I have a whine noise coming from my engine when it warms up..
On idle the noise is there but when i rev the bike it goes away.
And when it goes back to idle its back again..

When the engine is cold its alright but when it warms the noise comes into it..if i stop the engine for 1 or 2 minutes its stops the noise for 5 mins or so but then it comes back..

and suggestions ..

I'd be looking at the water pump, starter motor and gears, generator rotor and clutch areas first.
Main and big ends normally knock, cam chains mostly rattle.

Use a big screwdriver as a stephascope or get a stephascope from eBay and listen to the engine to find where the noise comes from .

Is the noise there when the clutch is pulled in.

hunter wrote:Is the noise there when the clutch is pulled in.

Honestly dont know Hunter as have not the clutch cable to the lever yet but will check in the morning..
I have just put in the engine today to the bike but it was running 100% when I last started it a few weeks back..
But will check pulling the clutch tomorrow..

Will inspect the water pump and starter too have a few spare of each lying about..

What did you do to the engine when it was out ?

Evilchicken0 wrote:What did you do to the engine when it was out ?

Done nothing to the engine ..
It was in my Track bike that I am building and I ended up buying a road bike with the motor gone so putting the 400 engine in the road bike and putting a 600 in the track bike..
I started the bike this morning and have not heard the noise since ..But not happy knowing it was there but now not showing up. Think I will run it for a while more this evening and see if it plays up.. The bike was sitting up for a few months not started unless it was something to do with that ..
HAd a listen all over with the screwdriver and all sounds smooth ..
Only thing i done different today was put the clutch cable to the lever but cant see that make a difference but going to disconnect that again and double check..

UPDATE

The noise is from the cooling system..
When the bike is running a while and I increase the rev the noise comes into it when the rev drops ..
And when I looked closer the pipe at the water pump leaks out the odd drop of water but only when this noise appears ..
So it seems as if it creates pressure when it warms ..
Would this be down to a stat or would it be more incline to be the pump itself..
Have spares of both so suppose swapping both would be the better option..

Sounds like when the stat opens you get the niose so I'd assume it's in the rad part of the circuit. Flush the system, take the pipes off andclean any corrosion off the solid ally pipes (Mr Muscle limescale stuff) bleed it all, then see.

It might be the pipe isn't sealing and the air causes the system to loose pressure - the engine might overheat because of the lower pressure

Sounds like the water pump is worn,
When the stat is opening, the water flows through the pipework to the pump at a slow speed,
When revved the pump spins faster and is probably the reason the noise goes away.