.com/images/downloads/manuals/42595.pdf

More great advice, duly noted. Already figured out to price out my time: it's completely worthless.


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## pepe_silvia (Apr 9, 2016)

big mog said:


> if your going to be doing a lot of milling on big dia hardwoods, start looking at a move to stihl pmx chain, 3/8picco, a lot smaller kerf, an 050 gauge, and match it to a GB bars milling bar, uses a lot les power for the same cuts, screw your oiler up to maxand run the thinnest best quality chain oil you can afford, your fuel tank should empty just before your oil one, and on a 3' by 12' elm, 1 cut should be about 1 tank on a 660(sharp chain....very important)



Suggestion on where to pick up the GB milling bar?


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## pepe_silvia (Apr 9, 2016)

lone wolf said:


> Too lean of an air mixture or a vac leak maybe.


Sounds like I was running too lean. Hypothetically though, if it were a vacuum/air leak, how do I know that's happening before it's too late? What would make me say "I have a vacuum leak right now, I better stop cutting before I turn my piston into a molten blob"?


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## DTrap (Apr 9, 2016)

You can tune a saw to run properly with whatever mixture you prefer. The problem is most people don't properly tune their saw when adding the extra oil causing a lean running saw. Which leads to the saw running hot and causing excessive wear on it. Todays saws will hold up well with a 40:1-50:1 mixture. Anything more and you are really just wasting oil and breathing in more of it as well. At least in the case of a milling application.


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## pepe_silvia (Apr 9, 2016)

DTrap said:


> You can tune a saw to run properly with whatever mixture you prefer. The problem is most people don't properly tune their saw when adding the extra oil causing a lean running saw. Which leads to the saw running hot and causing excessive wear on it. Todays saws will hold up well with a 40:1-50:1 mixture. Anything more and you are really just wasting oil and breathing in more of it as well. At least in the case of a milling application.



By tuning the saw properly, you basically mean richen it until it 4-strokes, then lean it up a tad? Is there something else I should be doing to make sure I'm not too lean?

This saw had the limiters in it and I couldn't get them to turn far enough to start four stroking, so I just richened it up as much as a could. I'll know better next time.


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## big mog (Apr 9, 2016)

i get mine from a guy here in the uk, chainsawbars.com, they are really good quality, he also does sugahara, but as of yet, I havent tried them, hes a first class guy to deal with


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## pepe_silvia (Apr 9, 2016)

Since I'm here, any thoughts on 7 vs 8 tooth sprocket?


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## DTrap (Apr 9, 2016)

I would stick with a 7. The 8 will give you more chain speed but less torque. It wouldnt really matter to much in small wood but on anything big it will bogg the saw down easier.


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## Blisters (Apr 9, 2016)

pepe_silvia said:


> Since I'm here, any thoughts on 7 vs 8 tooth sprocket?


Has anyone seen a lawn mower engine on a csm? Thought it was a lil slow, but it was a 4 stroke engine. My thoughts are like a 2stroke lawnboy would make a good one. What are your thoughts guys?


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## ChoppyChoppy (Apr 9, 2016)

moondoggie said:


> 30:1 is rich..... 50:1 is leaner.....



No, more oil means less fuel which is lean.


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## Mad Professor (Apr 9, 2016)

I always run my own mix. To the few I will lend a saw to, I give them my mix to use.

Going from 30:1 to 50:1 you will need to retune.

I retune if I change from 100LL to non-corn pump gas with the _same_ oil ratio.

I've ran nothing but golden spectro in all my two strokes 45-50:1 since the 1970s and no oil/mix failures. Dirt bikes, saws, weed wackers........


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## DTrap (Apr 9, 2016)

Well that's part of it. I'm by no means an expert but You should try to tune it in the cut. It should still 4stroke when not under load and then stop in the cut. Did you retune the saw when you switched to your buddy's 50:1 mix since you had tuned it for the 30:1 you were normally running.


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## DTrap (Apr 9, 2016)

Well I guess Mad Professor beat me to it. I also will not use someone else's mix. I just don't trust people to properly mix it. If I didn't make it I don't use it. I also send my mix if someone is using my equipment.


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## lone wolf (Apr 9, 2016)

pepe_silvia said:


> Sounds like I was running too lean. Hypothetically though, if it were a vacuum/air leak, how do I know that's happening before it's too late? What would make me say "I have a vacuum leak right now, I better stop cutting before I turn my piston into a molten blob"?


