Burnt Valves at 15K miles? - Page 3 - Honda CBR250R Forum : Honda CBR 250 Forums
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post #21 of 113 Old 09-05-2014, 05:46 PM
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Well they only get tighter with burning, not back into spec.
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post #22 of 113 Old 09-05-2014, 08:07 PM
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Mike has a good point. I bought a Honda CB125 Twin back in the 1980's. A pretty nippy little bike in it's day, for a four stroke. It had 17,000 miles on the clock, and I don't think that the valve clearances had ever been checked. It was running rough on one cylinder, so I thought that I'd check the valve clearances. The rough cylinder was so tight on the exhaust valve, that it couldn't be adjusted enough to correct. It needed a new valve and regrind.



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post #23 of 113 Old 09-12-2014, 06:40 PM Thread Starter
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Quote:
Originally Posted by jkv357 View Post
You need them to show you exactly what they mean when they say "burnt valves". If there isn't oil to the top of the engine the roller rockers and cam lobes should be damaged and blue from the friction. Typically if an engine has a burnt valve it's from hanging open too long (incorrect adjustment), a very lean mixture, incorrect ignition timing, or detonation. What does the plug look like? That will tell you something about what caused the problem.

I would want to see the valves (and plug) and hear a good (better) explanation from the tech of what he believes caused the problem. I would also contact Honda technical service and hear what they have to say. I don't see the explanation of "bad gas" as a real possibility unless the octane was too low and you were detonating consistently. It's possible, but you would have to be under heavy load at low RPMs to do that. If that was the case the plug should be a melted mess.
Interesting about the plug. It was replaced because it fouled at 12k miles. Husband was not tacking high enough. He wouldn't listen to me so the tech explained to him. I wonder if the past riding activity caused it? Tech is stumped. He says everything looks perfect inside (including the newly replaced spark plug) except the burnt valves. I'm not a techie and he explained it to me fully and I understand what he said but couldn't repeat it properly if I tried. It is covered under an extended contract. The inspector will be out to see for himself before covering the job. So far my tech has talked to three different honda techs, my father one and I talked to the service dept on another island and none of them have an explanation. Nobody has heard of it. The other dealership here that has two of them in the shop for the same reason.....is because the bikes had oil pressure problems and never had one service. Engines look destroyed inside. Mine looks perfect...except the heads. I'm thinking we will never know why it happened.
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post #24 of 113 Old 09-14-2014, 05:32 PM
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You mentioned the possibility of an oil pressure problem.
The engine has an oil pressure relief valve that almost
never fails but on rare occasions they do. Both too high
or too low oil pressure could cause serious engine problems.

It is located on the back side of the oil pump assembly. Its
like a small cylinder with a spring loaded piston inside that
covers or exposes holes to regulate oil flow. On rare times
they become sticky, become stuck and stop working.

You might want to call the service center where your bike
is and ask if they have checked the 'oil pressure relief valve'.

See pic to have an idea what it looks like.

Last edited by gromit; 10-15-2014 at 07:53 PM.
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post #25 of 113 Old 09-14-2014, 07:51 PM
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Not to sound like an idiot, but that's how it goes these days....wouldn't it be cheaper to replace the engine completely with maybe a working salvage, new 250 or maybe even a new 300 engine and gear box? Any thoughts on that or am I delirious?

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1978 Honda CB400T II Twin
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post #26 of 113 Old 09-15-2014, 12:31 AM
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Quote:
Originally Posted by cmoretti View Post
Interesting about the plug. It was replaced because it fouled at 12k miles. Husband was not tacking high enough. He wouldn't listen to me so the tech explained to him. I wonder if the past riding activity caused it? Tech is stumped. (SNIP)
That doesn't make sense to me either. A fouled plug? It takes a lot to foul a plug on a F.I. bike with electronic ignition. Just lugging around won't do it.

Again, if he was detonating by lugging it too long and too hard I would expect the plug to show damage from the detonation - but not "fouling". An engine that is burning oil can foul a plug, and it would look black and wet. If there was enough oil in the cylinder to do that you would see white smoke from the exhaust and the oil level would drop significantly and quickly.

If you can, get pictures of the damaged parts.

It's still all not adding up for me.
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post #27 of 113 Old 10-04-2014, 01:15 AM Thread Starter
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solved

upon repair and total dismantle it was found to be caused from carbon buildup from a new rider (my husband) lugging the engine. The same reason for the spark plug foul at 12.000 miles. Moral of the story: Don't teach someone to use a manual transmission 1) on a motorcycle 2) who can't tell the difference between normal and not normal sound or identify by sound when shifting is needed. I tried to explain when to downshift and upshift.....what worked is my mechanic telling him to make it sound as annoying to other people as possible....like he's racing all the time. Go figure. Thank you for all of your input!
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post #28 of 113 Old 10-04-2014, 10:37 AM
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BTW is there a value for minimum RPM for each gear?
I usually run my bike on lower RPMs and shift up as soon as possible which can get me down to 3500rpm in the first three gears, 4000 rpm in 4th and 5th and 4500 rpm in 6th gear. Are those values ok or is that too low? Couldn't find anything with the search function on that.

My computer is fighting Aids and Cancer in it's idle time, and yours?
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post #29 of 113 Old 10-04-2014, 10:44 AM
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I try to keep it above 5k. It does get a bit loud but that's fine by me!

The MOM has values for when to shift / mph
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post #30 of 113 Old 10-04-2014, 11:06 AM
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Originally Posted by kadookoo View Post
I try to keep it above 5k. It does get a bit loud but that's fine by me!

The MOM has values for when to shift / mph
Is the MOM the normal user manual? Because mine doesn't have any values for that. I just keep the RPM in a range where the engine doesn't "complain" by growling deeply and not running smoothly.

My computer is fighting Aids and Cancer in it's idle time, and yours?
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