How bad is this piston? 550xp Project

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HumBurner

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I picked up a 550xp with a punctured fuel tank (chain was tossed, which is no wonder if you saw the inside of the saw and the drive sprocket) for $125. Couldn't get them to come down any more on it. Saw starts and runs, though I didn't let it run more than a couple minutes what with the leaking fuel tank.

Knowing that the pawn shop that had this saw is kind of a crappy place, i was aware that the saw might have some issues. So, i decided to tear it apart to clean it and check the piston/cylinder. Here is what we have, via terrible quality photos. Gonna swing by the saw-shop today and have them take a peak. If they think it's worth exploring further, I'll take off the cylinder and replace the gasket, have them check the hours and run conditions, etc...



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There was a solid 1/4"-1" layer of pitch on EVERYTHING; the exterior of the saw, the clutch-case, the plates against the case, the flywheel, up under the muffler. Arguably, the cleanest thing was the carb and the air-filter. The sprocket looks like it had never been replaced on this early 2013 550xp (dark gray, old-style caps).

The muffler gasket was cracked and brittle, note the fibers splitting apart.

Here is the current parts list, if this saw is worth putting any money into:


- Nuts (the ones on it weren't even standard bar nuts, allowing extra pitch into the case)
- New clutch (and likely a new drum), sprocket, and needle bearing
- Muffler gasket
- Pulley screw (no screw currently)
- Brake-handle bushing/ring

Could use a new air-filter, though it could get by without affecting too much. Spark plug also isn't too bad but would be better replaced. If the piston itself isn't too bad, it's likely the ring will need to be replaced. From what I can tell, it looks pretty rough. I also had to replace the starter-rope, as it was over a foot too short.


Worst case scenario, i'll sell it to a co-worker as a parts-saw and lose a little money on the deal. I'm still learning as I go, so the experience alone is worth the time/cost.
 
Thanks for the fast response!

I'm less worried about the brown marks on the piston, unless they aren't just carbon deposits, and more concerned with the top, which is probably the worst of the photos, unfortunately (go 4th gen ipod touch 0.7mp camera!!!) and the beginning of the scoring marks. None of them appear too deep, but you can see some shiny-places atop the piston, through the roughness, which don't seem smooth.

However, your initial reaction gives me some hope, and I appreciate your time and input. Again, I'm just starting out on this path of used saws and what is good vs. what is trash.


Unfortunately, my truck bill today is ~$350 more than what I was expecting, so now the spare parts list and this project may have to wait until summer....or I'll just have to work a couple rainy days to get on it sooner!
 
I was gonna say the crown of the piston looks a little chewed up. Agree that the piston wall looks okay; can you do any pics through the intake side (looking at exhaust wall and through the plug hole to get a better look at the crown?
 
I was gonna say the crown of the piston looks a little chewed up. Agree that the piston wall looks okay; can you do any pics through the intake side (looking at exhaust wall and through the plug hole to get a better look at the crown?


I tried to do that, but the light mixing with the poor quality of the camera yielded nothing but darkness. If the carb were off, too, it would probably work, but I'm not that far along yet.

Took it into the shop last hour. Head guy looked at it for a couple of minutes. Said the scoring is negligible at this point, but he also had some concern on the top of the piston. However, he felt, assuming there are no other hidden issues with it, that it should be just fine once all the needed parts are replaced. Looking at ~$122 retail for the parts, so probably about $100 or less, excluding a fuel tank assy if needed. He did note that the earlier models of the 550xp were notorious for developing micro leaks in/around the cylinder. So hopefully i won't throw a couple hundred bucks into this and have it still fall on its face when it comes to the tests. Didn't have time to throw it on the diagnostic today, so maybe next month i'll get the hours and running conditions known so I can decide from there.

Will have my buddy throw his compression gauge on it.
 
How did your air filter look? Sometimes the tops of pistons can be pocked up by foreign material making its way up the transfer ports in instances where the air filter is compromised or removed. Rarer would be that a bearing, or something metal inside the crankcase broke a piece of and it went up the transfer ports, similarly and pocked up the crown. The edge looking craggily like that to me merits investigating.
 
