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Discussion Starter #1
Hey guys, just wanted some opinions on what caused my pistons to look this way. Bought a (working) motor off of someone over the summer and it had about 125 psi in each. Dropped it in and ran it for a grand total of about 8 miles the other day before this happened. Just wanted to know what you think happened. Thanks
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looks like 4 corner sieze co pistons.
so did not get up to tempature before flooring it.
or not enough oil in the gas.
 

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I was gonna go with 4 corner score as well. these things can make some some similar signs even though there are other problems. as an example; you might see signs of a four corner score but in actuality the crank seal was out causing the piston to show similar signs of aggressive warm up.
 

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Discussion Starter #10
So I’m not really familiar with the phrase “4 corner score”, is that what auburn6887 was talking about with the whole not up to temp thing? If not could you explain further? Thanks, I know it wasn’t started and rode hard immediately but I wouldnt say I rode it for miles before it happened.
 

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4 corner score is when the piston gets too hot and the thickest parts of it expand. This is on each side of each wrist-pin hole, thus 4 spots of seizure.
It can be a general overheat, lack of oil, or running a cold engine too hard. In the last case, the piston expands faster than the cylinder head and it will seize up as those 4 “corners” push out and dig into the cylinder wall.

Did your engine seize up solid or did it run and die, to not start back up due to lost compression?
 

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Was the other piston damaged?
 

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Discussion Starter #13
Yes both were damaged, and now that you say something, I do remember that when it died, it seemed like the motor did seize or something. Went to start it back up and it wouldn’t pull over. Towed it home and by the time I got back it was fine. I totally forgot about that till now.
 

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Discussion Starter #14
So does this mean that it was indeed a cold engine being ran too hard or could it still be either that or a lack of lubrication? I’d like to know so if I rebuild it whether or not I should be worried about the oil pump not working properly.
 

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if I opened an engine up like that (which is common) I'd suspect the crank seals, lube system, carbs (one could be running lean and the other cylinder pulling it along) , the carb boots,...... it doesn't matter at this point if it was warmed up or not it's f'd. start from the bottom because you'll have to anyway and look for clues as you build up. good luck! sincerely! I hope ther bearings aren't toast as well! put some sweet wisecos in that ole girl!
 

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I’ve heard that when the oil pump fails, it has a failsafe in that it over-oils the system when it goes bad.
There is a possibility for the oil line to get plugged between the tank and the pump which would starve the engine of oil. Unlikely, but still possible.
I’m leaning towards a lean burn down on yours. It’s just odd that it happened on both sides about equally. What did the plugs look like when you tore into it?
 

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I have seen a new sled out of the box get starved for oil, by the motor being installed on the oil hose between the motor mount!! Sad day for CAT!!
 

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cold seize is another term. Called that because it happens when the coolant isn't up to temp. Metal gets bigger as it gets warmer, and the largest amount of metal in the piston is in the 4 corners around the wrist pin. When you load the engien hard you put a lot of heat in all at once. the piston having much less mass than the cylinders and entire volume of coolant in the sled warms up at a faster rate, so it grows at a faster rate. If the engine and cooling system is at operating temps this is no big deal. But if the sled isnt' warmed up the piston gets bigger than the cylinder and sticks.

Clean the cyinders with acid, and a ball hone, use cast pistons, an oem base gasket. bleed the oil pump, and adjust it by aligning the marks at WOT
Take a good look at the exhaust valve pin and cable
pre-mix the first tank of fuel 50:1 and fill it to the top
mark the oil level on the outside of the tank with a sharpie
run the sled until the rear cooler is hot to the touch before riding
go for a nice easy ride trying to burn at least 3/4 a tank of gas
Fill the tank at a pump and write down exactly how much fuel it takes
Fill the oil to the line using a measuring cup marked in oz.
(gal of gas*128)/oz of oil = ratio
ratio should be between 40 and 50
 

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That doesn't look like any 4 corner that I've seen. Looks like flat out lube failure to me.
 
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