Looking for piston wisdom

gbic1

gbic1

New member
Joined
Feb 16, 2007
Messages
292
Age
65
Location
Peotone Illinois
Last winter my son rode my spare sled too hard on 2 year old gas. ( he had to keep up with the big dog) . That being said. This was my primary sled that I semi retired when I tore my right shoulder up and could not pull start it. Sled is a 1998 700SX I bought from a friend who bought it new. It had sit for two years and I cleaned the carbs and it ran fine. Told my son to keep it below WOT till we ran the gas out of it and installed fresh. First ride in Wisconsin Northwoods he WOT on the first lake and scored on cylinder on far left. Pulled the belt and towed to a bar and left it till later when we pushed it on the trailer. Fast forward 9 months and I got it in the shop today. Has 145 lbs compression on 2 cylinders and 35 on third. Poked a bore scope in the cylinder and it is toast. MY plan is to install one good used cylinder and 3 new pistons and rings. Sled has about 5k on it and was never apart. It will only be ridden once a year for 400 miles or so. I just got it where I want it. Electric start, reverse, RX1 shocks on the skid, new boogies and it had no issues before this.I can buy a different sled and have to make it mine and hope i get a good one. I would hate to part it out. It is too good for that to me. Is this a good plan? Cant afford to replace all the jugs and pistons. If it needs that it is going to have to sit. Let me know what you think.
 

X2...just want to add I would pull the motor and split the cases. Some guys would leave the motor in and just do the top end. Splitting the cases you can give the crank a good look see as well as get all the debris out. A little more work, crank case seals and some yamabond and your back in bussiness
 
I would check to make sure you don't have a bad seal on that side, that's probably why that side blew( sucking air). especially after sitting for two years .
 
gbic1 said:
I also add extra oil to fuel. Smokes like a chimney.
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I would not do that other than for break in. There was a post earlier this year about that. Extra oil = lean and it will burn up again. Looking at that piston if it weren't for the scuff mark in the middle I would say it looks like a 4 corner cold seize.
 
Backwoods M Max said:
I would not do that other than for break in. There was a post earlier this year about that. Extra oil = lean and it will burn up again. Looking at that piston if it weren't for the scuff mark in the middle I would say it looks like a 4 corner cold seize.
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That's what I was thinking as well but the top of that piston is pretty ate up with detonation. Whats the other 2 look like?
 
What is cold seize? Other two were perfect. Actually looked as good or better than the 1900 mile replacement piston I installed. Carbs were clean as I could see. Yes I added oil just for break in. Cant remember for sure but odometer showed 100 miles since fill up. when this happened. Dont remember if we had just left a bar when this happened. My son was running it. I told him to to run it had since it had been sitting 2 years. It did happen at WOT on a lake. No seal leaks showed when testing engine. I have ran this engine about 20 minutes now. Should I pump out this fuel oil mix and start over fresh.
 
Cold sieze is from not letting sled fully warm up. Hopping on it to soon and dropping the hammer. Piston heats up and swells up faster than cylinder. Aftermarket pistons are worse than OEM in regaurds to this but any piston can do it. How much extra oil did you add? When I have an engine apart I pre-mix 2 gallons 50:1 to make sure oil pump is primed and baby it while running the 2 gallons out.
 
cold seize is when the engine isnt warmed properly and the piston expands faster than the cylinder. also appears to show signs of the bad fuel as well. if you premixed no more than 100:1, you should be fine leaving the fuel in.
 
I have 5 gallons fuel in the tank. I added 16 oz oil. Ran 20 minutes. Was going to top it off with fuel before running. That should get me about 100 to one?
 
Loosely doing the math in my head based on tank being 12 gallons you should be in the 100 to 1 range but this puts you running a whole tank of pre-mix. Refer to directions on back of oil jug to verify math. If the other 2 cylinders look fine I wouldn't be so quick to blame it soley on old fuel. If carbs were clean maybe you had a boot that was loose or something that put that cylinder over the lean edge into danger zone.
 
I guess I will run one more heat cycle on it and drain the fuel oil mix out of the tank and start with fresh. I was hoping for snow like we had last week to run it up and down the ditch with what I had in it. Snow is all gone here now.
 
the crown is burnt back on the piston exposing the ring, it is from lean condition, meaning main jet or needle settings, low octane fuel can also do that. The marks on the 4 corners are more of what a cold seize shows but that could have been from before or trying to run it with the damaged piston.

you dont need to add oil to the gas, just drain some out(5 gallons) and dump in your car or lawn mower and fill it up with fresh premium and ride it.
 
mrviper700 said:
the crown is burnt back on the piston exposing the ring, it is from lean condition, meaning main jet or needle settings, low octane fuel can also do that. The marks on the 4 corners are more of what a cold seize shows but that could have been from before or trying to run it with the damaged piston.

you dont need to add oil to the gas, just drain some out(5 gallons) and dump in your car or lawn mower and fill it up with fresh premium and ride it.
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I pumped most of it out this morning. Some going in the mower and some in the generator. Carbs seemed clean except I did not see any thing in the pilot jets but when I sprayed that carb it came out the end but not the holes on the sides. I ran a wire through and still did not see anything but carb sprays out the holes now. I always buy premium fuel in Wisconsin with no alcohol in it and never ride it Illinois so I don't think it is a octane problem. My guess is the pilot jet and not letting it warm up. I sprayed around the end seal with it running and hear no change in the rpms so I dont believe I have a seal problem. Thanks everyone for your help. Cant wait to ride it. This was my second overhaul. First on was a SRV that burnt down completely . That one had to have the crank straightened. I reassembled it and was served with divorce papers so never got a chance to ride it. Talked to the new owner two years later and said it was still running strong.
 
gbic1 said:
Last winter my son rode my spare sled too hard on 2 year old gas. Told my son to keep it below WOT till we ran the gas out of it and installed fresh.
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This is what I am referring to as low octane fuel problem,(snipped from your first post here).
2 year old fuel will be low on octane,resulting in burning back the crown from excessive heat. octane is the fuels ability to NOT burn resulting in a cooler combustion and this is what keeps away detonation.

as long as you have stock jetting in it you should be good to go now.

as you have learnerd the hard way, dont EVER run old gas and run the sled without cleaning the carbs every year, it almost always results in this damage.

Ride Safe,Merry Christmas to you and your family!
 
I put fresh premium it it and ran it about 3/4 for a hundred and 30 miles. Is she ready to rock and roll now?
 
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