Cylinder wall scratch

Bogaurd

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Local time
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Joined
May 15, 2008
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Location
Adelaide, Australia
Hey guys,
Had the head off my 80cc tonight, noticed a couple of very small (less than 1mm) scratches on the nikasil coating of the cylinder wall. They're right at the top of the cylinder, and my guess is that they might have occurred when the engine was started for the first time, given that the cylinder wouldn't have been oiled at that stage. The bike has probably done a thousand km or so, and I'm not having any issues, loss of power etc, so I figure they're probably harmless. When the engine eventually gives out I'll either buy a new piston, jug etc & do a rebuild, or just put a new engine in.

Just curious to see if anybody else has noticed anything similar... I'll get some pics up at some stage so you can see what I mean. :)
 
If you can catch your fingernail on it, you should probably do something about it. I'd hone the cylinder and re-ring the piston. For chrome or nikasil plated bores (I think the HT is chrome) use a 240-320 grit Aluminum Oxide flex hone. Just 10 strokes with the hone will clean up the bore nicely.

On the other hand, if it runs good - just run it until it dies! If you never head the head off, you never would have seen the imperfections. So put the head back on and "out of sight - out of mind."
 
Any idea what would cause this? I'ts a new Zada80 and I'll loose and gain compression as the motor heats up. I ordered a new cylinder, piston ,and head but worried it may happen again if there's something in the crank.
 

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hard to tell from pic, but is top of piston pitted too?

cylinder appears to have lost the plating, was mix at 32:1?
 
I had the same! All the plating came off! Mine was 32:1! I ran without the muffler part of the exhaust though, so probably too lean + high revs for couple of seconds at least twice.
 
Top of my piston is still good and intact, I was still running it at 16-1.
I thought I heard some kind of ticking so I pulled the head and cylinder to take a look, didn't see anything so I put it back together. Ran it again and lost compression tore apart again and found the wall scratched like that. No clue?
 
I had only taken it apart, at the point when I had to pedal to maintain speed at full throttle.
 
I'd guess factory defect or running hot due to lean carb setting (or air leak). Not the kind of thing one sees often unless motor has several thou on it.

Not hard to fix with new parts, but requires keeping a close eye on it to see if something is still wrong.

EDIT: just remembered one customer had this due to head studs being really bent, so cylinder was a bit out of line
 
Thanks, come to think of it my bolts were a little out of wack also. New coming soon. I’ll give an update when all comes in and back on the road.
 
If you need your cylinder wall fixed hit North Texas Motor Bikes he is awesome it done very quick and now mine runs like brand new again
 
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