Compression on newish Stihl MS 362 C-M

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Travis-Mc

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Hey guys! I'm new here, but have done a lot of reading over the last couple of years. I have some questions I couldn't quite find consistent answers for.

I bought a Stihl MS 362 C-M about a year and a half ago used (it was made Oct 14th of 2015). They said they cut down one tree with it and then it sat, and I believe it. The chain was a slightly dull, but the bar was almost perfect and everything else looked perfect as far as scratches etc. It started right up when I bought it. I checked the compression and only got about 125psi. I took the muffler off and the piston and cylinder looked like new. I figured it might still need to be broke in. Or maybe they didn't something while cutting that one tree that made the rings not seat well? A bad break in? I asked what mix the previous owner used and he said 50:1.

So now that I've run a few gallons of gas through it (only premium non-ethanol gas with Stihl HP Ultra oil at 50:1), what compression numbers should I be seeing on this saw? Everything I try, I can't get a reading over 140psi cold. That's with 10 hard and fast pulls. I checked multiple times and it's always between 135 and 140psi. I've tried taping the throttle open and it didn't change. I also tried pulling the decomp and cleaning it. I checked my compression tester with my air compressor and the gauge is accurate. Other saws I've owned are 150 or 160psi. The gauge is the type with the schrader valve at the bottom of the hose.

Everything I've read people say compression on a new Stihl should be over 150psi. When I called Stihl they said anything over 110 is fine, and they don't have specs other that that. That's where the confusion is. Is my saw fine?

I guess reason I even bother is I feel the saw should have more power. I don't have a ton of experience with chainsaws, and none with anything over 50cc until this saw, but have owned two Stihl 031 AVs, a Husqvarna 345, and a craftsman something.

Am I just expecting too much? I can press quite hard on the saw when cutting oak before it'll slow the chain down too much, but when I lever off the dogs it doesn't take much to bog it down. I have 3 different chains and it doesn't change whether one is sharp or dull or the rakers are cut more or less, etc.

Thanks in advance!
 
More information.. I've reset the mtronic a few times over the time I've had the saw. A few months ago I opened up the exhaust by drilling another hole. And today when I reset the mtronic, after about 95 seconds I shut off the saw and it wouldn't restart. It was flooded. I finally got it started and it cut the same as it always does for about an hour. Not sure what that was all about or if it related. I've attached some pictures trying the show the cylinder, two of the piston, and one of muffler mod.

20181029_105644.jpg 20181029_105722.jpg 20181029_105826.jpg 20181029_110314.jpg
 
Compression numbers mean nothing to me. I NEVER check compression on a saw. A quick look at the intake and exhaust sides of the piston will tell you almost everything you need to know about the cylinder.
Check the fuel solenoid on the throttle body. One that is leaking will cause low power and/or poor idle. Search the site for the procedure. It is easy to do. The solenoid often leaks- its a common problem. The solenoids have a 2 year Federal emissions warranty.
 
Thank you very much guys.

The instructions I found for performing a leak test on the solenoid requires MDG 1 for steps 3 - 6. I followed steps 1 and 2 and the pressure didn't drop at all. I'm not sure if that tells me anything since I can't complete the rest of the steps.

I think I may have been just expecting too much out of the saw. I've watched too many youtube video of big ported saws. :D I don't really need the saw to be any stronger/faster because it does what I need it to do. I keep thinking this saw has twice the power as my Husqvara 345, but I looked that up and it's rated at 2.2kW vs the 362's 3.5 kW. So that's 60% more power, but with a bigger bar and bigger chain with bigger teeth to pull. I guess I should have bought a 461!

Just for fun I measured the squish and it came out at .031". Maybe I should try my hand at porting the cylinder and reducing the squish a little. I have a lot of reading to do before I tackle something like that though.
 
Damn! 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. 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 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 and the husqvarna is still at 165psi. I've attached pictures of the 362 piston. Think I should keep running it since the compression hasn't changed?

Top
top.jpg
Middle
middle.jpg
Bottom
bottom.jpg

That deeper scratch on the left side in the middle has me a little worried.
 
Wow, that really sucks.

I wouldn’t keep running that. You may be able to salvage the cylinder still.

Part of my hatred of autotunes, you can’t fully tell what’s going on.

FWIW, 50:1 is EPA stuff. Saws lubricate and run just as well at 32 or 40:1, even autotunes.

That looks like carbon scoring to me. Stihl oil is known to build up a lot.
 
I've never seen a stock Stihl make over 150psi, albeit 140-145 seems to be the norm.
That's just the way they are.

I'll put up pictures of my MS362 piston later on as a meter of comparison, but DRF is right. Stihl oil is junk and there's a reason they don't bother with JASO rating. The carbon buildup it causes, even at 50:1, simply defies belief, especially on their 4Mix engines.
 
Dang. I guess It's time to take it apart and really check it out. I'm thinking I should leave the base gasket out, or make a thinner one to reduce the squish just a little. Right now it's at .031". Maybe now is the time to try doing a mild port job. I'm pretty handy with tools and fabricating and research the hell out of everything, so I might be able to pull it off.

Without starting a 'what oil is best' thread, what oil do you guys use? I have a friend who has been telling me to switch to Amsoil Sabre.
 
I took a couple of pictures of my MS362C-M for comparison:

i-v6XfdjX-XL.jpg


i-qjmzHVF-XL.jpg


There's definitely some scoring on your piston.
Also notice the difference in carbon buildup on the exhaust port between my saw and yours. My saw is almost two years old but I think I have about the same hours as yours: that's a big part of the reason about a decade ago I switched from using engine oil to JASO rated lubricants for premix. I've also run 50:1 premix over the same decade without a single seizure so far.
However... I don't believe that carbon buildup caused the scoring. I've seen saws in far worse shape than yours (including my old ones) as far as buildup goes and the piston was just fine.
Your scoring looks like it was caused by the saw running way too hot... a lean condition? Perhaps brought about by an M-Tronic reset gone awry? I honestly don't think your saw is old enough to have a leaky crankshaft seal or even a bad gasket but sadly **** happens. A leakdown test would be advisable, as would having M-Tronic checked by a Stihl technician trained to look into it.
 
I've never seen a stock Stihl make over 150psi, albeit 140-145 seems to be the norm.
That's just the way they are.

I'll put up pictures of my MS362 piston later on as a meter of comparison, but DRF is right. Stihl oil is junk and there's a reason they don't bother with JASO rating. The carbon buildup it causes, even at 50:1, simply defies belief, especially on their 4Mix engines.
I use a 4mix and the carbon is unbelievable, always run aspen fuel 50/1 so maybe it's not down to the oil. I'm not a fan of 4mix and it seems stihl have not developed it any more, maybe it's all a scam to do with emissions
 
I've never seen a stock Stihl make over 150psi, albeit 140-145 seems to be the norm.
That's just the way they are.

I'll put up pictures of my MS362 piston later on as a meter of comparison, but DRF is right. Stihl oil is junk and there's a reason they don't bother with JASO rating. The carbon buildup it causes, even at 50:1, simply defies belief, especially on their 4Mix engines.
Do you use a small engine compression tester or an automotive tester? On my automotive testers a lot of my saws are 140ish or less. With a small engine tester I'm at 160 to 170 psi on my 261 and 026..
 

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