What Could Have Caused This

[Sprig]

Here's the cylinder from that same saw. Good/No good? Dosen't appear to be near as bad as the piston.

Not a great pic but is that a chip outta the right hand side of cylinder's edge? Just wondering if that may be the source of your grief, and yes, doesn't look near as bad as the piston.



Serge

 

[oldbigred]

If you are talking by the ports, no it is supposed to be that way (new cylinder is the same)

 

[huskydave]

Those look too deep to hone out in my opinion.

 

[computeruser]

http://arboristsite.com/showthread.php?t=46280

The great "debate" about suck back was born when I found some retard selling modified mufflers with a Stihl string trimmer screened outlet grafted on a stock muffler front cover over on eBay, arguing that the introduction of this second exhaust port would in some way prevent the much misunderstood but deadly "suckback," whatever the $%*# that is. I guess this is the kind of silliness and home brewed engineering we get, what with MIG welders being so cheap these days...

 

[oldbigred]

Heres a better pic

 

[ray benson]

Thanks for satisfying my curiosity...I think :greenchainsaw: pioneerguy600 - you wouldn't know what your manual says about torquing the cylinder by chance? as i already have a p/c kit and the rebuild is kinda underway. thanks.

Looking at a Stihl failure analysis manual - your pictures look like lean seizure. Homelite manual lists the cylinder nuts torqued to 100 in/lbs minimum with max torque 20% higher.

 

[huskydave]

i noticed some grit in the transfers and cylinder you should flush out the crankcase good to remove any foreign particles.

 

[oldbigred]

i noticed some grit in the transfers and cylinder you should flush out the crankcase good to remove any foreign particles.

Duly noted...planned on it anyway

 

[oldbigred]

Suckback...heres my problem with it...when the piston travels downward it is compressing the air/gas in the crankcase, which forces it up the ports into the cylinder. And a basic scientific principle sates that dense air will displace less dense air, so the air coming up the ports has more pressure than that of which could be sucked in the exhaust. Plus the piston should displace just as much air from the crankcase as need in the cylinder. Thus there would be no need for air from the exhaust. That is what makes a two stroke work..no?

 

[WidowMaker]

Looks like the damage caused by "suckBack" of an improper fuel mix...:greenchainsaw: :greenchainsaw:

 

[huskydave]

Suckback is a joke that started on ebay when a seller did a mufflermod and said it would prevent suckback. we had some fun posting suckback in numerous threads as a joke and some people bought it hook line and sinker.
There actually is an exhaust pulse that goes back into a 2 stroke but The racers would know how to explain that better than me.

 

[oldbigred]

Yeah, thats what I gathered...so I still think cold seizure or lower end failure as mine has excessive play, i think.

 

[huskydave]

really you might be able to save that cylinder if you really wanted too. I looked at it again and if you could get the grooves out of the upper portion and smooth out the lower part it might still be good. The compression comes from the port up and those scratches don't look too bad in that area. What caused it hard to say could be carbon scoring or lean siezure Lakeside could tell you if it was running lean.

 

[oldbigred]

Like I've said before I have a new cyl for the saw. If i ever did anything I would have it replated, more or less just wondering if replating would fix it to 'like new' Ont that note where could it be replated any idea on how much....not that im nessicarily gonna have it done.

may have been running lean...believe this was my grandfather's saw and he is notorious for absent mindedly putting straight fuel...just worked on his stihl 026 that i think had straight fuel in it...i would say its going to need a new p/c or piston and rings at the least.

 

[huskydave]

Boring and replating with nikasil is real expensive about $200-$250 and not really worth it unless you can't get a new cyl. you can get a cylinder chromed for less but will still cost quite a bit of money.

 

[oldbigred]

well...on that note think the old cyl is prolly headed for the scrap pile. prolly cheaper just to look for another nos one if it ever comes to that. thanks

 

[wood4heat]

From what I can tell by the piston pic it doesn't look like it was lean or run without mix. A pic of the piston top and intake side would help determine that though.

 

[RaisedByWolves]

Suckback:


Suckback occours when something sucks so bad that it "Sucks Back" the last sucky thing that happened and they meld together to form a Cluster fark.



Cluster Farks are notoriously hard on an engine and have spawned the invention of the "Suck back prevention devise", to help prevent foreign Sucks from entering through the exhaust port.




+1 for cold seizure.



.

 

[RaisedByWolves]

you guys are going to have to post slower if my jokes are to be timed well.....



.

 

[oldbigred]

oh ok suckback...more or less the same stuff i hauled out of the barn the other day that the bull left. Along those lines? haha