How did your air filter look? Sometimes the tops of pistons can be pocked up by foreign material making its way up the transfer ports in instances where the air filter is compromised or removed. Rarer would be that a bearing, or something metal inside the crankcase broke a piece of and it went up the transfer ports, similarly and pocked up the crown. The edge looking craggily like that to me merits investigating.


The air filter was pretty darn dirty. Took some scratching with a thin screw-driver and two rounds of gas-baths to get it remotely decent. Considering the muffler gasket was done for and there was a 1/2"+ layer of pitch/gunk underneath and all around the muffler, i'm HOPING it's just debris from the outside. Oddly, the intake (?) that the air-filter latches onto was nearly spotless inside, only a slight bit of grease came out when wiped with a rag.

But I am very intent on inspecting the top further before putting a dime into the saw (aside from the pull-rope which i had spares lying around.) Your reinforced concern is noted.
 
Plan on at least another $35 for a carb kit and crankcase seals. The fuel tank vent may also need attention.
This thing has been running hot from leaning out.
 
Plan on at least another $35 for a carb kit and crankcase seals. The fuel tank vent may also need attention.
This thing has been running hot from leaning out.


Thanks for the advice. I'll add those to my list. I take it you would recommend doing both clutch and flywheel sides? I haven't checked yet, but was the 550 the same as the 562 with the series of carbs (EL44/46/48) and one working better than another? If so, I might just throw on a new carb.


Would you have any guesses as to whether it was the fuel mix, the congestion, or the carb itself causing the lean? I wouldn't be surprised if this saw had been run dull quite a bit. The bar that came with it has chunks/divets missing from around where the sprocket inserts. Basically looks like someone took a chisel or jackhammer to it. It even came with a brand new chain! Doesn't look like it's been filed once, little wear on the tangs.
 
The splotches on the exhaust there look like lubrication breakdown, possibly precipitated by a really dull chain. Could also be using crappy oil, old gas. Bad seals in my experience (not nearly as vast as some on here) wouldn't cause that particular type of shite to build up on your piston. Usually the extra air means lean running & scored piston.
 
I like a challenge looks like a project. I’d fix it if I were you. Pop a cold one and work on it.
 
I like a challenge looks like a project. I’d fix it if I were you. Pop a cold one and work on it.

Definitely agree, worth the time to find out more about it. A course if your bearings are toast, your rod is cracked and your piston crown looks like swiss cheese, might not be cost effective, buuut....
 
one must do an assessment first on what it needs. Then figure the cost vs value when it’s done. I grabbed some parts donor saws because they were cheap. One 262 I disassembled has a good cylinder that I just Ported. Another 262 needs rebuilding.
Parts is parts too.

I think about what some of these saws cost new. Then we buyvthem not running between $100 to $200. Some need little fixing. I seen some silly things wrong with saws. One was lacking compression the compression release was frozen in. Now she runs awesome. I’m working on a 350 husky I never seen a rim on the clutch so worn. I won’t start it up. The rim makes a horrendous ratchet noise while pulling the chain while sharpening it. A new rim, some missing screws, a new huztl top cover and dressing the bar, sharpening the new chain it came with she’s a runner.

I purchased a 268xp that’s in mint orginal condition. Plenty of compression. The stop switch had three detente off/ inbetween nothing happens/ a third click on. New stop switch. Done fixed.
 
Sounds to me like you approach the job from a pretty logical perspective. I like to hear that. I've talked to "mechanics" before who just, "Oh I put a new carb on it, see if that gets it going." As if competing for the sloppiest possible workmanship. Man. Have some pride in what you do.
 
one must do an assessment first on what it needs.


And learning how to make the assessment is the point i'm starting from. Thankfully, the guys at the shop are very cool and willing to help, so long as they aren't bombarded with repair work. Not having internet access complicates the learning process, as does being 16 miles from any shop, and ~90 miles from the good shop.

I'm strongly considering taking a small engine repair course at a community college this summer.....if I can afford it. Not mechanically inclined, but wanting to learn.
 
Has not been performed yet. Assessing the piston/cylinder and carb are the first steps to determine whether the saw will be kept for a project or whether it will be sold as is.
I may have checked case for gasket or seal leak first, but it's not my saw or build. Like knowing why saw had problems as tear down begins, figuring that out is best part for me.
 

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