Topic Approved.

Can you give a situation recap like, since when did the machine start sounding like that, what changes did the earlier owner make, when was it last serviced and how old it is?

Although, I can't help with RE as I never had any experience with them. Bullet lovers, kindly pour in your suggestions.

As per the previous owner, sound started around November 2011 and he did the service immediately after that and not touched the engine for any kind of work, after servicing he barely ridden the bike for 60-70 kms. Bike is 2003 model. Is has run around 20k.

Is there anybody who knows about the problem? I wanted a advice guys.

Its cleared man. Your engine needs to be decarbonize. Excess carbon built up on the combustion chamber reduces the combustion area, hence, knocking!
Go to the good mechanic, as ask him to decarbonize it (in hindi, head ka carbon saff karwana hai). They will not understand the mean decarbonize. Its needs opening the head, which requires new head gasket, and head oil seals if found damage. Better to change if its cheap.

@paul-did you saw the video? I have shown this problem to 3 different mechanics. Everyone has said that piston+block needs be change.

I also have bullet 350 the standard one, but yours sound is so weird. Piston block cant be gone in 20k kms. That sound looks like crank is gone but i'm not sure. May be those mechanics are correct. This is not a knocking. Just wait i'll so this video to my father, i think he also experienced this problem once. Let me see what he suggest.

Whoever has told you that "piston + block will need to be changed" are in my opinion (and experience) 100% right... Your engine has blown man..!

When my engine had blown this was the EXACT sound it was making. I thought something was wrong with the tappets. Turns out the head was in perfect condition. One side of cylinder had become rough since some part had melted due to heat. The same side of piston was blackish instead of shiny silver.

So I would suggest, get the head opened, which you will need to if you want to follow other people's advise and "decarbonise" the head (which you shouldn't need to do for atleast 40-50K kms, RE owners would advise better). Once the head is opened, see the condition of cylinder walls. High chance that they are bust and have become rough and colour of burnt metal. In which case the piston has gone bust too. Change block+piston and your bull will be back to original glory. And get this done at service centre for peace of mind.

Edit: This is not the sound of a knocking engine by the way. That's not how detonation or pre-ignition sounds.

Thank you Plasmabhai. I bought a new piston block kit. Engine is opened now and 1 more problem is there with the crank and connecting rod. It's got loose, needs to be lathe. I have given to known mechanic in New Panvel. It will take around 4-5 days to get ready because he has some more bullets to repair.

Awesome! Your bull is gonna be raging in no time soon! Cheers!

good to see your problem solved!! How much did it cost ?? Block and piston ??