So I'm fixing up a chainsaw that's been in and out of the shop and someone gave it to me to fix. It's a Stihl ms311. At first the pull chord would nearly bind to a stop and be really hard to turn once every rotation seeming like on the compression stroke. Acting like it was hydro locked. Couldn't even try to crank it you pull as hard as you can and get one turn before it stops, release and same thing, one turn before a hard stop. Pull the pull chord recoil and it spins freely on its own. Pull the spark plug and there's no fluid in the cylinder and the engine spins free with no resistance. I suspected excessive carbon buildup so I pulled the cylinder to see what was going on and the cylinder was perfectly clean with no ridges, the piston had some carbon but nothing that seems like it would cause such high compression to me. I'm going to include pictures of the cylinder and piston. Any help or advice is appreciated.
Stihl ms311 too much compression.
- Thread starter iago
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Check your flywheel keyway, or it's a malfunctioning coil.
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What about the compression release?
How about the recoil rope binding on the spool. You loose all mechanical leverage when this happens thereby causing the necessary force to pull it over. Also, the rope may have been shortened and again loosing the mechanical leverage. A worn rope will narrow with time and use and the rope will bind against itself. Check the recoil spool for cracks.
Or, coil rubbing flywheel?
Check those crank bearings for cage failure and pitting. Starter recoil has a plastic pulley and a plastic stem the pulley rides on, if either wear they cock and bind
At this point a full tear-down is a no-brainer...bearings/seals are cheap, even oe or quality, non-chinese aftermarket
You haven't used Superslick 985631568732 and version 2.
Loosens up tight bearings in a jiffy. Comes with a can of Aircraft Remover and newer biker fluid
full synthetic 
Seriously though the RTV smeared everywhere begs the question who diagnosed it and did repairs before.
My 084 likes to hydraulic when the carb dumps past the needle. My ported 660 did it last month. Once they clear out they run fine.
Has anyone reported getting it running before it came there?
Checkout that flywheel key.
My 084 likes to hydraulic when the carb dumps past the needle. My ported 660 did it last month. Once they clear out they run fine.
Has anyone reported getting it running before it came there?
Checkout that flywheel key.
The red rtv looks normal for clamshells, imo. I tore down 10 170s recently and they all looked like that.
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Yes, they are generous with the sealant, I actually had a jerk send back a block because of the sealant.
But back to my earlier question, what about the compression release?
But back to my earlier question, what about the compression release?
It does the same thing weather the compression release is pressed down or not, it seems to work as it should but makes no difference. The pull chord recoil assembly spins free and returns on its own as it should when pulled off of the chainsaw. Spinning the fly wheel by hand with the chord assembly off does the exact same thing, hard to turn on compression. With spark plug out and no compression the engine spins freely as it should and piston rises and returns without contacting anything. I will check flywheel key and bearings but like I said with spark plug out everything rotates as it should. I agree it's due for a full teardown and rebuild and that's my plan just want to try and figure out what's going wrong so Im not just just changing parts and it happens again. Can't do a compression test obviously it builds up too much to turn, I can press the air release button on my compression gauge and the air leaks out and the engine spins over.
take the recoil apart, you will not see the plastic wear or smear just pulling the handle. I do not think your issue is engine internal, something is rubbing or binding.
With the recoil off, and the spark plug in. it does the exact same thing
This one is really weird 
Looking forward to the conclusion
Looking forward to the conclusion
with the clutch/drum/worm removed? what plug is in it? try it with piston rings removed and inspect ring lands and pins? clean entire cylinder of carbon?
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So the compression release is somehow not working then?
So problem only exists under compression. All parts seem to work without compression.
I would take another look at the starter. Rope size and length correct? Sparkplug correct?
Any rubbing on flywheel (usually from ignition module)? Bearings and cages OK?
Did it ever run correctly in its existence? Did someone install an aftermarket piston or crank? Or try to make it a 391?
As stated before- flywheel key and ignition module.
You have interference, not just too much compression. Trying things when not under load proves nothing.
Something we techs don't usually do- check squish.
I would take another look at the starter. Rope size and length correct? Sparkplug correct?
Any rubbing on flywheel (usually from ignition module)? Bearings and cages OK?
Did it ever run correctly in its existence? Did someone install an aftermarket piston or crank? Or try to make it a 391?
As stated before- flywheel key and ignition module.
You have interference, not just too much compression. Trying things when not under load proves nothing.
Something we techs don't usually do- check squish.
I never found red on a one. They were always grey on clamshell engines.
It sounds more and more like a bad bearing or excessive starter drag internally. Bad wrist pin bore, pin bearing or lower rod bearing is a great place to look for galling on the shinny spots like the wrist pin and crank journal.
