FODed 441C

[CTYank]

That's Foreign Object Damage- seems a sorta-spherical piece of steel of about 3-4 mm diam got caught between the piston crown and the upper edge of the exhaust port right in the middle of the port. Impact pinched the upper ring tight and deformed the edge of the port enough to put a deep clean score in the piston. Otherwise, the saw's like new.

Saw was built in '12, but is out of warranty. The Foreign Object is gone; suspicion is that it came from or through carb. Owner has p & c etc. on order for yers truly to r&r.

Never been into a 441C, so I'd very much appreciate any informed guesses as to what might have done the damage, and any tips & tricks for the opening & closing of the patient. The saw is going to be used for milling, so I'd like to make it ready for severe duty as possible. (Repair manual & IPL are in hand- thanks atpchas.)

 

[anlrolfe]

Start by checking all your bearings and bearing cages. Mains and piston pin bearings will be easier to see trouble but give the rod bearing some good attention. Its harder to see around the tight fit parts and many people assume it good.

 

[CTYank]

Big problem is carb removal. According to Stihl repair manual, once the fuel & pulse lines are popped off the brass carb tubing, the carb should be free to leave. But the fuel & pulse lines, though free, will not go easy, there are still multiple potted electrical connections, and the carb seems well connected to the boot. Of course, much of this is concealed.

Clues most welcome.

 

[TK]

If it's anything like a 362, getting a prybar and start reefing.

 

[zogger]

Small and semi spherical sounds like a bearing.

Unless your friend has a two year old and was working on the saw and left the room with no air filter on it, then it could be anything in there.

 

[CTYank]

If it's anything like a 362, getting a prybar and start reefing.

I've been fighting the temptation to fire up the saber-saw and grab a hammer. And fighting the temptation to ask him why he didn't get a 372xp or Dolmar 7900, instead of this Rubik's Cube. (And I thought a 35cc JennFeng "Mac" was a real trip for a carb r&r.)

Somebody's gotta know the shtick, and I'm hoping I'll hear about it. Or else put it back together and ship it off to TN? Open for new business yet, Randy? (New p&c is from Hyway.)

Zogger,
No youngsters near it, ever, I'm told. Whatever got in there seems to have left no other marks in the chamber, and the squish band is about 3/8" wide. Only impact I can see was at the edge of the piston crown. My main suspicion is that it came in from the muffler. Assemply oversight?

 

[zogger]

Well, if you have the IPL it should show the carb coming off. It went on, and they don't weld them on, so...

 

[TK]

Any pics available of the setup?

 

[JC360]

You may want to check real good inside the muff. I had a broken ring on a saw, and was missing 1/4 inch of the ring, right out of the middle. I sloshed the muff around in a coffee can of mineral spirits and washed 3 fragments of ring out of the muff.

 

[Duke Thieroff]

Could it have been a ring locating pin?

Is all the junk that's supposed to be in the carb actually in the carb, butterfly screws and what not....

 

[splitpost]

Did it have a new plug?

 

[sgrizz]

opcorn:

 

[CTYank]

Well, if you have the IPL it should show the carb coming off. It went on, and they don't weld them on, so...

A reasonable person might think so. Doesn't apply here though. Carb & strato throttle body have multiple connections (pulse, fuel, electrical, etc.) and are attached somehow out of sight to rubber boots concealed within a plastic "clamshell" cover.

Info in manual & IPL just doesn't get it done. I'm guessing you've never been into such a spaghetti farm. Lucky you.

Pix in the manual don't tell much, certainly not what you need most. Manual sez: pop the pulse & fuel lines and the throttle cable, then pull the carb out. Right! Pix I could take of it wouldn't help much, because of how the pertinent stuff is hidden from view.

OEM Bosch plug was swapped for NGK. I'm told the Bosch plug came out intact. Minimum pock-marking on the piston crown, so I'm thinking the debris came in the exhaust. I did check inside the muffler, but was told that debris in there could have been lost. I'll have to postpone the detective work until the blessed cylinder can be gotten off.

 

[mp5n]

I rebuilt a Stihl MS461 about 2 months ago that had one of the cap screws that held the muffler on back out and rattle around inside the muffler till it bounced into the exhaust port. Needless to say the saw stopped abruply and left a nice M5 thread impression on the top of the piston and the roof of the exhaust port. The saw was used in a commercial application and the 3 month warranty was up. Stihl did give the OP a $400.00 credit towards a new saw. I ended up getting him a top end and putting it back together. It's been running well since.

 

[zogger]

A reasonable person might think so. Doesn't apply here though. Carb & strato throttle body have multiple connections (pulse, fuel, electrical, etc.) and are attached somehow out of sight to rubber boots concealed within a plastic "clamshell" cover.

Info in manual & IPL just doesn't get it done. I'm guessing you've never been into such a spaghetti farm. Lucky you.

Pix in the manual don't tell much, certainly not what you need most. Manual sez: pop the pulse & fuel lines and the throttle cable, then pull the carb out. Right! Pix I could take of it wouldn't help much, because of how the pertinent stuff is hidden from view.

OEM Bosch plug was swapped for NGK. I'm told the Bosch plug came out intact. Minimum pock-marking on the piston crown, so I'm thinking the debris came in the exhaust. I did check inside the muffler, but was told that debris in there could have been lost. I'll have to postpone the detective work until the blessed cylinder can be gotten off.

No I haven't had the pleasure with a saw like that, just regular weirdo car plumbing and wiring a few times.

I did get two minimacs running fine, does that count?

edit: the rubber boots, they should slide out too most likely, might give ya better access

 

[splitpost]

I only asked cause i seen a few plugs mainly bosch lose the electrode or porcelin insulator

 

[CTYank]

I only asked cause i seen a few plugs mainly bosch lose the electrode or porcelin insulator

Your guess is at least as good as mine, and helpful.

Meanwhile, if you hold a LED light just right shining into the exhaust port, you can clearly see a couple of marks in the middle of the port. They look just like they were made by pieces of ring.

Then, if you rotate the crank by hand, with plug out, you can clearly feel what seem like brinelling (lumpy bearing race deformation) near TDC & BDC. I've already braced owner for dealing with crank probs, as source of debris. (Not a self-fulfilling prophecy though.)

 

[CTYank]

Just in case anyone was interested in the outcome.
Turns out, the carb & strato throttle body were just well stuck to the rubber boots behind. They came out, as did the double boot assy, once the lower carb cover was loosened so the boot assy screws were accessible.
New p&c went in quick & simple. The rest of the assy is moving forward, but takes a bit. May be running Tuesday.
The original p&c damage was as seen from the outside, interestingly. Only one piston impact, at the exhaust port, where essentially spherical object about 4mm got caught between piston crown and upper port lip. Both rings were intact, but pinched in their grooves at the point of impact. No debris found in crankcase, or anywhere else for that matter. Everything in intake tract was in place. The strange feeling on turning the crank by hand is from flywheel magnets.

 

[splitpost]

Hope your right,cause it really suxx having to build something twice