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Discussion Starter #1
My bike is a 96 250 I have had it since new it has about 40,000 miles on it. The engine started to develop a pinging noise that I had determined was detonation in the left cylinder. I disassembled the engine serviced the valves, replaced the rings and honed the cylinders. A new gasket kit was installed with new valve seals. I assembled the engine and every thing looked perfect and it started up smartly on the first crank. I ran it easy for the first few miles and then increased the power, soon after within 200 - 300 miles the left cylinder started to smoke heavily and evidence of detonation returned. The right cylinder was clean with no smoke. I disassembled the engine the second time and the left cylinder valves are heavily caked with carbon, the piston has no carbon on it and is very clean. The rings are new and in pristine condition, the valve seals are new and still in good condition and there is no slop in the valve guides. Even if the valve guides were faulty they still wouldn't convey the amount of oil that it is consuming. The entire lane behind me is a cloud of blue smoke. At this time I can see nothing out of the ordinary. I am going to return it to my tech and see if he can diagnose the issue. The only thing I can think of that would cause this amount of oil consumption on one cylinder would be a crack some where, hopefully not. I will report later what the tech has to say.
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From the pics it looks like oil is being pulled in from the inlet side. If the valve or guide are worn then new valve stem seals won't be able to keep out the oil.
 

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Discussion Starter #3
The valve guides are very good with no excess movement and the seals are new but the oil is entering at a wholesale rate from somewhere. I am suspecting a cracked guide or a crack somewhere. There is so much uncontrolled oil it is not anything normal this is completely outside of the box of normal.
 

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Any possibility that the valve stems could be bent?
 

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Discussion Starter #5
The valves are perfect with no evidence of any deformity, just heavily caked with oil carbon. As I have said before you have to think outside of the box for this one. Everything and I mean everything appears to be in order nothing bent, new seals, good guides no excess movement, cylinders in excellent condition with new rings with gaps 120* apart. I think I will press the sleeves out and have a look. The only way the amount of oil that is being consumed would have to be caused from a crack.
 

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Discussion Starter #7
The bores are in spec and they were honed by a professional who just does bikes, the rings are new from Honda and the pistons have no indicators of any faults. The amount of oil the left cylinder is consuming, there would have to be no rings on the piston. The right cylinder is perfect and clean with no indicators of faults.
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Discussion Starter #8
I have dismantled the engine and taken the parts to the tech for review, he could find nothing out of sorts with the head, valves or the cylinders and suggested that I must have installed the second (scraper) ring upside down I assured him that I had not. I doubled checked the pistons and all the rings were installed correctly. He had mentioned that the second ring is tapered and works as a scraper to return the oil. The installation instructions infer that there is a taper and the widest part of the taper should be facing downward, however when the second ring was inspected there is no evidence of any taper nor any wear evidence. The new rings were installed and had 300 kilometers on them. There was no evidence of any wear and no evidence of any taper.
 

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Discussion Starter #9
Faulty oil-ring(s)? Any pictures of the piston? Bore? Measured piston-clearance? Ring-gap?

4-STROKE PISTON RING ASSEMBLY TIPS : (PDF):


There are no issues with the assembly that part is routine but your comment about "faulty rings" may be a valid point. The rings are new from Honda and I have run them about 165 miles and they look like they have 50,000 miles. The top ring appears to be like new with a contacting center with the edges removed, the second ring has some different surface marks, the entire surface is not smooth it has some mottling and non smooth areas . There are two areas that have parallel machine or manufacturing lines along the edges and there is an area where it looks like it was exposed to acid and/or where the chrome didn't take. When the tech looked at the rings he was unsure as to the condition and attributed it to normal break in with some apprehension. I commented to him that the markings are not consistent with normal break in. His final comment, it is a mystery. I am going to buy some new rings and compare. These look like Chinese knock offs.
 

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Discussion Starter #10
There are no issues with the assembly that part is routine but your comment about "faulty rings" may be a valid point. The rings are new from Honda and I have run them about 165 miles and they look like they have 50,000 miles. The top ring appears to be like new with a contacting center with the edges removed, the second ring has some different surface marks, the entire surface is not smooth it has some mottling and non smooth areas . There are two areas that have parallel machine or manufacturing lines along the edges and there is an area where it looks like it was exposed to acid and/or where the chrome didn't take. When the tech looked at the rings he was unsure as to the condition and attributed it to normal break in with some apprehension. I commented to him that the markings are not consistent with normal break in. His final comment, it is a mystery. I am going to buy some new rings and compare. These look like Chinese knock offs.
This is what the new rings look like X15
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Never seen rings magnified before, so this may be normal. But that pitting would concern me.
 

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Discussion Starter #12
Never seen rings magnified before, so this may be normal. But that pitting would concern me.
I presented photo to the Honda Parts manager and also to the journeyman engine tech the they both commented as you have. I have ordered new rings that are on back order and the Honda Parts manager
commented that because they are on back order they may be from a different batch. He felt that it may be worth it to present the photo to the Honda Corporation Technical Department. I will wait and see what the new rings look like. The compression ring is solid with no pitting. The tech commented that the second ring is tapered and works as an oil scraper, also the Honda Manual indicates there is a taper, however there is no taper on this ring.
 
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