880 threw a chain now it's throwing a fit.....advice please

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JS929

JS929

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I want to start by saying that I meticulously maintain all of my saws. I was milling a 54" red maple a few days ago, and I threw the chain off the 60" bar. This has happened twice. I had the chain tightened as far as I dare tighten it. I worry about screwing that clutch side crank bearing up. I think it was my help pulling up a little too hard on the sprocket end of the bar that made her throw the chain. I let go of the throttle immediately, but it did race for at least a second. Now to the problem....

I got this saw used. It was advertised as like new by a somewhat local guy. I inspected the piston and jug, ran it, and it sounded fine so I stopped there. It has always been hard to start, carb a little tricky to tune, and it backfires Or something to that extent on occasion. It also will quit running once it's warmed up a bit.

So after the chain came off, I replaced it, did one more slab, and the saw just died as soon as I let off the throttle. I thought I hit the choke lever and immediately restarted the saw so as to not just shut off a saw that had been at WOT for 8-10 minutes. Well, I heard a subtle knocking sound after it restarted, and it died again as soon as I unlocked the throttle. The knock scared the crap out of me. I checked the piston and jug and noticed a slight bright mark, not a scratch, just a smooth bright line on the exhaust side of the piston. The jug appears to be fine too. The piston had some carbonization on top, but the rings were fine, ring pins in place, and what I could see of the crankshaft while holding the piston didn't appear to be broken. After this I did noticed what looked like a small piece of metal or maybe just some trash stuck to the roof of the jug. I then decided to see if the crankshaft bearings were bad just behind the clutch and flywheel. The clutch side was nice and tight, no movement from what I could tell. The flywheel side however, looked odd. The flywheel had a bit of a gouge or rub mark around the back edge of the fins, which would be in close proximity to the coil while rotating, and when grabbing the center hub of the flywheel and checking for play, there is about 1/8" of wiggle in it.

Should I split the crankcase open? Is it like just the bearing behind the flywheel? I am picking up a pressure/vacuum tester in the morning. I'm not removing the flywheel unless the pressure/vac test proves to me that I need to.

I also noticed that the grommet that holds the fuel pickup line in the gas tank was leaking from around the grommet and blowing bubbles from around the grommet after I had drained most of the gas and removed the carb to inspect the intake side of the piston.

I'm losing sleep for worrying over this guys. I've got to have this saw running. I appreciate any and all help and thank you in advance.
 
definitely gonna need pics of this. if there was schrapnel in the combustion chamber then i'm guessing a bearing cage took a dump. hopefully a main but i believe they may be plastic caged now. either way, an 1/8" of movement is alot of movement. if i am understanding everything correctly your flywheel side main is most definitely cooked. just hopefull the crank is ok cause those be pricey :envy:
 
I have worked on a few saws that were used on chainsaw mills.
They seem to kill bearings from heat and wear out the rings.

I don't think saws are really built to run WOT for long periods of time.

In any case it's not that tough to pull a saw apart to put in new parts.

Not sure where you live, if it's in S. Central AK bring it by.
 
I do a fair amount of milling and the trick to keeping the saw is a heavier ratio along with frequent breaks for the saw. Cut a few feet and let her idle for a minute or two. As for splitting the case they're not too bad to do. I just split two 084's with a Husky case splitter and it worked out fine. As long as the jug and piston are okay you should be fine. As long as you have it apart you might as we'll put rings in it too.
 
ValleyFirewood said:
I have worked on a few saws that were used on chainsaw mills.
They seem to kill bearings from heat and wear out the rings.

I don't think saws are really built to run WOT for long periods of time.

In any case it's not that tough to pull a saw apart to put in new parts.

Not sure where you live, if it's in S. Central AK bring it by.
Click to expand...

WOT is what they're designed for.
 
Did you read my whole post?

I said WOT for long periods of time.

How many milling saws have you worked on? We get a few a month.
 
Hey guys. I appreciate all of the comments. I'm sorry I haven't been on since my last post.

I run all of my saws at 40:1. I've thought about giving them even more oil in the mix, but I see a lot of mixed reviews on that. I trust many of yall on here, and many of yall know much much much more about this than I do.

Brad, I heard the knocking sound and immediately shut it down. I haven't fired it up since. The piston and jug look ok. There is a shiny line on the exhaust side of the piston, but I don't know well enough to make the call. The pictures will tell yall everything you need to know. I got a Stihl flywheel puller, and I just pulled the flywheel off last night. There is a fair amount of play in that flywheel side bearing. I saw a bit of trash in the crankcase when I had the jug off. I'm going to pressure and vacuum test it this evening when I can get back to it. I appreciate all of the help yall.

On a side note, my local stihl dealer quoted me $80 for the stihl flywheel puller, and they weren't sure if I was even allowed to have it. I had already seen a factory Stihl puller on eBay for $34 with free SH. I know they were just wanting me to bring the saw in. They quoted me over $450 to replace the flywheel bearing, and I just don't have that right now. I'm trying to do this to save money.

Valleyfirewood....I wish you were here in Georgia. I would take you up on it.

If I cant figure this thing out, then I would rather send it to someone on here like Brad. I'd rather pay one of yall than this tacky local dealer.

I will get this pics up tonight or in the morning guys. Again, I can't thank yall enough.
 
If it's pitted you had water in the fuel. Saws tend to make a ping noise when moisture is in the fuel . It's not a certainty that's the issue but you can't rule anything out until you start looking.
 
That puller is $8-10 at best

Send the saw here, I'll do it for 1/2 what they quoted you.

The knocking you heard was most likely the counter weight knocking the case.
I've seen crank bearings in an 044 so bad that it actually wore a groove in the case.




Just the flywheel side though.
PTO side wasn't rubbing

 
There's no point in pressure testing your saw at this point. The case has to be spilt in order to replace the bearings. Replace them both while you're in there. Hopefully the rod bearing isn't damage. That can happen. You'll be going back together with new seals and gaskets. That will be the time to pressure test.
 
Running 10 or more mins milling will really build some heat . There isn't a saw out there that would take that kind of beating for long . 32:1 mix and let it idle a bit every few minutes . Take your time and save your saw . Sounds like you do need some bearings ... Hopefully your crank is ok


Sent from my phone when I should be working
 
Knobby57 said:
Running 10 or more mins milling will really build some heat . There isn't a saw out there that would take that kind of beating for long . 32:1 mix and let it idle a bit every few minutes . Take your time and save your saw . Sounds like you do need some bearings ... Hopefully your crank is ok


Sent from my phone when I should be working
Click to expand...
I've seen my uncle rip board after board with his 3120. The best you can do is richer up the H screw some to help cool the piston and cylinder.
 

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