Cylinder wear, shiny patches

[RJTodd]

Piston picture for reference. Cylinder is below.

Is the Nikasil worn through in the shiny areas? I've only been inside a few saws, but I've never seen this before. It is from an 044 basket case that I would like to put back together. No idea of the saw's history. The piston looks grit blasted to me. Looks like the saw may have some hours!! SN: X41509000

Thanks,

Randy

 

[Farmer_Nate]

I am no pro at all on saw rebuilds so I will defer to others. I can guess and see how it turns out...

I'd guess

1) the saw was run with almost no oil in the gas? It got hot and scratched it?
2) the saw was run very hard often with no warm-up?
3) the saw has a lot of hours?

 

[SteveSr]

Piston picture for reference. Cylinder is below.

Is the Nikasil worn through in the shiny areas? I've only been inside a few saws, but I've never seen this before. It is from an 044 basket case that I would like to put back together. No idea of the saw's history. The piston looks grit blasted to me. Looks like the saw may have some hours!! SN: X41509000

Thanks,

Randy

View attachment 1052277


View attachment 1052276

Looks like some turd used a hone in there and removed most of the nikasil... AND then didn't clean out the leftover abrasive before putting it all back together. If that is the case the bearings & crank are probably shot as well.

Another tell-tale is the fresh horizontal scoring in the aluminum areas... like hone marks.

 

[Yukon Stihl]

OEM or aftermarket cylinder ?

 

[huskihl]

I don’t believe the dull silver color is bare aluminum. That same color is around the lower transfer ports and nothing rides there that could remove the chrome. In that area is all open skirt. But there is definitely something going on. I’m guessing it was scored at one time and someone replaced the piston without cleaning up the scoring completely

 

[Mad Professor]

Overly aggressive/coarse hone marks for sure. Those alone could account for piston wear

 

[RJTodd]

It is an OE Stihl cylinder. I worked it by hand with 120 grit cloth backed abrasive and it actually looks pretty good. I don’t see any spots that look like aluminum, and the cloth never picked up the black color aluminum gives. There are a couple of scratches left on the exhaust side, but I’m thinking it may be salvageable. I’ll get some pics in good light shortly.

 

[RJTodd]

Looks like some turd used a hone in there and removed most of the nikasil... AND then didn't clean out the leftover abrasive before putting it all back together. If that is the case the bearings & crank are probably shot as well.

Another tell-tale is the fresh horizontal scoring in the aluminum areas... like hone marks.

Hey Steve, how do I check crank and bearing condition? The bottom end needle bearings in particular since I’m not sure how to go about replacing those. I have two case assemblies, so I can pick the better of the two if I can figure out which is truly better.

 

[RJTodd]

 

[RJTodd]

So I added some Kroil to the abrasives and worked another 5 minutes. Can’t feel anything with a fingernail, but scratches are still visible. Good enough and leave it alone, or work until the scratch disappears?

 

[huskihl]

So I added some Kroil to the abrasives and worked another 5 minutes. Can’t feel anything with a fingernail, but scratches are still visible. Good enough and leave it alone, or work until the scratch disappears?View attachment 1052589View attachment 1052589

I think you’re fine now. It’s hard to tell, but make sure the edges of that scratch don’t protrude into the bore. If you have an old piston that isn’t any good but is still smooth enough, you can slide it up into the bore and tip it towards that scratch and see if you can feel it or hear it. If you feel some resistance, it’s probably still a little bit proud and needs to come down

 

[Mad Professor]

It is an OE Stihl cylinder. I worked it by hand with 120 grit cloth backed abrasive and it actually looks pretty good. I don’t see any spots that look like aluminum, and the cloth never picked up the black color aluminum gives. There are a couple of scratches left on the exhaust side, but I’m thinking it may be salvageable. I’ll get some pics in good light shortly.

120 is too coarse. Those marks are not going to wear in like a cast iron liner, they are going to abrade the piston.

120 only for thick deposits, or use acid. Then go to 240 and finer. I polish up with 400 to finish.

 

[Mad Professor]

Hey Steve, how do I check crank and bearing condition? The bottom end needle bearings in particular since I’m not sure how to go about replacing those. I have two case assemblies, so I can pick the better of the two if I can figure out which is truly better.

Bottom rod bearing is not a service item. Should have no up/down play and be smooth without any damage to the cage.

I've replaced those bearings on dirt bikes, but you need a source for correct bearing, special tools: a press, drifts, v-blocks, magnetic dial indicator, machinist flat surface. You press the crank apart then press in the new bearing. Then you need to check runout with v-blocks and dial indicator.

 

[ballisticdoughnut]

120 is too coarse. Those marks are not going to wear in like a cast iron liner, they are going to abrade the piston.

BRM (flex-hone) recommends 240 grit aluminum oxide abrasive for honing nikasil plated cylinders, 120 grit emery is definitely too coarse. If I have to do any sanding to remove transfer I use 400 grit emery with some kind of penetrating oil then hone in a solvent tank.

 

[huskihl]

120 is too coarse. Those marks are not going to wear in like a cast iron liner, they are going to abrade the piston.

120 only for thick deposits, or use acid. Then go to 240 and finer. I polish up with 400 to finish.

All I’ve ever used is 80 followed by a red scotchbrite drum. Either way, 80 barely leaves a mark in nikasil or chrome. But it certainly removes aluminum faster

 

[Farmer_Nate]

Amazing the cylinder cleaned up that well. Nice work.

 

[Mad Professor]

BRM (flex-hone) recommends 240 grit aluminum oxide abrasive for honing nikasil plated cylinders, 120 grit emery is definitely too coarse. If I have to do any sanding to remove transfer I use 400 grit emery with some kind of penetrating oil then hone in a solvent tank.

Use dish detergent rather than oil.

 

[Mad Professor]

All I’ve ever used is 80 followed by a red scotchbrite drum. Either way, 80 barely leaves a mark in nikasil or chrome. But it certainly removes aluminum faster


View attachment 1052669View attachment 1052670

Piston




Cylinder

 

[ballisticdoughnut]

Use dish detergent rather than oil.

Good idea. I’ll try that, got a few cylinders I need to clean up.

 

[Vintage Engine Repairs]

It’s common to have polished areas like that. A quick scuff up with 120 followed by 320 and you’re good to go.