It would not idle right for one thing. You my not notice a leak at full speed. A vac test should be done on this saw before you have another meltdown. Check the spark plug it should be tan not white after a hard run. Make sure the plug is the correct one for that saw. Are you using regular grade gas or super? Is your gas fresh from a high volume station or could it be old?


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## pepe_silvia (Apr 9, 2016)

lone wolf said:


> It would not idle right for one thing. You my not notice a leak at full speed. A vac test should be done on this saw before you have another meltdown. Check the spark plug it should be tan not white after a hard run. Make sure the plug is the correct one for that saw. Are you using regular grade gas or super?


92 octane.


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## lone wolf (Apr 9, 2016)

Pictures of the damaged piston, a shot of each side may help diagnose the problem.


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## pepe_silvia (Apr 9, 2016)

This is all I've got at the moment.


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## BobL (Apr 10, 2016)

big mog said:


> .....every tooth is identical, every raker the same, it shows in the surface finish of the boards,



I disagree that a grinder gives a better finish and that every tooth has to be identical. All that has to be approximately the same is the raker angle. That's the angle between the raker - the cutter edge and the wood. If that is the same then every cutter will take the same amount of bite and that's what keeps the chain square on the rails. I stopped worrying about cutters being the same length back in 2008.

This is my standard finish, full comp, hand filed.


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## KiwiBro (Apr 10, 2016)

Yeah, but you're milling granite. But seriously, some time ago I changed my sharpening around to the raker angle notion you have mentioned before. I went so far in testing to grind cutters different lengths and rakers different heights, as long as the angle stayed the same. As long as I didn't get too crazy with it, the chain still cross cut OK. The trick now is working out how far i can push it in different woods and uses (steeper raker angles for bucking for firewood compared to felling in the same woods, for example). Thanks for the raker info. That original thread was one of AS' gems.


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## BobL (Apr 10, 2016)

KiwiBro said:


> Yeah, but you're milling granite.


Not all the time 
I can make the finish as crappy as anyone else.
Note zig-zagging.
This is also a full chisel skip chain which is one of the hardest to get a good finish 



I can't deliberately generate a good washboard but I do come across it occasionally.


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## lone wolf (Apr 10, 2016)

pepe_silvia said:


> This is all I've got at the moment.


That could be from gas with no mix or a lean seize. Got any one there that could have screwed it up? If I could see the other side of the piston I could tell more. Straight gas will do that but it could be an air leak. How is the air filter? That saw needs a rebuild and a vac test. Dont run it with out the vac test. Ship it to me and I will fix it for you if you need help.


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## lone wolf (Apr 10, 2016)

pepe_silvia said:


> This is all I've got at the moment.


http://www.madsens1.com/saw_piston_fail.htm


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## Mad Professor (Apr 10, 2016)

I posted a pdf quite a while ago from husky that had pics of piston failure and causes. Lost it on my old HD when it crashed. Might be worth a search?

It does look like a lean sieze or straight gas. have also seen the same when someone saw some water in the tank and they dumped in a good portion of dry gas


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## Timberframed (Apr 10, 2016)

One more thing on the oil/gas mix. The saws I use for milling are concrete demolition saws designed to run wot 24/7 25:1 manufacturer mandated. Even the tech guy over the phone said don't deviate from that. There are two labels printed on the saws 25:1. Anyway after milling Lord knows how many linear feet, inch feet, both saws still run crazy strong and periodic inspections show unscathed interiors. Just something to consider when taking a saw designed to fell/buck buck idle buck idle and make it run wot for hours.


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## marshall (Apr 10, 2016)

Timberframed said:


> One more thing on the oil/gas mix. The saws I use for milling are concrete demolition saws designed to run wot 24/7 25:1 manufacturer mandated. Even the tech guy over the phone said don't deviate from that. There are two labels printed on the saws 25:1. Anyway after milling Lord knows how many linear feet, inch feet, both saws still run crazy strong and periodic inspections show unscathed interiors. Just something to consider when taking a saw designed to fell/buck buck idle buck idle and make it run wot for hours. View attachment 497398


Timberframed - what manufacturer and model saw are you using? I am definately interested in any saw designed for WOT on a 24/7 basis. Thanks in advance.


