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I have a ss125 I just did a top end overall. I've had the bile for about 5 years. The bike had gotten low on compression and starting to smoke so rebuilt it. Bored 10 over, new pistons, rings. Back together it's only run a couple minutes at a time before it dies. Squirting oil in the cylinder helps it crank. Compression is even on both cylinders at about 90 psi. I have done all the obvious. Something I'm missing, not sure.
 

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I have a ss125 I just did a top end overall. I've had the bile for about 5 years. The bike had gotten low on compression and starting to smoke so rebuilt it. Bored 10 over, ( I'm assuming that 10 is 0.010"or .254mm) new pistons, rings. Back together it's only run a couple minutes at a time before it dies. Squirting oil in the cylinder helps it crank. (By "crank" I assume you mean start) Compression is even on both cylinders at about 90 psi. (IIRC, spec is 123 PSI to 149PSI I have done all the obvious. Something I'm missing, not sure.
Did you stagger the ring gaps, and are they within spec?
Other than that, sounds like it was bored too big for your pistons and rings........

You may phone to discuss........
 

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Discussion Starter #8
Please phone
Premixed a couple ounces of mystery oil in a gallon of gas. Squirted a little in the cylinders no start. Squirted some 30w oil in in the cylinders ran about 3 minutes. Wouldn't start back up.
 

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Ok, any suggestions, bike started with some oil squirted in the cylinder, Done it about 3 times letting the engine warm up good each time then cool. Will these rings ever seat? Should I tear it back down and get some measurments? Don't understand a fresh rebuild not cranking.
 

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Klaus had a similar problem with his 175....Turned out to be Std or 0.25 mm rings on a 0.50 mm oversize piston....
Broken rings would have similar symptoms....Since you checked ring end gap in the cylinder bores before installing them on the pistons, are you sure the bores are round and the taper is correct?
It is almost certainly a "sealing" problem if added oil temporarily cures it.....
Rings in correct sides up?........
 

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Discussion Starter #11
Klaus had a similar problem with his 175....Turned out to be Std or 0.25 mm rings on a j0.50 mm oversize piston....
Broken rings would have similar symptoms....Since you checked ring end gap in the cylinder bores before installing them on the pistons, are you sure the bores are round and the taper is correct?
It is almost certainly a "sealing" problem if added oil temporarily cures it.....
Rings in correct sides up?........
I
Klaus had a similar problem with his 175....Turned out to be Std or 0.25 mm rings on a 0.50 mm oversize piston....
Broken rings would have similar symptoms....Since you checked ring end gap in the cylinder bores before installing them on the pistons, are you sure the bores are round and the taper is correct?
It is almost certainly a "sealing" problem if added oil temporarily cures it.....
Rings in correct sides up?........
I didn't check bore, counted on machines to get that right, rings installed correctly, as a last effort I adjusted valves to be a tad loose. Didn't make any difference, no start
 

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90psi is a very low compression reading. When testing did you open the throttle and choke to full open? If you didn't then retest and see if the readings are at least 115psi and above. That's the low spec figure you should see. If it is above that, say 125 or more then your problem may be something other than compression, perhaps ignition.
Guy
 

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90psi is a very low compression reading. When testing did you open the throttle and choke to full open? If you didn't then retest and see if the readings are at least 115psi and above. That's the low spec figure you should see. If it is above that, say 125 or more then your problem may be something other than compression, perhaps ignition.
Guy
I took the engine back apart today. Saw no obvious issues. Took measurement of the pistons and bores. Clearances were .001 to.0015, clearly within limits. The only logical thing I can figure out is rings are just not seating. Should I get it honed again and start over? Thanks
 

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Did you check the rings end gaps in the cylinders? There was recently another instance of something like what you're experiencing and his issue turned out to be incorrectly-sized rings supplied with oversized pistons
 
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