I just couldn't stand it anymore. Last year after I got the thing I posted about some scuff marks on the piston then took it to the dealer and they said it was fine. So last fall my curiosity got the best of me and I did a mm on it, the scuff marks had gotten a little worse but I said the heck with the warranty and did it anyway. Its been a year so I took the muffler off today to check and see how it was doing and it looked about the same, but then I got frisky and went ahead and pulled the cylinder off and this is what I found.
Well, I did it, I tore into my 550xp.
- Thread starter skylogger
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Now this saw has been running great and have no problems at all I just couldn't stand the marks on the piston. The cylinder marks I can't feel at all its like its just been rubbed on. The piston marks I thought was scoring is mostly just colored I can feel two scratches like it's been rubbed with the end of a needle. Now that rubber piece that was pinched by the carb is ridiculous could it have been the source of the problem? I don't know if came like that from the factory or the dealer did it the one time it was there.
old-cat
Fir Man
I have zero experience with the 550 but that looks like tiny air leak or just carb too lean? Either way, what I'd do is use a fine file and smooth off the piston then make sure when you put it together there is NO air leak. If it's possible, richen the high speed?
certified106
ArboristSite Member
So I have no idea what the history on the saw is but if I took it to the dealer and they told me those kind of marks were fine I can guarantee we would a have had a long and spirited discussion. I have much older huskys that don't have any marks on the piston at all so to me something's not right. Is it still under warranty? If so tell them you want a new piston and cylinder.
In my opinion, pic one tells us what caused the scuffing. I'd show that to the 'dealer', not that he's going to do anything for you.
If it were a saw I was going to keep, not sell, I'd probably get a new boot, clean up the piston, and stick a new ring in it. A new piston would be a better repair. I think you need a new boot, regardless.
If it were a saw I was going to keep, not sell, I'd probably get a new boot, clean up the piston, and stick a new ring in it. A new piston would be a better repair. I think you need a new boot, regardless.
old-cat
Fir Man
^ Yep
troylee
ArboristSite Guru
New boot for sure, and I would do the piston/ring also. That being said, I am also the type of person that changes the wheel bearings on both sides, if one goes out. You have it apart, why not go the whole way.
SawTroll
Information Collector
Likely an air leak at the intake, that the AT wasn't fully able to compensate for - the P&C likely would have been much worse on a saw without AT.
Thanks for the replies so far guys I'm gonna bypass the dealer on this one I want the opportunity to learn how these dang things work and figured learning from y'all has got to be the best way. This is the first time I have opened a saw up so be gentle
If anyone wants anymore pics or a measurement or two just ask I haven't ordered any parts yet.
If anyone wants anymore pics or a measurement or two just ask I haven't ordered any parts yet.
I believe Autotune cant fix everything. On a manual tuned saw a good operator can pick out an air leak. I picked one out on a Husky 385. It was on the compression release. Very sporadic but knew something wasn't right by the rpms in the cut. The rpms went way up then down. Reconizing these symptoms saved me a P& C. I believe it is not so reconizable in an autotune due to its self adjustability . I believe an all out air leak cant be fully compensated for!
nmurph
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hmmm, Houston, you might have a problem with that adjustment.
old-cat
Fir Man
Ya I know, I really should have kept shut.
nmurph
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You could probably get away with cleaning that piston and a new ring. OEM pistons are about $65 and would be what I would do. But I tend to not cut corners so as to save problems down the road. I'm 99% sure a new ring and a clean up would be just as good. Rings are going to cost $15, so the piston is $50...cheap insurance in my book.
Definitely replace the boot, and definitely delete the base gasket and mod the muffler.
Definitely replace the boot, and definitely delete the base gasket and mod the muffler.
nmurph
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sunfish
Fish Head
Increases compression. A good thing!
