New 660 piston possible/probable issue

[sammer]

Hi all,

As the title suggests, I sent in my 660 to a chainsaw repair mechanic after the piston failed, probably due to over-revving. I usually do my own service work but was not in a position to on this occasion. The piston was clearly scored, grey and dry with seized rings in a manner consistent with over-revving, possibly with too dilute a mix of 2 stroke.

Anyway I asked the guy to take a look and replace the piston but when I finally got it back today (after a 4 month wait) I opened the muffler to see the new piston and to my dismay I see vertical score marks cover the face. There was lubricant of some kind sprayed in making everything looking nice and shiny as I know it should look, but the rings didn't look too free. It's almost as if the cylinder wasn't polished properly before the piston was installed and the new piston was scored by the damaged cylinder walls when the mechanic tested the saw.

I ran the saw to test cut a couple logs and took the muffler back off to reexamine; the lubricant had almost dried off, the rings look even less free, the ring near the head looks seized but I can't be sure. Would appreciate if any more experienced mechanics could offer an opinion here. I feel the guy may have carried out substandard work and is leaving me with a failure waiting to happen. I have no idea why it took 4 months for him to do but I feel suspicious for some reason. Does it look ok to run the saw (it doesn't to me) or would I be better off to return the saw to the mechanic to complete the repair to a better standard? I don't want to run it if it's just gonna seize up...

2 videos attached the first showing just after I picked up from mechanic but before I ran the saw.

2nd video shows after 5 mins of running the saw and cutting a few small rounds.

Any insights/ideas are appreciated.
Cheers

 

[Mad Professor]

I wonder what cylinder looks like?

The mech sure did not bother to clean things up as Ex port is still filthy with carbon. Carbon scores?

 

[pioneerguy600]

There is still something in there scratching the piston, only way to find out what is to pull the jug. Take it back and demand a re inspection, likely some aluminum transfer left in the jug.

 

[sammer]

I wonder what cylinder looks like?

The mech sure did not bother to clean things up as Ex port is still filthy with carbon. Carbon scores?

Thought the same myself about the dirty exhaust. Feels like a rush job, I don't imagine those lines would be there if the cylinder was slightly rebored before the new piston went in but never checked it's condition before sending in the saw. Very frustrating.

 

[sammer]

There is still something in there scratching the piston, only way to find out what is to pull the jug. Take it back and demand a re inspection, likely some aluminum transfer left in the jug.

I think i'll do that. Could you elaborate on the idea of aluminium transfer? Do you reckon the piston/rings is still ok looking as it does or will need another replacement?

 

[pioneerguy600]

Aluminum transfer is actually melted aluminum left on the cylinder walls from a scored piston, it takes a good bit of work to get it all off. I actually don`t know of a shop that will reuse a previously scored cylinder but many of us on here clean them up properly and run them again with no problems. I think your piston could be saved with some cleanup, the rings might as well be replaced and the ring grooves/lands will need some cleanup as well where some small smears has occurred. If I was repairing your saw for commercial purposes I would use a new piston and rings, clean the bore judiciously.

 

[pioneerguy600]

The aluminum transfer can be cleaned off with machine sandpaper and finished up with red Scotchbrite, it takes a bit of time but can be done . Some people have used Muriatic acid to remove the aluminum from the bore, it will work but there are pitfalls and hazards possible when using acid.
Use the search function near the upper right corner of the page and you will find plenty of threads dealing with cleaning transfer off the cylinder bores. Do not use a hone to remove aluminum transfer, get it clean first and a very light hone won`t do much damage to the very thin bore plating.

 

[Wood Doctor]

"I finally got it back today (after a 4 month wait) I opened the muffler to see the new piston and to my dismay I see vertical score marks cover the face."
-----------------------
Four months wait? Sounds like he gave up, but he should have at least told you that after 30 days or less. Sorry to hear that. I've fixed several 660's. Dang!

 

[sammer]

The aluminum transfer can be cleaned off with machine sandpaper and finished up with red Scotchbrite, it takes a bit of time but can be done . Some people have used Muriatic acid to remove the aluminum from the bore, it will work but there are pitfalls and hazards possible when using acid.
Use the search function near the upper right corner of the page and you will find plenty of threads dealing with cleaning transfer off the cylinder bores. Do not use a hone to remove aluminum transfer, get it clean first and a very light hone won`t do much damage to the very thin bore plating.

