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General Forestry => Chainsaws => Topic started by: Coach on January 28, 2014, 05:40:11 PM

Title: Scored cylinder - please advice
Post by: Coach on January 28, 2014, 05:40:11 PM
You chainsaw guys, can you advise me if this cylinder needs replacing? I'm really hoping not. It's scored a little just underneath the muffler outlet. It's off a Husky 375k

 (http://www.forestryforum.com/gallery/albums/userpics/31914/image%7E60.jpg)

For some reason the piston had a piece break off.  I've replaced pistons, and taking this one apart it looks like it may have been installed back to front. I could be wrong on that though.
Title: Re: Scored cylinder - please advice
Post by: Andyshine77 on January 28, 2014, 06:03:57 PM
What was the location of the ring pin? should have been the intake side of the cylinder, not the exhaust side. It looks like a piece of plating is chipped off on the bottom of the exhaust port, If so I looks like a pretty big chunk and may be a deal breaker. The bottom of the port looks rough as well, but a little blending would likely fix that, the rest of the scuffing is pretty light and should hone right out. Looks like she was running a bit hot and dry, so wherever you end doing with the saw, pressure and vac test after the rebuild. 
Title: Re: Scored cylinder - please advice
Post by: Coach on January 28, 2014, 06:22:05 PM
Ring pin was on the exhaust side, that's what makes me think it was installed backwards.  Husky wouldn't do that, or? 

Yeah, it is the chip I'm asking about. The large pic makes it look worst than it is. 
Title: Re: Scored cylinder - please advice
Post by: ehp on January 28, 2014, 06:45:59 PM
Man she blew up pretty hard , you got a ton of crap in port transfer and ext. ports , combustion chamber as well , you need to polish where that piece is missing real good so the ring does not catch it and your ring pin should of been on the intake side and being a 371 it should of been a single ring  My rule of thumb is after cleaning the cylinder up if I can feel any kind of grooves or anything that my finger nails catch the cylinder is most likely junk , But if you were to have a piece of chrome missing in your cylinder you got the right place to miss it , if it was on the top side of the ext. port that changes things alot . Check your crankshaft over before putting it back together to and make sure none of the crap got into the lower rod bearing or crank bearing , but from what I can see in the picture , yes clean the cylinder up real good and put a piston in it and you should be good to go , that piece missing will not hurt the power of the saw but make sure its polished so the ring does not catch in it
Title: Re: Scored cylinder - please advice
Post by: Coach on January 28, 2014, 08:37:19 PM
Aside from the chip, the cylinder is smooth. Doesn't look to have damage otherwise. I think i'll go with it.

This is the piston. It's off a Husky 371K cutoff saw. (Correction, 375k)

 (http://www.forestryforum.com/gallery/albums/userpics/31914/image%7E61.jpg)
Title: Re: Scored cylinder - please advice
Post by: ehp on January 28, 2014, 10:30:32 PM
where is the piston ring pin  ;D ?  make sure you clean all the junk out before putting it back together
Title: Re: Scored cylinder - please advice
Post by: Andyshine77 on January 29, 2014, 03:34:00 AM
Looks like the pin is sitting on the crank lobe. :)
Title: Re: Scored cylinder - please advice
Post by: Al_Smith on January 29, 2014, 04:14:12 AM
That does seem odd .Usually the ring gap rides on one side or the other between the intake and the tranfers .
Title: Re: Scored cylinder - please advice
Post by: joe_indi on January 29, 2014, 04:26:06 AM
Aside from the chip, the cylinder is smooth. Doesn't look to have damage otherwise. I think i'll go with it.

This is the piston. It's off a Husky 371K cutoff saw.

 (http://www.forestryforum.com/gallery/albums/userpics/31914/image%7E61.jpg)
If you examine the inlet side of the piston on the skirt, probably it will be polished.
Exhaust side piston top as shown in the picture and a polished inlet side skirt indicates (IMHO) that the saw was under a bit of overload. At TDC the piston kind of wriggles under load and too much of this wriggle(my term) and the top gets damaged on the edge. In a twin ring piston the bit of aluminum between the rings snaps off.
Smoothen the edges of that 'crater on the cylinder wall and its good to go, with a new piston.

Joe
Title: Re: Scored cylinder - please advice
Post by: ZeroJunk on January 29, 2014, 07:54:01 AM
When you finish working on the cylinder if there is anything about it that you don't like I would consider one of the aftermarket kits. They may not be OEM quality but for the price it might be better than a jug you don't trust.
Title: Re: Scored cylinder - please advice
Post by: bandmiller2 on January 29, 2014, 08:09:05 AM
I'am with Zerojunk your jug is a temporary fix at best get an aftermarket jug and piston and be done with it.  I have had good luck with them and their not that expensive. Frank C.
Title: Re: Scored cylinder - please advice
Post by: Andyshine77 on January 29, 2014, 03:23:04 PM
That does seem odd .Usually the ring gap rides on one side or the other between the intake and the tranfers .

