Help ZXR250C - Rebuild V2

There is not a lot of clearance in these little things to start with. If the conrod bearings are shot you can easily get piston to valve and plug contact.
Let us know what you find.

 

Are you saying that you might have run out of oil?
Oh dear.
I bet you will not do that again.
I have had similar issues on cars, where it appears that there is oil on the dipstick.

 

Fingernail test on the crank, if your nail catches anywhere on it it's no good. You should also visually inspect the radius on #3 journal, and the outer edges of the rod. Were the bearing shells in place or did they spin?

You will need to check the valves on #3 to make sure they are not bent. Easy way is to stick them in a drill and spin at low speed and observe for wobble.

I would also not re-use that piston, it's made contact with the plug and could be compromised.

Given it's a bearing failure you need to check and clean the lubrication system closely.

 

Spun bearing is bad, it means crankshaft damage is likely. Get us some good pictures of #3 rod journal against the others. You should check the mains as well.

Pull off another rod and fingernail test the journal against #3

For measuring etc you will need some good micrometers - the very-nears (vernier calipers) are not accurate enough for this task.

Not sure on Kawasakis but the crankcases, crankshaft and/or rods may be stamped or otherwise coded with which bearings they used at the factory. The colour or letter codes tell you which sized bearings are standard.

Bad news is no new OEM crankhsafts available, however it looks like rod assemblies and bearings are all available.

You need to identify which ZXR250C you have, post up the engine number. There are lots of model variants - A1/A2, B1/B2, C1 through to C7 and D1

 

Have you not split the cases? It might not be possible otherwise.

 

Yep those shells are well and truly cactus. Check all the other bearings. From the pics you have of the pistons, it looks like a witness mark on 3 of them indicating they have kissed the plug. You might be lucky with the valves as no obvious visual indication of contact on the top of the pistons.
I would also suspect that the pistons will be reusable as the plug contact looks to be relatively minor. I have seen a lot worse

Inspect the crank journals very carefully. Also inspect the rods.

I have found with other failures like this that the crank can often be reused. It will never be like new though.
If you can find undersize shells, then grinding the crank might be an option. However the costs might not justify the effort.
It might be easier to find another crank/engine/donor bike.

You will most likely need to remove the engine, if you have not already done so, and split the crankcase to get at all the bearings. You will need to clean out the oil galleries in the engine and crankshaft when you put it all back together.

 

This is what my old R6 and FZR250 did when they spun bearings. You need to make 100% sure that there is no damage, otherwise you will be doing the same work all over again in short order. In the R6's case, it had a cracked nikasil bore and was worn all around. The FZR250, someone else had been in there and installed #3 rod backwards.

When the bearings spin, you often get bits of bearing welded onto the crank and rod. While they may clean up, often it is too far gone to save.









This is #3 journal on the FZR250, it failed the fingernail test (that big vertical line towards the centre was catching)

 

If the crankshaft can be linished you do actually have a few micron available in the shell thicknesses, great thing about Kawasaki is that they give the dimension of all of the parts, so depending on what was installed originally, you may have some range for installing another shell.

The rod may be able to be closed and honed, @Murdo is the man to chat with regarding that.