big problems with metal in the cylinder

at the end of last year i had a screw come out of a vforce reed cage and wind up lodged in the top of the piston. it caused severe damage to the jug as well as the slug. i had the jug repaired and replated by a machine shop and installed a new wiesco 2 ring prolite. rode the bike for about 10 hours and it started making bad noise. i have since split the cases. in the process i found a chunk of steel lodged in the top of the new piston. it destroyed the head, but was somewhat nice to the jug. after splitting the case i have found bearings that are noisy when rotating them by hand, but there are no pieces from them missing. i inspected the gearset and shift forks, all is ok (no chips on the teeth, etc) so to be honest im at a loss with where the piece of steel came from. any suggestions for commom bottom end failures would be appreciated. or suggestions for what to look for. to throw this in, im a certified volkswagen tech, ive rebuilt plenty of german engines and manual transmissions. so i have some idea of what im looking at.......but im baffled with the source of the metal chunk......any 2t expertise would be greatly appreciated because as it is now it seems that im gonna have to replace the crank, rod, and all of the bearings within the case, clean out the head pipe and hope......and i dont like hoping. thanks again


what bike are you referring to? There might be a common issue in the bottom end with that specific bike.

Also is there any chance that it could have been part of the bolt or material from the piston or cylinder that got taken out the first time around? When something goes wrong with one of my bikes I always think the worst and it get completely torn down and cleaned out before any parts are replaced only to be taken out again. In reality it could be a chunk of piston, needle bearing, PV, plating... the possiblities are endless unless the cases were split the first time and cleaned.

Picture of the metal lodged in the piston may also be helpful in determining the source if possible.

What year and model bike are we talking about?

Nothing in the bottom end could get into the jug. The chunk of metal in the piston had to go through the intake somehow. Anything from the airbox, carb, reed cage, etc could have been the source of a small chunk of metal. Another possibility for a piece of metal is the spark plug. I've seen both the electrode and ground break off from plugs over the years.

What does the piece of metal that was imbedded into the piston look like? Do you have some picks of the cylinder, head and piston that you can upload?

Bottom end bearings do wear out, especially if the previous owner didn't change the transmission oil at least semi-regularly. Same for the crank. If it isn't properly maintained, it will wear the crank bearings faster.

It sounds like you are on the right track. New bearings and seals all through the engine, and ensure that everything meticuously clean during reassembly, and you should be fine.

sorry for the wiff on information. the bike in question is a 2005 yz250.......and i will attempt to upload some pictures tonite when i get home from work.

Has to be the rod or main bearings everything else is sealed off from the crank area.

Iv'e seen the bearing cages fail and ending up embeded in the head and piston.

it has v-force 3 reeds in it.......the ones that dont have the screws. given that at the end of last year the cylinder was hungry for one of those screws.......but i like the thought.......thanks a lot guys, sorry for no pics yet......i have a busy week/weekend coming up........gotta get deaf to some A7X, Seether, and Sevendust this weekend :smirk:

it has v-force 3 reeds in it.......the ones that dont have the screws. given that at the end of last year the cylinder was hungry for one of those screws.......but i like the thought.......thanks a lot guys, sorry for no pics yet......i have a busy week/weekend coming up........gotta get deaf to some A7X, Seether, and Sevendust this weekend :p

The information you are supplying is contradictory.:smirk:

Screw from V-force...... V-force 3 no screws???????

Bigend bearing washer probably

I had a similar problem with my 01. Im not sure what sequence these failed in but these problems were all addressed in one teardown: Chunk of metal sitting in crank- part of the stock piston skirt had broke off, I didnt notice it right away because it broke with the shape of the skirt and the piston still looked somewhat normal, I wonder if its possible for a smaller chunk to break off into the intake and get sucked back on top of the cylinder on the upstroke? Replaced jug (gouged and scored), then noticed the crank wasnt quite right, replaced the bottom end with a Wiseco rebuild kit, the change in freeplay and tolerance lead me to believe my old crank carrier bearings had worn and the bottom end of the connecting rod was pretty sloppy too. Im not sure on an 05 but are there any thin pieces of cast metal that could have broken or been fractured just enough to where it would not have held up to the violence of acceleration? Just my two cents, hope it leads to something.

Tough to call this one without pics. A case split will solve the issue though.

my posts dont contrict......i had v force reeds with got sucked in, so i replaced those reeds when i replaced the top end with v force reeds than were screwless.......and the chunk is steel (sticks to a magnet). and i have split the case and nothing seems amiss, hence the post. again i have a technical background so it really adds to me being puzzled over the source of the metal.

I had a similar problem with my 89. The cylinder wall got all scraped up and the piston looked peppered. Turns out, the lower needle bearing assembly came apart so some needle bearings are just on their own inside the I-rod. So, one or more came out and got sucked through and destroyed the piston and cylinder wall. Hope this helps for some people.

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