Bar's sprocket is freezing

[Chainsaw Pete]

I'm running a Stihl MS250 with the original 18" OEM Stihl bar. I'm a homeowner who helps out friends with downed trees or trees that need to be taken down. The last three times I used this saw, the nose sprocket on the bar froze solid - the chain would not move. After every use, I sharpen chains, pull off the side cover and clean out wood shavings and sawdust, and empty the saw of gas and oil prior to putting it away.

When the sprocket freezes, and sawing is over for that saw, I've pulled the bar, cleaned out the slot, oil hole and as much as possible around the sprocket. Then I've squirted WD40 around the nose, and by pressing the sprocket on a piece of soft wood (usually and old 2x4) and pushing back and forth, I have managed to loosen the sprocket and get it to turn freely. I also spray WD in behind the tip to loosen/wash out any dirt. After cleaning, I lightly oil the tip (WD is not a long life lube). While sawing, I use Stihl bar and chain oil exclusively (orange gallon size) and it seems I'm pumping about 1 1/2 reservoirs of oil to one full tank of gas - that has been consistent since the saw was new and tells me the pump is working. If I start the saw up, put a piece of clean cardboard just beyond the tip I get a light spray of oil as the chain rotates - oil is being pumped as designed. I stop and file the chain if it seems to be cutting slowly, and after maybe 3 or 4 hand sharpenings I use an Oregon chain saw sharpener to keep the proper chain profile.

I've had NONE of these issues on my MS311 (but it gets the same cleaning/sharpening/maintenance).

What is causing the nose sprocket to seize up on my 250? It seems to happen after a couple of tanks of gas. The wood I have been cutting is mostly downed trees, sitting up off the ground (not dirt encrusted logs), mostly hardwoods. Chains vary from Stihl to Oregon, though I doubt the chain is a contributing factor.

 

[Jonny Quest]

Highly unlikely that this is due to the saw. That bar could be on any number of Stihl saws. Most likely you have a nose sprocket that has damaged bearings. Time for a new bar. Doesn't have to be OEM Stilh. Oregon makes a fine bar also.

JQ

 

[SteveSr]

I use Stihl bar and chain oil exclusively (orange gallon size) and it seems I'm pumping about 1 1/2 reservoirs of oil to one full tank of gas -

That's NOT right. Should be 3/4 oil tank to tank of gas. Where is all that oil going?

WD40 is NOT a lube. It will also flush out any bar oil in the sprocket tip. The only thing that you should be lubing the sprocket tip with is bar oil.

Is the bar tip getting clogged with sawdust or is it just the sprocket getting tight? Sounds like you might have an oil delivery problem. The bar tail AND the bar pad on the saw have to be PRISTINE clean to make sure that the oil gets to the bar instead of running down the bar pad to the ground.

 

[buzz sawyer]

How long have you owned the saw? Approx. how many hours? For the amount of oil you're using, the tip should be getting plenty. Sounds like time for a new bar. Do you have another saw that uses the same bar? If so, try switching to see if the bar still locks up.

 

[Philbert]

Sometimes dirt gets wedged in there. Sometimes a wood chip. Sometimes string. Could be a damaged bearing.

People will try soaking the tip in various oils and solvents to free it up. At some point you will decide to buy a new guide bar. *

* When you do, and have ‘nothing to lose’, consider the following:

https://www.arboristsite.com/threads/nose-sprocket-rescue-illustrated.256640/

Philbert

 

[Chainsaw Pete]

That's NOT right. Should be 3/4 oil tank to tank of gas. Where is all that oil going?

WD40 is NOT a lube. It will also flush out any bar oil in the sprocket tip. The only thing that you should be lubing the sprocket tip with is bar oil.

Is the bar tip getting clogged with sawdust or is it just the sprocket getting tight? Sounds like you might have an oil delivery problem. The bar tail AND the bar pad on the saw have to be PRISTINE clean to make sure that the oil gets to the bar instead of running down the bar pad to the ground.

No idea where the excess oil is going. I assume it is lubing the bar, it does not leak down and show up on the outside of the saw unless the saw is sitting for several days w/ a full reservoir. Then the newspapers I put under the saw show a fair amount of oil after a week or so. I was told by my stihl dealer this leakage is normal. (Yes, I know all about motorcycle, car, and probably now Sthil 'stealers').

I know WD is not a lube. I use it to flush out the dirt and junk that is clogging the tip sprocket because it is an aerosol under pressure. Have you ever tried to flush out dirt and crud with sticky bar and chain oil? After freeing up the sprocket i lightly oil it w/ b&c oil - though i was not specific about the oil used in my post.

