Broken drive teeth

[AddisonEcho]

I purchased an Echo 620p a few months ago. I have mainly used the 27 inch bar with no problems. However the 20 inch bar is the problem. I have broken off 4-5 drive teeth on 3 chains and today the sprocket tip gear broke apart. Every time the drive teeth broke I was just cutting into a log with. little pressure and no binding.I always check chain tension whenever I refuel.Today when the sprocket tip gear broke I was cutting a medium size limb off when the chain came off the bar and I found half of the sprocket gear on the ground. I have been cutting trees for firewood for over 30 years and I have never broken a chain let alone the sprocket gear. I recently cut up a 51 inch diameter maple tree with the 27 inch bar with no problems. I lube the gear everytime I refuel. I have a few questions. First, what could cause the chain drive teeth to shear off, second what could cause the sprocket to break? Could the bar have been bad from the beginning? The bar tip is replaceable but I cannot find one and my dealer does not know how to get one. I cut over 25 trees a year for firewood, so what aftermarket bar would you suggest as I prefer not to purchase another Echo bar.

 

[Philbert]

Photos might help:
- broken drive links;
- broken nose sprocket parts;
- replaceable sprocket nose (‘RSN’) assembly, including where it attaches to the bar.

Drive teeth don’t typically shear off, unless they have a problem with the drive sprocket (spur or rim?) or nose sprocket.

If you were already breaking off drive links, without the chain jumping the bar groove, I am speculating that there was something wrong with the nose sprocket to begin with. Or they were not compatible pitches. But that is just a guess.

Philbert

 

[TheJollyLogger]

Pitch is wrong

 

[AddisonEcho]

I checked the bar which is marked 3/8 pitch, .50 gauge as is the chain. The manual also says the same and both bar and chain part numbers are correct. The sprocket gear broke in half and mushroomed the end. The nose sprocket is replaceable but the local dealer cannot find it and I cannot find it on the net. I checked the rim sprocket and it looks good with hardly any wear. On my previous chainsaws the grease came out by the sprocket teeth, on this on the grease come out of two holes on each side of the bars. I do not see how the grease gets to the teeth-what am I missing? I still am looking for an aftermarket bar but I did buy an Oregon bar that is laminated to test to see if was the original bar as the problem. I am cutting down about 10 walnut trees this week so if it was not the bar I will know . It has not taken long to break the drive teeth.

 

[ray benson]

I checked the bar which is marked 3/8 pitch, .50 gauge as is the chain. The manual also says the same and both bar and chain part numbers are correct. The sprocket gear broke in half and mushroomed the end. The nose sprocket is replaceable but the local dealer cannot find it and I cannot find it on the net. I checked the rim sprocket and it looks good with hardly any wear. On my previous chainsaws the grease came out by the sprocket teeth, on this on the grease come out of two holes on each side of the bars. I do not see how the grease gets to the teeth-what am I missing? I still am looking for an aftermarket bar but I did buy an Oregon bar that is laminated to test to see if was the original bar as the problem. I am cutting down about 10 walnut trees this week so if it was not the bar I will know . It has not taken long to break the drive teeth.

If it is a replaceable tip - standard Oregon 3/8" tip?
https://www.jackssmallengines.com/jacks-parts-lookup/part/oregon/30853

 

[Philbert]

I do not see how the grease gets to the teeth-what am I missing?

Some nose sprockets are greased with a grease gun. Some (including STIHL and some newer Oregon bars) expect to get sufficient lubrication from the bar and chain oil.

If you post a photo of your bar tip, someone may recognize it, and be able to recommend a source for replacement.

Might take a standard Oregon tip.

Philbert

 

[hacskaroly]

First, what could cause the chain drive teeth to shear off, second what could cause the sprocket to break?

From saws I have seen come through that had driver issues, most of them come from running loose chains or have worn out spur/rim sprockets. I have seen grooves in spur sprockets deep enough to actually wedge the driver and lock it into place. All of the other drivers have similar wear. Another possibility is running a tight chain that creates heat and when you finish cutting and the hot chain cools down, it will contract putting excess pressure on the spur/rim sprocket and the nose sprocket potentially causing premature damage.

The first two chains you broke drivers off of, did those chains come off the bar like the third or did they remain on? How did you come to notice these two chains had damaged drivers if the chains did not come off like the third? Also, before the nose sprocket split, when replacing the other two chains, did you notice if it was freely rolling or was it giving you resistance?