Me thinks I may have a problem

[Schilling]

This. There is no question in my mind, (and I do a LOT of forensic mechanical investigation $$$$$) that that circlip was dropped in the sump (and not retrieved) by a doofus at assembly. There is no damage path on the piston big enough for it to have escaped.

the pictures I took with my phone aren't the best in the world, not good enough to show the inboard side of the right hand piston pin area. but, the inboard side of the right hand piston where the circlip used to be does have enough of a damage area/path to have allowed the circlip to come out of its slot. and the pin was really loose (i was able to push the pin from the outboard end inboard with virtually no pressure, it really did just slide out). what puzzles me, still, is the amount of damage on both the outboard side of the right hand piston and the outboard side of the right hand cylinder,,,,both of those locations show a lot of damage,,,but the outboard circlip on the right hand piston was securely in it slot and the pin would not migrate outboard beyond that circlip

 

[concours]

Which one of these three are you referring to?

 

[Nater_Potater]

In the second piston close-up picture of this group https://www.accessnorton.com/NortonCommando/me-thinks-i-may-have-a-problem.26544/page-3#post-398524 the picture shows where the circlip could have possibly gone either through the top or the bottom of the piston, but there's an aftermarket circlip still occupying the groove! Is it possible the engine "builder" put them both in there? That way, the outer clip would have nothing to latch on to, and would be moving around on its own free will.

 

[cyclegeezer]

Which one of these three are you referring to?
View attachment 7619 View attachment 7620 View attachment 7621

the pictures I took with my phone aren't the best in the world, not good enough to show the inboard side of the right hand piston pin area. but, the inboard side of the right hand piston where the circlip used to be does have enough of a damage area/path to have allowed the circlip to come out of its slot. and the pin was really loose (i was able to push the pin from the outboard end inboard with virtually no pressure, it really did just slide out). what puzzles me, still, is the amount of damage on both the outboard side of the right hand piston and the outboard side of the right hand cylinder,,,,both of those locations show a lot of damage,,,but the outboard circlip on the right hand piston was securely in it slot and the pin would not migrate outboard beyond that circlip

My suspicion is that the clip broke, was shaved thinner by contact with the cylinder wall, pieces migrated through the pin, damaged the side with the intact circlip, and at some point one was thin enough to squeak by the skirt into the sump. Just my WAG.

 

[Dances with Shrapnel]

In the second picture the square section wrist pin clip appears to be in place and maybe intact though the gap at the eye ends is suspect. So my question is, if the circlip is in place, exactly what caused the swallowing out of the wrist pin bore. As for a potential path for a wrist pin path into the crankcase, in my opinion, in this instance it is premature to say it can't happen. I have seen some bizarre things during failure anayses.

 

[comnoz]

In the second picture the square section wrist pin clip appears to be in place and maybe intact though the gap at the eye ends is suspect. So my question is, if the circlip is in place, exactly what caused the swallowing out of the wrist pin bore. As for a potential path for a wrist pin path into the crankcase, in my opinion, in this instance it is premature to say it can't happen. I have seen some bizarre things during failure anayses.

Combustion heat leaks past the rings where the pin has dug into the cylinder wall. Then the heat passes through the center of the wristpin and erodes the piston on the other side.
Not uncommon. It just takes a couple thousand miles to do it.

PS, I did find your lost box.

 

[Dances with Shrapnel]

Wow, interesting phenomena Jim. Good news on "the box"! Looking forward to replacing the fast parts with faster parts!

 

[Schilling]

Which one of these three are you referring to?
View attachment 7619 View attachment 7620 View attachment 7621

the top (first picture of the three) photo is the inboard side of the right hand piston,,no circlip is there and the portion of the piston where the slot for the circlip is gone,,,,the middle (second picture of three) photo is the outboard side of the right hand piston, the circlip is there and in its slot (the wrist pin in that picture has migrated a bit inboard), the bottom (third picture of three) photo is the outboard side of the left hand piston, the circlip is there and in its slot (the same situation exists for the inboard side of the left hand piston).

 

[Schilling]

My suspicion is that the clip broke, was shaved thinner by contact with the cylinder wall, pieces migrated through the pin, damaged the side with the intact circlip, and at some point one was thin enough to squeak by the skirt into the sump. Just my WAG.

I think your WAG may explain some of the damage on the outboard side of the right hand cylinder wall as well

 

[Schilling]

Combustion heat leaks past the rings where the pin has dug into the cylinder wall. Then the heat passes through the center of the wristpin and erodes the piston on the other side.
Not uncommon. It just takes a couple thousand miles to do it.

PS, I did find your lost box.

and two thousand miles is almost exactly how long (in miles) i've owned the bike. the head, the barrels and the rest of the engine are on their way to Colorado, I've included the pistons and pins in the boxes just for curiosity's sake

 

[Esmerela]

Hi
What make were the pistons ? Sorry if you gave this information in a previous post, I was wondering if they were Emgo, there has been some criticism of the std clip supplied with the Emgo pistons. maybe the engine builder never had the benefit of the collective knowledge available on this forum.