Thanks for explaining that to me Pioneerguy600, this is a real help. I've since spoken to the mechanic to let him know I'm unsatisfied with the work, which he seemed to accept. Sure we'll have to see what happens when I bring it back, I'll update you in another 4 months or so He maintains the bore was sufficiently cleaned prior to installing the piston but the scores obviously tell another story. Will be bringing it back for him to resolve before the end of the week. Worst case I'll take it home and redo myself, I've already done a similar bit of work to a 200t a few years back and she's still running perfectly, but one tends to do a better job on their own equipment imo. Cheers

 

[sammer]

"I finally got it back today (after a 4 month wait) I opened the muffler to see the new piston and to my dismay I see vertical score marks cover the face."
-----------------------
Four months wait? Sounds like he gave up, but he should have at least told you that after 30 days or less. Sorry to hear that. I've fixed several 660's. Dang!

Yep, not too sure what his motive was here. Guess he was really busy, perhaps?! He said in response to my asking what took so long "I didn't think you were in too much of a hurry to get it back...", not that my phoning him 6 or 7 times asking what the holdup was about could have indicated I wanted my saw back or anything. Pity I'm not based on the other side of the pond where folks seem to take a bit of pride in their handiwork. If you know of any good mechanics in Dublin, Ireland please let me know! Cheers

 

[pioneerguy600]

Not all of the shops over here take pride in their work but most members on here could direct you to one. There are many members on this site that can and would do top notch work on saw repairs. You just have to weed out the shops in your area, that is tough though if there is only one or two local enough to take your saw to. It is one reason so many of us have gotten into doing our own repair work. Personally none of my machines ever see a dealership or even a repair shop, I have seen their work on machines brought to me to repair after other places have attempted repairs. Some places are good, have higher standards while others are just get em back out the door as fast as possible.
Hope to hear all is well after the next round of repair is done on your saw.

 

[MG porting]

First i like to say that sucks and very sorry that this happened to you. Now i would go back to that guy and get a full refund......... Do not let him work on it he should had known better than to just stick a new piston and rings in it.

 

[MG porting]

Here is a 064av cylinder looks like after a few acid treatments and three passes with a ball hone this is a cylinder I will keep running until I can't hold the saw up anymore. That guy took you for a ride and I'm really sorry that he did that to you.

 

[captain dangers]

Hi all,

As the title suggests, I sent in my 660 to a chainsaw repair mechanic after the piston failed, probably due to over-revving. I usually do my own service work but was not in a position to on this occasion. The piston was clearly scored, grey and dry with seized rings in a manner consistent with over-revving, possibly with too dilute a mix of 2 stroke.

Anyway I asked the guy to take a look and replace the piston but when I finally got it back today (after a 4 month wait) I opened the muffler to see the new piston and to my dismay I see vertical score marks cover the face. There was lubricant of some kind sprayed in making everything looking nice and shiny as I know it should look, but the rings didn't look too free. It's almost as if the cylinder wasn't polished properly before the piston was installed and the new piston was scored by the damaged cylinder walls when the mechanic tested the saw.

I ran the saw to test cut a couple logs and took the muffler back off to reexamine; the lubricant had almost dried off, the rings look even less free, the ring near the head looks seized but I can't be sure. Would appreciate if any more experienced mechanics could offer an opinion here. I feel the guy may have carried out substandard work and is leaving me with a failure waiting to happen. I have no idea why it took 4 months for him to do but I feel suspicious for some reason. Does it look ok to run the saw (it doesn't to me) or would I be better off to return the saw to the mechanic to complete the repair to a better standard? I don't want to run it if it's just gonna seize up...

2 videos attached the first showing just after I picked up from mechanic but before I ran the saw.

2nd video shows after 5 mins of running the saw and cutting a few small rounds.

Any insights/ideas are appreciated.
Cheers

I to have seen quite a number of scored pistons on stihls of this era and put it down to carbon build up due to the restricted exhaust which will build up, scrape and or, get sucked in etc. a number I have worked on actually still had good compression due to rings not been seized whilst the actual alloy can be heavily scored on the exhaust side only, which would suggest the carbon issue/build-up on the exhaust port , try a new piston, muffler mod it and hopefully the muffler mod with keep the carbon build up from happening? its something I'm currently experimenting on. C.D

 

[captain dangers]

Hi all,

As the title suggests, I sent in my 660 to a chainsaw repair mechanic after the piston failed, probably due to over-revving. I usually do my own service work but was not in a position to on this occasion. The piston was clearly scored, grey and dry with seized rings in a manner consistent with over-revving, possibly with too dilute a mix of 2 stroke.

