What caused this damage?

[DennisG01]

Just doing some "googling" and I came across numerous threads on various forums discussing this. An "issue" that the wallowed hole can then allow is for the pin to eventually work it's way out of the hole (at an angle, allowed by the large hole) and cause other problems such as the pin getting stuck between piston and cylinder wall, and of course causing damage and/or then allowing the rings to move, as mentioned above.

Every thread I came across said "most" 2-stroke engines use pins. I don't know if there really are any that do NOT use pins as I didn't see it mentioned. It could just be the terminology that people are using. Is there a different way to accomplish the same thing (keeping rings from moving)?

[TownsendsFJR1300]

So even things like weedwhackers and chainsaws? Curious minds, you know?

If it's a two stroke, yep, pin's.

All two strokes have ports ("holes") in the cylinder to pass gases, intake and exhaust thru the engine. The rings cannot rotate or they'll catch in the ports and ruin the engine.

[pstephens46]

Is there a right/wrong way to align a piston? In other words, rotate another 180 degrees and then bolt to crank. Putting the pin side nearer to an exhaust port. Where erosion might occur? Is that even a possibility?

[DennisG01]

If it's a two stroke, yep, pin's.

All two strokes have ports ("holes") in the cylinder to pass gases, intake and exhaust thru the engine. The rings cannot rotate or they'll catch in the ports and ruin the engine.

Thanks, Scott. I was also curious if there was another method of accomplishing the same thing. But in some googling, I couldn't find another method.

[TownsendsFJR1300]

Is there a right/wrong way to align a piston? In other words, rotate another 180 degrees and then bolt to crank. Putting the pin side nearer to an exhaust port. Where erosion might occur? Is that even a possibility?

Two stroke (and likely many 4 strokes) pistons usually have an arrow atop the piston facing forward (at least on bikes).

Unlike most car engines, (where the piston pin is pressed into the connecting rod/piston(and won't come out), most two strokes, the piston to connecting rod pin simply slides in and is held in with circlips on each end of the piston.

Marine two stroke engines, I suspect the arrow on the piston faces upward.

Someone here, can check their TWO STROKE shop manual re piston installation. It should say the direction of the piston for installation..

There's really NO "erosion", simple wear and tear as with any engine. As the rings are stationary on the two stroke, it's especially important to keep the engine running clean, proper oil use, etc to keep carbon down to a minimum.

Those damaged pistons posted above, obviously, something was not correct, whether the engine was running lean, no oil, etc and eventually failed.

The above is why I spend the extra $ for non-ethonol fuel, RING FREE, etc. Anything to keep the engine running clean and normal will extend it's life..

[boscoe99]

Is there a right/wrong way to align a piston? In other words, rotate another 180 degrees and then bolt to crank. Putting the pin side nearer to an exhaust port. Where erosion might occur? Is that even a possibility?

[TownsendsFJR1300]

There's your arrow ^^^^, and you can see the cylinder ports which is why it's critical TWO STROKE rings stay put!!

Ya know Boscoe has a pic!

[pstephens46]

Where is the pin located on this piston in the pic?

[boscoe99]

Pics are good. Worth ten thousand of my words.

[boscoe99]

Where is the pin located on this piston in the pic?

Which pin? There are two?

[pstephens46]

Which pin? There are two?

Pin that failed...

[99yam40]

my guess is this is not the same motor he started talking about

[pstephens46]

Ahhh, the exercise continues. Somebody needs to solve this puzzle before Rodbolt comes along and tees off....

[TownsendsFJR1300]

Ahhh, the exercise continues. Somebody needs to solve this puzzle before Rodbolt comes along and tees off....

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)..

[rodbolt17]

that pic was taken from a Yamaha marine tech guide.
was a factory boo boo.

the pics of the pin coming loose is typically evidence of overpropping.

do this for about 30 yrs and you may see it in real life.