550xp mark 2 piston

[v-ridge]

i recently purchased a pile of 550xp part saws. one is a mark 2 and has little compression. removed top end and to me the cylinder bore looks good but the piston land (clocking bump?) is gone. would this alone cause such low compression? thanks for any advice in advance,

 

[old guy]

That piston & ring are worn way past any use.

 

[v-ridge]

old guy, do you think the cylinder looks ok? i found a new oem piston kit for $40. but do not want to put as much money as a new jug costs

 

[old guy]

From what I can see it looks ok.

 

[ballisticdoughnut]

Yeah that piston and ring are worn pretty badly.

 

[v-ridge]

thanks for the input guys, think i will order a new piston and ring and go from there. also wondering if and one knows when putting it back together if the carb can be pushed into the intake boot on the cylinder then slide the whole thing down on the piston? rather than fight the carb back on in that tight area.

 

[Saw Fixr]

One important point… where did the piece of the broken pin end up? Is it still in the case somewhere?

 

[wcorey]

Looks like someone sanded the heck out of that piston/ring, doesn't appear at all like natural wear.

 

[v-ridge]

One important point… where did the piece of the broken pin end up? Is it still in the case somewhere?

great point. yeah i don't know for sure. i've blown the crankcase out and noticed no catching or binding in the rod. maybe the ring was rotating back and forth until it wore it off?

 

[Saw Fixr]

Wouldn’t t hurt to add maybe 4-8 oz of mix fuel down there and run the crank forward and backwards a few dozen times to flush anything, then dump it out.

 

[Captain Bruce]

That piston & ring are worn way past any use.

NHRA fuel car teams would give that away.........with an autograph.

 

[lloyd786]

I have a jonsered 2253 that got a tree landed on it, low hours. It was a real snot rocket. The piston and jug should be in great shape if you want another parts saw. I’ll deal.

 

[v-ridge]

Looks like someone sanded the heck out of that piston/ring, doesn't appear at all like natural wear.

yeah i think this saw has been used hard.

 

[huskihl]

I’ve seen that ring locating pin loosened up on a few different saws now. I believe it is caused by excessive over revving. The rings begin to flutter, and they end up pushing the pin upward, allowing the ring to spin. If you’re lucky you catch it before it does any damage. I’ve seen the ring spin all the way around and snag in the exhaust port.

 

[v-ridge]

I have a jonsered 2253 that got a tree landed on it, low hours. It was a real snot rocket. The piston and jug should be in great shape if you want another parts saw. I’ll deal.

hey lloyd, appreciate the offer but man i got 4 almost complete 550xp's, one 550xp mark 2, couple of extra crankcases, rear handles, and one 346xp with this deal. if i buy another saw my wife know for sure i've gone insane. although i did get 2 piston rings today and a coil that now has 2 of the 550s and the 346 running.

 

[v-ridge]

I’ve seen that ring locating pin loosened up on a few different saws now. I believe it is caused by excessive over revving. The rings begin to flutter, and they end up pushing the pin upward, allowing the ring to spin. If you’re lucky you catch it before it does any damage. I’ve seen the ring spin all the way around and snag in the exhaust port.

i think you are correct. i'm almost positive when i removed the jug the ring end gap was rotated closer to the exhaust side.

 

[huskihl]

i think you are correct. i'm almost positive when i removed the jug the ring end gap was rotated closer to the exhaust side.

Yep I can see that it was. It’s been clipping the edge of a port for quite a while. That’s why the end of the ring is all rounded off.