Chain keeps falling off saw (stihl ms 290)

[spudulike]

If your bar rails are worn down you can get a situation where the drive tangs don't sit in the groove correctly . If you can rock the chain from side to side ( a significant amount ) after tensioning the the bar at best needs the rail dressing and worst its shot .

 

5mm is around the minimum bepth that is needed - the tie plates of the chain should run on the rails - worth putting the bar in a bench vice and puting a straight edge across the rails at 90 deg to the bar. The edge should sit square to the bar - if one rail is longer than the other then the longer of the two needs grinding down to square it up.

 

Usual signs of this are cuts wandering off from square, cutters on one side of the chain wearing faster than the other and the reluctance to keep cutting in big cuts with the saw just going full bore with no cuting happening.

[Marc]

Worn clutch sprocket particularly the star type not the rim n spline.

[recycledsole]

thanks everyone. took it to the shop today and he said nothing wrong he could see. said that i might have installed it with the chainbrake on. i dont think so. no problems today about 2 hours of bucking.

thank you this site is really excellent