Oops, broke through top of piston on Stihl MS 180 CB-E

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phred45

phred45

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This actually started out in the Milling Forum and then I took the saw apart :cry:
Previous post:
Log wizard on Stihl MS180
Can the log wizard be used on the Stihl MS 180? What can I do to keep the saw from burning out? My wife is cleaning some cedar logs and the saw gets hot and quits running. We usually run 40:1 (Stihl requirement is 50:1) with premium gas but switched to 25:1 will that help or hurt the motor?

Unfortunately that is the only saw my wife can start. We are using the logs whole for a pole barn and don't have the option to wait until Spring when freshly cut life cedar is easy to peel. We are using dead standing and fallen trees.
It is a MS 180 CB, not electric, runs on gas. Displacement 31.8cc,
it is an occasional use saw. The wife has been cutting smaller cedars and oaks and debranching etc. for 2 years without problems.

It runs the wizard but suddenly has a really hard time starting. Once it runs on full throttle it does fine but when you let it go down to idle it dies and then doesn't want to start again. Acts as if it is flooded.
I'll go out later and clean her up put fresh gas in with less oil etc. and see what happens.
Well, Ive cleaned everything up and didn't see anything suspicious. However, I heard a hissing sound where the fuel hose goes into the tank. I turned the saw upside down and it seems to leak gas somewhere in that area. So I guess I will be taking everything apart to see what's going on and also check the crank seal.


The hissing sound comes from the little valve on top of the gas tank and when the saw is sideways it leaks.
Now I still haven't figured out why the saw doesn't want to start or run in idle :confused:
I'll have to order a new piston. Is there anything else I need to replace?

In the meantime is there another easy to start saw that I could get for my wife?
 
Last edited:
OH NO!!!!! This does not end well, I fear. There was a very frequent member here who had poked a hole in a 180 piston a while back, and bent the rod on one as well. Regular piston stops do not work well in those!
 
Saw Dr. said:
OH NO!!!!! This does not end well, I fear. There was a very frequent member here who had poked a hole in a 180 piston a while back, and bent the rod on one as well. Regular piston stops do not work well in those!
Click to expand...

Thanks Saw Dr.,
Do you remember who that was? Maybe he has some idea what tto do next.
 
Saw Dr. said:
OH NO!!!!! This does not end well, I fear. There was a very frequent member here who had poked a hole in a 180 piston a while back, and bent the rod on one as well. Regular piston stops do not work well in those!
Click to expand...

And sheared the flywheel key, and broke a clutch. If procedure is followed carefully, they can be worked on successfully, but they are built VERY lightly, and will break easily.
 
It was blsnelling. Tread lightly. This event caused a months-long debacle about the strengths of the Stihl rods and pistons...

You're going to need a new piston. Use the original piston stop or rope and lots of it. For the cost of those saws, if you need it now you'll probably be better off just going to get another one.
 
Saw Dr. said:
It was blsnelling. Tread lightly. This event caused a months-long debacle about the strengths of the Stihl rods and pistons...

You're going to need a new piston. Use the original piston stop or rope and lots of it. For the cost of those saws, if you need it now you'll probably be better off just going to get another one.
Click to expand...

Do not use rope. That's what caused my bent rod. The piston needs to be close to TDC with the least rod angle possible.
 
Brad, I have been trying to resist responding for the last 20 minutes or so. The rod sees the least load when the piston is slighty past halfway up the bore. (I.E. the centerline of the crankpin and crank axis is 90 degrees to the centerline of the rod holes) If it is only a few degrees from TDC, the compression force on the rod goes up exponentially for the same applied torque on the crank. This is the same principle (any physics) as a felling wedge applying a force to fell a tree rather than just hitting the tree with a hammer. If I were better at paintbrush, I'd draw a picture to illustrate.

Sorry to dig this back out, but rope can be used just fine in 170's and 180's if the piston is in the proper place when you do it. I did learn alot from your thread before, and I am much more careful when I remove a 180 clutch or flywheel now. I do however still use rope. I have never used nor will ever use a universal hard piston stop. I am always afraid of damaging the piston.
 
