Judging condition of top end?

This is a followup to an earlier thread about my troubled Husky 350.

I've pulled the P&C and taken some better photographs. Along the way I discovered that the spring that makes the connection between the spark plug and wire was broken, so there's a chance that most of the running problems were ignition-related. As I said in the earlier thread, compression was around 120 PSI, which I know isn't great.

Here are today's pics of the exhaust sides of the P&C.



I don't want to throw cash into this unnecessarily, but because I haven't done much top-end work aside from replacing a totally worthless set, I have no basis on which to judge what of this is salvageable. So a couple of questions for those more knowledgeable:

First, how does piston damage like this affect compression? If the ring is in good condition (and it looked like it was), why does the scoring above and below the ring matter unless it gets severe? I would've thought that the seal was between the ring and the cylinder wall, so why would low spots in the piston surface matter?

Second, please help me understand what this cylinder needs. There are visible lines, obviously, but they feel totally smooth, not perceptibly raised, and they don't catch a fingernail dragged across them.

I realize that even with decent photos it's probably difficult to judge parts that you can't handle, but if you've dealt with top ends like this then I'd appreciate any thoughts you can offer to help me get oriented.

 

Looks awfully carboned up. I would saw get a new piston and clean up cup if smooth. It is scratched. Can't help you on why it would matter? I am no expert here. 120 is not great but obviously it runs!. If you dont want to out cash into it get a new set of rings clean it all up and reassemble and run it.

 

I noticed the carbon too of course. Is this typically caused by running it too rich? With the carbon looking so flakey and loose on top of the piston, is it plausible that the scoring is the result of scratches from loose bits of carbon being dragged over the surfaces, rather than the usual problems of running too lean or straight-gassing? The scratches were already there when I got the saw, so I can't refer back to any known history.

 

Carbon is from running too rich. But the weak spark could be the culprit. Or the guy not running g it wide open when working. Say running 3/4 throttle trying to "save wear" on the saw. Possible that carbon caused scratches but I would have to yield to someone with more knowledge and exp here?

I run oil always 40:1 or more. I have pulled a saw down for internal work and it looked nothing like that running husky semi syn low smoke oil that you

 

You could get by with just a ring since you say the scratches wont catch a fingernail. Use very little oil when assembling (ie. oil it then wipe clean with paper towel)

Back in the day when I worked at a MC shop, I had a discussion with the Suzuki service rep about how a higher oil/fuel ratio actually makes more power, and shortens engine life. The reason being is because of the change in viscosity of the pre-mix. It is slight, but is present, therefore 20:1 is thicker than 50:1, and therefore run leaner.

There's your knowleducation for the day.

 

It runs leaner bit if you adjust your carb???

If you dont care much about the saw and wasnt a runner I think a ring will boost you back up there, but what do I know?

 

Exactly

 

To clarify, I don't mind replacing the piston if it's necessary. I would like to understand why I'm doing it, though.

I would very much prefer to keep the original cylinder, and since there's little to no scratching there I suspect it could work fine. Any suggestions on carbon removal techniques, for cleaning up the exhaust opening and the top of the combustion chamber?

 

I had an 034Super come my way with very similar scoring. Since I'm confident with acid and had the material, I pulled the jug and cleaned everything up. I put in a Meteor (decent price from weedeaterman) piston and I was back in business. I gave that saw to my old man and it is one of our best. IMO I would do the same thing with your saw, but possibly use Mastermind's techniques to clean up your jug.
In terms of diagnosis, I spent a while looking at Madsens and AS for piston failure analysis... but I still think no one can know for sure on every piston. If I had a guess, you're running a bit lean/hot. The carbon may have had an impact but I've seen much worse. As it turns out, I found a leaky seal on the 034Super during the rebuild. All lines and sealed were replaced and it is good to go.
In a nutshell:
1. The cylinder is probably salvageable. Get all the transfer outta there and it'll look close to new.
2. Some guys clean up pistons and put in a new ring, but yours had some decent transfer...
3. Meteor pistons are great
4. Replace rubber lines, clean/tune carb, give the saw a good cleaning and run the snot out of it.

