Honda CBR 250 Forum banner

21 - 40 of 113 Posts

·
Registered
Joined
·
3,789 Posts
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.
 

·
Registered
Joined
·
37 Posts
Discussion Starter #23
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.
 

·
Registered
Joined
·
218 Posts
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.
 

·
Registered
Joined
·
7 Posts
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?
 

·
Registered
Joined
·
1,771 Posts
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.
 

·
Registered
Joined
·
37 Posts
Discussion Starter #27
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!
 

·
Registered
Joined
·
1,826 Posts
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.
 

·
Registered
Joined
·
1,826 Posts
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.
 

·
Moderator
Joined
·
2,015 Posts
For a 250 cc bike, I have always tried to ride in the 50-75% of red line region, except for starting from a stop or accelerating to pass. That worked well with my NX 250 single.

Lugging the engine is something that you want to avoid. And, you are riding a motorcycle, enjoy it. :)
 

·
Registered
Joined
·
613 Posts
I just try to keep it below 6k-ish until its warmed up then I keep it above 5k (normally in the 6-8k range) for the rest of the ride.
Below 5k I don't feel like I have any power.
 

·
Registered
Joined
·
186 Posts
So let me get this straight, burnt valves due to low rpms. Because low rpms generate sooooo much heat. Not sure I buy the explanation of carbon build-up due to low rpms. Sounds like hand waving blaming the rider instead of Honda for a touchy design.
 

·
Registered
Joined
·
368 Posts
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.
American owners manual page 27

[Shifting Gears]
[UP]
From;
1st to 2nd - 12mph (20kmh)
2nd to 3rd 19mph (30 km)
3rd to 4th - 25mph (40km)
4th to 5th - 31mph (50km)
5th to 6th - 37mph (60km)

[Down]
From;
6th to 5th 28mph (45km)
5th to 4th 22mph (35km)
4th to 3rd 16mph (25km)

Box that reads;
NOTICE
Improper shifting can damage the engine, transmission, and drive train. Also, coasting or towing the motorcycle for long distances with the engine off can damage the transmission.
 

·
Registered
Joined
·
1,826 Posts
Thanks. Then I'm not lugging the engine and can actually even shift earlier into 6th gear.
Funny that the US version comes with a different manual. The English version of my 2011 manual tells me something about the steering lock on page 27...:rolleyes:
 

·
Registered
Joined
·
11 Posts
Thanks. Then I'm not lugging the engine and can actually even shift earlier into 6th gear.
Funny that the US version comes with a different manual. The English version of my 2011 manual tells me something about the steering lock on page 27...:rolleyes:
I confused, I believe lugging is putting heavy load to engine with incorrect gearing ratio. In short, too early shifting up. Correct me if I am wrong. My Thailand manual page 27 is about Brakes. I read the English version manual as I am Malaysian. Non is telling about Shifting rpm for 2013 manual. But if 1-2nd gear not more than 20kmh, I am in trouble..mine usually 30-40kmh 2nd gear shifting depend on hot and cold engine. If final gear not more than 60kmh shifting to 6th, more trouble to me. At least I will cruise 70kmh in 5th for 10 minutes or more to heat up early morning commuter. I took a good 180 degree corner at 80kmh in 5th before entering highway. Depend on traffics, but normally as soon as out of the corner at rpm 6k approximately 85kmh, it smoothly asking for 6th effortless (almost no clutch involve)..and if I am in the mood to catch the fast lane earlier, 5th gear always winner..up to 9k rpm easy and 10k with anger..I consider my self over raved but is that means lugging too? Mine 2013 now clocking 33000km never had problem except for rear sprocket bearing damage at 30000km+-. Never change sprak plug, using fully synthetic oil every 3k, commuting 1 hour 140-150kmh most of the time on highway. Advice me if these will cause an issue for my next 1600km journey kuala lumput to puket island. .I will be the smallest among others in convoy. I have seen kawasaki er6n getting problem with exhaust valves for its metal fatigue. .I am worried if honda does the same?
 

·
Registered
Joined
·
1,826 Posts
@kuchaix

From my understanding lugging is putting too much load on the engine in a too high gear (shifting up too early).
The numbers kadookoo mentioned are safe speeds to shift, not the only speeds you can shift (actually I don't think I'll use 6th gear at 60km/h). You can of course rev the bike higher before shifting for better acceleration if you want to. I just like to shift early when I'm going with the flow in city traffic when I don't need acceleration.
 

·
Registered
Joined
·
1,096 Posts
You could of got bad gas that has been leaving carbon deposits, it gets under an open valve, when the valve closes it doesn't close all the way.... That will burn a valve out.
As for premium fuel it may reduce hp but won't get the carbon build up like e10 or crap gas.
Maybe the oil rings didn't bed in correctly, it may not burn dino oil enough that u notice its level is going down then if you put in synthetic oil in it may be burning more of it off ( causing carbon deposits).
There's no way the vc could have been rite with a valve partially open.....
 

·
Registered
Joined
·
1,771 Posts
So let me get this straight, burnt valves due to low rpms. Because low rpms generate sooooo much heat. Not sure I buy the explanation of carbon build-up due to low rpms. Sounds like hand waving blaming the rider instead of Honda for a touchy design.
I agree - it still doesn't make sense.

As I said before, to foul a plug in an engine with electronic ignition and F.I. is unusual. Lugging or bogging shouldn't make it run rich or build-up that much carbon in that amount of time. Look at the RPMs that cars are running consistently - 2000 or less - without issues. If you had a significant amount of carbon chances are you would be detonating (from increased compression), and possibly damaging a plug in the process.

There would need to be some reason that the valve started hanging open in order to burn it. Carbon deposits in the chamber wouldn't be enough to do it. I would also expect it to be hard to start and not run well if that was the case.

I typically spin up to redline regularly, but other times I will short shift and just cruise. The high-mpg guys on Ninja 250s and CBRs are cruising at low RPMs all the time, and I've not heard of any valve issues.

I run a strong fuel system cleaner like Chevron Techron Concentrate (1 oz per gal) once every season to keep the injectors and intake clean, but I don't think that if you didn't you would have issues in 12,000 mi.

Also - high octane (Premium) won't burn any cleaner than Regular - and it will cost you power and economy. Some companies claim to have more detergents in their Premium, but if you feel there could be carbon issues just run a fuel system cleaner annually.
 

·
Registered
Joined
·
186 Posts
Look at the RPMs that cars are running consistently - 2000 or less - without issues CBRs are cruising at low RPMs all the time, and I've not heard of any valve issues.
This is what I was going to point out -- the new D.I. Honda Fit w/CVT runs at very low rpms compared to the M/T model! Hmm, but the CBR250R isn't direct inject, only port injected.
 
21 - 40 of 113 Posts
Top