Scoring on cylinder

Okay,
I pulled the cylinders off of my 750E to repair a stripped out tensioner bolt hole. When I did I found some scoring in the #3 cylinder and on the piston as well. The scoring on the piston is barely visible, but I can feel it when I run my finger across it. The scoring on the cylinder is visible to the naked eye. What I need to know is:
1. How did this happen?
2.Can the cylinder be saved with a good honing? And what about the piston?
3. If I have to do an over-bore, should I do all four? That could be pricey, and I'm on a budget.

Every time I turn around, this project gets more and more expensive. :pinch: By the time I get done, I'm going to have a $5000.00 KZ750! :lol:
Any help is greatly appreciated. I'm feeling very frustrated.

scoring may be due to contaminated oil or debris thru plug hole or mechanical falure like rings breaking, id inspect the skirt of the pistons also.

only a machine shop can tell you for certain if its a light honing clean up or it needs bored to the next size, if so youll need pistons and rings and you only wanna replace them as a set.

How about some pictures ? Are the rings stuck in the pistons grooves.
Any measurements taken you can share ?
Would love to be able to tell you to give it a lite hone and rering it , but Im working in the dark. :whistle:
Dave

Is it possible a previous owner ran the bike without an air filter? I know it may sound odd, but I have seen some folks on this site running with no air filtration at all - just open carbs or open velocity stacks. If that happened a bit of grit or small piece of gravel could have been sucked into the cylinder. Ed

geohaydook1 wrote: Okay,
The scoring on the piston is barely visible, but I can feel it when I run my finger across it. The scoring on the cylinder is visible to the naked eye.

Less scoring on the piston (which is aluminum) and worse scoring on the cylinder wall which is steel. Indicates the scoring agent is "attached" to the piston and the scoring on the piston occurred from rubbing against the scored cylinder wall. Sounds like it's "ring related" like a broken ring or some crud wedged into the rings.

Is the scoring evenly distributed around the bore or mainly in a narrow area?

The depth of the scoring determines if it can be honed out. More than a couple of thou and you really need to bore it.

Sorry, but the damage doesn't show up on my camera, so no pics. And I have no snap gauge to measure it with, so we're still in the dark.

The only history I have on the bike is the previous owner put the motor together and never started it.And so far, everything he touched, he f**ked up. He even broke the carburators while "rebuilding" them. Argh.

The rings appear to be ok. The scoring is limited to a 10mm "stripe" down the front of the cylinder.

Does anyone have a good set of pistons and jugs they want to part with?

You answered my question before I asked it ! :laugh:

The scoring is limited to a 10mm "stripe" down the front of the cylinder

That scoring is on the thrust face, and is normal.

Imagine the piston is at bottom dead center, as the crank rotates and pushes the piston up, it pushes the piston toward the front because of the angle of the connecting rod, and the skirt contacts the cylinder wall.

I have seen some motors without the scuffing, and I think the difference is probably oil related, as in change interval and/or oil quality, but I can't prove anything.

Put it back together, worst case is excessive oil consumption, but maybe you can live with it till you have the bucks available for a Wiseco 810 kit


Edit:
The Kawasaki twins rotate backwards from the fours, so the scuffing occurs on the back of the cylinders.

Steell,
So I should just hone the cylinder, button it back up, and save up for an 810 kit?

That sounds like pretty good advice. If you can hone out the scratches in a couple passes, you should be in good shape. Be careful with reassembly, yhe oil sweeper rings are easy to collapse if you try to cut corners or go too fast. After break-in, check the plugs and compression. Put away your paper route money for a few months and you should be all set