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General Product Question

    Mary Louise Smith
    I have a Husqvarna 455 rancher with 20 inch bar. I purchase...escalated
    General Product Question posted August 25, 2013 by Mary Louise Smith 
    10145 Views, 11 Comments
    Question:
    I have a Husqvarna 455 rancher with 20 inch bar. I purchase the Husqvarna chains for it. The chains get stretched after about 3 or 4 tightenings. Why? Plus when I put on a new chain, it takes up at least half of the area allowed for future tightening and adjusting. Is it the chains? I don't see the need for a new chain so soon all the time. What is happening? This is less than a year old chain saw.
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    Answer

     

    • Karla

      Mary Louise,

      A few things to check, stamped on your bar should be some numbers, and one of the numbers will be the drive links. On a 20" bar the drive links should be 68 DL for a 3/8 pitch, or 72 DL for a .325 pitch chain. After you read the DL number on the bar, then count the drive links on the chain. The model 455 will accomodate two different chain pitches but its important that everything matches, starting with the drive sprocket (pitch), Next, the bar (pitch) especially if the bar has a sprocket nose, and finally the chain pitch, Do Not Mix and match pitches.

      Next, the possibility of stretching a chain, yes the chain will stretch. You can minimize this by making sure the bar is getting plenty of lubrication, on some of the Model 455 chainsaws there is an adjustable chain oiler, if your using a 20" bar then the oiler should be turned up to Max oil position (Check owners manual for this adjustment).

      Finally, Tension of the chain, many users over tighten their tension, I think they believe the chain will stay on the bar better if they tighten the tension. I have even seen tensioners on chainsaws where they have bent the tension screw, tightening the chain - Ugh, and don't do that! The Bar nuts are what holds the chain in position, and yes they need to be tight, but the tension afjustment does not need to be that tight, so loosen it up a little, make sure the drive links are completely in the groove when tensioning but thats all. Also, only tension a cold bar and chain. You mentioned stretching a chain, Yes if you keep tightening the chain on a hot bar trying to continuously take up the slack, you will stretch the chain. A tight chain, or not enough oil creates heat on the bar, even without cutting anything, the heat then allows the chain to stretch, so the key is to reduce the heat.

      Also as a chainsaw is being used it is normal for the chain to develop a little slack as long as the drive links are not hanging completely out of the bar, where the chain could then possibly come off the bar. A good check after tensioning a cold chain and bar, is with a gloved hand pull on the chain after installation, two or three pulls the length of the bar, and the chain should pull and move freely, If it does not you may have the tension too tight, and you may need more bar oil.

      I hope this helps.

       

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    • Mary Louise Smith

      Thanks for the information. I ended up putting on a new bar and chain. Plus I did change the oil setting. So far so good. I had put that chainsaw through the mill. There were things that needed to be taken care of and removed, even at the cost of a few chains and a new bar at the end of the job. Not all trees to be removed or downed ones are in good spots to make it easier on operator and chainsaw. At least I can say a job well done and finally over! Thanks again for the helpful hints.

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    • Lou Miller

      I have the same saw, and the same problem as Mary Louise, and am a bit confused by your explanation of the numbers on the bar.  The numbers on my bar (which is original) are      3/8   72 DL   107799 NF     Assuming the 3/8 is chain pitch,  this appears to contradict your saying that it should be 68 DL for 3/8 pitch.  My replacement chain is an Oregon D72, which has 72 drive links and is 3/8 pitch.  How does one determine the pitch of the sprocket?  I'm not over-tensioning, and the chain oiler is oiling as it should.

      I've had this saw for a couple years, and am quite pleased with it, except for the tension adjustment being half used up  with a brand new chain.

      What am I missing?  Any clarification would be much appreciated.  Thank you.

       

      Lou

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    • Karla

      Lou, and Mary Louise,

      Oops - I may have goofed on the Info that I provided. Always use the Info provided on the bar, I also use a website "Oregonchain.com", It has a selector guide to help with finding bars and chains, and also the following link, which will provide sprocket Ino: /pdf/pro/pro_home.htm

      I double checked, and I have No clue where I got the 68 drive links from, unless I typed in the wrong chainsaw model or transposed something.

