251 Stihl problem

[Jesse Duke]

I bought a brand new 251 Stihl exactly 5 years ago and it's been great. I'm mostly a weekend burner but now that I just retired that will change next winter. This is my second saw and first Stihl. It's gotten a decent amount of use but hasn't been overworked. I just replaced the chain with a brand new one and just put a new (correctly gapped) spark plug in it and cleaned the air filter. I'm having problems starting it now and before that it occasionally didn't sound right....not too bad though. The manual said check the spark arresting screen but when I loosened the bolt it didn't come out even though it's real loose. What else should I check? I have another question later. Thanks in advance. 

[Jesse Duke]

Even though I didn't get a response on the last post I'll ask the other question I mentioned. When I turn the saw upside down and look at the gear that drives the chain the gear is off a little bit. In other words, the shaft the gear mounts on isn't exactly on a 90 degree angle compared to the bar. When I move the chain it does hit spots where it is not turning as smoothly as I think it should and it makes a bit of a noise.

[sawguy21]

It sounds like the drive sprocket or 'gear' as you call it is worn, time to replace it. Do you have a dealer nearby that could fine tune it? The saw is due for some tlc after 5 years.

[Pine Ridge]

Needlenose pliers will pull the screen out of the muffler for you, but i think you may have more going on than a plugged spark arrestor. 

[Weekend_Sawyer]

Did you try putting the old spark plug back in?

have you ever adjusted the carb?

[Jesse Duke]

Did you try putting the old spark plug back in?

have you ever adjusted the carb?

No to both of these. Thanks for the advice you 3 guys. I do know a guy who works on saws so the advice about a 5 year TLC check-up makes sense. Thanks again. 

[Jesse Duke]

Needlenose pliers will pull the screen out of the muffler for you, but i think you may have more going on than a plugged spark arrestor.

It's not the screen itself but the bolt. It is as loose as can be but still won't come out. I didn't want to force it and risk breaking something. 

[Weekend_Sawyer]

Put the old spark plug back in and see how it goes.

I've done this to myself too many times.
When you make a change and something breaks try to restore it back to where it was before it broke.

If you have never adjusted a chainsaw carb it isn't too hard.
There are some very good you tube videos on it.

Jon

[Jesse Duke]

Thanks again for your time and responses. I went to a friend of mine who is real good with saws. The first thing we did was check the spark arresting screen. After I loosened the bolt he took a little hook and pulled up the piece while I continued to turn the bolt. It came out and looked fine. When he grabbed the chain he immediately said "that's way to tight". I told him that I always have my chain that tight. He loosened it and then the saw started right away and ran fine. I'm a bit confused since that has never been a problem before but I'm not complaining. I am a little worried because when you turn the chain when the saw is not running you it feels and sounds like it has a spot where it hangs up.....this is even with the loose chain. Is it possible I have done some damage by running the saw with too tight of a chain for 5 years? I'm giving it a workout today (unless it rains after I get my mowing done) so I'll know more. Thanks again....awesome website you guys have here.

[firefighter ontheside]

If your sprocket is worn, I would say that is because of running your chain too tight.  I like to have my chain such that if I lift up on the chain, in the middle of the bar the saw lifts up just before the chain fully comes out of the bar.

[Real1shepherd]

You should be able to pull the chain up from the middle of the bar and just see the bottom of a drive tooth. And/or you should never see the chain sagging in the middle of the bar on the bottom. Sounds like you've had it way too tight....hard to say without being there.

Have the saw guy teach you how to adjust the carb. They put limiter caps on now and sometimes seal the high speed adjustment....don't know on your particular saw as I run/collect older stuff.

If your clutch drum and drive gear are all one, it's called spur drive. The better systems have a floating rim sprocket that's replaceable. Sounds like a spur drive and it's worn enough to replace. Get the saw guy to make that evaluation....he should know.

Make sure your chain/bar are getting plenty of oil. If not the chain will go tight in hard use and slacken when it's cool....that will drive you nuts trying to figure that out when all it is, is lack of oil.

Yeah, running a chain too tight can definitely damage an engine....even spin a crank bearing if the engine labors and the chain doesn't spin. Only time will tell there.

Kevin

[Jesse Duke]

Thanks again everybody. Saw got a 2 hour workout yesterday and is running great. This website is fantastic because of you guys!

[Jesse Duke]

I cut down 10 dead ash trees today. 4 of them were pretty big (by my standards....probably medium for you guys) The saw is starting fine when I first get it going but after I shut it off to add fuel or oil it doesn't start first crank like it always used to when it was warm. Sometimes it takes as many as 5 cranks and sometimes it stalls right away but starts the next crank. After I get this batch of ash cut up I'll probably give it to my saw guy for some TLC.

[Greenerpastures]

You really need to replace the clutch bearing and probably the
clutch drum, that bearing will destroy the shaft it runs on, if not
already done so.

BUT, before you spend any money, take off the muffler and look
in through the port, take note of any marks on the cylinder wall,
take out spark plug so you can pull engine over slowly to get the piston
up to where you can see it for scores chips missing or carbon buildup.

Your carb may need adjusting, when a saw is not getting enough fuel
it will be hard to start, initially you use the choke so you have enough
fuel going in to start, maybe put the choke on for one pull when the saw is hot would help you start it, if so, you are running way to lean, not enough fuel
going in, this alone will destroy your cylinder and piston.
Your piston and cylinder can also score if you have destroyed the main shaft bearing from over tightening the chain.

Spend no money until you confirm the cylinder and piston are not damaged, and the end of the crank that the clutch bearing runs on
is not damaged.

[Jesse Duke]

Thanks a lot. It is greatly appreciated!

[Jesse Duke]

Well, it's gotten serious. I suspect I am finally getting punished for my sin of running the chain too tight for so long. Yesterday it stalled 10 minutes into using. I started it up again and it only ran a minute and then stalled again. I noticed the chain was tighter than I just had it. I adjusted it properly and seconds later it stalled again and the chain was tight again. I also noticed oil leaking out. I have a shirt tailed relative who works on saws professionally and works on the side cheap for family so I guess it's heading there. Clutch issue? 

[Greenerpastures]

Probably destroyed engine issue.

[Jesse Duke]

Probably destroyed engine issue.

A destroyed engine can start and run? 

[JohnW]

Don't get scared yet Jesse.  This bad running thing could easily be due to bad fuel line or filter or a carburetor problem

[Jesse Duke]

Thanks John. My relative is heading out of town for 2 weeks so I'll just wait until he gets back. I'm fine with that since I have a lot of hauling, splitting and stacking to do. Since I do everything by hand (wheelbarrow and maul) I have enough to keep me occupied for awhile. 

[Greenerpastures]

Probably destroyed engine issue.

A destroyed engine can start and run?

Well what would you call an engine with shot bearings, or scored cylinder, to me it's destroyed because of how it was run, it could run intermittently for a short time, like the OP says.