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.
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.
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.
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?........
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?........
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
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
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
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
Have you verified a good,hot spark? Is it timed correctly? Are the spark plugs wet or dry? New,dry plugs or plugs already gas-fouled from previous starting attempts?
Yes, the marks are lined up as close as possible. One thing I noticed is after setting point gap, the ignition timing is spot on but at the end of adjustment.
I've never worked on the SS125 engine, but what Mike said - combined with what you said about the ignition timing - makes me wonder if you don't have the cam timing a tooth retarded as Mike suggested. If the cam was retarded a tooth, it would require that you use more advance in the ignition timing to account for it to set the timing correctly. I'd imagine that slightly retarded cam timing would change compression readings as the intake valves would close later
Do you know if the rotor has ever been off? Woodruff key in place? Use a straw or a screwdriver down the spark plug hole to see if the tdc mark coincides with the top of the piston travel.
Yes I've had the rotor off, key is in place tdc matches piston position.
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