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jjones

stihl ms250 nose sprocket jamming

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Hi.

 

Having some issued with a couple of years old ms250 running an 18 inch bar.

 

It seems that sometimes the nose sprocket on the bar gets jammed solid, enough that the engine sounds like the chain brake is on and you have to switch off and get the sprocket moving.

 

When this happens the sprocket area of the bar appears to be quite hot.

 

The saw was using half a tank of oil to a tank of gas which seems the norm. I took it back to the dealer who sprayed the oil off the bar and declared it was normal.

 

With the bar removed you can see the oil pumping out. I thought the problem could be a lack of oil so I purchased and installed the bigger oil pump thinking this would be the answer. It now dispeces about 25% more oil but I still have the problem.

 

I am cutting ash currently and have had problems with beech (beech was quite sappy).

 

Tried a new chain and 16 inch bar and the same problem.

 

I think I have the chain tension right, if anything on the loosed side rather than tight.

 

- added a picture of a cut that resulted in one of the nose sprocket jams.

 

Any thoughts?

 

Thanks

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Edited by jjones

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is the chain pitch ok is the clutch bearing ok thats about all i can think off if you turn the saw upside down is the chain running in line with the bar and sprocket

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You say with the bar removed you can see the coming out. But are you sure it's getting into the bar and onto the chain? I presume you clean out the bar's oiling holes when you remove the bar/clean the saw/flip the bar over. As no amount of pumped oil is going to do any good, if it's not entering the bar.

 

Visually check the condition of the sprocket nose teeth for excessive wear, e.g. sharp pointed teeth. And for uneven wear on the bar rails, burrs and the like. Dress the bar if needed and replace the bar if the nose sprocket is cream crackered.

Edited by TGB

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Sounds like the bar sprocket has been pinched at sometime - had a similar one once on an 024 - swapped it out in the end!

 

Just under a tank of oil per fuel fuel tank is normal - it the sprocket tip flings a line of oil at speed free running, all is as it should be!

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I had an 18 on an 362 jam recently. Sharpened chain and then couldn't move it around at all. Took chain off and bar tip wouldn't move even pushed with a screwdriver. Was going to throw the bar away as seized but tried washing it in a jug of white spirit. Soon got going and now good as new. I'd been felling a sweet chestnut and seemed to be some gumming up. No grit came out but some oily residue. Not sure if relevant but very odd at the time.

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