Chain tension tight then loose at another spot

[Ford3000]

I put a chain on a new to me saw today, as I checked the tension it would be
slightly tighter at one point then loosen up slightly as I pulled it around with
the help of a screwdriver behind the cutters.

I have only had one previous saw that did this and I sold it because I feared
the shaft must of been out of true, and that this would be bad for the bearings
and ultimately lead to increased vibration stress and failure of the moving parts.

This was using a new bar and chain, I even used a second new chain to rule out
a chain issue.

Am I worrying about nothing here, my two EA4300 saws had no such runout,
and they were smooth in the hand to use, I have not started the new to me saw
yet as I may be returning it, so I have no way of experiencing what effect this
slight runout may have. The saw is fitted with a Sprocket and a Sprocket nosed
large radius bar, maybe the sprocket on the clutch drum is the culprit, I cant strip
this saw down as I am concerned about returning it in the same condition I got it
if I need to.

 

[Canadian farm boy]

How worn is the sprocket?

 

[Ford3000]

How worn is the sprocket?

Its all new, the saw in question is an Efco MT5200, new saw, and new to me.
It came at a good discount, even so if I though thee was going to be trouble now would be the time
to send it back.

 

[Ford3000]

The saw says assembled in Italy, so I was hoping it would be a cut above their siblings
that are made and assembled in China, am talking of the MTH models, its odd that they
are made in China, yet have a full metal case and yet they sell for a lot less than the MT models do.
Right enough the piston in the MTH models looks very lightly built, and not too refined,
that's why I ventured on the MT model, which does have better components, albeit in a plastic
case rather than metal.
The plastic on this MT5200 is real light, I would say the first accident with it falling will
be the last too, nothing like the Stihl Husky or even Echo plastic on this saw.

 

[Nutball]

I have had uneven tension caused by a slightly off center bar nose sprocket. I still put a lot of use on it. Sometimes the chain can get uneven stretching too, I still run those chains.

 

[dahmer]

Off center rim on the drive gives same symptoms.

 

[Ford3000]

I have had uneven tension caused by a slightly off center bar nose sprocket. I still put a lot of use on it. Sometimes the chain can get uneven stretching too, I still run those chains.

Hi @Nutball , what do you mean by off center, is it the nose sprocket that is slightly to the left or right of the bar,
I don't think that a sprocket too high up or down on the vertical plane would cause any issue as it would remain there all the time and cause no lengthening or shortening, the side to side off center I never experienced yet.
All the chains and bar are new, so the chain didn't get a bad tug on anything to stretch a few links, even it did, why would it be loose then tight on the bar.

 

[Ford3000]

Off center rim on the drive gives same symptoms.

That's what I would think too, just waiting on the seller to advise
whether or not to try and find the exact cause or return it, I don't
want to go messing with it less I have to.

 

[kneedeepinsaws]

I have had chains with loose and tight spots, in my opinion pretty normal. The more you run that chain the more it will all loosen up evenly.
At high rpm’s if you are getting violent kick back or getting the chain pinched I’ve found leads to irregular stretching.

 

[Ford3000]

I have had chains with loose and tight spots, in my opinion pretty normal. The more you run that chain the more it will all loosen up evenly.
At high rpm’s if you are getting violent kick back or getting the chain pinched I’ve found leads to irregular stretching.

Hi @kneedeepinsaws
What I mean is, when rotating the chain around the bar, it will be tight to the
bar and won't lift up much when tried, then rotate the chain a half turn and it
will be loose enough to lift off the bar with a lot less effort.
These chains have been steeping in a sealed plastic container containing 3 inches of clean engine oil since new, about two years old now.
I will try on the bar and chain that came with the saw, if I get the same result I will know its not the bar or chain. Annoying when these things come along, hopefully it will be a simple fix.

 

[kneedeepinsaws]

Hi @kneedeepinsaws
What I mean is, when rotating the chain around the bar, it will be tight to the
bar and won't lift up much when tried, then rotate the chain a half turn and it
will be loose enough to lift off the bar with a lot less effort.
These chains have been steeping in a sealed plastic container containing 3 inches of clean engine oil since new, about two years old now.
I will try on the bar and chain that came with the saw, if I get the same result I will know its not the bar or chain. Annoying when these things come along, hopefully it will be a simple fix.

I hear you, and that’s what I understood you said

 

[Nutball]

The bar sprocket may have its hole machined slightly off center, so it actually sticks out farther when turned one way, turn it 180deg and it will stick out less, so it tightens and loosens the chain as it spins. The uneven tension interval should be based on the amount the sprocket rotates. If it changes based on a full revolution of the chain, then the chain is stretched unevenly.

 

[pbillyi69]

if both chains do it then there is an issues with one of the sprockets or the clutch drum being worn uneven. how does the clutch drum and sprocket look? if only one chain did it i would say its the chain. what kind of bar is it?

 

[Ford3000]

The bar sprocket may have its hole machined slightly off center, so it actually sticks out farther when turned one way, turn it 180deg and it will stick out less, so it tightens and loosens the chain as it spins. The uneven tension interval should be based on the amount the sprocket rotates. If it changes based on a full revolution of the chain, then the chain is stretched unevenly.

Thanks for pointing this out, I understand what you mean, anything seems
possible, I will try a different bar and see if the issue goes away.

 

[Kiwioilboiler]

Sorry, someone has to ask...
Rim, chain and bar nose sprocket are all matched in pitch ay?

 

[Ford3000]

if both chains do it then there is an issues with one of the sprockets or the clutch drum being worn uneven. how does the clutch drum and sprocket look? if only one chain did it i would say its the chain. what kind of bar is it?

Hi @pbillyi69
It is a new saw, so the clutch drum should be good, I did not see anything wrong with it, though measuring it may tell a different story.
The bar is a Carlton 01W, that is Carlton speak for a K095 mount,
it is a few years old but never used, other than I put it on a Shindaiwa 490
which I bought it for, I took it off because bar oil came out around it in bucket loads, and I could not find a reason for this, it was modified to fit the Shindaiwa by cutting a slot from the tension-er hole in the bar to the K095 oil hole in the bar, all surfaces were smooth and clean, yet a lot of oil came from somewhere, I took it off and put on the longer original Shindaiwa bar and oil problem went away.

 

[Ford3000]

Sorry, someone has to ask...
Rim, chain and bar nose sprocket are all matched in pitch ay?

They seem to be, its an outboard clutch so not easy to know / see, but its from
the factory, untouched, I know the bar and chain are .325, don't want to
be taking off the clutch as I have no tool to do so.

 

[kanscruzer]

They seem to be, its an outboard clutch so not easy to know / see, but its from
the factory, untouched, I know the bar and chain are .325, don't want to
be taking off the clutch as I have no tool to do so.

Rim sprocket is my worldly & wise guess

 

[pbillyi69]

i misunderstood I thought it was a new to you saw not new out of the box. if it hasent been run yet there just may be rough spots some place it may just need to be used for a bit and sort itself out. you will know if something is out of whack pretty fast

 

[huskihl]

Sometimes rims sprockets can have little boogers in them that won’t let the drivers set down in completely. I would run it a little bit and see if it gets better