      Anyhow, Lou  you are absolutely correct, the Chain should be 72 drive  links, sorry  Mary Louise and Lou for the error and thanks for the correction.

      The drive Sprocket pitch is primarily determined by the number of teeth on the drive sprocket and the diameter of the gear, The easiest way is to check the number stamped on the drive sprocket, and compare it to the  selector guide link. Also If you have an IPL parts list, which you can download from the Husqvarna site, by entering your model number. You will notice on the parts list for the model 455, that there are two different drive sprocket part numbers, a .325 pitch (part#  537291702 ) and a 3/8 (part # 537291602). The important digits are the "17" which is ,325, and "16" which is 3/8 drive sprocket. Oh, I just checked three drive sprockets for a 3/8 - 7, which is a 3/8 pitch with 7 tooth and measures 1.37 inches in diameter around the gear, I don't have a .325" one to make a comparison measurement of the gear, but I suspect it will be a little smaller in diameter, but the difference will be very slight since 3/8 (.375) and (.325) are very close. I hope this makes sense.

      Oh, just to confuse matters the Part # "......16..."  3/8 and Part# ".......17...." .325 both have the same number of teeth which is 7 tooth, on some pitch changes they change the number of teeth, ( like to 8). On the three Drive Sprockets that I looked at they all were stamped with the part number and the pitch size (3/8-7) but I know that is not always the case, and would make it to easy.

      I hope this helps!

      Again sorry for the confusion, and It would have been easier If Husqvarna only made the Model 455 in one pitch.

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    • Karla

      Lou, and Mary Louise,

      Please see attached photo of different model 455 drive sprockets, also these do not have the husqvarna part number.

      Also note: They are both 7 tooth sprockets, but the size is stamped on the drums of the spur gear.

      I hope this helps.

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    • Lou Miller

      My solution was the same as Mary Louise's.  I replaced chain, bar, and sprocket (which appeared to be pretty beaten up), and increased the chain oil flow from medium to high.  I am still put off by the tension adjustment travel being half gone even with all new components, but at least the chain is no longer stretching like a rubber band.  Thank you all.

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    • TRACY LAMANEC

      I have had the same problem with my Rancher 460.  The original bar had a replaceable sprocket tip and is slightly longer.  Replacing the whole bar cost less than replacing just the tip on the old one when it went bad but that's when the trouble began.  Both bars are marked for 72 drivers, 3/8" pitch, 0.050"  gauge. I have been using 70 driver chains with a 20" bar from my old McCullough 3.7 CID saws.  They were great saws in their day but they have been retired in favor of the Rancher 460.  I think my drive sprocket has seven teeth and there may be one with eight, both 3/8" pitch.  I came across this forum while trying to research that.  

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    • Karla

      Tracy,

      Yes - There is a 7 tooth and also an 8 tooth drive sprocket, which both have the same 3/8 pitch. but this is because the diameter of the 8 tooth is just a little larger in diameter. Which actually does a number of different things, and gets very chainsaw "geeky" but I will try to explain, by going to a larger diameter drive sprocket like the 8 tooth, you will slow down the speed of the chain. If you slow down the speed of the chain, then you increase the torque of the chain, which some professionals like having more torque. There is a relationship between an Engines Horsepower, Speed & Torque, and a formula that relates the three variables. You can probably google "Horsepower Formula" If you are mathematically interested in the relationship.

      As far as the pitch doesn't change because you are putting more teeth into a larger diameter, and the pitch is determined by the diameter of the Gear (hence drive sprocket or nose sprocket) divided by the number of teeth, which keeps the angle of each tooth at the same pitch. Another google, and you can find the mathematics for calculating a Gears Pitch.

