3120xp Husqvarna Flywheels

[Thejdpuller]

I bought a used flywheel to replace the one on my saw. The new to me flywheel appears to be the same (fins, magnets, key placement, crankshaft hole size etc etc they seem to be exactly the same, even the part numbers stamped in them are the same. However, the new to me replacement flywheel has a bolt and spacer on the bottom of it, my old one doesn't. On all of the parts diagrams I look it it doesn't show that, or even have that as an option even when I look at the 3120k parts diagrams. The bolt and spacer are removable. My question is, should I remove it since my original one didn't have it, or leave it on there. I know single cylinder engines aren't super balanced to begin with, but if that is what this bolt and spacers function is I hate to remove it. Thanks in advance.

 

[s sidewall]

Strange way to try to balance a flywheel. Seems like it would hit something and throw it out of balance.

Steve

 

[Thejdpuller]

Strange way to try to balance a flywheel. Seems like it would hit something and throw it out of balance.

Steve

I have had the flywheel on the saw and it doesn't hit anything when spun by hand. I agree it is very strange. I know these saws really spin and this is highly unscientific and probably pointless, but I did take the flywheel and hung it on a nail and spun it. With or without the weight it doesn't always stop in the same spot. I figured if it was there for balance it would possibly always stop opposite of that and that was on there as a balance of some sort, but that doesn't seem to be the case. The local husky dealer has never seen or worked on a 3120 but he said he hasn't seen a flywheel like that with something tied into the back. I have no idea what it came off of but like I said any year 3120xp or 3120k it doesn't show that in a parts break down. Like I said everything else about the flywheels including the numbers stamped in the bottom and the magnets are the same.

 

[tomdcoker]

I think that I have seen that on a flywheel some years back, not sure and not sure what saw. The only possible reason for it would be to balance it (I think). If you have a balance for a mower blade try it on that and see what it looks like. Tom

 

[s sidewall]

Most the time flywheel are balanced on a machine which detects the imbalance, it also shows how much weight needs to be removed, then the holes drilled and hollow or something heavier than aluminum is added. I've never seen one like that on any saw I have ever worked on. Hard to say run it or not, unless you want to try and see what happens. It's your saw, me, I'd be kind of hesitant.

Steve

 

[s sidewall]

If you had and electric motor it would mount to and spin it up to see if any vibrations are felt. If it vibrates, I would not run it.

Steve

 

[SawGarage]

I have seen this on 338XPT flywheels...

My presumption is it was to make the flywheel as a whole heavier for more torque through kinetic energy....
I can't see this as a concern with a 118cc saw, though...

Make sure it's secure, install and start... if it vibrates, shut it down.

What is wrong with your old one?


J

 

[pioneerguy600]

I have seen this on 338XPT flywheels...

My presumption is it was to make the flywheel as a whole heavier for more torque through kinetic energy....
I can't see this as a concern with a 118cc saw, though...

Make sure it's secure, install and start... if it vibrates, shut it down.

What is wrong with your old one?


J

Two fins broken off the original.
I have never seen a flywheel that would need that much weight added or removed to balance it, I would remove and toss it. It looks like something backwoods/backyard engineered component.

 

[jr27236]

I have seen this on 338XPT flywheels...

My presumption is it was to make the flywheel as a whole heavier for more torque through kinetic energy....
I can't see this as a concern with a 118cc saw, though...

Make sure it's secure, install and start... if it vibrates, shut it down.

What is wrong with your old one?


J

counterweights are designed to offset the weight of the rod and pistons. You have the weight of the crankshaft and the pistons and rods on that engine that is very large and possibly needed some external counterweight to possibly achieve a true balance.
But on the other hand they also bring around more crank torque im sure. As for yours needing them I'd say no because you didnt have it. If the flywheel is the same otherwise. On another hand was it put there to just balance THAT flywheel??? Hmmm im back to 0.

Im gonna say that weight is there to balance THAT flywheel.......but i might be wrong lol
Can you remove that weight and see if that flywheel stops at one point all the time (heavy point on bottom) just put it on a dowel and spin. Then reinstall the weight and try again. Make sure if needed the weight get locktighted in.

 

[SawGarage]

I have seen this on 338XPT flywheels...
J

I retract my original statement: I did not actually open the picture and take a look at said counterweight on the 3120 flywheel… That is definitely some custom fabricated/additional item; not a factory part like the added weight plate on the back of the 338 flywheel...

 

[jr27236]

I retract my original statement: I did not actually open the picture and take a look at said counterweight on the 3120 flywheel… That is definitely some custom fabricated/additional item; not a factory part like the added weight plate on the back of the 338 flywheel...

But why would anyone add a weight like that onto a flywheel? If that thing ever let go I could only imagine its outcome.

 

[SawGarage]

If we are talking about the 338 factory weight, it's not much beyond the realm of what the factory does with the magneto's for heated handles...

My thought is like perfectly secured small loads to the back of a small truck, or in a pickup truck bed... by the time that part becomes a real concern, we would have much more to worry about!

That custom weight.. well, I assume they locktited the screw