The bar tail and oil delivery area on the saw may not be pristine, but they are as clean as I can get them using q-tips. As said, this problem is specific to this saw and this bar, and not to my other saw.

I have a couple of brand new bars - a Stihl and an Oregon sitting on the shelf (both 18" like the OEM). I don't like throwing parts at a problem unless I understand the cause of the problem, but it is beginning to sound like @Jonny Quest might have nailed it.

 

[Chainsaw Pete]

How long have you owned the saw? Approx. how many hours? For the amount of oil you're using, the tip should be getting plenty. Sounds like time for a new bar. Do you have another saw that uses the same bar? If so, try switching to see if the bar still locks up.

Saw is probably 10 years old. Hours? I doubt I use it for more than half a dozen times a year, maybe 4 to 6 hours run time each time. I always empty the gas and oil tanks between usages.

No to another saw that uses this bar. I have the MS250 and a MS311.

 

[Chainsaw Pete]

* When you do, and have ‘nothing to lose’, consider the following:

https://www.arboristsite.com/threads/nose-sprocket-rescue-illustrated.256640/

Philbert

As I said, I have two brand new bars on the shelf. The Sthil bar managed to hide from me well enough that I bought the Oregon bar thinking I should have a spare - and later the Stihl was found and I have two. While I do not think disassembly is beyond my skill set, I have enough other projects that I'll try a new bar and see what happens. I don't own a chain breaker to remove the rivets though I do have more than enough punches and access to other tools to do the job.

Thanks for the link - good to see how the nose sprocket is put together.

 

[J D]

That thread philbert linked to has some good information & images that show how the nose sprocket is constructed & may help you work out what may be wrong.
I've seen sprockets that had play due to missing rollers which I could not for the life of me see how they got out as nothing was damaged or deformed. If there is any significant splaying out at the sprocket you will get all kinds of intermittent binding issues

 

[singinwoodwackr]

Soak the bar tip in degreaser like Purple Power several hrs or overnight. Use compressed air to spin the tip at very high speed. Sprocket should easily spin freely. If not, repeat. When thoroughly cleaned out, rinse with water and air out again. spray with wd40 or other lube to prevent rust. Re-install on saw.

The roller bearings are most likely clogged with pitch and crud.

I’ve been restoring bars like this for decades…rarely have to replace a tip or bar.

 

[Chainsaw Pete]

Soak the bar tip in degreaser like Purple Power several hrs or overnight. Use compressed air to spin the tip at very high speed. Sprocket should easily spin freely. If not, repeat. When thoroughly cleaned out, rinse with water and air out again. spray with wd40 or other lube to prevent rust. Re-install on saw.

The roller bearings are most likely clogged with pitch and crud.

I’ve been restoring bars like this for decades…rarely have to replace a tip or bar.

I like this suggestion best - since I plan on cleaning the bar anyway and trying to free up the tip. I will add, however, that one should NEVER use compressed air to spin ball bearings at high speed. I've read in multiple places that after cleaning them with solvent the high speed spin can damage them. Be that as it may, I will blow the area clean and lube them. I suspect that the abuse the tip of a chain saw endures probably guarantees that the bearing situation is not the same as a precision ball bearing.

 

[singinwoodwackr]

I like this suggestion best - since I plan on cleaning the bar anyway and trying to free up the tip. I will add, however, that one should NEVER use compressed air to spin ball bearings at high speed. I've read in multiple places that after cleaning them with solvent the high speed spin can damage them. Be that as it may, I will blow the area clean and lube them. I suspect that the abuse the tip of a chain saw endures probably guarantees that the bearing situation is not the same as a precision ball bearing.

BS, imo
First off, they aren't ball bearings

 

[Philbert]

While I do not think disassembly is beyond my skill set, I have enough other projects that I'll try a new bar and see what happens. I don't own a chain breaker to remove the rivets though I do have more than enough punches and access to other tools to do the job.

Yeah, a block of wood with a hole in it can go under the bar, and a basic punch can drive the rivets.

Sometimes, I do ‘autopsies’ on ‘dead’ parts just to see what is going on.

Replacement nose sprockets used to be available from dealers, but probably can only find the entire replacement bar nose (RSN) assemblies today, for higher end bars.

Philbert

 

[NSEric]

Bars are cheap and dont last forever, 10 years of use is pretty good.
Toss it and run your spare bar.
Why waste hours fixing a 40 dollar part?

 

[lone wolf]

Maybe the bar is pinched at the sprocket area, take a close look if it is in too far, twist a flat blade screwdriver in there to get it back out to where it should be..

