MS440 sprocket question

[wseibert]

Hi all - I'm new here and new to chainsaw repair. I picked up an MS440 at auction today, with a 16" bar and chain, and spent the afternoon disassembling and cleaning. I will be using it to get firewood and possibly for some milling, but I know that's a whole other topic for another day.

My first question is whether this sprocket is shot, or if I can run it. The first photo is the front of the sprocket. The needle cage seems to have melted away, leaving the pins. I will get a new needle cage.

I hope the second photo is clear enough to show the worn holes.

Can I just flip the sprocket and run it so that the chain runs agains the unworn end of the openings in the sprocket?




Holy ****, looking at the photos, it looks like a couple of teeth have sheared off the sprocket. Wow. I'd tear into it again but it's dark now and I put everything away.



Could the original problem have been this spring breaking (#13)? It's behind the clutch. I forgot to take a photo - the bent end is broken off.



The two plastic covers around the clutch show a lot of heat damage.



I can't seem to get it to idle without the chain moving. If I turn the idle screw down to stop the chain, it stalls. Am I going in the right direction diagnostically? Compression is 163psi. Spark plug was coated in white. A wire wheel made it look new.



Piston looks great - no scoring - horizontal fine lines.





Thanks for your patience with my rambling thoughts. Any assistance is appreciated.

Will

 

[lone wolf]

It looks like the bearing is shot and possibly the clutch drum where it rides, take it all apart and post more pics. Who can tell if the sprocket is bad, you can't tell from the blurry pic, I think it is shot though.

 

[bigbadbob]

Looks like it was run with the brake on,, bet the clutch springs are toast ,,,
bearing is shot,,
IMHO

 

[cookies]

When they get run with the chain brake on like that you need to replace everything because the heat changes the metal hardness in the drum, clutch shoes, clutch springs, melts the plastic worm gear and likely damaged the brake band and oil pump. If your lucky the oil pump survived without excessive leakage from the pump shaft when running and after shutoff or excessive heat damage to the crankshaft.

 

[wseibert]

Thank you for the replies.

It did sling oil from the chain when I ran it today, so the oil pump seems ok...?

In the coming days I'll post photos of the disassembled clutch.

Any thoughts about the broken spring behind the clutch? What does that spring do anyway?

Thanks again,

Will

 

[Lawless]

Just replace the clutch and get a new rim sprocket too.

 

[atpchas]

Any thoughts about the broken spring behind the clutch? What does that spring do anyway?

The spring is what drives the oil pump. If the spring is absent or broken, the oil pump is not going to move any oil which will result in lots of damaging heat. There is no question that the saw shows signs of significant over heating - you need to determine the heat source(s) and remedy it(them).
If it were my saw (with such a pristine looking piston), at a minimum I'd replace the clutch drum, rim sprocket, bearing, and worm/spring. As has been noted, the clutch springs likely need replacing or just go with a new clutch. With luck the oil pump is still OK.

 

[Aknutter]

Nevertheless, don't forget to grease the crank/oiler worm sleave/spacer.
Request a service manual if you want for helpful information on assembly/ disassembly.

 

[wildwes]

If it were mine I would toss the bearing, clutch drum, clutch and sprocket, and replace all. I would also inspect the crankshaft well for damage, along with the oil pump and related parts.
It might cost a few dollars to replace that stuff, but better than doing it halfway and ruining even more parts or even the whole saw.

 

[wseibert]

Nevertheless, don't forget to grease the crank/oiler worm sleave/spacer.
Request a service manual if you want for helpful information on assembly/ disassembly.

Thanks! Request made.

 

[wseibert]

If it were mine I would toss the bearing, clutch drum, clutch and sprocket, and replace all. I would also inspect the crankshaft well for damage, along with the oil pump and related parts.
It might cost a few dollars to replace that stuff, but better than doing it halfway and ruining even more parts or even the whole saw.

Thank you! Should I also get a new chain brake band? That looks like it saw a lot of heat. Is there a strong argument for OEM parts in this situation vs aftermarket?

 

[ZeroJunk]

Generally speaking they will not turn at all with the chain brake on. That is why they have them.

More likely they just dogged the crap out of it with a dull chain.

