Really Bad Luck

[fisha69]

I have a 99 YZ125. I've been having trouble starting my bike with the kickstarter. My mechanic tried leaning it out and adjusting the carb. Still had trouble starting it... I would just pushstart it most of the time. I still need to figure that one out.

However, thats besides the point... I was out riding and got tired so I rode my bike about 8 minutes full speed back to the garage and then suddenly the engine stalls and when I try to kickstart the bike, the kickstarter stays stuck in the upwards position.

Did I seize my piston?

What could have caused this? And what do I do now?

 

[David Trustrum]

Sorry yes seized solid it sounds. :(

Um, lean jetting at some part of the throttle setting perhaps? I mean I don’t want to throw it back in the face of your mechanic, as it might not be as simple as that at all.

Running it flat out for an extended time on presumably mx gearing means you were over revving it to the extreme for ages. Maybe the crank bearings called it a day.

Hard to say I’m afraid but the hard run may have been a contributing factor to keep in mind before pointing the finger too much.
Strip the engine & try to diagnose what happened.

 

[Jaybird]

Take a look at the crank and see if there isn't a big ugly bit of melted plastic.

 

[fisha69]

I'm not pointing the figer at anyone... I was just trying to give a background of whats up.

I am so mad right now grrr... what do you mean by plastic in the crank?

 

[jmics19067]

when you had problems starting it with the kickstarter that kinda tells me that you possibly had a worn piston to begin with.

When Jaybird was talking about the melted plastic, the cranks on a lot of bikes are drilled with some relatively big holes for balancing and then capped off with plastic. If you lower bearing on the rod got hot the plastic would melt.

sounds like the only recourse you have is to take the engine apart to find the damage ,inspect , measure and then repair,rebuild or replace the parts that are bad.

A worn piston could have tried to go up the cylinder sideways cocking itself in siezing up. Lean jetting could have made the bearings in the rod or crank sieze and /or stick the piston to the cylinder.

 

[dell30rb]

the fact that your mechanic leaned it out probably did not help the siezing.

 

[fisha69]

I can't reach my mechanic I'm going nuts...

It wasn't a worn piston, I did a test and it had 150 pounds of compression. Oh well I'll let you guys know what happened.

 

[FDR492]

how did you get to the compression with a stuck kickstarter?!

 

[fisha69]

I checked the compression the day before the piston seized.

 

[jmics19067]

dependng on all the circumstances, altitude, accuracy of the gauge, whether or not you held the throttle wide open while checking just to name a couple. 150lbs sounds kinda low for a modern mx 125 to me, not nesseceraly bad but low. Plus if it had a a cast piston in it they will tend to crack the skirts off more than a forged piston when they get old.

if and when you take it apart and you see broken things something worn past its limits is probably the culprit, if it is blue and seized/welded together lack of lubrication is most likely the culprit.n Unfortunately most of the time when you take something apart after a catastrophic ending like this you will find broken and blue parts .

Jaybird, any insight on the compression readings for a 125? this is something that I believe you would have a lot more info on than me.

 

[Rockey5000]

I think that a 125 should make around 200 lbs. of compression. My KX makes 206. 150 sounds really low!

 

[fisha69]

Okay... My bike was taken apart and the problem is a seized crankshaft. It won't even budge.

So I have seized crank... I'm no expert at all but I've thought that I've had a left side crank oil seal leak for a while due to trouble starting and fouling plugs. Could that have caused a lack of lube to the crank? What are other causes of this kind of damage?

Any insight?

 

[David Trustrum]

um, over-revving it by running it flat out for 8 min?

Over revving can be catastrophic for bearings esp needle rollers in the rod assembly. The bearings will handle probably 12000 rpm all day but much faster & there is the possibility they will skid which will cause a flat & then they don’t roll any more & it’s “Goodnight Nurse”.

I am assuming this is the first crank rebuild the bike has had so the std bearings will have been correct specification, but they were probably getting pretty worn anyway.


Crank seal leaks are never a good thing either.