What causes this ?

[bathtub28]

Lean?
Debris in fresh motor rebuild?

 

[Director]

Spark plug tip?

 

[52weekbreak]

A guess as you didn't mention the engine but in the days of carburetors the general pitting and worse was due to overheat/lack of lube due to running too lean. Not sure if you cleaned before taking pictures but used to be normal to see some carbon build up in a few spots and don't see that here.

I haven't looked inside an engine since my first fuel injected motor so been 20+ years.

 

[bathtub28]

Early 80’s citation. 377 motor , looks like wrist pin clips are broken.

 

[Lund]

Looks like a mechanical failure, pieces of metal pounded down on the pistons, you say your motor is fresh. Explain.
Did you refresh the top end after a failure?
Did you do a full overhaul, right down to the crank?
Its interesting the damage is in both cylinders as they are independent to each other and both suffered the same damage.
If i didn't know any better it looks like a top end repair after a previous failure.

 

[Lund]

Well, after seeing the second set of pictures it looks like poor assembling techniques. Is this your first?

 

[bathtub28]

Motor was failed, mag side piston was melted. Entire motor was taken down to the crank, sent in for cleaning , new bearing o rings , crank seals, new gaskets new pistons carb rebuilt , set to factory specs, ring look fine but like I said , it looks like the c clips broke on each piston, on one side only. What would show as poor assembly?

 

[Lund]

Motor was failed, mag side piston was melted. Entire motor was taken down to the crank, sent in for cleaning , new bearing o rings , crank seals, new gaskets new pistons carb rebuilt , set to factory specs, ring look fine but like I said , it looks like the c clips broke on each piston, on one side only. What would show as poor assembly?

Your problem was a mechanical failure from poor assembling, hey poop happen's. Those "C" clips are not the easiest to install and if the "mechanic" didn't seat them properly they will fail very quickly.

There is a trick to getting them installed properly, a lot of home mechanics will use a screw driver and pliers to get them in. End up distorting the C clip and it will not seat and hold once that is done.

 

[imdoo'n]

get a better mechanic!

bad assembly,

 

[bathtub28]

Maybe the 240 main instead of the factory 280 could cause this , wish I had noticed that

 

[HotShotHarry]

I notice that the c clips are installed horizontally instead of laterally. Seems to me that that is incorrect as the up/ down motion of the piston can cause the clip to work its way out of the slot. I thought the c clip had to be installed sideways to prevent this. Lund ?

 

[Lund]

I notice that the c clips are installed horizontally instead of laterally. Seems to me that that is incorrect as the up/ down motion of the piston can cause the clip to work its way out of the slot. I thought the c clip had to be installed sideways to prevent this. Lund ?

The correct way is laterally but he seem's to think its a lean burn from being jetted too lean......LOL...its his motor, his money, don't see any indication of a lean burn but what the heck, live and learn right....he'll learn

 

[bathtub28]

So, this was my first, I was just trying to trouble shoot with as much info as I could , it was mentioned above that the pitting is typical of lean conditions. If it’s “ bad assembly “ then fine , was it the clips that look installed wrong? It’s coming apart and will be attempting to right whatever wrong there was so whatever wrong anybody sees and maybe a tip to fix or not make the same mistake again would’ve been helpful. I think it’s a good idea to become a better mechanic and have an idea of what your running rather than just pay someone to always fix your stuff for you.

 

[Lund]

So, this was my first, I was just trying to trouble shoot with as much info as I could , it was mentioned above that the pitting is typical of lean conditions. If it’s “ bad assembly “ then fine , was it the clips that look installed wrong? It’s coming apart and will be attempting to right whatever wrong there was so whatever wrong anybody sees and maybe a tip to fix or not make the same mistake again would’ve been helpful. I think it’s a good idea to become a better mechanic and have an idea of what your running rather than just pay someone to always fix your stuff for you.

A lean burn doesn't closely resemble the damage your piston's incurred. Your piston's got beat up because material went through the motor.
The bad part is your going to have to strip the entire motor down and completely clean it out and inspect it, especially the crank. As all the little pieces that ended up doing damage to the top of the piston's first had to go through the engine bottom cases. At this point, who knows what you will find, the crank might be "F" up.
Its never a good thing when metal goes through a two stroke, generally it causes a lot of damage.

 

[ABMax24]

A lean burn doesn't closely resemble the damage your piston's incurred. Your piston's got beat up because material went through the motor.
The bad part is your going to have to strip the entire motor down and completely clean it out and inspect it, especially the crank. As all the little pieces that ended up doing damage to the top of the piston's first had to go through the engine bottom cases. At this point, who knows what you will find, the crank might be "F" up.
Its never a good thing when metal goes through a two stroke, generally it causes a lot of damage.

I agree with this, no signs of a lean melt down. The second pic on post 4 sure has some weird damage between the rings.

That engine had pieces of metal go through it, its weird that it was both of them.

 

[bathtub28]

Ok, sounds good , I’ll pull it all apart , have someone look at the crank I guess, , and give it a shot again, good idea to put new bearings? Or is there a way to flush them or make sure nothing is left behind?

 

[Lund]

Ok, sounds good , I’ll pull it all apart , have someone look at the crank I guess, , and give it a shot again, good idea to put new bearings? Or is there a way to flush them or make sure nothing is left behind?

A good mech. should be able to help you determine if the bearing's are ok.

 

[Tchetek]

There is a trick to getting them installed properly, a lot of home mechanics will use a screw driver and pliers to get them in. End up distorting the C clip and it will not seat and hold once that is done.

Well help the guy out and share your tips! Continually saying he needs a better mechanic isn’t gonna help him learn.

 

[Tchetek]

A good mech. should be able to help you determine if the bearing's are ok.

Useless post offering the guy no help!

 

[mikeydoo]

https://www.youtube.com/watch?v=qpP6WXxLmXI. helpful explanation.