Ran my first tank of fuel through my new dolmar 7900 today, cutting up an oak tree that fell over the fence about 5 years ago - finally had a track hoe close enough to the fence line that he went over and plucked the tree off the fence for me, avoiding the inevidable smashed fence I would have had otherwise. Was able to bury the 20" bar into the dry oak and it cut like butter, much more power than my ps510 - will make cutting larger wood a pleasure! Made some noodles cutting large rounds in half - and worked like a dream. Can't wait till the DNR opens the state forest for cutting (sep 15)
First tank through 7900...
- Thread starter willisl64
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i would be getting a longer bar for sure. That saw can run a 32" real nice if set up right. Should pull a 28" set up as stock i believe.
I hear ya - dealer looked at me funny when I told him I only wanted a 20" bar, but I really don't have much need for anything bigger, and it really pulls through the wood quickly set up this way...in the last 3 years, I've only had 2 trees that were too big for my 18" bar on the 510, so the 20" bar should be fine. I'll buy a second bar this fall before we start the heavy cutting, and it will be a 24" - just in case we get into some bigger wood.
I've been running with a 16 inch bar on a 65cc saw for decades. Never really needed anything bigger but lately I've been thinking a 20 inch would save me a bit of bending.willisl64 said:
willisl64 said:
Did you explain to him that you drank the HearthDotCom Kool-Aid and now insist on under barring your saws?
+1
I run the 20 inch on 7900 mostly. Can cut up to 24 inch from one side and that covers 90% of what I need. Bit nose light, but handles well, and spools up much quicker with less rotating chain mass.
May not be 'cool' but it is way more functional for me.
k
I run the 20 inch on 7900 mostly. Can cut up to 24 inch from one side and that covers 90% of what I need. Bit nose light, but handles well, and spools up much quicker with less rotating chain mass.
May not be 'cool' but it is way more functional for me.
k
I also have a 7900 with 20" bar. I have had it for about a year now and with the exception of one oak I cut down this spring I haven't needed a bigger bar. 7900 is a great saw, enjoy!
You easterners with your little hardwood trees could probably get by just fine with the short bar. Here's an odd question.... if you are only engaging 12" of the bar then does it matter as far as cut speed whether that bar is 16" or 32"? Other than bar drag on the chain it would seem that the same number of teeth are cutting but then I hear you folks say that it cuts faster with a small bar.
I guess in theory the cutting force should be the same in 12 inch wood whether 16 bar or 36 bar. The drag friction (bar and air) will be more with the extra length top and bottom run. Sprocket friction will be the same either way. I have to think the added friction, in proportion to the wood cutting load, would be fairly small. However, we are talking very small numbers of torque and force (just high rpm) so maybe there is a signficant factor in the extra drag. I dn't think it is much or very noticeable though.
Just personal opinion, but I don't think the average cutter could notice the hp loss between long and short. Chain sharpness is way more important.
I think the differences are more personal preferences due to the following regional differences:
-Smaller trees, thus don't need the bigger bar length much. Why carry it, or balance it. For example: SawTroll is from Norway, they run bars really short there, his setups match the needs of that area.
-More hardwood and dead wood, so a bar works harder for a given tree size.
-For the occasional large tree where the bar would be buried, longer bar would pull harder and maybe overpower the motor.
-More limbing and maneuvaring around differently with hardwoods than softwoods, so the long bar is at a disadvantage. Sort of like long barrelled shotgun in open country for geese vs. in the thickets and swamps for deer.
-Longer bar for reach can be nice for limbing and bucking small stuff on the ground. Which contradicts what I just said.....
-Firewood hardwood cutters do more limbing and moving than western fallers and loggers.
-What I really notice is the momentum and inertia difference to spin up the chain. I have to think it loads the clutch a bit more also. Comparing a 16 and 20 on my 026, the 20 (which I usually run for other reasons) is much more sluggish to spool up. It takes a blip and fraction of second pause before limbing. Doing that many times a minute gets a bit aggravating, but just the tradeoff. Same story on the dolmar. Brings a 20 inch up to cut speed in an instant, just takes a noticeable but slightly longer time on the longer bars. Course it is not a limbing saw anyway.
It does sound wierd for me to run an 026, for limbing, with 20, where the spoolup time is important, but also have the 7900 at 20 inch, where time is not so important. They look strange setting side by side. 'So why did you bring two saws of the same size....'
Ultimately, I think it is all about personal preference. Sure is handy they make assorted bars to fit the same saw.
kcj
Just personal opinion, but I don't think the average cutter could notice the hp loss between long and short. Chain sharpness is way more important.
I think the differences are more personal preferences due to the following regional differences:
-Smaller trees, thus don't need the bigger bar length much. Why carry it, or balance it. For example: SawTroll is from Norway, they run bars really short there, his setups match the needs of that area.
-More hardwood and dead wood, so a bar works harder for a given tree size.
-For the occasional large tree where the bar would be buried, longer bar would pull harder and maybe overpower the motor.
-More limbing and maneuvaring around differently with hardwoods than softwoods, so the long bar is at a disadvantage. Sort of like long barrelled shotgun in open country for geese vs. in the thickets and swamps for deer.
