Bigger Bars

[NickinMids]

Is there a method of assessing what is the biggest bar a saw can use other than manufacturers recommendations or is it just trial and error. My saw has 16 inch and MR say can go up to 18 inch, but on net I have seen people with 20 inch bars working fine. Is the drive sprocket/ engine capacity the key.

[Gus McWilliam]

Take the CC of the engine and divide by 3 I believe

[agg221]

There are several things which you can vary in theory. In practice, not all the parts are available to do them all.

 

Bar mounts: what is the longest bar which fits the mounts on your saw and lines up with the oil holes, assuming you're not inclined to re-drill these? Some saws share the same mount, so in theory you can fit the longest bar available for the biggest saw to the smallest saw. For example, the Stihl MS660 and 034 share the same mount so you could in theory fit a 42" bar to an 034....

Power: What will it physically pull? Longer bars mean more friction so more of the power of the saw goes into pulling the chain round. This means there is less power for cutting. This means counter-intuitively that the longer the bar, the narrower the cut the saw will actually handle. A smaller capacity saw will not pull as long a bar.

Torque vs. revs: There is a power curve for torque vs. revs, so the faster your saw is pulling the chain the less torque available, so the easier to bog it down. If you use a sprocket with fewer pins it will slow the chain down, so although it will cut more slowly it will not bog down.

Chain pitch: smaller pitch chains bog down less as they take a smaller 'bite' but cut more slowly.

Chain type: the fewer teeth engaged in the wood, the less power needed to drag them through so semi-skip or skip tooth chain will allow you to run longer bars.

 

For the ultimate then, you would find the biggest saw you could with the same mount to identify the longest bar physically made (with a replaceable nose sprocket), use 3/8" lo-pro chain in skip configuration and associated sprockets and use the clutch sprocket with the smallest possible number of pins, which would mean running a rim sprocket and finding one with the right splines to match. I'm not convinced that this would let you run a 42" bar on a 50cc saw, but it might. It would be slower than a very slow thing though!

 

Alec

[miker]

ported engines,sprockets,skip chains will allow bigger bars on smaller engined saws

[Logit]

and the longer bars need increased oil flowrate, so the oil pump could also be a limiting factor. If the saw has a variable flow rate pump, then set it to max for the longer bars. It is also possible with some saws to fit a higher flow rate oil pump.

[wisecobandit]

Maybe worth mentioning what saw it is you have? Im sure most of us have experimented with bar length.

As Gus said a good rule of thumb is 1" to every cc of the engine tho. Obviously as said ported, muffler mods etc make a difference.

[adowning7]

I have just inherited some large beech butts and need to get the biggest bar possible, the Stihl catalogue says 25 inch max for my 441 (71cc) but having read this thread and looked around I can get a 30 inch bar to fit.

 

Has anyone ran a 30" bar on a 71cc saw or will I be biting off more than I can chew?

[Steve Bullman]

Maybe worth mentioning what saw it is you have? Im sure most of us have experimented with bar length.

As Gus said a good rule of thumb is 1" to every cc of the engine tho. Obviously as said ported, muffler mods etc make a difference.

 

cm I think you mean

[agg221]

I have just inherited some large beech butts and need to get the biggest bar possible, the Stihl catalogue says 25 inch max for my 441 (71cc) but having read this thread and looked around I can get a 30 inch bar to fit.

 

Has anyone ran a 30" bar on a 71cc saw or will I be biting off more than I can chew?

 

I have run a 36" bar on an 044 once - I don't wish to repeat the experience. Basically, anything which fits the 660 will fit the 441.

 

If you need to run the bar to make a small number of cuts for ringing up, I would get a skip-tooth chain to go with it. Halving the number of teeth in contact with the wood has a significant impact on the load on the engine.

 

Not common in the UK but Rob D may have some left.

 

Alec

[peatff]

cm I think you mean

 

You mean this 40" bar I just bought isn't going to work on the 135 then