 

Sea foam cleans carbon pretty good. And soaking in carb cleaner gets stuff shiny.

 

Forgot to give you an average estimate for my top end rebuilds over the last year -- Some are AM, some are Stihl prices. When deciding if a saw is "worth it," the darn things that add up are usually small and cheap---
1. Meteor Piston- $40-$50
2. Fuel line- $10
3. Impulse line- $3?
4. Gaskit kit (with seals) - $16
5. Spark Plug- $5
6. Air Filter - $15
7. Carb cleaner - $5 (will last a while)
8. 6M HCl (Muriatic Acid)- $10-$20 (will last a while)
9. Misc. Scotchbrite, sand paper, etc. -$10 (I get all mine for free, so no idea here)
10. Labor $5- seal removal and install...sometimes my dealer lets me use their puller for free and they will test vacuum as needed.
11. Fuel Filter- $7

You probably have the needed tools, and I don't know about Husky seals/lines.

 

This works very well on carbon

 

Don't have to replace piston. Clean it with some scotchbrite (scoring marks) and reuse. Now If I was rebuilding it for you, I would put a piston in it. Why, you ask? Because it's insurance for me paid by you. If for some reason the motor gernades (weather it was fuel, carb etc.) I would be buying you a motor. I would also rebuild the carb for the same reason. A lean condition kills 2 strokes quickly.

The carbon build up could be any number of things, none of witch I'd be concerned with. Could be... short run times, chitty oil, clogged air cleaner, chitty gas (regional thing-fuels are formulated bassed upon region), chitty ignition system, etc.

Put a ring in it, do a pressure/vacuum test (should have been done prior to tear down as well), run the fuel you always run, and run it like you stole it. The scuffing on the piston is usually caused from little to no warm up, and maybe a high speed lean condition (among other things).

After a tank of fuel, tell us what your compression numbers are.

If you wanna get crazy, measure your piston at top, mid, bottom and then measure your bore top, mid, bottom, then 90 degrees top, mid, bottom. You're checking for out of round, and piston to cylinder clearance.

edit: Don't loose your mind on the carbon, it won't do any harm. Just get the big loose stuff off. Run some Techron (or Yamaha Ring Free) in your fuel at the recommended amounts. That will clean your carbon!

 

Yea im building a husky372 with a chicom big bore kit. And all the handles and such and covers are more than the AM piston cylinder.

 

Jug is totally useable... Piston could be salvaged also, but don't... It's the dished model, probably 45mm... That is the worst piston set up the 350 has ever had for compression... Replace it with a flat top piston off e-bay.. Even a cheap one.. Don't look back... Huge gain in performance.
As far as the aluminum transfer above the exhaust port, you can lightly sand it in a twisting motion till most of it's gone, or get a q-tip and some muratic acid and rub it on there till it eats the aluminum off the nikasil. rinse with water every so often and check to see what's left..
A little bit of transfer ain't the end of the world... These buggers ain't as delicate as you'd think...

 

The OP said

"Second, please help me understand what this cylinder needs. There are visible lines, obviously, but they feel totally smooth, not perceptibly raised, and they don't catch a fingernail dragged across them."

This tells me there is no transfer. If this is the case, don't touch the cylinder. No acid, no sandpaper, no scotchbrite. The crosshatch is plainly visable even in the scored area. If for some reason you decide to not heed this advice and take an abrasive to the cylinder, you must wash it at least twice in hot, soapy water, otherwise the is a very good chance that some of the abrasive will remain in the cylinder. Then you get to do the whole process all over again, this time with a cylinder, and piston too. Buy an OEM ring, clean any rough edges of the piston, clean the ring groove real good, assemble and make some chips!