Stihl MS250.. cleaning and clunking

[mserke]

I got a used Stihl MS250c from my in-laws. I am pretty sure by the looks of it, that it was used to cut wood that wasn't very clean and the saw was NEVER cleaned.

I scrape some of the large gobs of junk out of the saw and took apart the carb to clean it as the saw will not run, had old gas, and sawdust in the carb, and a totally clogged air filter.

Here are a few pictures:

I still need to do more cleaning but this picture does not do justice to the pile of gunk that came out so far....

I also did some cleaning on the clutch side which was equally as filthy. I should have taken a few pictures but did not. While cleaning the clutch side I had to reset the spring for the chain brake as that was not in the right position on the lever. To get some of the crud out the saw was tapped on the bench with the clutch side down.....

The piston moved freely prior with good compression, there is still good compression now however, there is a "clunk" and some resistance as if there is something binding inside when the flywheel is turned now.

What could it be???

Here is a video with the sound of it.

 

[HarleyT]

Take out the plug, and take the starter back off.

Then look....

 

[Peter Y]

I am betting that when you were banging it around knocking out chunks that the crank shifted a little bit toward the clutch side. I had that happen and my flywheel was rubbing the bottom of the jug. A light tap on the crankshaft on the clutch side popped it right back into place.

 

[Khntr85]

Crank seals are bad I bet....


Will have to break down to see how bad internal damage is..

 

[mserke]

I will try tapping the crank back a bit.

Would all the build up of grime, and dirt be a sign of bad crank seals? Especially on the flywheel side where there is no oiler.

 

[Khntr85]

I have seen both sides go bad, usually the bearing and seal go on pto side first...

Hell I have seen some that looked bad from the factory, nothing perfect I guess...

 

[bitsumishi]

I had what looks like, maybe the same thing, with my 250. Turned out that the hard to pull, clunking issue was the flywheel rubbing on the coil. There are two small bolts with no washers holding the coil in place, which considering the vibration and the magnetic pull, is not an ideal situation I would have thought. Over time I suspect that the coil could move and even a tiny amount would be enough to cause the issue I had.
If this goes on long enough, the continual rubbing/overheating of the coil will cause it to burn out causing an ok start but a stall as soon as it gets hot.

Here's how to check:
Either take the flywheel off and check for bright areas on some of the fins.
Or take the plug out, put a business card into the gap and check the clearance. Make sure you rotate the flywheel all the way round to ensure you are checking the widest parts of the flywheel.
Be very careful with tightening the nuts holding the coil. The plastic just wants to strip out the threads at the first opportunity. Its really difficult to tighten them enough but not too much that they give way. IMO there should have been studs in there from new. And obviously they need to be tight or the coil will move again.
If the the threads do strip, you can make some studs and epoxy them in (see pic) and I would put on some spring washers with a nylock nut just in case.




Studs:

 

[HarleyT]

The coil is essentially a non-moving part, so the coil bolt thread stripping thing is not common at all.

 

[bitsumishi]

The coil is essentially a non-moving part, so the coil bolt thread stripping thing is not common at all.

I said, they are easy to strip when you try to tighten them. The reason the coil would have a tendency to move is that there are no washers to stop the bolts from loosening and with all that vibration and no washers, they almost certainly will tend to loosen slightly over time and slightly is enough to cause the coil to move as there is a sideways force from the magnet.
If bolts couldn't loosen over time due to vibration, then no one would have bothered to invent spring washers.

 

[HarleyT]

A common problem with this model, as it gets older, is shrinkage/wear/whatever of the plastic of the plastic crankcase/housing, of which the engine sandwich is bolted to. And some "slop" occurs at the bottom mounting bolts of the engine block, and there can develop movement between the crancase and engine block.
A cure that I have used is tapping out the metal bushings in the bottom of the crankcase, and grinding a little off of the top of them, so the crankcase and block bolts together tightly, and then re adjusting the coil gap may be needed.

 

[HarleyT]

I said, they are easy to strip when you try to tighten them. The reason the coil would have a tendency to move is that there are no washers to stop the nuts from loosening and with all that vibration and no washers, they almost certainly will tend to do over time.

Nahh.

 

[bitsumishi]

Nahh.

I think you are just trying to start an argument for the sake of it. Exactly how do you explain why my coil had moved if the nuts had not come sufficiently loose for the coil to have moved?

 

[HarleyT]

I'll agree that self tapping screws in plastic is a weak point, but it becomes weak when someone in the past likely over-torqued the screws. But in usual daily life, it is not usually a problem.
To be honest, unless a coil is rubbing a flywheel, I never bother checking the gap.

 

[bitsumishi]

Harley, the other day you tried to ridicule me over the use of the word Tacho which turned out to be your misunderstanding of how the word is used in this country.
You then went on to wrongly and publicly accuse me of blocking you, which I had not done.
And today you put words in my mouth which I had not said, again apparently an attempt to ridicule me. When I corrected you, you then respond with an arrogant "nahh".

I realise you like to have a joke and that is fine with me but this is beginning to look like like you are out to cause trouble. I would ask you to stop please.

 

[bitsumishi]

I'll agree that self tapping screws in plastic is a weak point, but it becomes weak when someone in the past likely over-torqued the screws. But in usual daily life, it is not usually a problem.
To be honest, unless a coil is rubbing a flywheel, I never bother checking the gap.

As I keep saying and you dont seem to be 'hearing' it. The first issue is that the coil will have a tendency to move because the nuts have no washers. The stripping issue happens when someone tries to tighten them to correct the initial coil movement caused by the lack of washers.
If bolts couldn't loosen over time due to vibration, then no one would have bothered to invent spring washers.

 

[HarleyT]

With the model in question, the problem I stated earlier is a common thing. Which, when the bushing/crankase holes get wallowed out, then the coil may start rubbing. And folks may or may not over-torque fasteners in a mistaken attempt to cure a coil-rubbing problem. Kind of like folks stripping out bar studs, while all along the problem lied elsewhere {worn out sprocket}....

 

[HarleyT]

You just say that the fault is because they have no washers. That statement has no validity.

 

[HarleyT]

I joke around here, so what?

Do I need a lawyer? Are you going to start a lawsuit?

Do you work for the "Nuts have no washers" lobby????

I also ask pointed questions here, so other members don't start/spread a lot of bogus crap on chainsaws.

If a member here is the only one that has this particular problem, then the fault may not be with the saw model, but with the member.......

 

[bitsumishi]

You just say that the fault is because they have no washers. That statement has no validity.

You have just as much or as little evidence for your theory of shrinking casing as I have for mine, of why the coil ends up rubbing. Mine appears to be far more obvious a theory than yours but both are just theories because in reality the cause may be different for different saws. What I find so interesting is that you got so exercised in trying to come forward with a theory only AFTER I made a suggestion that the cause of the issue could be the coil. Including twisting what I had said, in an attempt to dismiss it.

Trolling in the guise of debating, is still trolling.

 

[HarleyT]

As I said before, the ignition coil is basically a "non-moving" part...