help me troubleshoot a 3120xp

[wisecobandit]

Bearings would not cause a fuel delivery issue tho. It sounds more like a lean heat seize due to lack of fuel which you've got away without bore/piston damage.

Whilst im reluctant to say its not bearings causing the locking up I would say worn bearings are rare and mainly replaced at full overhaul stage. That's not to say they don't fail but a saw like the 3120 wont have been used as often as smaller saws and had the use. The obvious exception is milling and how much its done. Did the previous owner mill with it?
Im not even sure the 3120 uses the shielded bearings? Certainly the 394 I rebuilt yesterday didn't have shielded bearings in and the 385/390 range only have them on 1 side.

Personally I would treat it to a new fuel filter, fuel line (they can go soft as well as crack) and give the carb a clean and run it and see how you get on. If your unhappy once its up and running or its locking up again stop using it so you can look into it deeper.

 

[agrams]

wiseco, that was pretty much the exact same conclusion I am coming to.

I've got a new filter/fuel line on the way. I broke down the saw tonight (short of taking the carb off and splitting the crank) and checked the piston head, the case and rings, and they looked good. The fuel hose didn't look brittle or hard or failed anywhere, but those are all things that you can only really see when you have it alone.

I went over the flywheel and the crankcase around it with a fine tooth comb to see if I could see any dings or dents that would indicate a piece of debris being caught to explain the catch, but nothing stood out, and the spacing on the ignition coil looked good. pushing the crankshaft axially via the flywheel nut and the clutch nut had zero slop, so no red light there.

I think the least I am educated on is carb's. But in regards to the lean heat seize, what should I pay attention to more in the future to avoid? Run a heavier mixture of oil in my fuel? (was 50:1 today).

It is odd though, I ran the saw 5+ hours of heavy milling last saturday, not a problem. Today, I had it out for about 5-10 minutes of a few log bucking cuts and this happens. I don't think the saw even had time to really get up to full temperature.

One thing I did notice is that the bar oil lever, its tension wire was really sloppy, so that control effectively does nothing until I fix that. Not sure how though, as the wire has a flat grommet on the end that mounts in the back of the lever, so I can't crimp or shorten the wire there.

 

[nmurph]

It's not going to "lean seize" and not leave some scuffing on the piston.

If it's hydro-locking bc of a malfunctioning carb, you're going to see a wet plug and it's not going to restart with 2-3 pulls after it locks. That is a sloppy-wet cylinder and requires some serious pulling or flame to clear.

Since you didn't see any signs of UFO's in the cylinder, I think bearings are more likely the problem.

 

[SEAM]

If it really locks up badly (won't move forward at all) it might be the lower rod bearing (roller missing or cage dissolving). The rod will get stuck on the crankcase with the piston returning from TDC.

 

[Grande Dog]

Howdy,
3120's have solid mainfolds, an they will vapor lock. 50-1 should be fine but, use as high of octane as possible. There is something that should be checked before you work it again. Since the saw is new to you, you should check the fixed main jet in the carb. There are 2 different types. The original style is a press-in with a retainer washer, and the other is a screw in. If I remember right, the jet you want should have has a 113 stamped on it.
Regards
Gregg

 

[Grande Dog]

Howdy,
The wire is connected to a cam lever that when activated adds more cam action to the pump. Usually when it's in the full on position, it'll empty the oil tank way before the fuel. If you have more wire than you can adjust, and it's not slobbering tons of oil, the oil pump end of the control cable has slipped from it's holder. If it is puking oil with slack in the control cable, more than likely the oil pump cam is stuck.
Regards
Gregg

 

[Jacob J.]

Howdy,
3120's have solid mainfolds, an they will vapor lock. 50-1 should be fine but, use as high of octane as possible. There is something that should be checked before you work it again. Since the saw is new to you, you should check the fixed main jet in the carb. There are 2 different types. The original style is a press-in with a retainer washer, and the other is a screw in. If I remember right, the jet you want should have has a 113 stamped on it.
Regards
Gregg

When he bought this saw, the seller converted the carb to an adjustable high speed screw. So it should be a fully adjustable carburetor.

Like Neal said- if this was some kind of lean seize- there'd be some kind of markings on the piston. If this was a fuel lock- then fuel would come gushing out when the spark plug was removed.
So far the OP hasn't indicated either of those circumstances.

