Stihl 362 C-M scored piston

[Travis-Mc]

Hey guys I'm new here... I posted on another site about this same issue, but thought I post here too.

The piston in my Stihl 362 C-M looked great last week. I know this because I took pictures when I was asking about if the compression of 135-140psi is okay for this saw with about 3 gallons of gas through it.

Well now I have a real problem. I was out cutting on Saturday and after maybe 10 minutes the saw starting having problems idling, and then wouldn't start. I figured the solenoid crapped out since I've been told they can be a problem. I grabbed my little husvarna 345 and after several minutes it started having problems running too. I dumped all the gas in both saws, mixed up some fresh stuff and both saws worked fine after that.

So today I pull the muffler cover off the 362 and the piston is scored. Ugh! I know the gas has oil in it as I've been using it for a while (weeks) without any problems. Premium 91 octane gas with no ethanol, and Stihl Ultra oil mixed at 50:1. It was probably 2 months old.

What the heck! Both saws have the same compression as before. The 362 is at about 135-140psi. I've attached pictures of the 362 piston. Think I should keep running it since the compression hasn't changed?

Top


Middle


Bottom


That deeper scratch on the left side in the middle has me a little worried.

 

[Armbru84]

Definitely don’t keep running it...it’s gotta get pulled down and it’s going to need some top end work.

 

[CR888]

I'd wanna pull the jug to inspect it for piston transfer and clean it up. Buy a new piston/rings and install it. Many consider 2 month old gas fresh......I don't.

 

[Travis-Mc]

Thanks for the replies!

Alright, time to take it apart then. Hopefully the cylinder is okay. I have always tried to keep my mix 2 months or less, and usually dump it when one machine or anther isn't acting quite right. The only thing I can think of that is different this time is the gas station I went to doesn't get a lot of traffic, so maybe the premium gas in their storage tank was already old.

I was already considering porting the saw. Maybe now is the time to remove the base gasket or use a thinner one (my squish is at .031") and do a mild port job on it. I have a lot more reading to do before tackling that though.

 

[andyshine77]

Fuel can go south quick, especially in the heat. I have to also say, from the pics you provided, things look quite dry, like no oil dry. It is entirely possible to run a saw quite awhile with no oil in the fuel, not saying that's definitely what happened, but everything sure looks like it lacked oil. Now because you ran the saw on fresh mix it will be hard to tell if you made that mistake or not, brain farts do happen all the time lol.[emoji111]

 

[Travis-Mc]

If I straight gassed them, that would mean I've been straight gassing 3 saws and my brush cutter for the last several weeks. Both saws started acting up within 10 minutes of each other, so I have to blame the gas, and not the saw. But the gas seemed fine a week before when I bucked up some oak for about 25 minutes.

If the mix sits for a while and you don't shake it before pouring it, will the oil settle? I usually swirl the gas a bit before adding it to the saw, but maybe I didn't last time. Plus when I gassed them up the day everything went to hell, both saws were already half full from the last time I used them.

 

[Chainsaw Jim]

It sounds like it's time for a complete servicing with new fuel line/filter, tank filter, crank seals, carb kit/boot.
The piston doesn't quite appear out of spec yet and can be cleaned up for reuse, but the rings may need replaced.

 

[Travis-Mc]

Finally got around to tearing the saw down. Pressure and Vacuum tested good. I wiped the cylinder out with a rag and wiped the piston off. No further clean up yet. Think this cylinder is okay? I can post more after I try to remove the little bit of aluminum from the walls.

 

[Travis-Mc]

A couple more pictures since I'm limited to 5 per post

 

[Redbull661]

50 to 1 strikes again. No fudge factor. no room for error.

and it only costs a measly 20 to 25 cents more per gallon mixed up to run 40:1.

ps. stihl ultra sucks!

 

[Dustin4185]

I’ve heard a few people mention this issue with this particular saw on the old YouTube. I think Human had an issue with one of the first ones he got made in USA. I think HotShot101 or whatever his name is mentioned it also. Something to do with the strato.

I would agree with @Redbull661 on this one. I run my mtronic saws on 40:1 and they run fine, and have a little extra coming out the exhaust ports.

I am no expert saw mechanic, but that muffler looks DRY! I would switch to a different oil at 40:1. For recommendations, feel free to read the 10,000,000 posts in the oil thread. I have been running Red Armor, and just switched to Yamalube 2R. I’ve had zero issues with either. I don’t check my piston that often, but I pulled the can on my 362 to see what it looked like. Still has machine marks and I am on tank 25.

 

[andyshine77]

Strato saws have stright air entering the engine, air that has no fuel oil mixture in it. Strato engines get less lubrication, run hotter and have heavier pistons.

 

[Pincher]

Could you post the pictures of when you checked the piston last week?

 

[Travis-Mc]

I have since switched to Amsoil saber in my other saw, and plan to run it in this saw too once I get it back together. I'm running a little richer than 50 to 1 rather than 80 to 1 they recommend.

I'm planning to clean up and reuse this cylinder and get a new piston.

@Pincher This thread is a few months old, but here are the before pictures:

 

[Wood Doctor]

I rebuilt a 362 C with a similar "straight-gas" score that eventually led to no compression. The new top end got her running again. I also have to go along with 40:1 mix for this engine. That's also what I use on my 361 and its got about 500 hours on the original top end.

 

[MustangMike]

I run Saber at 40:1 in my 362 C, no problems. I would get a new piston (OEM or Meteor) and clean the transfer from the cylinder (there are videos).

Also, open up the muffler a bit, 2 - 1/4" holes in the muff cover on the right side (above where fumes will hit the saw) S/B just fine, like I did on this 462:

(The saw will run cooler and last longer) No screens or deflectors needed.

 

[Travis-Mc]

40:1 it is from here on out. That seems to be the consensus!

I ordered an OEM piston this morning from my dealer (it's on backorder), and will clean up the cylinder and give it a go. I've already watched a few videos about it.

I have a stainless deflector from Red97 to put on the muffler cover, so I'll try it. I also plan to use a screen since I've actually started a fire once without one.

Thanks for the help guys.

 

[MustangMike]

2 Cycle oil has stabilizer in it, so it is important to mix the gas and oil ASAP. I have never had problems using my mix over a 3 month period.

I leave my saws fueled, but I make sure that all get started at least once every 3 months (they are all dormant during my 2.5 month tax season).

I also keep them in the garage so they don't freeze + thaw repeatedly, that can't be good for gaskets long term.

 

[Slacker]

I bought my first "pro" saw a few months ago, a used MS362 carb version.
I buck with it, leaving it at 3/4 throttle or more for 5 mins or so, just moving down the hardwood logs and letting it self feed.
I may spend an hour like this.

I mix stihl orange bottle at 40:1 with non ethanol fuel.

This thread has me all worried.
I'm going to inspect the piston tonight.
I bought it to treat as a professional grade tool that would save me time.

This would really sour me on Stihl if I cant use it without worry of it getting damaged by normal use.

 

[Cobby08]

I bought my first "pro" saw a few months ago, a used MS362 carb version.
I buck with it, leaving it at 3/4 throttle or more for 5 mins or so, just moving down the hardwood logs and letting it self feed.
I may spend an hour like this.

I mix stihl orange bottle at 40:1 with non ethanol fuel.

This thread has me all worried.
I'm going to inspect the piston tonight.
I bought it to treat as a professional grade tool that would save me time.

This would really sour me on Stihl if I cant use it without worry of it getting damaged by normal use.

For what it's worth, 90% of all small engine 2 stroke should be run at idle or wide open. These newer saws are a little more protective circuit wise but a good general rule to follow is wide open or nothing.