Destroyed Piston 1993 YZ250. Pics.

[pintilie503]

Hey Guys. I just rebuilt my top end on my 1993 yz. I did a very meticulous job cleaning every nut bult, cylinder etc. After the rebuild I let my bike idle, warm up, and then cool down. I did this several times and then took my bike riding. After ten minutes into my ride the bike bogged and locked up. Upon removal of the Cylinder Head I found a eaten up piston and heavily gouged cylinder wall. I was running 32:1, had standard factory jets in there, and set the needle to the richest setting. I found what appears to be itty bitty fragements of my air filter in the reed assembly. Could that be the culprit of this. Also, where do I go from here. This is my first bike and I need some advice. Is it worth replating the cylinder, putting in a new rod and bearings, and putting in a new piston. Not including the other things Ill need such as air filter, gasket kits, etc. I kind of like the idea that its an older bike and that you can find cheaper parts for it. It was also running great just before the rebuild, but after inspecting the oem piston i found a cracked skirt and then proceeded to do the top end. Thanks for your input.

Also any recommendations on where to send out the cylinder and some good parts websites would be greatly appreciated.

 

[dirt bike dave]

All the damage to the top of the piston was probably caused by bits of crankshaft bearings or big end bearings getting pounded into dust.

My guess is you were in need of a new bottom end anyways. Did you check for play in the rod and in the crankshaft when you had the top end off?

It sucks it let go on you and trashed a bunch of your new parts.

In any event, it looks like you will be needing a new or rebuilt crank, crankshaft bearings, some cylinder work, full gasket set, a new piston, etc...Be sure to inspect your power valve, cylinder head and cylinder too.

As for parts being cheaper on old bikes, that is not my experience.

Mach1 Motorsports in Vacaville, California has a website and usually has good parts prices. You might want to call directly, as lots of websites do not show parts for the older bikes.

I think you are looking at splitting the cases and a very large bill for parts.

IMO, you could easily be looking at $700 - $1,200, depending on how much got trashed and how much work you do yourself. Probably not worth spending that kind of coin when you could get a newer, better bike for well under $2,000.

 

[Uchytil]

What DBDave says is true. I know where there's a 2004 YZ250 for about 2500 dollars and that may be on the high side. If you do the work you will save a ton of cash but do the homework for the parts DBDave mentioned.

 

[OriginalRider]

My brother had a 87 CR80R and the piston looked identical and what happened was the 1 cir clip wasn't set properly came off and tore up the piston and scored the cylinder so bad i had to throw in the trash.Because it was worth the cost of big bore it.

 

[whenfoxforks-ruled]

Big end of the rod bearing went out the exhaust pipe. Send the top end to Forward Motion, he will have what you need, and for a really good price. Get the complete engine rebuild kit. The head will need replaced or he may be able to rework it? The cylinder can go a little bigger or more? And he ports them anyways! http://www.eric-gorr.com/index.html

 

[pintilie503]

I did forget to mention that the head is also fairly mangled and that I purchased my Piston from ebay. It was made by Namura Tech. I also checked the crank and it did snag a little but i thought it was from the stator. How would the bearing gut up on top of the pison and wreak this kind of havoc. The skirt directly opposite of the exhaust port of the piston was broken off to. I was wondering if it was a cheap piston. I did not hone the cylinder. Was this a possible culprit?

 

[_JOE_]

Sounds to me like crank bearing failure. Honing the cylinder wouldn't have any effect on the lower end. I've heard the Namura pistons aren't great. If you want to run them be sure to measure, measure, measure when you put it together. The tolerances tend to get a bit off with cheap parts. Pay particularly close attention to the piston to cylinder clearance and ring end gap. Taking the time to measure and verify is ALWAYS worth it!

 

[whenfoxforks-ruled]

There is not a person on this site that would love to tell you more than I that the piston caused this. Check the big end of the rod. And in the future, when you do the top end, the book says 7 hours or so, check the crank.

 

[IndyMX]

Doesn't seem to make much difference to me at this point what caused it.

The end result is you are going to have to replace the piston.. And probably the head.. And have the cylinder replated..

And since there was so much shrapnel bouncing around in that cylinder, you would be stupid to not at least have the crank rebuilt. But it'd probably be cheaper in the long run to just replace it with a Hot Rod crank if they have it available for your bike. Plus a set of crank bearings & seals to make sure, and you should be all set.

 

[dirt bike dave]

Powervalve parts are also subject to damage when things go boom.

The loose crank could have also damaged the crank case, but you won't be able to see it until you split the cases.

Unless by some miracle the crank and big end are sound, parting out the bike and buying something else is probably the best use of his time and money.

