Piston Refitting Question

[max2cam]

I'm reassembling my 024 that "slightly" stuck its piston due to an air leak.

I am using the old piston with a new ring. The old piston has about a 1/2-inch strip that was galled somewhat when it seized (luckily while idling).

From another thread I plan to use some 320 grit emery cloth and diagonally "hone" the the piston skirt, giving special attention to smoothing out the galled area. I won't remove any metal, but only to crosshatch the surface and clean up the galling, which is pretty light.

The cylinder bore looks okay. Should I leave it alone?

Should I bevel the cylinder ports?

Anything else I should do or watch out for?

 

[SilverBlue]

As long as you don’t leave any scratches on the piston that could lead to stress cracks, a little hatch pattern will help to hold oil. Cleaning up and polishing the exhaust port will help to reduce the chance of carbon buildup in the bevel and possible piston scoring and most importantly removing sharp edges reduces hot spots.

 

[Jacob J.]

<p>Hi Max<p/>
<p>Here's a small list of watch-out items:<p/>
<p>Check the ring grooves on the piston for carbon build-up or slag from the scoring. Clean these out carefully with emery cloth or sandpaper. Use a new wrist pin bearing. Use new gaskets. Run the connecting rod bearing checking for cracks in the cage or undue wear. Check for up and down slop in the connecting rod. Make scratches on the cylinder walls with a ball hone and follow up by hand with emery cloth and cutting oil or solvent, using your fingertips to engage the port openings looking for snags. Run clean rags through crankcase, and check the bearings for carbon or foreign material build-up. Check the oil seals for hardness or cracks in the rubber. Run your fuel and impulse lines for hardness or cracks.<p/>
<p>Check the diaphragms in the carb for hardness or wrinkles. Check the inlet needle and lever for wear. You shoul go ahead and rebuild the carb regardless, as today's gas really eats up rubber parts fast.<p/>
<p>Clean the flywheel thoroughly and the laminates on the ignition module. Check the plug wire for wear. Clean out the fuel filter well or replace. Sandblast and repaint the muffler inside and out. This will lessen the chance that a piece of carbon will break loose and get sucked back up into the exhaust port. Hopefully others here will fill in the gaps.<p/>

 

[Tony Snyder]

I would be afraid to mess with the cylinder bore, might do more harm than good. If it is clean and smooth, I would let the bore alone.

Is it a plated or nikosiled bore? What specific saw?

If it is a plated bore and you start rounding port edges you might promote ealing of the plating like old Homelites sometimes did.

 

[Jacob J.]

<p>Hi Tony<p/>
<p>It is necessary to at least create some scratches on the cylinder wall so that the new rings can "break-in" or re-seat themselves. This is documented in all major saw manufacturer literature dating back to the early 50's with McCulloch, I.E.L., and Disston factory service manuals. The wear component that some people worry about is virtually non-existant in a hard chrome or Nikasil lined cylinder. A ball hone takes about 3 seconds to make the cross-hatching necessary, and using emery cloth by hand isn't going to produce any wear at all ( meaning it can't be measured via feeler gauge or even digital calipers ). Rounding the port openings only extends to the point of removing any snags that may be present, this can be done so without breaking through the chrome or Nikasil plating. The 024 cylinder is hard chrome lined. Stihl didn't switch to Nikasil until 1998 and that was mostly in small saws.<p/>

 

[max2cam]

Thank you for the good advice.

I'm a bit unclear about relieving the cylinder ports.

Should i barely touch the ports, just enough to slightly break the sharp edge?

I was previously thinking I should grind a small but distinct angle all around the port.

 

[Jacob J.]

<p>Hi Max<p/>
<p>Hand sanding with your fingertips usually does a good job. It creates a slight rounding. Your hands will get tired fast so make sure you take a break. Doing an entire cylinder by hand usually takes me about 20 minutes.<p/>

 

[bwalker]

Throw that bird out of your pocket thats going cheap-cheap and buy a new piston and ring set. Then ball hone the cylinder and clean well before use. As far as port edges go. Jacob is right sharp edges that somtimes result from a seizure will gouge a piston in short order. If you have this condition I would take it to amachine shop and have a machinist dress the port chamfers. One reason ported cylinders sometimes last longer is because the factory port chamfers have been known to be less than desirable.

