piston siezure cause?? w/ pics

[jar944]

****i bought it this way**** 2002 yz250

I belive i've found multiple issues that caused the demise of this engine but im not sure which one dealt the death blow.
the Previous owner stated that "the crank was going bad (making noise) but we kept riding it it got hot and it quit. i think the rod took out part of the piston" well it still turned over and had *some* compression 90lbs.......

the orings in the head were shot and the bottom end was full of coolant....the cylinder plating was worn off around the intake and exhaust ports and now for the pics...

siezed intake side
<img src="http://img.photobucket.com/albums/v695/jar944/DSC01072.jpg" alt="Image hosted by Photobucket.com">

slight siezure mark on the exh side
<img src="http://img.photobucket.com/albums/v695/jar944/DSC01075.jpg" alt="Image hosted by Photobucket.com">

intresting crown....i belive being immersed in antifreeze had something to do with it
<img src="http://img.photobucket.com/albums/v695/jar944/DSC01076.jpg" alt="Image hosted by Photobucket.com">

burnt underside
<img src="http://img.photobucket.com/albums/v695/jar944/DSC01077.jpg" alt="Image hosted by Photobucket.com">

so i think
it was running to lean....
the cyl was worn beyond spec...
the orings in the head failed and allowed coolent into the cyl
and maybe it was run on straight gas

oh and the crank and main bearings seem to still be within spec (i have no idea why)

anyone have any different thoughts as to what killed it??

 

[nickyd]

cylinder worn beyond spec? isn't it plated? how about some pics of the cylinder. at first glance I'd say yes you have seizure, obviously - it could be due to anything - jetting too lean, run dry on anti-freeze and it overheated (do the crank halves show signs of overheating - they would have burned or blue'd marks next to where the rod attaches. Your crank seals could be gone. there's a bunch of things it could be.
you say the bottom end was full of coolant - you sure that didn't happen when the jug was pulled?

 

[dirt bike dave]

FWIW, seizing or lots of scoring on the intake side is a sign the bike was not properly warmed up before it was ridden.

Not sure what is going on with the crown - could be little bits of bearing got crushed between the head and the piston top. Perhaps detonation made the pits.

 

[jar944]

cylinder worn beyond spec? isn't it plated?

yes it's plated but even plated cylinders have wear specs. The plating was worn through and was down to the aluminum in certain spots...

how about some pics of the cylinder.

here you go
intake side... the discoloration would be the bare aluminum
<img src="http://img.photobucket.com/albums/v695/jar944/DSC01081.jpg" alt="Image hosted by Photobucket.com">

exhaust side
<img src="http://img.photobucket.com/albums/v695/jar944/DSC01083.jpg" alt="Image hosted by Photobucket.com">

trashed o-rings
<img src="http://img.photobucket.com/albums/v695/jar944/DSC01088.jpg" alt="Image hosted by Photobucket.com">

do the crank halves show signs of overheating .

you bet they do
<img src="http://img.photobucket.com/albums/v695/jar944/DSC01091.jpg" alt="Image hosted by Photobucket.com">

Your crank seals could be gone.

i assume that they are

you say the bottom end was full of coolant - you sure that didn't happen when the jug was pulled?

yes i'm sure it was pumping coolant out the exhaust port before i tore it apart

Not sure what is going on with the crown - could be little bits of bearing got crushed between the head and the piston top. Perhaps detonation made the pits.

actually there not pits there little bits of congealed coolant

<img src="http://img.photobucket.com/albums/v695/jar944/DSC01079.jpg" alt="Image hosted by Photobucket.com">

 

[nickyd]

wow, that was the most thorough post I've ever seen!! so it sounds like you'll be rebuilding the crank and putting in new bearings, seals, piston, etc - cylinder replated, etc.

 

[jar944]

wow, that was the most thorough post I've ever seen!! so it sounds like you'll be rebuilding the crank and putting in new bearings, seals, piston, etc - cylinder replated, etc.

Yeah thats the plan. I was hoping that i wouldn't need to replate or replace the cylinder, but i planned on it needing all of what you mentioned, including a new cyl before i bought it...

 

[nickyd]

you're at least going to have to replate - how did you measure the cylinder - you said its out of spec - I'm not convinced you have an accurate reading especially considering what I've seen with plated cylinders - they wear very slowly. are you using a bore gauge or telescoping t-handles, or worst a caliper..I've found a bore gauge is worth every penny - you will never get a correct reading with any of the other aforementioned - I have tried them all unsuccessfully. I could be wrong - you could be on the right track here but just wanted to double check.

 

[Masterphil]

Overbore to 265 time?

 

[84cr125flyer]

I'm going to throw my two cents in and may have covered some of what was already discussed but, I looked in Eric Gorr's book "Motocross and Off-Road handbook" second and third edition and according to this it was, in his words, a "loss of lubrication." He gives three reasons: 1, "No pre-mix oil" 2, "serparation of the fuel and pre-mix oil in the fuel tank and 3, "Water passing through the air-filter and washing the oil film off the piston skirt." Without knowing exactly the circumstances this may all be just speculation on my part. As pointed out before there were some issues with parts being worn out and needing to be replaced so, all these issues together with a loss of lubrication, in my opinion, added up to the seizure. :think:

 

[84cr125flyer]

I missed one thing, the bottom of your piston, it had a black spot. This happens from the pre-mix oil burning onto the piston because the piston's crown was too hot which is from either lean carb jetting, failed crank seals or coolant system failure, once again from Eric Gorr's book.

 

[steve125]

Get some muratic acid( be careful don't get on bare skin or breathe it) and remove the aluminum from the intake port. Most home stores carry it, it's used for cleaning brick. The acid will liquify the aluminum without harming the plating. The cylinder bore may be OK?

 

[jar944]

Get some muratic acid( be careful don't get on bare skin or breathe it) and remove the aluminum from the intake port. Most home stores carry it, it's used for cleaning brick. The acid will liquify the aluminum without harming the plating. The cylinder bore may be OK?

I think you misunderstood my earlier post about the aluminum showing in the cylinder. what is showing is the base metal....the plating is completly worn away around those ports....

I would venture to say that this cylinder has a lot of hours on it, and or was allowed to suck in a lot of abrasive materal (bad/old/worn out filter)
plus all the other issues allready mentioned