CB125F not working! Your help is valued!!!

[Eximius]

Hello everyone, 

 

Firstly I would like to say I cannot thank you enough for taking the time to read this and hopefully help me.  
 

(Especially as this is fairly long as I’m trying to provide as much detail as possible). 
 

Basic bike info: HondaCB125F, 2016 Reg, 4K miles. 
 

What happened: I was riding my motorcycle down a long and very steep hill while staying on the rev limiter (red line) in 5th gear the whole time. 
 

Its very difficult to say for how long I was on the Rev limiter .. probably 5 seconds +. Maybe 6 or 7. 

My bikes top speed is usually 65 on a flat road and without the wind in front of me but I think I was doing about 70 as the hill was so steep.
 

Approximately 10-15 minutes later my motorcycle starts losing power and makes horrible noises. Sounded like noises related to metal parts. Maybe.. Metal parts rubbing each other.

 

I then pull over after a minute or 2. Switch the engine off for a few seconds. Start the engine again and I’m riding along for a minute or 2 without any strange noises at all. 
 

Then after 1 or 2 minutes of normal engine noise.. I lose power .. I pull over quickly and the engine has not started ever since. 

 

The ignition comes on.. then it sounds like what I’m guessing is the starter motor trying to start the engine but no engine noise at all. 
 

Spark plugs were replaced by AA but this did not fix the problem. 
 

Please can you help? Thank you. 

Edited October 10, 2021 by Eximius

[Mississippi Bullfrog]

Running at the rev limiter for short periods should not of itself cause a major issue. When I had my Suzuki VanVan I fitted a smaller front sprocket to allow it to hold top gear on dual carriageways. I regularly ran it for quite long distances on or very near the rev limiter.

 

But it's possible other factors are involved so from what you've said the first thing I'd do is to remove the spark plug and try turning the engine over by hand. A socket on the drive sprocket nut will do the trick so long as it's in gear.

[Bianco2564]

Hello and welcome.

Few things I'd look at.

Check the valve clearances, you may have oversped the engine and run into valve float.

Check valve timing in case its jumped a tooth.

Do a compression check to check for any valve to piston contact.

Did the oil light come on while going down the hill? If it was so steep the oil pickup may have become uncovered especially if the oil level is low.

 

Assume this was an attempt to see how fast it will go?

Normally going down a steep hill requires a lower gear to control your speed.

Not judging, we have all done it.

 

[Fozzie]

First port of call, drop the oil out of the engine into a container, and see if there's any metal in the oil. Usually when something metallic grinds like that, it's a good place to start.

[Mississippi Bullfrog]