Damaged Nikasil coating

[t_andersen]

Hi Guys,

Thanks to Lakeside and other good advice here, I have now (finally) overhauled my 084. The piston was scored, so I installed a new. The cylinder was also damaged. First, I used 30% muriatic acid to remove the aluminum on the coating of the cylinder. It seemed to work ok but it was rather slow, it took some hours to get most of the aluminum removed. Below the exhaust port, I saw some bubbling in the acid, so I figured that there were holes in the Nikasil coating and I stopped using the acid. I then continued with 800 grit emery paper in oil by hand at that location. It was pretty easy to get the aluminum away in that way. Following that, I used a ball hone with oil for about 20 seconds trying to get a 30-45 degree grinding pattern. The effect of the ball hone was very impressive. Finally, I gave the inside of the cylinder a very light touch with the emery paper to remove any burrs from the ball hone.

The inside of the cylinder looks fine but there are some flaws. I believe that there are 3-4 very narrow axial lines of damage of the Nikasil coating above the exhaust port. Also, where I saw the bubbles under the exhaust port there is pitting in the Nikasil coating, say 4 spots with damage of 0.5 mm (1/64") or so. Will these damages in the Nikasil coating give me serious trouble? How many hours would such a cylinder have?

I have assembled the saw and it is easy to start. Tomorrow, I will set the carb so I still have a good chance to screw up things

 

[RiverRat2]

I'm curious to see what all the experts say on this one how much is a new cylinder kit,,, good luck

 

[ericjeeper]

If it were I

I believe I would not want to risk toasting a brand new piston. Is there any way to salvage the old piston and just re ring it? Maybe get you by for a while til you can locate a bargain on a good jug.
It might last for years. or it might last minutes..

 

[RiverRat2]

IMHO the axial lines will probably not be that big of an issue if you cant hang your nail in them, ive seen them run as stated by eric for years with no problem you will loose a little compression there but it will fill in with carbon and as you said it starts easy and runs good,,,but, its that spot were the nikasil is peeling that would make me cautious. Is that a new stihl piston if so I know what it cost,,,,,,,,,, Im like eric. if you could clean up the old piston and re ring it and tryit a while,,,, another option you may want to consider is sending the Jug & your new piston to http://www.mt-llc.com/technology/index.shtml and have it re-plated to fit your new piston!!!! Just a thought if you cant find another good used jug....

 

[Lakeside53]

I wouldn't worry about the problems you have below the exhaust port as long was they are not in the ring area, and even then... not too concerned. The fine lines above the exhaust - they will just leak a small amount of compression... It won't be perfect, but you may be surprised how well it runs. A new piston (no skirt wear) does wonders...

Try it... Start rich, and use a full synthetic mix if you can.

But did you ever figure out why it got toasted the first time??

 

[04ultra]

IMHO the axial lines will probably not be that big of an issue if you cant hang your nail in them, ive seen them run as stated by eric for years with no problem you will loose a little compression there but it will fill in with carbon and as you said it starts easy and runs good,,,but, its that spot were the nikasil is peeling that would make me cautious. Is that a new stihl piston if so I know what it cost,,,,,,,,,, Im like eric. if you could clean up the old piston and re ring it and tryit a while,,,, another option you may want to consider is sending the Jug & your new piston to http://www.mt-llc.com/technology/index.shtml and have it re-plated to fit your new piston!!!! Just a thought if you cant find another good used jug....

There 15 miles from my house ..US Chrome is another source..Fond du lac Wi. 40 miles from me..

.

 

[BLACKeR]

Try it... Start rich, and use a full synthetic mix if you can.

dont mean to hijack, but lakeside you recomend full synthetic on break in? i have always swtiched to full synthetic after break in. i have heard that the synthetics dont provide enough friction to properly seat the rings.

 

[Lakeside53]

I talked to Stihl at length about this and they say it's not an issue... Their full synthetic is for use from day one. I can't image it's much different to any other... Ther cavet was (of course) - only there saws - the factory bore is now finished very finely requiring little "break in". Their rings have very fine ridges that quickly wear off.

I'm suggesting full synth in this case just because the first few seconds/minutes can be critical, but it probably won't make much difference.

 

[drmiller100]

holes below the top of the exhaust ports can be called "boost ports." no worries there.

lines above the exhuast port. THe closer to the exhaust port, and the further from the head, the less they matter. big lines near the top can blow torch out eventually, but mostly like they said they just affect midrange due ot loss of compression.

Personally, I dump a teaspoon of oil down into the crankcase on my 2 strokes. a little extra oil on startup sure seems to prevent streaking.

 

[Lakeside53]

Hey Tom

How did it run???