 

[Crofter]

To hone or not or with what!

Pretty well hashed over on this old thread. "prepping for new rings"

http://www.arboristsite.com/showthread.php?s=&threadid=6720&highlight=honing+cylinder

Frank

 

[Tony Snyder]

Jacob J

This is intended to be polite discussion not a shot at you. Buttt.

The early saws you speak of in many cases had iron cylinder liners.

Also I do not think you can round or chamfer ports without going thru the plating or Nikosil. That my be O.K. on Nikosil but risky with plating.I know from experience that plating can start pealing back from the ports.

I'd like to hear what Ken Dunn has to say on this. Threatment of modern saw cylinders vs risk of rapid wear.

 

[Jacob J.]

<p/>Howdy Tony<p/>
<p>The hard chrome plating in Stihl, Husqvarna, and Jonsered cylinders ( all the big saw cylinders were manufactured by Mahle from the early 70's until now ) is about .018"- .024" in thickness. You can de-snag a port opening with emery clotch using your fingertips without breaking all the way through this plating fairly easily. I've done literally hundreds of cylinders this way and I've never had a failure. In fact, I've only seen chrome flake twice in a modern cylinder, one in a Stihl 075, and one in a Stihl 064. Both saws had been run on straight gas for some time before blowing up and the intense heat and friction most likely flaked the chrome. Stihl and Husky both recommend in their technical classes to run your fingers around the inside of the cylinder when fitting a new piston or rings and if encountering any snags to lightly sand them out by hand.<p/>

 

[bwalker]

The hard chrome plating in Stihl, Husqvarna, and Jonsered cylinders ( all the big saw cylinders were manufactured by Mahle from the early 70's until now ) is about .018"- .024" in thickness

I would bet any cylinder made by Mahle would be Nicasiled. Nicasil is actually a process that mahle invented. Further more chrome went the way of the dodo in the seventies in most applications. Chrome plated cylinders stink compared to nicasil and even iron liners.
BTW nicasil cylinders are not that hard to do a port chamfer on provided you use the right tooling. Emery cloth will not even put a dent in the plateing so it would be quit safe.

 

[Jacob J.]

<p>Ben, you're right. I often make the mistake between telling the difference on Nikasil and the chrome. And yes, it is impossible to put any real wear or damage in Nikasil plating using emery cloth.<p/>

 

[max2cam]

024

So my 1981 vintage 024 Stihl would be Nikasil then?

If Nikasil is superior, why does Echo still use hard chrome bores as I believe they do?

 

[bwalker]

I would be willing to bet that echo does nbot use chrome plating. Chrome has real issues with adhesion, flaking, premature wear, corrosion, and its ability to retain lubrication.

 

[Jacob J.]

<p>Ben-<p/>
<p>Do you know anything about the new "TTI" plating process Kawasaki was using andn how it differs from Nikasil? I've tried searching the web but can't find any real technical info on it. Thanks, JJ<p/>

 

[Mike mandry]

OK guys, I have some questions for you. Esp. the "Chrome" experts.

I have a Homelite SXL that I am restoring. I plan on having the cylinder re-plated with hard chrome.

I just sent the cyl out to have it stripped, & after inspecting it & etc.. Will send it back out to be plated.

I am working with a vendor whom I have been using for 5 years @ my job (rebuilding industrial control valves) and they are very good. Not to mention, I am getting a deal.

I have never done this before & am wondering if any of you have & what results I might expect. I have a new piston & rings that I will be using.

What about break in & etc...???

This is more of an "experiment" than anything, as I don't plan on spending much on it.

Any advice, comments appreciated

Mike

 

[bwalker]

Jacob, The stuff Kaw is using on there bike is basicaly nicisil. Its silcon carbide matrix in other words. It is light years better than the old eltrofusion crap they used before.

Mike, I would not waste your time chrome plating a cylinder. Get the thing nicisiled. If you need a source email me. For a saw cylinder its pretty cheap and I know of a company that does excellant work.

 

[Mike mandry]

Ben, how cheap is it ??

I was once quoted around $160 for nikasil

The chrome is going to cost me around $45

Mike

 

[Weatherby]

Seems to me if it was that much, you could just buy a new cylinder.