Loose-tight-loose chains?

[Wolfie]

Anyone knows why this happens?

[dan494]

Is the saw oiling properly? Just had this with a 200t, changed the oil pump this morning and fixed it

 

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[Peter]

1. Lack of oil, usually from clogged pump, either causes overheating, or the links of the chain to kink up.

 

2. A very worn sprocket.

[spudulike]

Hi Ed - yes, lack of oil from the pump is the most common cause and the simplest to see, the chain will sound like the tracks of a tank - squeeky, notchy and dry and there will be no oil residue on the chain - it should mist oil when the saw is reved flat out with the sprocket tip pointed at a clean piece of wood.

 

A worn sprocket can cause it - usually if you pull the chain backward and it feels real bad, the sprocket is worn.

 

In an extreme case you may have a slightly bent crank shaft, damaged needle sprocket bearing or very worn nose bar sprocket. Oh - or a real bad chain that has seen use with a very worn sprocket!

[blazer]

Had this problem with a ms260 when new 7 yrs ago - never found out the cause, just had to keep checking it.

 

Sometimes if everything is ok wear wise or crud in the sprokets, it could be simply the expansion difference between the bar and chain - check it cold before starting, again when hot and when cooled down in case it contracts and puts too much tension on the crank bearings.

 

Plus I have found all chains (bikes included )will stretch unevenly, cheaper ones are worse so spin and check when adjusting tension.

[WorcsWuss]

Alternative...

Do you mean your chain is loose, you tighten it up, start to cut and it goes loose again straight away...? A bar can 'droop' when the side panel is loosed for adjustment causing it to appear tight when you wind it out a bit, but as soon as you put some weight and load on it the bar levels out and the chain goes slack again, the chain naturally trys to lift the bar up as it's running.... lift the nose of the bar a touch when you tighten the chain [or try overtightening it and watch the nose lift to see the difference it makes], make sure it's aligned then back it off a fraction before tightening up the side panel nuts...

'S what I found anyway...

[Wolfie]

1. Lack of oil, usually from clogged pump, either causes overheating, or the links of the chain to kink up.

 

2. A very worn sprocket.

 

Yes, i did think about both of these when it was happening today.

 

The sprocket is a bit worn but not the worst that i've used. The chain did look a bit dry and has probably had it's last sharpen.

So I think a new chain and sprocket and while the sprocket is off I will have a look at the oil pump. Fingers crossed, that should sort it.

 

Many thanks all.

[Al Smith]

A bent driver on the chain can cause that same thing .If let go long enough it can take out the clutch side bearing also .

[pleasant]

Never considered you could have the incorrect drive link thickness chain fitted. When cold would fit ok in your bar groove, but when in use would heat up and expand in the groove causing the chain to tighten and then loosen off when cooled?