076 v 090 v 880 v 3120

[Karl Robbers]

welding stihl chainsaw components

I know that I will possibly start a riot, but heres my 2 cents worth anyway.
Magnesium welds quite nicely with the Tig process. However. The alloy that Stihl chainsaws are made from contains so much assorted crap that it pops, farts and flames when you weld it and is very prone to porosity, even when cleaned. I have welded many different chainsaw components from many different manufacturers, ( I am a certified welder) and to be honest Stihl is the worst of the lot.
Come to think of it they are the only ones that I have ever had to repair the front handles on too.
Stihl may have some good features, but their weldability certainly isn't one of them:biggrinbounce2:
Back to the subject while 3120's and 880's may be coil limited to 900 and 12000 rpm respectively, don't forget where their maximum horsepower lies, in the case of the 3120 at least it is at, you guessed it, 9000rpm. The 880 would be similar I imagine.
Just something to think about.

 

[Meadow Beaver]

I know that I will possibly start a riot, but heres my 2 cents worth anyway.
Magnesium welds quite nicely with the Tig process. However. The alloy that Stihl chainsaws are made from contains so much assorted crap that it pops, farts and flames when you weld it and is very prone to porosity, even when cleaned. I have welded many different chainsaw components from many different manufacturers, ( I am a certified welder) and to be honest Stihl is the worst of the lot.
Come to think of it they are the only ones that I have ever had to repair the front handles on too.
Stihl may have some good features, but their weldability certainly isn't one of them:biggrinbounce2:
Back to the subject while 3120's and 880's may be coil limited to 900 and 12000 rpm respectively, don't forget where their maximum horsepower lies, in the case of the 3120 at least it is at, you guessed it, 9000rpm. The 880 would be similar I imagine.
Just something to think about.

An MS880 and 3120xp can both be easily changed to be non-rev limited.

 

[gemniii]

An MS880 and 3120xp can both be easily changed to be non-rev limited.

Why are saws rev-limited? EPA?

 

[BobL]

Why are saws rev-limited? EPA?

I always thought it was to reduce the possibility of engine damage. If the saw is tuned on the lean side it will rev higher than it should so it can damage the engine or even seize the saw if it used for too long in that state. It's not foolproof but apparently it saves saws.

Just removing rev limitation from a CS does little or nothing for their stock performance since they should already be operating at peak power at somewhat fewer RPM than their limit. The latest 3120 and 880 are rev limited to 9500 and 12000 rpm, with peak power at 9000 and 9600 respectively. The only way to increase the RPM at which max power is developed requires things like porting and/or muffler modding and if required rejetting the carby.

In the case of a rev limited 3120 there is only 500 rpm above the max power RPM to play with so things like a muffler mod which might make it breathe more easily might also push the theoretical max power RPM close to 9500 but having the saw operating at close to its rev limit is not ideal as it just won't develop it's full power. This is when it makes sense to remove the rev limiter. However, the 3120 also has fixed H setting so that may be enlarged as well otherwise the saw may be running too lean.

With the 880 you have 2400 rpm above the max power RPM to play with as well as having a variable H screw. This means it can accommodate mild muffler and other mods without the need for removing the rev limiter.

Max rpms are somewhat meaningless in the cut, it's the rpm at max power that counts.

 

[mtngun]

There have been reports of late model 3120's hitting the limiter while milling, and sometimes at pretty lame speeds. Apparently, some of the limiters are set pretty low.

Saws don't necessarily run at the rpm that makes max power, just as your van doesn't necessarily run at the rpm that makes max power.

The motor can exceed the max power rpm as long as there is a surplus of power. Higher chain speeds require more power, at some rpm the power required to spin the chain equals the power produced, that is the equilibrium RPM.

 

[Hillbilly3995]

I have tig welded magnesium automotive parts that had oil residue and it will not weld if it's not cleaned of all oil. If it's not clean when you strike an arc, it blows the magnesium or aluminum onto the 2 percent tungsten tip specific for welding magnesium or aluminum.
jerry-

Jerry, go back at look at your electrode box. its not 2 percent tungsten...

its mostly tungsten, the 2 or .2 or .02 percent is thorium, a radioisotope
you should be very cautious when sharpening these so as to minimize exposure and risk of inhalation of any debris. (its radioactive)

I know an old man (well, older than me) that replaced 40% of a magnesium boat prop blade with a tig torch,
when he was finished it looked and worked like a new one.

 

[mtngun]

Why are saws rev-limited? EPA?

