Dirt Bike Repair & Maintenance Forum

Hey all,

Just replaced my grooved clutch basket with a barnett basket. Worked like a charm, clutch feels brand new.

So, I was riding along, enjoying myself (at a high speed), my bike starts to sputter... so i think oops, i forgot to turn on my fuel, no biggie, so i turned it back on, and away i went. 5 seconds later, the bike loses power. I pulled in and released the clutch a few times only to find my rear tire locking up.

At this point i pulled over and checked out my bike. here is what i found.

1) Kick starter was solid... won't budge.

2) Oil is about 3/4 full, no problem.

3) Coolant is Full, no problem.

4) Clutch works fine, I can find 1st and 2nd gear and neutral fine. (and bike can be pushed no problem in gear when clutch is depressed)

5) Tranny fluid I noticed a small bit dripping around my gear shift lever. I noticed a small nick in my engine casing by the shift lever. (I know it's tranny fluid cause it's red)

So, I don't know what to do here. I have had a few opinions thrown at me about what's wrong and I want your guys input please.

One service guy @ honda told me "Your valves probably screwed up and siezed your piston".

Another guy told me "It's more than likely NOT your top end because that's very uncommon with this type of engine. It's probably a crank shaft bearing or something in the bottom end"

Well I was hoping that the top end was damaged, cause I hear it's much cheaper to rebuild a top end.

Thanks guys.  

X I just did an 05 CRF250r . it was the crank that locked up. And the guy described it just like u did.

he bought a hotrods crank assembly with bearings and seal kit for 330$ not a bad price if u ask me.

Ill get u the companys name and post it later.

i put it in for him. He added a cam too so his total was around 600$ when he was done.

it was a pretty basic job and didn't take that long.

Let me know if I can help in any way. Just PM me.  

Wow, that's actually kinda comforting to hear that. I wasn't even all that mad, i just wanted to know what the heck was wrong.

I will look into ordering that crank assy now.

PM me when you get more info man,

Thanks!

Tony  

Wow, that's actually kinda comforting to hear that. I wasn't even all that mad, i just wanted to know what the heck was wrong.

I will look into ordering that crank assembly now.

PM me when you get more info man,

Thanks!

Tony  

X the company he bought his parts from was
www.lukesracing.com

He used item code # ERKCRF250

Nice stuff. The hotrods crank was heavy duty and seal kits are from K&S.

It all made for a nice smooth rebuild.  

lol my friends bike (05 crf250r)recently did the same thing, his valves were fine but something in the crankshaft went out cause of old age. forgot what was :/ he got the hotrods one though along with new piston and camshaft. that thing pulls hecka now  

when you are going at a high speed. throttle pinned and you suddenly let off the throttle, the piston is moving so fast that it will swell from the heat in the engine because fuel lowers the temperature in the engine. so that is why the piston swells, so that is why the piston will swell when the fuel is taken away suddenly. so when the piston swells it seizes. you should not feel so comfortable because you might have a major catastrophe in your engine or it could have just screw up your crank. but wat i am saying is that because your fuel was off when all the fuel that was in your carb ran out it caused your piston to swell and seize. also when you have a bike pinned let off the throttle easy.  
1998 cr125
2002 cr80

It is possible the piston seized if it was at hi speed and starved for fuel, only way is to pull top end and check.  If its OK then its likely crankshaft bearings.  
Dave H 2006 YZ250
(2008 YZ 125 son)

That actually makes a lot of sence too guys... the fuel starving and piston swelling...

Well, I will repost when I find out what the heck happened. I am taking the engine apart in like 2 days.

Thanks again for the input.