      Ok - I am not trying to be overwhelming, but pitch is an important factor when driving a chain on a bar, and unfortunately chainsaw manufacturers use different pitches, Even some chainsaw models that are available in multiple pitches, so that is why you need to be so careful with changing the bar and chain, or using a chain from another chainsaw. 

      Also, Not to complicate things further but a "Nose Sprocket" also is a Gear, and will come in different number of teeth, depending on the diameter of the nose (ie like the nose on a wood carving bar. will have less teeth because its smaller in diameter). That is why it is important to check the "Pitch" that is stamped on a bar because it relates to the number of teeth in the nose sprocket. A typical 3/8 pitch bar will have 11 teeth in the nose sprocket but that is Not always the case. 

      To Measure Pitch you would have to have a special set of gauges which measure gear pitch, or Calculate the pitch.

      I hope this helps, and makes sense. If I can help in any other way please let me know.

      Karla

      PS. I am Not a Husqvarna Representative or a Repair Service just an experimental chainsaw person

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    • TRACY LAMANEC

      Karla,

      Thanks for your input but I think you are a little off base.  An 8 tooth drive sprocket will result in faster chain speed and less torque than one with 7 teeth, (both 3/8" pitch).  For a given RPM, the chain will move 8 teeth (3 inches) per revolution as opposed to 7 (2-5/8 inches).  Measuring pitch is not complicated, no special gauges needed.  On a gear/sprocket, it is the number of teeth divided by the circumference, not the diameter.  On the chain, it's simply the distance between drivers.  To get a more accurate measurement, measure across several drivers with the chain laid out straight and divide by the number of spaces between drivers  If the pitch of the sprocket is not the same as that of the chain, they will not mesh.

      Back to the original problem, as I noted, the bar with the replaceable sprocket nose is a little longer than the one piece sprocket tip bar, though both are marked 72 drivers, 3/8" pitch, 0.050" gauge.  I think going from a 7 tooth sprocket to an 8 would compensate for that difference. 

      You have aroused my curiosity.  Just what is an experimental chainsaw person?  Do you design or customize them?

      Tracy

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    • TRACY LAMANEC

      Karla,

      Sorry, it was late last night.  I meant to say, divide the circumference by the number of teeth on the sprocket, not the other way around.  Anyway, it's the circumference, not the diameter.

      I think I have found both the replaceable sprocket nose tip kit and the eight tooth 3/8" drive sprocket on the Bailey's web site.  I will call them to discuss this issue before ordering.  I think the 7 tooth sprocket needs the longer (replaceable tip) bar.  The one piece bar that the dealer sold me is at the limit of chain tension adjustment with a new 72 driver chain.  Once the chain is broken in it won't stay on the bar.

       

      Tracy

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    • Karla

      Tracy,

      Thanks for the correction on speed reduction, and Yes that is correct, I guess I have been spending too much time on my bicycle. LOL. Also most Engineering equations use "Diameter" or "Radius" in their equations because (PI) or 3.14 ..... is constant for calculating circumference, and for some reason my brain thinks in diameters, Although I am sure there are equations that use circumference too. I am Not an Engineer, and Do Not work for Husqvarna or for any repair service, I enjoy analyzing chainsaw problems, and Hence "Experimental Chainsaw Person" , I take them apart and like to find the problems and solve why it is not working correctly. Your problem with the chainsaw bar sounds like an interesting problem, but I am Not sure I totally understand the problem, but I do know there are many Chainsaw owners that are probably baffled by all of the combinations of bar lengths, chain sizes, chain pitches, bar gauges, different manufacturers of bars and chains, and the various different purpose bar and chains, and I probably forgot one or two of the variables that go into that equation, In most cases an individual just wants to know what part number do I use for the bar or chain, and where do I get one. Oh, the other variable the age of the chainsaw, over time things change, like bar design, chain design, and shapes of bars and cutters and chain links, Anyhow, Good Luck with your pursuit, to finding or creating the correct bar, and sorry I can't be of further help. Please let me know what you find as a resolve, I am always curious as to what is the solution.

      Karla

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