Anyway I asked the guy to take a look and replace the piston but when I finally got it back today (after a 4 month wait) I opened the muffler to see the new piston and to my dismay I see vertical score marks cover the face. There was lubricant of some kind sprayed in making everything looking nice and shiny as I know it should look, but the rings didn't look too free. It's almost as if the cylinder wasn't polished properly before the piston was installed and the new piston was scored by the damaged cylinder walls when the mechanic tested the saw.

I ran the saw to test cut a couple logs and took the muffler back off to reexamine; the lubricant had almost dried off, the rings look even less free, the ring near the head looks seized but I can't be sure. Would appreciate if any more experienced mechanics could offer an opinion here. I feel the guy may have carried out substandard work and is leaving me with a failure waiting to happen. I have no idea why it took 4 months for him to do but I feel suspicious for some reason. Does it look ok to run the saw (it doesn't to me) or would I be better off to return the saw to the mechanic to complete the repair to a better standard? I don't want to run it if it's just gonna seize up...

2 videos attached the first showing just after I picked up from mechanic but before I ran the saw.

2nd video shows after 5 mins of running the saw and cutting a few small rounds.

Any insights/ideas are appreciated.
Cheers

the exhaust port is coked up and hasn't been cleaned by the person who repaired your saw, before he fit the piston, you can clearly see where a lump of carbon has flaked off, and presumably got sucked into the cylinder?

 

[sammer]

Not all of the shops over here take pride in their work but most members on here could direct you to one. There are many members on this site that can and would do top notch work on saw repairs. You just have to weed out the shops in your area, that is tough though if there is only one or two local enough to take your saw to. It is one reason so many of us have gotten into doing our own repair work. Personally none of my machines ever see a dealership or even a repair shop, I have seen their work on machines brought to me to repair after other places have attempted repairs. Some places are good, have higher standards while others are just get em back out the door as fast as possible.
Hope to hear all is well after the next round of repair is done on your saw.

Yep, it's the same reason I took it upon myself to learn how to repair; I pay attention to my work because it's in my interest to do so. High standards seemed far less of a concern for guys who gets in 10 saws in a day with no long term interest in keeping the saw running in top condition. Unfortunately I just didn't have the time last October following a big storm and was too busy to consider getting stuck in to a 660 repair (a big project for a novice mechanic such as myself). I'm going to give the guy a chance to put it right, it will be interesting to see how he responds and will hopefully set the record straight for his attentiveness and decency. Bringing it in to him today, I will update! Cheers

 

[sammer]

First i like to say that sucks and very sorry that this happened to you. Now i would go back to that guy and get a full refund......... Do not let him work on it he should had known better than to just stick a new piston and rings in it.

Thanks MG porting, I said that to him in so many words before he agreed to take it back in on the grounds I wasn't happy with his work. I have taken saws to him for repair in the past and for straightforward repairs he wasn't the worst, albeit a bit pricier than the rest. For better or worse I'm going to give him a chance to put things right since I have been a customer of his for over 12 years. His actions and quality of repair will determine whether or not I continue doing business with him; and there are plenty of folks in the local arborist community who would want to hear tales about sloppy work... and hopefully redemption! Worse case scenario, I'll take it back myself and consult with you kind folks on the nitty gritty of repair. Cheers

 

[sammer]

I to have seen quite a number of scored pistons on stihls of this era and put it down to carbon build up due to the restricted exhaust which will build up, scrape and or, get sucked in etc. a number I have worked on actually still had good compression due to rings not been seized whilst the actual alloy can be heavily scored on the exhaust side only, which would suggest the carbon issue/build-up on the exhaust port , try a new piston, muffler mod it and hopefully the muffler mod with keep the carbon build up from happening? its something I'm currently experimenting on. C.D

Thanks Captain Dangers, this is a really good idea. I'm hoping it won't be necessary if he puts things right but if there's any grumbling or further rush-job repair then I will look into this option as something to do myself. Yes it does look like he rushed the repair and didn't clean the exhaust port which is vaguely ironic considering he had the thing for over 4 months... Cheers