lost piston pin

[jasper's YZ]

Went to rebuild my top end in my 2000 yz 125 and was examining the piston and noticed where the 2 ends of the ring meet the pin was gone. Looked at my jug and the was a nice gouge in it. Has anyone experienced this before? It was an oem cast piston. Brought it to the machine shop and we looked at it again and on the front side the bridge that seperates the 2 ports has a wave in it. He thinks that may have cause the ring to jump and put pressure on the pin? Any way it has a sleeve in it and I am going to bore her out. Just wanted to see if any one experienced this before.

Matt

 

[chevyss_98]

weird man, never had that happen before, ive had circlips disappear...you can imagine what happened after that, but anything is possible when your dealing with 2 strokes, lotsa crazy stories, shove a wiseco forged piston in there, lot stronger than oem, cast is really bad for letting chips of metal off, im in mechanical engineering, my final semester and trust me, cast blows chunks, its garbage

 

[jasper's YZ]

I had a wiseco ready to go in now that has to go back and waiting to hear how far over I have to go.

 

[BigRedAF]

weird man, never had that happen before, ive had circlips disappear..., im in mechanical engineering, my final semester and trust me, cast blows chunks, its garbage

I guess that makes you an expert :coocoo:

 

[Rich Rohrich]

Went to rebuild my top end in my 2000 yz 125 and was examining the piston and noticed where the 2 ends of the ring meet the pin was gone. Looked at my jug and the was a nice gouge in it. Has anyone experienced this before? It was an oem cast piston. Brought it to the machine shop and we looked at it again and on the front side the bridge that seperates the 2 ports has a wave in it. He thinks that may have cause the ring to jump and put pressure on the pin? Any way it has a sleeve in it and I am going to bore her out. Just wanted to see if any one experienced this before.

Matt

There is nothing wrong with the stock OEM cast pistons.

If the shape and the edge chamfer of the exhaust port is incorrect then the ring can get hammered to the point where it will lever the locating pin out. It can happen with cast and forged pistons. This is common with cheap replacement sleeves for plated barrels.

Before you put it back together you should have a professional reshape the exhaust port so it won't happen again.

 

[souphmars]

there is nothing wrong with oem or wiseco pistons, but wiseco pistons which are forged, are stronger than oem pistons

 

[griffbones]

there is nothing wrong with oem or wiseco pistons, but wiseco pistons which are forged, are stronger than oem pistons

This has nothing to do with the pin falling out. As Rich stated it is probably another underlying problem that caused the pin to come out, and that will need to be corrected in order to ensure the problem doesn't happen again.

 

[Jeromeo]

weird man, never had that happen before, ive had circlips disappear...you can imagine what happened after that, but anything is possible when your dealing with 2 strokes, lotsa crazy stories, shove a wiseco forged piston in there, lot stronger than oem, cast is really bad for letting chips of metal off, im in mechanical engineering, my final semester and trust me, cast blows chunks, its garbage

Lesson one in mechanical engineering:
-DO NOT USE CAST pistons, they blow chunks. :bang:

I wish they passed on that wonderful knowledge to me in my university courses.

Cast pistons are fine.

 

[souphmars]

it could be from a bad piston- i have heard of this happening on certain brands of pistons- or there could have been too much clearance between the piston and cylinder and it could have vibrated loose- that is just a guess- if the piston was not a bad piston, something had to vibrate it out

 

[BigRedAF]

Last time I checked every bike made and sold at your local dealer came with an OEM piston and ran fine.

It's lack of maintenance, running a worn piston in a bike that sucked dirt or improper repair that causes the piston failures that I've seen.

 

[griffbones]

Last time I checked every bike made and sold at your local dealer came with an OEM piston and ran fine.

It's lack of maintenance, running a worn piston in a bike that sucked dirt or improper repair that causes the piston failures that I've seen.

+1
I run the Wiseco forged pistons, but that is mainly because I can buy them at cost, but I can not buy the OEM pistons at cost. Either one would work just fine for my purposes, as I do frequent top end maintenance on my bikes.

