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SY250 Engine rebuild - how bad is it? (With pics)


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Hi,

I stripped my bike down to inspect the cylinder, had planned to just do a top end rebuild but the cylinder looks quite damaged on the inlet side. Would you leave it or what are my options? Does it need replating? 
My nail does catch on the marks.

Additionally - the crank has some minor pitting. I’ve not done this before so unsure if it’s anything to be concerned about. A more experienced set of eyes would be appreciated! 
 

Cheers! 

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Edited by nitjay - hrc
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  • nitjay - hrc changed the title to SY250 Engine rebuild - how bad is it? (With pics)

Ouch looks like she swallowed some sand pit, new parts are in order.  Service manuals will show you how to test measure the crank short of taking it apart.  

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11 hours ago, nitjay - hrc said:

Hi,

I stripped my bike down to inspect the cylinder, had planned to just do a top end rebuild but the cylinder looks quite damaged on the inlet side. Would you leave it or what are my options? Does it need replating? 
My nail does catch on the marks.

Additionally - the crank has some minor pitting. I’ve not done this before so unsure if it’s anything to be concerned about. A more experienced set of eyes would be appreciated! 
 

Cheers! 

IMG_6060.jpeg

IMG_6059.jpeg

IMG_6062.jpeg

pitted big end pin = conrod kit

pitted big end rollers = conrod kit

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That's a definite new piston and re-nikasil. Having said that, there were plenty of times back in the distant past (about 1980!) when I got a seized kart engine back out for the next race by judicious application of wet'n'dry to the piston and barrel. But it did go for a hone and new piston the following week.

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