-Longer bar for reach can be nice for limbing and bucking small stuff on the ground. Which contradicts what I just said.....
-Firewood hardwood cutters do more limbing and moving than western fallers and loggers.
-What I really notice is the momentum and inertia difference to spin up the chain. I have to think it loads the clutch a bit more also. Comparing a 16 and 20 on my 026, the 20 (which I usually run for other reasons) is much more sluggish to spool up. It takes a blip and fraction of second pause before limbing. Doing that many times a minute gets a bit aggravating, but just the tradeoff. Same story on the dolmar. Brings a 20 inch up to cut speed in an instant, just takes a noticeable but slightly longer time on the longer bars. Course it is not a limbing saw anyway.
It does sound wierd for me to run an 026, for limbing, with 20, where the spoolup time is important, but also have the 7900 at 20 inch, where time is not so important. They look strange setting side by side. 'So why did you bring two saws of the same size....'
Ultimately, I think it is all about personal preference. Sure is handy they make assorted bars to fit the same saw.
kcj
Thanks Kevinj, that's what I was thinking. I find the balance of the saw to be very important since I don't want the bar spinning up into my head or down into my feet. On my oober heavy 290 the 20" balances pretty well with slight nose bias.
I run a 20" on my 7900 almost all the time. I have a 28" that I will mount if I need to cut big wood, but I would say that is less than 5% of my use... OTOH, I DO use the the 7900 for a limbing saw quite frequently - if I use it to drop a tree, I buck and limb with it as well, rather than swapping to my Pull-on.... OTOH, if I know that the next batch of cutting will be all brush and limbing, I might grab the Pull-on for a change.
You want to try no effort cutting, go for a 2" branch w/ a 7900, pull the trigger and let go, by the time the saw spools up, you have finished the cut... It's only above about 3-4" that you actually have to hold the trigger down for longer than it takes to pull it...
IMHO the 7900 is just about perfectly balanced with a 20" and full comp chisel - if I hold it by the just the top bar, it seems to naturally hang with the bar tip down about 5-10* from horizontal.
As I've said before, the 7900 is overkill for the majority of my cutting, I probably could do just as well for 90%+ of it with a 5100 and a 16 or 18" bar, but I was essentially looking at the "one saw plan" and wanted a saw that I knew could handle 100% of my needs if it had to.
Gooserider
You want to try no effort cutting, go for a 2" branch w/ a 7900, pull the trigger and let go, by the time the saw spools up, you have finished the cut... It's only above about 3-4" that you actually have to hold the trigger down for longer than it takes to pull it...
IMHO the 7900 is just about perfectly balanced with a 20" and full comp chisel - if I hold it by the just the top bar, it seems to naturally hang with the bar tip down about 5-10* from horizontal.
As I've said before, the 7900 is overkill for the majority of my cutting, I probably could do just as well for 90%+ of it with a 5100 and a 16 or 18" bar, but I was essentially looking at the "one saw plan" and wanted a saw that I knew could handle 100% of my needs if it had to.
Gooserider
Wasn't trying to cause problems...just excited about my saw. For those of you offended by my 20" bar, pretend I said 28"...if it really makes you feel better about the whole deal. Or better yet, 32" with full comp chisel. "Wait a minute, you mean to tell me you pull 32" full comp with a 7900..." Here we go again.
willisl64 said:
The rule of thumb that I like to follow is to try and stay with between 3 and 4 cc's of engine per inch of bar... I think I first saw this mentioned on arboristsite, but it isn't just my idea. A 20" bar on the 7900 is right at 4cc/inch for the low side size, and the 28" is pushing a little past that at 2.8cc / inch for the upper size limit (26" is exactly matched at 3.04cc/inch) Dolmar says you can pull a 32" on the 7900, but IMHO that is pushing it a bit at 2.47cc/inch, I'd probably go with skip chain if I put more than a 28" on the saw...
By the same token, I put a 12" bar on my 36cc Pull-on, for exactly 3cc/inch and that makes it work relatively well - especially when compared to the 16" bar (2.25cc/inch) that came on it stock... With the short bar and full chisel chain, it's a little wood eating monster, but makes me have to spend most of my cutting time bent over or at full arm reach in order to get at the stuff I'm trying to cut - it's a lighter saw, but requires a more stressful working position, so it's a toss-up as to which is more tiring to use.
Gooserider
Don't now about easterners but one of the last trees I cut with my 681 (close to this saw) was about 38" in diameter. I have a 28" bar and the saw ran through like butter. Would I want to walk the forest with this saw, no, but when needed, I'll cut once instead of twice.Highbeam said:
The saw is spinning the same amount of teeth no matter what, you should use the smallest amount that can get through the wood. More teeth equals more spinning to get the same tooth around. I hope this makes sense.
Chad
Don't get down on yourself for running a 20" bar on that saw. Heck, I ran a 20" on an 066 most of the time when running it for firewood duty. The fact that the Dolmar is equally happy with an 18-20" bar or a 28-32" one is what makes saws in this class so versatile. Unlike our west-coast friends, we aren't usually walking conifer trunks, limbing down around our toes, so the longer bar is rarely an asset and often an encumbrance.
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