Stihl ms251

[woody paul]

Customer asked me to look at exhaust on his saw which has come loss after dealer repair, so bolts have come loss again one missing exhaust cracked and no sign of gasket. Professional repair?. 

So has anyone used Nord-lock washer to hold them tight. I know threadlock them but want a belt and braces job. 

[Deafhead]

Only cure on one of my husky s was to make some new bolts with the dies left slightly large.

[kram]

The threads could be stripping and a sloppy fit or likely will in future if it continues. The best repair is to helicoil the cylinder, new bolts, do it up tight with a torque wrench.

 

I just have a cheap import set of helicoils, used a lot and all worked perfectly.

 

[GarethM]

Thread lock will burn off, maybe exhaust paste instead 

[pleasant]

I suspect the saw had been used for a while with the exhaust loose and the bolts rattling around in the threads in the head so widening the thread opening. Only belt and braces job would be to check the threads by manually screwing the bolts back in and seeing how far they have to screw in to stop sideways movement....if it's a fair way before you feel a good secure grip then you're best replacing the cylinder...you could try and tap it and use slightly larger bolts, but it's a very thin wall and would most likely fail again very soon.

[openspaceman]

2 hours ago, Deafhead said:

Only cure on one of my husky s was to make some new bolts with the dies left slightly large.

251 exhaust bolts look like they are M5, so using @Deafhead's method get an M6 bolt with a shank that is long enough, grind off the thread by twiddling it in a bench grinder.  Buy a split M5 die and jam the set screw in the die holder to open the split and gently cut a new enlarged diameter M5 thread. Cut to length.

 

 As long as there's some thread left in the cylinder this will accommodate the slop and the 0.5mm extra radius will form  the aluminium to accommodate it.

 

[woody paul]

So everything turned up this morning.

One thread has been helicoiled by someone and both were tight. 

So will see if my idea of using Nord - lock washers works, when I was tightening them could feel evertime it went over ridges.