Husqvarna carb cover melted/welded to top cover.

[mredden]

Been a couple of months since I used my 390xp much - or cleaned the air filter. Decided to do so Saturday and couldn't get the filter cover off. Finally took the whole top cover off so I could see what was going on.

The crankcase side of the joint between the two covers just wouldn't budge. I could run a thin screwdriver through the top, bottom,and sprocket sides joints but not the crankcase side.

Finally (using more force than I liked), I got the seam to separate. Looked like the joint on that side had either been glued together or for some reason it had melted together in the joint. I know I haven't glued it and have no clue what I could have done to generate the heat to melt them together - in that one joint only. I can't imagine what would cause this along only one joint and not the other three. I have no memory of spilling anything that could cause this and there is no discoloration or "melting" damage except in this one joint.

cleaned it up and it closes up pretty well now despite missing some plastic that I removed here and there.

Any ideas? I don't want a repeat

[Andyshine77]

It ultrasonically welded together from the saws own vibrations, I've see it before and others have reported the same thing. So on new 390's I clean up the edges with 800 grit sand paper and apply a light coating of grease to the edge, this prevents it from happening. 

[lxskllr]

That's really interesting. There's about a 0% chance I'd have considered that a possibility.

[mredden]

It ultrasonically welded together from the saws own vibrations, I've see it before and others have reported the same thing. So on new 390's I clean up the edges with 800 grit sand paper and apply a light coating of grease to the edge, this prevents it from happening.

Wow. I never expected that answer. Is it unique to the 390s? I had run the saw heavily in milling from January through November last year with no issues. I cleaned the filter and put it up at that time. My use since November had been quite light. Like cranking it every couple of weeks and maybe running one tank of gas from November through last weekend when I bucked a big pecan log.
I guess I'll go back in and clean it up with sandpaper - and grease it from now on.
Thanks!

[sablatnic]

Most of them can do it, but you will not see it very often.
Andy's sollution usually prevents it from happening

[5000+]

Saw a low hour 365xt do it also. Rev one up and watch the starter handle.

[zimmie10]

Husqvarna released a bulletin on this exact issue, but I can't, for the life of me, find it at the mo.
Basically, after extensive research, they found that the covers were welding themselves together through vibrations caused from over-revving.
They said if your saw is showing this top cover problem, check the top end on it.