What’s happened here?
Discussion
There’s not much more I can add as anything else other than low compression is an unknown. I bought the car faulty. So this is what I’m trying to figure out. If it’s likely to be an oil starvation issue or over heated the piston? I don’t have any experience with these types of issues.
Looks like classic four point seizure, if the other side of piston shows the same seizure pattern. Usual cause too much thrash from cold before the bores have expanded. The thrust and opposite side are able to deform as they are not rigid so they do not seize. However, the areas around the gudgeon pin which are strengthened are not able to give so they seize. Very common in two stroke pistons.
Peter
Peter
acealfa said:
Causing low compression. Can anyone explain what’s actually happened to cause this contact?
I’m assuming the block is knackered but would the piston be ok to reuse with new rings?
Block could be repaired, re-linered, bored, whatever.I’m assuming the block is knackered but would the piston be ok to reuse with new rings?
Piston....harder to say without better pics. But generally no when scuffing and melting have occurred it would not be deemed re-usable unless you were absolutely desperate and the ring grooves still measured perfectly, as well as piston proper dimensions all round etc.
And you bought this with the engine f
ked and already apart ?is the second land cracked? Looks like it might be! (classic fatigue failure as most of the pressure loads come from the top ring, which cracks the second land, which sags, allows the ring pack to distort, and generally a bit of the piston (ally) touches the block with a point contact, pushing through the oil film, causing ally to overheat, pick up and wreck everything. If it lasts a really long time, then often the engine then dets of pre-ignited itself to death as well as the hot piston leaves bits of burning ally behind it as it drops down the bore.
Sometimes, the broken land isn't that obvious crack wise, because the scuffing both covers up the crack and can even friction weld it back together again.......
Sometimes, the broken land isn't that obvious crack wise, because the scuffing both covers up the crack and can even friction weld it back together again.......
Max_Torque said:
is the second land cracked? Looks like it might be! (classic fatigue failure as most of the pressure loads come from the top ring, which cracks the second land, which sags, allows the ring pack to distort, and generally a bit of the piston (ally) touches the block with a point contact, pushing through the oil film, causing ally to overheat, pick up and wreck everything. If it lasts a really long time, then often the engine then dets of pre-ignited itself to death as well as the hot piston leaves bits of burning ally behind it as it drops down the bore.
Sometimes, the broken land isn't that obvious crack wise, because the scuffing both covers up the crack and can even friction weld it back together again.......
I cannot see ring crack on second ring but then again it is always better to have the parts in front of one to view! Don't cracks usually show as an angular non vertical pair either as a vee if force from below rings and inverted vee if force from above?Sometimes, the broken land isn't that obvious crack wise, because the scuffing both covers up the crack and can even friction weld it back together again.......
Peter
The end of the second compression ring is trapped in its groove which means the groove has closed up. Photos of the top of the piston and combustion chamber would help but likely it's detonated leading to piston failure, piston overheating and seizing in the bore. Piston is certainly scrap. Bore looks to be also but hard to tell. Only the top part of the bore is really important for compression and power so it might clean up with a hone.
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