 

[thenne1713]

I'm running a Stihl MS250 with the original 18" OEM Stihl bar. I'm a homeowner who helps out friends with downed trees or trees that need to be taken down. The last three times I used this saw, the nose sprocket on the bar froze solid - the chain would not move. After every use, I sharpen chains, pull off the side cover and clean out wood shavings and sawdust, and empty the saw of gas and oil prior to putting it away.

When the sprocket freezes, and sawing is over for that saw, I've pulled the bar, cleaned out the slot, oil hole and as much as possible around the sprocket. Then I've squirted WD40 around the nose, and by pressing the sprocket on a piece of soft wood (usually and old 2x4) and pushing back and forth, I have managed to loosen the sprocket and get it to turn freely. I also spray WD in behind the tip to loosen/wash out any dirt. After cleaning, I lightly oil the tip (WD is not a long life lube). While sawing, I use Stihl bar and chain oil exclusively (orange gallon size) and it seems I'm pumping about 1 1/2 reservoirs of oil to one full tank of gas - that has been consistent since the saw was new and tells me the pump is working. If I start the saw up, put a piece of clean cardboard just beyond the tip I get a light spray of oil as the chain rotates - oil is being pumped as designed. I stop and file the chain if it seems to be cutting slowly, and after maybe 3 or 4 hand sharpenings I use an Oregon chain saw sharpener to keep the proper chain profile.

I've had NONE of these issues on my MS311 (but it gets the same cleaning/sharpening/maintenance).

What is causing the nose sprocket to seize up on my 250? It seems to happen after a couple of tanks of gas. The wood I have been cutting is mostly downed trees, sitting up off the ground (not dirt encrusted logs), mostly hardwoods. Chains vary from Stihl to Oregon, though I doubt the chain is a contributing factor.

Roller tips have a ball bearing, and you have a bad tip. If bar is solid, you will need to replace the entire bar, but if bar is two-piece, you can replace just the tip w/ roller sprocket. I recall reading one complaint some years ago the guy thought he had engine issues on a new saw, finally realized it was roller tip seizing causing his issues. It can happen, but I imagine MOST tip issue start with being pinched/ bound when downing or bucking. A simple 2-3-feet or longer of a 12-inch log can exert tremendous crush.

 

[lone wolf]

Roller tips have a ball bearing, and you have a bad tip. If bar is solid, you will need to replace the entire bar, but if bar is two-piece, you can replace just the tip w/ roller sprocket. I recall reading one complaint some years ago the guy thought he had engine issues on a new saw, finally realized it was roller tip seizing causing his issues. It can happen, but I imagine MOST tip issue start with being pinched/ bound when downing or bucking. A simple 2-3-feet or longer of a 12-inch log can exert tremendous crush.

Dont they have needle bearings?

 

[SS396driver]

Drying a bearing with compressed air is ok as long as you don’t let the bearing spin . One of the guys at the body shop was doing his front wheel bearings and was drying with an air gun .The spinning bearing was wizzing loudly till it exploded in his hand . He didn’t get hurt but it took out 3 flouresant tubes in the ceiling lights. One of those instances where we couldn’t tell him fast enough not to do it

I would say the sprocket is toast

 

[Philbert]

Roller tips have a ball bearing,

Dont the have needle bearings?

The ones that I have disassembled have roller bearings.


Philbert

 

[Sidecarflip]

The last three times I used this saw, the nose sprocket on the bar froze solid - the chain would not move. After every use, I sharpen chains, pull off the side cover and clean out wood shavings and sawdust, and empty the saw of gas and oil prior to putting it away.

The hole in the bar where the sprocket resides (newer bars don't have the hole btw or at least I don't think they do), is for GREASE, not WD40 or any other light viscosity penetrating oil. Again, for GREASING the sprocket, using a grease needle or tapered end disposable grease applicator. It's freezing up from lack of lubrication (dry bearing) and / or cutting swarf getting lodged in the bearing, but the most likely cause is a dry bearing.

You sharpen the chain after every use? Interesting. You must be really abusive on a chain or stick it in the ground or something. If I sharpened a chain after every use, I'd soon not have any cutter teeth left to sharpen and I do hope you are lowing the rakers an appropriate amount as well, using a raker gage. Secondly, why do you empty the saw of bar oil and gas? Seems really odd to me if you are planning on using the saw again in the foreseeable future. Only time I'd dump the fuel and certainly not the bar oil is if I was storing the saw, long term. something I don't do anyway, as I use canned fuel which has a viable life of at least 2 years and sometime longer. Bar oil i reality, never goes bad, why dump (waste) it. What you are doing seems strange to me.