I had a great weekend:banghead::foul:

My buddy let me borrow his 06 YZ250 for the last couple of weeks while he is out of town. (My RM250 has been waiting for a stator, which is a whole different sh-tstorm in itself). I rode it once last weekend, fixed a whole bunch of small problems with the bike not caused by me (that was part of the deal).

I rode it again this weekend (drove 3hrs to get get there), and after 20min it croaks, try to kick it over, no compression, great:foul:. Drive all the way home, take apart the head hoping it is just an o ring failure, but of course part of the piston came off and scared the hell out of the cylinder. Basicly I drove 6 hrs, spent a sh-tload of money on gas, rode for 20 minutes, and am now going to have have to spend a real sh-tload of cash on parts for a bike that isn't mine. So far we have piston kit, wrist pin, gaskets, cylinder, and bottom end rebuild (some pieces of ring got into the case I think):foul::foul::foul::foul::foul:

My buddy will proably pay for some of the parts because it was not my fault it blew up, but I still have to deliver the bad news "your bike blew up while I was riding it" (thats great news after returning home from a trip):foul::foul:

I did some research into the matter and it turns out the timing on the stock YZ250 is borderline too aggressive for 92 octane gas. I know my buddy never ran race gas in the bike, so it was only a matter of time before this happened. The bike doesn't have that many hours on it and ran great before it croaked.

The only good thing that this weekend was that my factory Suzuki stator from ebay showed up on saturday, so on sunday I got to ride my RM250. I never thought I'd be so stoked to ride my beat to crap RM250. My bike has waaay more (and harder) hours on it then that YZ and i've never had it blow up like that. I've rebuild the top end a couple times but never had the piston disinegrate and take everything else out with it.

So YZ owners, run very high octane or race gas!

The stock pistons in the YZ250's are known as the only real weak point on the bike. They need to be replaced frequently(30hrs tops) to stop the skirts from shattering, or you can put a forged piston in for longer life. The timing and the squish band are a bit off from the factory as well, as you stated, but can be taken care of with a low cost.

Well...I would have to disagree with the race gas comment. I had a 06 YZ250 and always ran 91 octane, which is what is in the manual and the highest available at most gas stations. Would have to say, no pinging and never an issue.

Always run mine on 93 as well, and a few guys i know do the same.

Sounds like your buddy's bike was a POS because he treated it like one..

yeah I have had a couple late model YZs and they have been some of the most reliable bikes I have ever owned. (all mx use) Never ran race gas either. While there are exceptions, doesnt sound much like the bikes fault. That sucks about the wasted trip though! Had that happen a couple times. lol

I have to run race gas in mine......50/50 wont even cut it!

BTW...... I will only run a OEM piston in mine.

Check out my buddy's YZ...."Ka-Plooooie!"

http://www.thumperta...0678&highlight=

"Ka-Ploooie" :lol::lol:
I better order some parts before I have some new snap shots for the photo album :smirk:

Jeekinz said:

Holy crap! The piston out of my buddy's bike wasn't quite that bad. One small piece of the piston broke off and took out the rings and wasted the cylinder.

After I put it all back together I will investigate the timing issue, as I have heard from numerous sources that some of the YZs are advanced too much.

Anyway when the bike is returned I will tell him to run higher octane gas (couldn't hurt), and also to clean the damn air filter more often (it was real bad when I got it from him).

Got a Pro-X piston kit for the bike, cylinder is being re-plated as we speak, and the bottom end is out of the bike and will be rebuilt today. I'll have this thing back together and out of my garage for good by friday.

Man that bites. That is the reason I NEVER accept someone's offer to ride their bike.

A bunch of us have found the timing off on our yz 250's. If the timing is set correctly, you're ok with pump gas.