smoked my saw (ms460mag)

[oilstinks]

Bucking some locust the other day and saw started to get low on power. About the 4th buck the saw set down like i hit the kill switch. Seems the piston started burning on the right of the exhaust port and scored the piston and cylinder. What the heck happened. I never leaned the saw out its only got 60 to 80 hrs on it. I use name brand oil and use FD grade when avalible. I mix 45:1 to 50:1 usually 2 gal at a time 50:1 and use 1.9something gal of gas instead of the full 2 which would lean it out slightly. thanx guys. got a big bore nwp nikisil cylinder on the way along w/dual port muffler. Guess ill just use this as an excuse to open this saw up.

 

[kenskip1]

Sorry for the premature demise of the saw. It could have been from a number of reasons, like a cracked gas line allowing air to enter and lean out the mix.Does the mix that you use contain methanol? This brew has killed more saws than small pox. A bad clamp on the intake boot could do the same. A cracked impulse line falls into this category. Ken

 

[oilstinks]

have use ethanol gas sometimes more than i like. That was my guess. Saw did seem to load up sometimes at idle. it also has the metering carb i think. A vac leak will require more investigation. it has been known to on occasion get a brew of 112 sunoco and bel ray h1r oil. elaborate more on the impulse line not famliar with that term.

 

[Bigg_Redd]

Bucking some locust the other day and saw started to get low on power. About the 4th buck the saw set down like i hit the kill switch. Seems the piston started burning on the right of the exhaust port and scored the piston and cylinder. What the heck happened. I never leaned the saw out its only got 60 to 80 hrs on it. I use name brand oil and use FD grade when avalible. I mix 45:1 to 50:1 usually 2 gal at a time 50:1 and use 1.9something gal of gas instead of the full 2 which would lean it out slightly. thanx guys. got a big bore nwp nikisil cylinder on the way along w/dual port muffler. Guess ill just use this as an excuse to open this saw up.

You may not have, but somehow a lean condition was created. Pistons don't magically burn themselves out. If I had to guess, based on the fact that you haven't touched the carb, I'd look at your air filter. It's probably defective in some way or another. Either that or you switched gas cans and put straight gas in it.

 

[oilstinks]

no go on the straight gas for sure and the carb compensates for dirty or clean air filters if im not mistaken. Maybe some dust got down and got it started.

 

[smokinj]

Hard telling what cause that. I have well over 100 hrs on mine it seems to keep getting stronger.

 

[Backwoods Savage]

I agree it will be difficult to determine exactly what happened or how it happened.

On the gas. I see absolutely no reason to go with a mixture of anything more or less than what the saw recommends. Filling a gas can part way in order to make the mix richer gains you nothing. Having the right mixture is always the right thing to do. Beware a rich mix the same as you do a lean mix.

 

[Danno77]

... This brew has killed more saws than small pox. ... Ken

Ken, just wondered how many saws died from small pox. lol

Anyway, bummer deal, I'd check everything very carefully to make sure this isn't a symptom of some other failure. Like you said, at least you have an excuse to bore it and make any other mods you want while it's on the workbench.

 

[HittinSteel]

Bummer man. Make sure to check the crank seals or have your dealer do it (intake and exhaust needs blocked off) or else you could install the new big bore and encounter the same problem again. Whatever you do, find out why it happened before installing the new P/C.

 

[Highbeam]

hittin is right. WOuld suck to just immediately burn out the new P&C

 

[oilstinks]

 

[Jags]

EEEKK! :ahhh:

Thats nasty. I'm with everyone else here. Check over the whole system. You don't have enough hours on that beast to be scorching a piston like that.

Edit: thats also a very isolated score. That tells me either a hot/cold spot or air introduction (which will cause the hot/cold). That didn't happen because of hours - that happened because something failed.

 

[HittinSteel]

I'm no expert, but it looks like it ate something........ any pieces missing that could have been ingested?

 

[atvdave]

Have you changed the spark plug? maybe to a hotter one?

 

[Lucky Phil]

That looks like the piston (what I could see of it through the exhaust port) on my 15 year old snow blower last year. The repair shop said that I had water in my gas, but I don't think so. It was time for a new one anyway, in my case.

 

[kevin j]

that looks like mechanical damage more. Lean seize is typically wider and on the exhaust port area, where there is more hot gas blowing over the piston and less contact for heat transfer to the cylinder wall.
Is it over the ring gap, like index ping might have moved out.
Any clues of carbon fouling cuasing sticking rings causing some blowby which heats up and scores?

whatever the root cause, it needs to be cured or the next pc will go also.
Can you clean up the cylinder with acid? often the transfered aluminum can be cleaned up and the nikasil or chrome layer is fine underneath it. Might just be piston replacement.

 

[oilstinks]

may be it ate some saw dust that got by the filter

 

[Singed Eyebrows]

Not the first I've seen this. I put a new piston & cylinder on an MS360 & the saw seized like this. Stihl is using some really junky main bearings on some saws. If they start to go chips will continually get into your saw. The days of German SKF's are over for all but Stihls upper level saws from what I've seen. Take a real good look at the mains, you can see parts of them & see if they are chipping, Randy

 

[taxidermist]

I would say aged gas with meth caused the lean out? How old was the fuel?

 

[oilstinks]

dont remember but think it was new fuel SAW DIDNT SIEZE i thought the 460 magnum was an upper level saw

 

[Singed Eyebrows]

The saws that are made in Germany are the upper level saws in my opinion. Does it say Made in Germany on the recoil cover plate? It is a very simple matter to look at the mains carefully to determine if they are coming apart, use magnifing glass if necessary. As a number of people have mentioned it looks like your saw swalled something, the damage is not typical straight gas seize or lean seize. I can only advise you to look at the mains, if you don't want to, well, it's not my saw. If they are good fine, if not they will probably take out the next P&C you put on, Randy PS, the rings are seized.

 

[smokinj]

dont remember but think it was new fuel SAW DIDNT SIEZE i thought the 460 magnum was an upper level saw

One of the very Best! and you will not find many threads like this on them.

 

[oilstinks]

Fot it put together and took it to local small engine shop since i dont have a tach. It hit almost 15k on the bench wow that dual port mufflar open it up. Gonna have to take off the limit caps so it can get some more fuel to get those rpms down way down

 

[smokinj]

Fot it put together and took it to local small engine shop since i dont have a tach. It hit almost 15k on the bench wow that dual port mufflar open it up. Gonna have to take off the limit caps so it can get some more fuel to get those rpms down way down

mine runs at 14200

 

[oilstinks]

the guy set it to run a little fat at 12000 he said it would lean out when under a load. Im not so sure about that. Dunno never claimed to be an expert though.