Opinions Please....Z250 Engine strip down.

Started to strip down the Z250 engine. I'm not sure if I'd see if anything is wrong or not, this is a steep learning curve for me thats why I got hold of this project bike.











This is the only bit that fell apart whilst taking the engine apart....



So what should I be looking for. The engine did look as if it had leaked some oil from the cylinder head at some time. I've got a complete set of gaskets. And ready to go.

Can these things be cleaned, are they ok to use, do I have to buy replacements.

I do have a spare engine in the yard but before tearing into that one I thought I'd best check with you guys.

Cheers in advance!

Tony (Fourtoes)

Post edited by: Fourtoes, at: 2007/04/23 09:21

did you do a comression test before tearing it down?

Nope cos it was a non runner to begin with......so I assumed that I couldn't do one.

Is this right?

Have you got a manual?

I've got a service manual.

I'm assuming the black is carbon deposit that I can just clean off.

Post edited by: Fourtoes, at: 2007/04/23 15:25

You want t be carefull cleaning that carbon off, if 1 particle drops down into the engine you could have a problem.

That head is beyond economical repair, the bearings (at least one and probably two) have spun and trashed it.

Post a pic of your cam, I bet it would need some work before it could be used, if it could be saved at all.

My guess is that the motor has been run with insufficient oil, and that means the bottom end is probably trashed as well.

The middle part in your last pic is the cam bearing, see how one end of it is mangled and flattened? There is supposed to be a layer of babbit (grey color) covering the part you can see in the pic, under that is the copper layer that is now showing, and it looks like it even got through that into the base, and that's real bad.

Time to take a look at your spare motor.

As requested.



Being new to this, the bearings you refer to, do what and where are they found in the head?

This particular kind of bearing is commonly called a bearing shell, or bearing insert. In the head pic above, do you see the three wide half shiny moon shaped recesses in line across the middle? That's where that copper colored piece in the bottom pic goes (the bearing shell), there should be two more of them. There are three more that go on top of those to form a circle.

Look at the three round areas on the cam where the bearings go, see the bluing? That's caused by heat due to metal to metal contact, and there is not supposed to be any metal to metal contact there, there is supposed to be a film of oil to keep that from happening.

In the bottom end Kawasaki used to different styles of bearings, bearing inserts (like the cam bearings) and roller bearings, and I don't know which style the 250 uses. However, the lack of lubrication displayed by the cam bearings would destroy either type, it would just kill the bearing insert style sooner.

The oil to the head lubricates the cam bearings then falls onto the head and some of it gets to the valve stems to keep them lubricated in the guides. So I would expect to see excessive wear in the valve guides.

Oh yeah, sometimes when bearing shells (inserts) suffer from lack of lubrication they weld themselves to the bearings surface on the shaft, and since the shaft is turning the bearing shells start turning also (they are not supposed to turn), resulting in a spun bearings. That leaves scoring (scratches) in the surface that supports the bearing insert, and that's what it looks like happened in your case. Sometimes the bearing sticks to the shaft and you have to pry it off, and sometimes it don't stick. In your case it don't look like they permanently welded themselves to the cam.

Post edited by: steell, at: 2007/04/24 09:37

So where do you think they have gone??? Doesnt look like the engine has been open before.And what you see in the pic is the only remains I have.

Where what has gone? I would also check the oil passages for blockages from worn parts. I would take the whole thing apart, I think that engine needs some loving.

The bearings, theres no sign of any remains apart from the bit in the photo. Have they just worn away?

Sorry but I don't know that much about engines and all info is of benefit.

Think its time to drag that spare engine in and take a look to see what condition its in.