 

[chevyss_98]

everyone seems to be ragging on me, not quite sure why, im not saying im above everyone by being in engineering, ive just studied these manufacturing processes under the microscope, the reason forged is stronger is that the grains of metal are elongated in a pattern that makes it so stress cracks are EXTREMELY hard to be developed from repeated loading and basically are never noted unless there is a fluke in the material

besides, i had a cast piston break off at the top and go out my exhaust before because i had a hung ring, im speaking from my experience, not just jabbering on about my schooling, im just using my education to back up the fact that forged is better

ever wonder why your ratchet is drop forged and not cast??? lol unless you get your tools on clearence at biglots or k-mart lol

OEM pistons can be fine as long as you monitor it, im just saying personally with my experience on my first bike, it just cost me alot for machining costs, so since then ive gone with forged since my negative experience with cast

sorry if i offended anyone

 

[griffbones]

everyone seems to be ragging on me, not quite sure why, im not saying im above everyone by being in engineering, ive just studied these manufacturing processes under the microscope, the reason forged is stronger is that the grains of metal are elongated in a pattern that makes it so stress cracks are EXTREMELY hard to be developed from repeated loading and basically are never noted unless there is a fluke in the material

besides, i had a cast piston break off at the top and go out my exhaust before because i had a hung ring, im speaking from my experience, not just jabbering on about my schooling, im just using my education to back up the fact that forged is better

ever wonder why your ratchet is drop forged and not cast??? lol unless you get your tools on clearence at biglots or k-mart lol

OEM pistons can be fine as long as you monitor it, im just saying personally with my experience on my first bike, it just cost me alot for machining costs, so since then ive gone with forged since my negative experience with cast

sorry if i offended anyone

I'm not trying to rag on you, I just don't think the fact that the guy had a cast piston in his bike was the cause for the pin to come out of the ring groove. And yes, forged pistons are stronger than cast pistons, absolutely.

 

[BigRedAF]

chevyyss98

I'm not busting your pair either. It's just the "I'm an engineer, trust me" comment.

The failure was most likely caused by something else and we should try and solve that issue.

When TWA 800 went down people swore they saw a missile. Engineers kept an open mind then set out to find the problem. It took over a year to issue a statement based on engineering data.

By the way, I think they're full of crap and the Navy shot it down :nener:

 

[2strokerfun]

By the way, I think they're full of crap and the Navy shot it down

My favorite recent quote from fellow attorney during trial: "I'm not a conspiracy theorist, I'm a conspiracy factist"

Judge about fell out of his chair laughing

 

[BigRedAF]

2strokerfun

There are so many conspiracies about that flight. There was a known terrorist on a 747 flight that was just ahead of TWA800. Of course that info didn't come out for well over a year. The people that swore they saw a missile tried to pin it on the Government attempting to shoot down that plane. Evidently the Navy was doing drills out there that evening. There are several books out that are interesting in there own way. What else can a guy do on a 5 hour cross country flight... ;)

I'm a commercial airline pilot and have been for the past 18 years. I'm type rated on the following aircraft, BE350, BE1900, EMB120, DHC8, B737, A320. This experience gives me some insight to aircraft fuel systems. The claim that a center tank fuel pump caused the explosion? maybe. Seems weird that the system had operated fine since the early 60's on the 707, 727, 737, 747. Other manufacturers actually copied Boeing's design. I suppose that anything is possible and accidents do happen.

There has been several AD's, (airworthiness directives) issued to modify the fuel systems in several aircraft models since the accident. Boeing would have cried fowl if it wasn't necessary, after all it's their design. Even the Airbus that I fly now has a limit on center tank temps while running the air condition system on the ground, the PAK's, (pneumatic air condition kit) generate a lot of heat and they're right against the center fuel tank, go figure.

In closing, I was just kidding about the missile comment. I wouldn't want W's group to pull my out of bed in the middle of the night... :yikes:

 

[jasper's YZ]

I admit this top end rebuild was a bit over due. Looking at the facts and the exhaust side of the piston this was from the ring squeezing the pin and breaking it. The engine builder who is boring it was very concerned about the wave by the port where the ring tries to expand. I do not know for sure but I am willing to bet if I had rebuilt the upper end this past fall it would have been a different story.

Lesson learned.

 

[BigRedAF]

I hope it works out for you this time around...

 

[Redrodent]

Wow! Kudos to you Jasper :cool:

All the blame that gets tossed around,. You are the first I can recall that took responsibility for running a piston too long.

 

[regal21guy]

this happed to my buddies kx 125