 

[wildwes]

Thank you! Should I also get a new chain brake band? That looks like it saw a lot of heat. Is there a strong argument for OEM parts in this situation vs aftermarket?

I can't give much input on that, I normally don't replace them, but I also normally don't use the chainbrake. If it looks bad it might be best to go ahead and replace it just to be safe.

 

[lone wolf]

Thank you! Should I also get a new chain brake band? That looks like it saw a lot of heat. Is there a strong argument for OEM parts in this situation vs aftermarket?

OEM is the only way to go, except some plastics or covers. China crap knock offs are a waste of time, effort, and money. Unless you like doing things twice and needing to spend more money and time.

 

[John Lyngdal]

Based on the piston skirt picture you have a low hour saw that appears to have been run with the chain brake on which then cooked the plastic.
I'm going to be a little more optimistic as to the internal damage perspective as MS440 saws can take considerable abuse without damaging the internals.
The clutch side seal will cook and become non-functional before bearing damage will occur when run for an extended period with the brake on. If you can vacuum test the seal with a gauge, that would be useful. If you don't gave the means to perform a vacuum check with a gauge, with the saw at idle change the orientation of the saw and see if the idle speed changes. Another check would be to remove the clutch and drum assembly and squirt a small amount of fuel mix on the crankshaft seal with the saw idling. If the seal is really trashed, enough fuel will leak into the crankcase and stall out the engine with a rich fuel mixture. If the seal is slightly compromised, the seal effectiveness could increase resulting in a faster idle with the application of fuel. No change is what you are looking for.
With the saw not wanting to low idle could be a sign that the crankshaft seal has deteriorated, but it could be the balance between the low set setting and the stop screw position.

How ever it turns out, when you are finished with the repairs, you will end up with an excellent chainsaw that will serve you well for years to come.
If you're going to run a 16" bar on your MS440, you could easily run a 3/8-8 rim and see some increased cutting speed.

 

[wseibert]

John - thank you for the detailed reply. I am learning so much from you all. I will try putting some fuel on the seal and see what happens - hopefully nothing!

Will

 

[wseibert]

Generally speaking they will not turn at all with the chain brake on. That is why they have them.

More likely they just dogged the crap out of it with a dull chain.

Would that explain all of the plastic melting around the clutch?

 

[wseibert]

Based on the piston skirt picture you have a low hour saw that appears to have been run with the chain brake on which then cooked the plastic.
I'm going to be a little more optimistic as to the internal damage perspective as MS440 saws can take considerable abuse without damaging the internals.
The clutch side seal will cook and become non-functional before bearing damage will occur when run for an extended period with the brake on. If you can vacuum test the seal with a gauge, that would be useful. If you don't gave the means to perform a vacuum check with a gauge, with the saw at idle change the orientation of the saw and see if the idle speed changes. Another check would be to remove the clutch and drum assembly and squirt a small amount of fuel mix on the crankshaft seal with the saw idling. If the seal is really trashed, enough fuel will leak into the crankcase and stall out the engine with a rich fuel mixture. If the seal is slightly compromised, the seal effectiveness could increase resulting in a faster idle with the application of fuel. No change is what you are looking for.
With the saw not wanting to low idle could be a sign that the crankshaft seal has deteriorated, but it could be the balance between the low set setting and the stop screw position.

How ever it turns out, when you are finished with the repairs, you will end up with an excellent chainsaw that will serve you well for years to come.
If you're going to run a 16" bar on your MS440, you could easily run a 3/8-8 rim and see some increased cutting speed.

The vacuum gauges that I'm seeing are being sold as brake bleeder kits - is that what I need to test vacuum and pressure?

Thanks

 

[WI_Hedgehog]

The vacuum gauges that I'm seeing are being sold as brake bleeder kits - is that what I need to test vacuum and pressure?

Thanks

Mityvac MV8500 Silverline Elite Automotive Test Kit, provides both Vacuum and Pressure
https://www.amazon.com/dp/B0002SQYUA

 

[ZeroJunk]

Would that explain all of the plastic melting around the clutch?

Yes. See it all the time. Same reason the clutch drum is blue. Moron operator or just don't care, take your pick.