In addition to what BobL said, the 120cc saws in particular are known to turn into a grenade if you over rev them. They just have a lot of rotating mass. Member Bob Steuwe blew up his 084 not so long ago by over revving, and not over revving that much, either.

 

[BlueRider]

Bob- nice explanation of the 4 saws. If you edit your original post to add the Displacement I think it would make an exclent sticky. There seems to be a questin every month or two asking about one or more of those four saws.

As for the rev limiter on the 075 it is probably the easiest of the batch to bypass. The rev limiter is a pressue activated jet that dumps fuel into the carb. To by-pass it all you need to do is remove the screw and place a small piece of a soda can under the screw.

 

[BobL]

Bob- nice explanation of the 4 saws. If you edit your original post to add the Displacement I think it would make an exclent sticky. There seems to be a questin every month or two asking about one or more of those four saws.

As for the rev limiter on the 075 it is probably the easiest of the batch to bypass. The rev limiter is a pressue activated jet that dumps fuel into the carb. To by-pass it all you need to do is remove the screw and place a small piece of a soda can under the screw.

Yeah I have seen that posted before about the 076, have you done it and what if so what difference does it make?

 

[820wards]

Jerry, go back at look at your electrode box. its not 2 percent tungsten...

its mostly tungsten, the 2 or .2 or .02 percent is thorium, a radioisotope
you should be very cautious when sharpening these so as to minimize exposure and risk of inhalation of any debris. (its radioactive)

Your right. Wasn't thinking.... I'm always cautious when sharpening those electrodes.




I know an old man (well, older than me) that replaced 40% of a magnesium boat prop blade with a tig torch,
when he was finished it looked and worked like a new one.

My brother and I had a ski boat and I fixed our props many times from hitting rocks. I guess I'm old... 58

jerry-

 

[046]

lots of great info in this thread!

 

[MCW]

3120; 9500 rpm coil limited, fixed H jet, outboard clutch, Outboard chain tensioner awkward to get at while saw on conventional mil and mill mounting to bar method means clutch cover must be retained, poor exhaust location.
880: 12000 rpm coil limited. inboard clutch and chain tensioner, poor exhaust location[/IMG]

Are you sure your mate's 3120 is limited that low Bob? My 2 year old Australian delivered 3120 is limited to 12,500rpm and the US versions are limited to 9,800rpm from memory. The main reason I purchased my 3120 in Australia unlike all of my other saws (sourced from the US due to price) was because of the rpm limit and no EPA garbage.
I'd say if your mate bought his 3120 in Australia and it is limited to the lower rpm's somebody has done a sneaky and imported a US saw to sell.
The US 880's are also limited less than the Aussie versions. Just like the Aussie delivered 660's have the high output oiler and dual port muffler (plus more power).

By the way, I haven't been milling lately but thought I'd drop in on the milling forum

 

[smokinj]

My 880 is stock and limited to 12500. Milling Hickory black locust and walnut. Not really thinking of modding it at all. Chain that stays sharp all day long now that would be a Sweeet Modd.

 

[MCW]

My 880 is stock and limited to 12500. Milling Hickory black locust and walnut. Not really thinking of modding it at all. Chain that stays sharp all day long now that would be a Sweeet Modd.

Is your 880 an older model mate? Sorry I should have added newer model 880's when I mentioned the lower rev limit. I know that some of the later US delivered 880's are limited to around 10,000rpm and I think Brad Snelling had video of it. The 3120's and 880's are turds with the lower limiters.

 

[BobL]

Are you sure your mate's 3120 is limited that low Bob? My 2 year old Australian delivered 3120 is limited to 12,500rpm and the US versions are limited to 9,800rpm from memory.

No I am not sure, I'm just going by the manual. Next time I'm down his way I'll get the tacho out.

By the way, I haven't been milling lately but thought I'd drop in on the milling forum

Neither have I - too bloody hot and too much else on the go.

 

[smokinj]

Is your 880 an older model mate? Sorry I should have added newer model 880's when I mentioned the lower rev limit. I know that some of the later US delivered 880's are limited to around 10,000rpm and I think Brad Snelling had video of it. The 3120's and 880's are turds with the lower limiters.

It was bought last May. Who knows how long it set. Manuel says 12,500. Sorry Just manuel out its "11,500"

 

[MCW]

No I am not sure, I'm just going by the manual. Next time I'm down his way I'll get the tacho out.




Neither have I - too bloody hot and too much else on the go.

Yeah I'll check my 3120 manual when I get home but I'm pretty sure mine says the lower rev limit too despite mine taching out higher. I'm the same in regard to heat and workload mate, got a few guys wanting logs milled but have had too many felling jobs taking priority