 

[Grande Dog]

Howdy,
If it has a HS screw, and a manual choke, that's way cool.
I was speaking of vapor lock. When the carb get hot enough to boil the fuel, and more or less, an air bubble is introduced not allowing the fuel to move. The 3120 was also classic for cracking, and or warping the intake manifolds blocks.
Regards
Gregg

 

[wisecobandit]

Howdy,
If it has a HS screw, and a manual choke, that's way cool.
I was speaking of vapor lock. When the carb get hot enough to boil the fuel, and more or less, an air bubble is introduced not allowing the fuel to move. The 3120 was also classic for cracking, and or warping the intake manifolds blocks.
Regards
Gregg

Just like the 394 can suffer from that also uses the similar solid plastic manifold block.

 

[agrams]

While vapor lock would be a cheap answer, it doesn't mesh with the scenario. The saw was running maybe 10 minutes, it wasn't that hot out (around 80-83) and it didn't start up when I tried a few hours later.

 

[Jacob J.]

While vapor lock would be a cheap answer, it doesn't mesh with the scenario. The saw was running maybe 10 minutes, it wasn't that hot out (around 80-83) and it didn't start up when I tried a few hours later.

Going by your initial posts, I didn't think so either. I've run 394s and 3120s in the woods for years and never had one vapor lock on me, even on 100° days. Husky also reformulated the phenolic intake block on the later versions of both those saws to address the cracking/warping issues. They made it out of a softer polymer that lasted much longer.

 

[agrams]

well, things got interesting. I took off the cylinder head and really poked around, and here is what I found.

It looks like somewhere/somehow a bolt/threaded piece broke off or backed out in the crankshaft housing, started to get ping ponged around and damaged the cylinder, the piston (extensively) and the crankcase. My first concern was lean seizure, but I don't think a lean seizure would cause a bolt to get loose/backout into the crankcase. I can't reasonably think of an operating scenario or a way that I could have used the saw that would cause this amount of damage. I haven't split the crankcase in half or been able to locate the bolt that got pinged around. But at this point, at worst case I am looking at a new crankcase, new bearings, a new piston, and possibly a new cylinder. With that much damage, is it even worth fixing?

Any thoughts or input would greatly be appreciated. This was a recent purchase and I had maybe 5 hours of milling on the saw when this happened, so I am trying to rack my brain to figure out what the heck happened.

 

[Jacob J.]

The bolt had to come from somewhere. I see pieces of something down in the crankcase. Your cylinder is salvageable and I'll bet the crankcase is too. There's a number of options on the piston in the aftermarket realm. The most important thing is: Determining where the bolt came from, whether your main bearings are still good, and if the case needs to come apart.

Yeah, I knew this wasn't a fuel delivery issue.

 

[RedFir Down]

Do you have any young ones running around?

 

[agrams]

At this point, given the metal debris that I can see from inside the crankcase, and the metal chunks missing from the bottom of the cylinder, I would really want to crack the case in half to see the full extent and to make sure all the debris is removed. At that point it wouldn't be much more work to replace the main bearings.

the part that concerns me about the crankcase is it looks like a piece of it is missing at about 5 O'clock at the bottom of housing for the crank rotation. This looks like it opens the crank rotation area up to another compartment. See the attached picture for a yellow square around the spot I am talking about (it is a pain in the arse to take a good picture of, but I tried....)

 

[agrams]

I've got a 2 year old, but the saw is locked in the garage, and no one has access to it besides me. But even then, where the heck would you even open the saw up to put something INTO that compartment? I don't think you could do it any way except by pulling the cylinder. Even then, other than checking gas and oil and changing the bar, nothing got done on the saw from the time I ran it for several hours until I took it out again and had this problem after about 5 minutes of operation.

 

[Jacob J.]

I couldn't see if the crankcase was actually broken or not. If there is a break in the mixing area, then splitting the crankcase and having that welded back up is an option. I have a local guy who has done many cases and cylinders for me and the repairs usually better than the stock part.

There's a short screw that helps secure the manifold. I'm betting it was that screw that ended up going through the intake into the motor.

 

[RedFir Down]

I was just thinking out loud is why I asked that question, here is why... say you put the saw on the bench to clean the air filter, need some more bench room so you put the saw on the floor for a bit. Than junior comes by to "help" and puts a bolt in the intake horn, you start the saw and you know the rest.
But from what you said this isnt possible.

 

[agrams]

I get it redfir, and while it may be a possibility in some scenarios, my kid can't even open the door to the garage.

 

[wisecobandit]

As Jacob says as such there are no screws actually inside the crankcase to come loose to cause the issue. The other possibility which I could see is if a longer bolt was used somewhere like on the oil pump mounting which would then have excess showing in the crankcase, caught the side of the crank and snapped off but it would have fouled from the start.