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## Timberframed (Apr 11, 2016)

The concrete/stone saw (ICS 633gc) is actually an Oleo Mac 999F modified however to run like a raped ape. Reggio Emilia, Italy. I know nothing of the newer versions other than they sized down the cc's on 695, 685 and others. Alpina is also made in Italy.


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## pepe_silvia (Apr 11, 2016)

Timberframed said:


> The concrete/stone saw (ICS 633gc) is actually an Oleo Mac 999F modified however to run like a raped ape. Reggio Emilia, Italy. I know nothing of the newer versions other than they sized down the cc's on 695, 685 and others. Alpina is also made in Italy.



I've seen the Stihl Rock Boss's floating around, just assumed they were MS461s at the core, with a some external features (better air filter, something to spray water on the chain, etc).


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## marshall (Apr 11, 2016)

Great info - thank you. Sounds like a good enough execuse to expand the saw collection.


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## Blisters (Apr 11, 2016)

Hello my name is Nate, and I'm addicted to chainsaws.


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## BobL (Apr 11, 2016)

pepe_silvia said:


> I've seen the Stihl Rock Boss's floating around, just assumed they were MS461s at the core, with a some external features (better air filter, something to spray water on the chain, etc).



They are - there's nothing special about rock cutting saws. 
According to the RB manual
- same basic specs except it's 5.8 HP versus 6 HP for the straight 461. Maybe the filter has something to do with this.
- it also uses 50:1 gas/oil ratio.
- Don't forget these have no oiler. Oil is superior to water in cutting wood as it reduces resin build up and I found it also reduces B&C wear and tear.
- The other right PITA is the upright fuel cap. This means the cap is sideways when milling and if you run out of fuel while milling it is much harder to add more fuel.

Even in the Stihl manual they referred to "oil rich mix"!


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## Grande Dog (Apr 12, 2016)

Howdy,
Single ended: http://leftcoastsupplies.com/?s=long+titanium&post_type=product
Double ended: http://leftcoastsupplies.com/?s=gb+double+ended&post_type=product
Regards
Gregg


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## Streblerm (Apr 13, 2016)

I suspect your saw has a vacuum leak. I doubt it has anything to do with mix. It is probably a fairly small one, but under severe duty it is enough to cause your problem. I bet the leak was what caused the first meltdown. The usual suspects would be intake or crank seals. The symptom was addressed with a new P&C but not the underlying cause. 

There is a ton of reading in the chainsaw forum on performing pressure/vacuum tests. The basics are seal the intake and exhaust and apply pressure/vacuum. There are all kinds of ways to do this. I usually just make block off gaskets out of inner tube for the carb and muffler and then I pump a few pounds of air through the plug hole. Then a spray of soapy water or a quick dunk in a bucket should reveal any leaks. It is a good idea to turn the crank while testing.


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## Paragon Builder (Apr 13, 2016)

A saw should be tuned every time it is used and for the type of use. I keep a little orange screwdriver on me when I cut. When you learn to listen to the saw when cutting you will know when something isn't right. When milling it is more important to tune properly, but needs to be done in the cut. And a dull chain will kill your saw in heavy use as easily as a a bad tune or air leak. 
If you can't wrap your head around constant tuning, buy mtronic or auto tune, then it's done for you.


Sent from my iPhone using Tapatalk


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## lone wolf (Apr 13, 2016)

Paragon Builder said:


> A saw should be tuned every time it is used and for the type of use. I keep a little orange screwdriver on me when I cut. When you learn to listen to the saw when cutting you will know when something isn't right. When milling it is more important to tune properly, but needs to be done in the cut. And a dull chain will kill your saw in heavy use as easily as a a bad tune or air leak.
> If you can't wrap your head around constant tuning, buy mtronic or auto tune, then it's done for you.
> 
> 
> Sent from my iPhone using Tapatalk


The dull chain is very overlooked as a cause.


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## Paragon Builder (Apr 13, 2016)

lone wolf said:


> The dull chain is very overlooked as a cause.


Agreed. I see a lot of it. Guys seem to think it's easier to just yank on the saw instead of sharpening or switching chains. A lot of heat is generated and you see scoring on the clutch side of the exhaust if you catch it before the whole piston goes. A sharp chain let's the saw work instead of you. And your AV will last a lot longer as well.


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