NSR50 siezed---help

I just bought my son an NSR50, and while I was out on the track, he took it out himself and apparently over-revved the engine too much, and the thing siezed up on him.

Will this be fixed with a new top end? I don't even know where to begin.

Thanks!

Travis

 

Well, lets hope he didnt seize the crank journal itself. Lets just hope that you have a top end that got stuck due to incorrect jetting.

Pull it apart, and get a picture of what you see and we can tell you more.

 

Post pictures. Sounds like a top end at the very least. Assuming the bore was stock before the seizure and the damage to the cylinder isn't that bad, instead of replacing the cylinder you can swap to a .25 piston/ring combo from the NS50 and simply have the cylinder bored to match. Details on that after pics.

 

On another note, I doubt he overrevved it. Those NSR's are such good reliable low horsepower bikes, they just quit pulling. We have raced a used one for over a year w/o replacing anything.

 

OK, thank you. I will start tonight and have pictures soon.

 

OK, i don't know if photos are necessary...you tell me. The piston is blown to pieces...dime size and smaller pieces are inside the cylinder and i can see some down in the bottom end. Do you want to see some pics?

 

pictures

Here's what's left of the piston. The Crank moves, but the crankshaft doesn't seem to want to move easily...?

 

Time to split the cases and make sure you get all of the pieces out of the bottom end.

 

if it were me complete bottom end rebuild.Theres no sense in putting a top end in the bike and then the bigend bearing fails and makes another mess.Think abou it,you're spinning around 10,000 rpm or so and then just suddenly stop!

 

Thats what happens when the piston is fatigued from to many running hours. Tdub

 

Definitely time for a top and bottom end. What condition is the cylinder in?

 

Hey Jordan.
Does that look a bit funny to you? I don't see any big score marks on the piston....doesn't look like a typical piston seizure to me. I'm inclined to wonder about metal fatigue like Tdub. If we could see the cylinder that might give more clues to what happened.

Another question.....were the piston pin, circlips, and bearing still in place when you removed the cylinder?

 

The cylinder has one nick in it, about 1/2 inches long, above the port, but not all the way to the top. I got all the pieces out of the crank and it turns fine now when i move the back wheel.

 

And yes, all the pins, clips, and bearing were in place. According to the guy i bought this from, it's nearly new, only ran a few times, so I would wonder about metal fatigue...?

 

What brand piston is that? OEM, or some aftermarket?

 

If you didnt split the cases, I gaurantee you didnt get all the pieces out. Tdub

 

I talked to Team Calamari today, they said to take the engine off the frame, and pour some gas or kerosene in the crank and flush it several times. What do you think?

 

If you do that you might.....maybe even probably.....will get all the little pieces out of the case. If it was mine, might and probably isn't enough.

 

THe cases need to come apart, most of the time when you lose a piston like that there will be a chunk wedged in the groove in the bottom of the rod. Its easier to do it right the first time than to half ass it then do it right the second time.

It was a piston fatigue problem that could of also been caused by extreme overrevving on downshifts, if that was the case the crank should be replaced also.

 

Definitely, that's why I wanted to see the cylinder.

When you say "now," does that mean it didn't spin freely before?

TCR's recommendation is a good one, they know their minis better than anyone, but I would still split the cases and rebuild. There's something to be said for peace of mind when you're winding the thing out to 12k.