Last edited:
Saw Dr. said:
Brad, I have been trying to resist responding for the last 20 minutes or so. The rod sees the least load when the piston is slighty past halfway up the bore. (I.E. the centerline of the crankpin and crank axis is 90 degrees to the centerline of the rod holes) If it is only a few degrees from TDC, the compression force on the rod goes up exponentially for the same applied torque on the crank. This is the same principle (any physics) as a felling wedge applying a force to fell a tree rather than just hitting the tree with a hammer. If I were better at paintbrush, I'd draw a picture to illustrate.

Sorry to dig this back out, but rope can be used just fine in 170's and 180's if the piston is in the proper place when you do it. I did learn alot from your thread before, and I am much more careful when I remove a 180 clutch or flywheel now. I do however still use rope. I have never used nor will ever use a universal hard piston stop. I am always afraid of damaging the piston.
Click to expand...

I used rope, and plenty of it, and that's what caused the bent rod. Thall proved that you can't bend the rod if using the proper stop, which leaves the piston much closer to TDC. Remember the video he did? He even replicated bending the rod when not using the proper stop, IIRC. In the case of a 170-180-210-230, I will never use rope again.
 
The same principle applies if you go to BDC (as in ALOT of rope). I do remember the thread, and I have learned alot from it. I just don't want this guy to go get a piece of 5mm starter cord and put one wrap of it in there and bend his rod. If rope is used, the piston needs to be approx halfway between TDC and BDC in order to safely remove the flywheel or clutch. Too close to top or bottom, and rod bending is likely. This is the case on all saws, just that most of them have the rods over-engineered a bit.
 
What gives?? I thought even the stihl god Lakesides recommended using a rope. I never had any trouble but ms180s are not usually on the menu.
 
Get your dealer to order you a 0000 893 5903 piston stop. It is a flat rubber coated strip that you put in thru the spark plug hole. It does not screw in like the other kinds. As long as you get it in there right and don't get the end caught in the exhaust port, they are much more forgiving than the screw in piston stops. Stihl does not really recomend the screw in piston stops for saws, they are just for trimmers. Don't ask me why.:chainsawguy:
 
One thing to remember when you go from 50:1 to 40:1 your running a leaner mix.
Especially going to 25:1.More oil less gas.
Sounds like you were on your way to a lean seize.

You can buy the 170/180 engines brand new on the bay pretty cheap.Swap it in and your good to go, a lot less hassle and you have essentially a new saw.
 
I could be wrong, But is a ms180 designed to use a log wizzard? It seems like it would be a lot of extended high rpms that an occasional use saw isnt designed for. But , what do I know.:dizzy:
 
I'm still sticking with impact gun working against inertia of the crank and fly wheel as well as compression of the piston on the air alone.

Doing it this way there are only forces applied as they would be under normal running of the engine. Also the compression of the air above the piston prevents exceeding the strength of the rod or piston crown while trying to undo the clutch or flywheel nut.

Electric impact is my preferance as it is easier to control avoiding spinning the clutch off and having it go running allover the shop.
 
I have a little dewalt 18v impact gun that I use on car lug nuts. Very light weight and you can easily control the speed. Never used it on a chainsaw but I just might give it a go. Just gots to remember which way the nut comes off.
 
Aaron441 said:
Get your dealer to order you a 0000 893 5903 piston stop. It is a flat rubber coated strip that you put in thru the spark plug hole. It does not screw in like the other kinds. As long as you get it in there right and don't get the end caught in the exhaust port, they are much more forgiving than the screw in piston stops. Stihl does not really recomend the screw in piston stops for saws, they are just for trimmers. Don't ask me why.:chainsawguy:
Click to expand...

Thanks, I used a generic piston stop that I had bought for my Poulan. I'll get the right one. Do I always need to replace the cylinder when I replace the piston?
What about the rod, how do I know if it's bend?
 

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