Spending $1,000+ to repair a bike that's maybe worth $1,000 just does not make much sense to me. Sell it for $200 and buy a $1,200 bike, or bite the bullet and buy a much newer, more reliable bike for $2,000 or so. There are plenty of them out there.

 

[2strokerfun]

I guess I'll be the Devil's advocate against several other posters here. Yes, you need to dump some cash and get some parts as they have said. But, if you like the bike, then it is sometimes worth the money and time to repair them. For me, I just like wrenching on them. But the real reason I say this is because even if you go buy a "good" used bike for $2,000, there are absolutely no guarantees you won't be looking at doing the exact same thing to it in a month or two. If you repair your bike and do it right, you can ride knowing it is as reliable (as a race bike can be, anyway). But, as you know now, the first thing you should do when you buy a used bike is pull the top end and measure and inspect it and at least check the lower rod bearing while you at it.

 

[Uchytil]

The 2strokerfun opinion is doodoo (just kidding). Actually I have some bikes made in the 70's that I've dumped thousands into yet I could buy a current steed for a few grand and ride all year with more power, more reliability, and the parts would be sooo easy to get. If you really like the 1993 YZ then by all means spend the money to fix it. If you have to hire a mechanic you can probably double that figure. My wife would say fix it. I'd say buy a new 2010 YZ250.

If you do need help Eric Gorr is the source as aforementioned by Foxforks.

 

[dirt bike dave]

My advice to replace the bike assumes a few things:

1) There is bottom end damage
2) The owner does not have an irrational emotional attachment to his '93 YZ.

Also, we have no guarantee this particularly '93 YZ is in great shape. If the crank is original, what about the wheel bearings, steering head bearings, swing arm bearings as well as more common wear items like plastic, tires, chain, sprockets, and cables?

Any used bike is a gamble, but chances are a bike that is 10 years newer is going to be in better overall shape, as well as having better suspension, better brakes, better handling, etc...

It's a buyer's market out there for used bikes. Parts from the dealer? Not so much.

 

[dirt bike dave]

FWIW, here is a listing for a '93 YZ250 with 1 hour on a rebuilt motor (new crank and piston, new power valve). Also has some aftermarket parts, new plastic and graphics.

http://georgetown-illinois.olx.com/1993-yz250-iid-22067058

This looks like a way better than average '93.

ASKING $1,500...

 

[2strokerfun]

All these years of blue and when I hear "YZ," my mind still sees the picture of the bike in my head as yellow...........sigh........... "Irrational attachment" is a very good phrase, by the way. A condition I am very familiar with !! I am currently building a complete backup engine for my elsinore, buying it one new or used part at a time. I figure it is only a matter of time before I can no longer find many parts for a 34-year-old engine. Which reminds me of another point: If you do plan on keeping and repairing this bike, and you have the space, might keep your eye out for a good donor bike for parts in the future or even a good donor engine you can rebuild and keep as a backup in case of catastrophic failure.

My own irrational attachment started because after a few months of whining several years ago, my wife told me I could buy a dirt bike. But, thinking I couldn't do it, she gave me a $400 limit. A few weeks on 'bay and 500 miles later, I got a bike (with a broken piston installed 180 degree from correct). She didn't tell me I couldn't put hundreds of hours and dollars in it after I bought it. It quickly became a matter of pride and hard headedness to keep it in great shape and I wouldn't sell it for $2,000 (not that anyone in their right mind would offer anything close to that). Now, at $2,001, I believe my irrational attachment would quickly dissipate.

 

[jsantapau]

I did forget to mention that the head is also fairly mangled and that I purchased my Piston from ebay. It was made by Namura Tech. I also checked the crank and it did snag a little but i thought it was from the stator. How would the bearing gut up on top of the pison and wreak this kind of havoc. The skirt directly opposite of the exhaust port of the piston was broken off to. I was wondering if it was a cheap piston. I did not hone the cylinder. Was this a possible culprit?

If a bottom end bearing fails it can get pushed/thrown up through the transfers If a new piston broke on the intake side quite possible something was seizing up on you putting some undue stress on it.

 

[whenfoxforks-ruled]

Dirt and metal follow the same path as the fuel and air charge, go figure.

 

[Patman]

Dirt and metal follow the same path as the fuel and air charge, go figure.

:laugh:

 

[FatBiker]

Dirt and metal follow the same path as the fuel and air charge, go figure.

= CATASTROPHIC FAILURE!

 

[whenfoxforks-ruled]

It is not that bad. A hundred dollar head? Now if that was a thumper? $$$$.$$ Some real fun? Around 400 dollars should do the engine in parts. If you want to make money, be a politician.