What caused this damage?

[pstephens46]

Easy peezy folks....

Yes, it's that simple! (RB)

You won't see either pin from that downward angle. Remember, the pins are machined into the ring grooves, on/to the piston, (on the SIDE, as shown in the previous pictures)..

I know you can't see them. Just wondered on the circumference looking down where they might be. In relation to the arrow especially.

[TownsendsFJR1300]

I know you can't see them. Just wondered on the circumference looking down where they might be. In relation to the arrow especially.

OK..

Well, with the piston installed CORRECTLY, the pins would be located where there is NO ports, IE smooth cylinder all the way up and down the bore...

[rodbolt17]

overpropping is the leading cause of pin failure.
it will also cause wrist pin bearing failures.

[pstephens46]

overpropping is the leading cause of pin failure.
it will also cause wrist pin bearing failures.

Overpropping causes motor to lug. Possibly knocking and detonation. Wonder exactly what happens in that combustion chamber under these conditions to force that pin upwards?

[boscoe99]

Looked at a piston. Pins are not where I would have thought them to be.

Bottom pin is the top red line and the top pin is the bottom red line.

[boscoe99]

Overpropping causes motor to lug. Possibly knocking and detonation. Wonder exactly what happens in that combustion chamber under these conditions to force that pin upwards?

That would be my guess. I don't see these pins just walking through aluminum without some powerful force behind them.

Could the aluminium be getting soft and allowing the pin to move more easily?

Could the extreme force on the piston, coupled with whatever inertia there may be in the steel pin, be causing the piston to slam into the pin?

Could a piece of ring be forcefully trying to lift up on the pin?

[pstephens46]

Perfectly aligned! Right over the ports.

But if rotated 180 degrees they would still be over ports, no?

[boscoe99]

Perfectly aligned! Right over the ports.

But if rotated 180 degrees they would still be over ports, no?

Perhaps not. I am guessing not. That is the only photo I have and unfortunately the piston is in the wrong hole.

That's what she said.

[pstephens46]

Well...once you are in, might as well stay in.

[TownsendsFJR1300]

well...once you are in, might as well stay in.

lol !!!!!!...........

[zenoahphobic]

I'd guess the wrong piston, or incorrectly (180 degrees out) installed on wrist pin.
That error, by whoever, might also explain what appears to me that the ring(s) at the pin are burnt, which may cause the rings to expand and distort at this point like oversized rings where the gap has not been set correctly to allow for ring expansion.

[rodbolt17]

like I said. that piston pic is from a Yamaha Marine Technical Guide.
it is a stbd side piston in a V6 that was installed in the port bank.
note the S ?????
note the UP?????
note the ARROW????
the arrow is supposed to point at the ex port.
it is pointing to port and the port cyl have the ex port on the stbd side of the hole.
nothing magical here.
a simple screw up.