Combustion chamber damage

Cylinder 1



Cylinder 3


Cylinder 1


Piston 1


2 is damaged. Less than 1, more than 3. All in the same location.

4-5-6 are perfectly fine.

Engine has 67,000 miles. Does NOT have an OEM head gasket.

All looks good except what is in the photos.

Exhaust valves have thick carbon. Otherwise valves/seats/guides look like they just need cleaning and lapping. Guide play is almost unmeasurable.

There is no sign of water getting by the head gasket. So I am wondering if the previous head gasket had a leak.

Any other suggestions?

Every cylinder head I've seen had at least a couple similar looking combustion chambers, with this kind of roughness always in a similar shape and the exact same area by the exhaust valve. I think this corresponds to where the gases were making their way out of the combustion chamber when the exhaust valve was open. I even thought that was some roughness left from the cast after machining. I'd just clean it and apply some sand paper over it. I think it's normal, but not sure why some cylinders would have it some not, thus that idea about post cast surface still there. It has never been anything drastic or very rough.

Pistons - every KZ13 piston I've seen look similar. They are cast and I think that's the surface they have after casting. Every piston has a machined top and I've never seen any pitting there - like your in the top center in the photo. There was metal there left after casting, and I think it was there to attach the piston to the lathe for turning and cutting the pistons skirt and ring groves. Once you put them in ultrasonic cleaner for 20 minutes they will come out shiny like new. I think you'r pistons are fine as well.

I showed the piston to show there was no damage to it. I’ve never seen detonation damage to a head that was not also obviou on the piston.

So, yes the piston is fine.

It is possible that this spots are “as cast” and the casting there was too low so it was not machined when the combustion chamber was.

That makes more sense than anything else I can dream up.

This is the head after I took it off the current bike, after the first quick cleaning. Very similar and suggests casting. The bike runs great.



This one will go on the engine I am currently putting together. Again, very similar and suggests casting. I think they way they did these heads is that somehow the molds were not uniform and left a bit of a rough surface after uniformly machining each chamber.

Second one looks the same. Surprised Kawasaki let that go. The head casting is very complicated, but they could have modified their pattern to fix that.

Aluminum shrinks as it cools and is not always consistent (temp of the mold and of the metal can very where the shrinkage happens). The pattern has to take that into account. I'm not an expert, so I tend to leave extra material where critical and just machine those areas as much as needed.

I am going to smooth those areas out to make sure they don't cause a detonation issue and don't collect carbon. Then call it good!

Thanks!

Hi on my cylinder head I also have this imperfections, bike is running fine, there is no significant difference in compression and it cant probably affect it that much. There is a method described in rep manual which allow to measure the volume of the combustion chamber. Its a page 174.