A lot of modern Husky's have the ring gap right in the middle of the intake, especially single ring saws.
Title: Re: Scored cylinder - please advice
Post by: Andyshine77 on January 29, 2014, 03:26:55 PM
I'am with Zerojunk your jug is a temporary fix at best get an aftermarket jug and piston and be done with it.  I have had good luck with them and their not that expensive. Frank C.

Blended correctly the saw will run fine for a long time, which is better than most of the AF stuff I've dealt with.
Title: Re: Scored cylinder - please advice
Post by: coxy on January 29, 2014, 04:44:21 PM
wow cant believe some of you would put that back together that way if I did that it would run for 30 sec and blow up again and brake some thing else  some people have all the luck :D :D :D :D 8)
Title: Re: Scored cylinder - please advice
Post by: sharkey on January 29, 2014, 11:31:50 PM
Maybe if it were my own I would try it, but not for anyone else. 
Title: Re: Scored cylinder - please advice
Post by: Andyshine77 on January 30, 2014, 12:34:37 AM
The ring doesn't have to seal there, as long as it doesn't catch it shouldn't be a problem. Again the scuffing is very light an will completely hone out.

Experience plays a big role here, myself and others like Al and EHP have made do with much worse. Sometimes parts are no longer available, too expensive and so on.
Title: Re: Scored cylinder - please advice
Post by: chainsawr on January 30, 2014, 06:17:44 AM
I think that chip on the bottom edge of the exhaust port is bad news.  Lot of plating gone there.  Then again, if you clean it up and put an inexpensive aftermarket piston in there, if it blows up again right away you're not exactly out a huge fortune, and it may just work for a while.

It's scary how often we find backwards installed pistons in saws that come in for service  :o
Title: Re: Scored cylinder - please advice
Post by: ZeroJunk on January 30, 2014, 08:17:25 AM
wow cant believe some of you would put that back together that way if I did that it would run for 30 sec and blow up again and brake some thing else  some people have all the luck :D :D :D :D 8)

I suspect they would not. I mean you might suggest it to somebody and honestly believe it would be OK, but if it was yours you would do it right.
Title: Re: Scored cylinder - please advice
Post by: Al_Smith on January 30, 2014, 03:57:24 PM
In my haste of grancing at the picture I failed to realize that in fact the danged thing is in backwards ,duh .In looking at it this morning at work I noticed the exhaust port higher than the transfers then in dawned on my pea brain what had happened .

I dunno if you  can clean up the cylinder and use craytex or something to buff out the missing plating so the ring will bridge over it you night be able to save it .Now I can't help but wonder how in the world the piston got turned around .
Title: Re: Scored cylinder - please advice
Post by: JohnG28 on January 30, 2014, 06:27:15 PM
In the first picture it looks like either the piston or the piece that broke off hit the squish band and top of the cylinder also.  :-\
Title: Re: Scored cylinder - please advice
Post by: Al_Smith on January 30, 2014, 06:39:19 PM
It must have snagged the ring on the down stroke which flipped the broken piston piece on top of the piston .I'll bet that thing came  to a halt when it hit the head deck .Clunk!

I'm not familiar with that model .Evidently by the orientaion of the ring it obviously doesn't go into the intake any. Some Stihls had a little protrusion of metal hanging from the top of the intake to keep the ring stuffed .
Title: Re: Scored cylinder - please advice
Post by: Coach on January 30, 2014, 11:13:50 PM
I have a few of these saws that need work. 2 different models. 371K and 375K. Bad news is this is the 375K, which looks to be rare enough to have no aftermarket pistons available. Bore size on this is 51.4mm.  So may be forced to go with a different size cylinder kit, which are lower cost than an eom piston.

Unless you guys have some different advice.
Title: Re: Scored cylinder - please advice
Post by: ZeroJunk on January 31, 2014, 08:31:28 AM
I have a few of these saws that need work. 2 different models. 371K and 375K. Bad news is this is the 375K, which looks to be rare enough to have no aftermarket pistons available. Bore size on this is 51.4mm.  So may be forced to go with a different size cylinder kit, which are lower cost than an eom piston.

Unless you guys have some different advice.

The vast majority of those who will tell you not to use an aftermarket kit have never actually done it. I have built a dozen or so and I have never been able to tell any difference running them.