Chain melting plastic guide bumpers?

effigy

effigy

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So I have a Stihl MS 391.
I have the chain oil valve fully open and the oil tank drains along with the fuel tank during use.
I verify oil gently sprays a surface if i rev the throttle with the chain spinning an inch or 2 away from that surface
I'm using Stihl's bar & chain oil sold at my local dealer yet I've noticed what's depicted in these photos...
this can't be normal...
I hypothesize that it is adding tension on the chain, resistance when it spins... which could explain the diminished performance i am observing....
i seriously can't be over-tightening the 2 nuts that hold the chain sprocket cover on / bar in-place... all i am using is the Stihl scrench and tightenting until it's snug...

any advice?
 

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Franny K

Franny K

xyz
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Does that have a spur sprocket? if so it might wear in so the chain rides exactly in the center of the bar groove. I have a different chainsaw that has similar nylon or hard plastic replaceable wear parts, bought a spare but have never installed it. The chain is drifting sideways, those things are keeping it sort of aligned. Intresting I have the MS251 similar bar mounts directly to the composite white stuff often called plastic but mine has a little rubber like piece where the oil comes out to better seal against the bar.
 
effigy

effigy

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Ur saw using bar plates?
no bar plates
Does that have a spur sprocket? if so it might wear in so the chain rides exactly in the center of the bar groove. I have a different chainsaw that has similar nylon or hard plastic replaceable wear parts, bought a spare but have never installed it. The chain is drifting sideways, those things are keeping it sort of aligned. Intresting I have the MS251 similar bar mounts directly to the composite white stuff often called plastic but mine has a little rubber like piece where the oil comes out to better seal against the bar.
spur sprocket
 
PV Hiker

PV Hiker

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I don't have it in my hands to see the big picture.

What bar model and chain number and size? Sprocket size?

Maybe some pictures of the chain etc to see more.
 
Stihl99

Stihl99

Stihl and AR15 Junkie
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IMHO it looks like your chain is floating on the 7T chain sprocket when the chain warms and loosens up a tad while running the saw, switch it over to the 7T rim sprocket assembly: 1125 007 1002
Put on a new bumper strip: 1121 648 6610
Then see how it wears the rim sprocket assembly
 
Old2stroke

Old2stroke

Never too many toys
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Are you the original owner? Maybe someone can tell us if that saw is supposed to have bar base plates on both sides of the bar that have gone missing.
 

J D

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The wear can be worse if you have a bar with a narrow tail (usually a result of being dressed down a fair bit) or a chain on the long side causing the bar to be adjusted a long way forward
 
Westboastfaller

Westboastfaller

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As said the nylon guide are a dime a dozen. Worth to have a few of the lower ones on hand and replace as you get only a little wear. Likely caused from derailing. The more they wear..the more they derail or throw chains, all though small bars on some saws are more forgiving That saw looks clean of chain throws altogether. Does it cut true otherwise?
 
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