mdmader

Member
Oct 9, 2001
31
0
I have a 2001 YZ250 that has been trashed. Out at the new MX track last Sunday when I heard an awful noise. I sounded like a push mower running over a rock and the rock comes out in little pieces. I was in upper revs statring to shift when it happened.

Of course the bike died immediately. After I removed the head, I could see a small piece of debris setting on the piston. I reached down to pick it up and the entire piston head fell down to the bottom of the cylinder. After I removed the piston head, I could see that the entire skirt on the piston had exploded.

The cylinder has some nicks in it so I know what is going to happen there. But what I'm confused about is how this happened.

From what I have read is when this type of failure occures, it's usually due to "The skirts of this piston shattered because the piston to cylinder clearance was too great. When the piston is allowed to rattle in the cylinder bore, it develops stress cracks and eventually shatters." According to the Eric Gorr web site.

The piston, rod, cylinder, berrings, gaskets, etc are all stock. This doesn't jive with that. Does anyone have any idea how else this could have happened, because I'm at a loss. Overheated? Fatigue? Lack of oil?

Some facts: Top end is no more the 15 hours old. Bel Ray MC1 at 40:1 with 93 Oct. Filter was fresh that morning. New plug NGK BR8EV. About 4 hours on the case oil. If there are any other facts you need to know, please let me know.

Thanks for any input anyone can offer.
 

luvtolean

Member
Oct 3, 2002
172
1
How many top ends have gone through the motor? Did you measure the bore and the piston before you put them in last time? Depending on how you are prepping your cylinder, in time the bore opens up and you will want to run a different piston to fit. Bummer no matter why.
 

Sawblade

Timmy Timmy Timmy!
Sep 24, 2000
1,491
0
Yamaha has different size pistons I believe in A, B, C, and D sizes. When you do a top end job you have to match you top end with the correct size. This is due to manufacturing tolerances. You didn't say but have you done a top end on your bike since you bought it? If so, did you match the top end to the correct size?

Sorry to hear your day ended early on Sunday. I'm bikeless at the moment, but took my son out on Sunday to the new track. The track looks like a lot of fun. We need to hook up in the spring and pound out some laps once I have bought a bike.
 

mdmader

Member
Oct 9, 2001
31
0
luvtolean. I can't say for certain how many top ends have been done on this bike, but I am certain that it was a fresh top end when I bought the bike in June. The local Yamaha shop has always worked the bike so I don't know (but I would hope they did) what the tolerances were when it was last done. I did note on the cylinder that it has “B” stamped on it. I can’t see any markings on the piston (due to damage), so I guess that it is possible that there is a mismatch.

Rcannon. The wrist pin and bearing looked just fine, aside from it not being connected to a piston <g>.

Sawblade. No, I have not done a top end on it when I bought it. Like I said, there isn’t more the 15 hours on it. I usually changed my CR at about 20 hours. I knew I only had a couple of rides left on it so after the first of the year it was going in the shop. The track was a bit sloppy in places but after a few hours, it was getting nice and tacky on most of the track. Let me know when you have a bike again, I still have my old CR. Did some rough estimates, looks like about a grand in damage. With Christmas I don’t have that kind of buck hanging around.

Which brings up another question. Service center says that they can have the cylinder replated. The nicks that are in it are not that deep but I was under the impression that you couldn’t do that to those type cylinders. Tech says that they can replace no problem. Anyone have any thoughts on that or have tried it?
 

bclapham

LIFETIME SPONSOR
Nov 5, 2001
4,340
0
it sounded like the wrong piston to me also. did you hear any chattering, or rattles or pinging? was there still water left in it? were the circlips still in the piston? snagged rings? who did the top end, was it you or ther shop?

i have the same bike and went way too long on a stock top end. when i did it, i put a wiseco piston in and was amased how much quieter the engine ran! maybe you can use this as an excuse to go for a big bore? at least this way, you can get a very precise bore/piston match up.
 

bclapham

LIFETIME SPONSOR
Nov 5, 2001
4,340
0
just re-read your post, out the whole lot in a box and send it to eric, i am sure he can get you going for much, much less than what you are expecting to pay. the only problem is that the bike will be loads faster afterwards!

good luck, let us know what you find out what went wrong.
 

mdmader

Member
Oct 9, 2001
31
0
From the sound of it, everyone I talk to is telling me to send it off to Eric. I see that he does entire engine rebuilds.

But, I'll call him to at the very least get a cost estimate, like I said, going with the local dealer is going to cost a bundle.

Thanks for everyone's input. I'll let you all know if I have any further developments. Thanks again.
 

whyz

~SPONSOR~
Nov 18, 2001
478
0
I know how you feel. My use to be YZ125 did that too.
Got the total rebuild and a EG133 kit to boot.

And Holy ka Moly. :confused:
 

rickyd

Hot Sauce
Oct 28, 2001
3,447
0
Maybe the skirt got caught up on the exhaust port, being that it has never been bored..
Rick
 

DEANSFASTWAY

LIFETIME SPONSOR
May 16, 2002
1,192
0
Eric or another good engine shop could weld up the gouges in the cyl , Sometimes the cases get cracked where the piston was wedged also, I have two or three late model YZ cyls where the whole lower intake sleeve area was broken off from running loose topends in sand out here . These cyls are shot , yours could probably be fixed .You should probably get a new rod installed on that cranky while youre there . Good Luck mdmader!
 
Top Bottom