Timing chain will not get damaged easily..that too when the head is opened,unless the mechanic plans on opening the head with a Crow bar.
If the bike had not seen timely change of oil or maintaining enough oil in engine then the timing chain and a whole lot of other parts will go bad.

Most of your queries have been answered by Psr sir.I had told you before K&N does more bad than good,the 'jetting and making mixture rich' is all trial and error method.Good that now you had reverted to stock filter.First of all,get the new airfilter box,donno the price.And it seems that the exhaust valve might be having less clearance.Set the valve clearance 0.06mm(inlet) and 0.08mm(exhaust), only, when the engine is cold.
Clutch plates changed at 7k!Seems you do a lot of burnouts,stunting :-P
1)For the rear tyre,you can switch to MRF Zapper C 110/80 17''(Dazzlers rear tyre),gives descent grip in dry and wet conditions.Cost around Rs.2500 here,check at your place.
2)Timing chain getting damaged once the head is opened is news to me.Psr sir please shed light on this.
3)Rotate the AFR screw at 2.5 full turns for optimum setting.
4)For the running in with the new bore,use Shell AX-5 mineral oil 20W40,its a very good oil,gels well with RTRs or else Elf moto4 20W40 gold will do.Both cost around Rs.220.

Its getting impossible here for any of the mechanics to set the AFR all have tried their best even the SVC guys have been unsuccesfull....I got my bike checked at the SVC...they said its Due to Damaged valve sealing and piston rings......when i enquired abt the piston rings they said....they can only give a new bore kit tht too in 15 days minimum....so out of discontentment i ordered the BIG BORE KIT FROM JOEL.....the kit will reach me in next 2-3 days.....as per joel.....and now i will get my bike's head opened at the SVC during the change of bore kit and will check for the valve sealing and valves....but the SVC guy said tht as u have ordered the bore kit ...then plzz get along the timing chain also as it gets damaged once the head is opened.....Now my questions are

1.Cost of new filter box
2.Rear tyre(im nt at all worried abt the grip i just want performance as of now)
mention the size and make plzz
3.Which engine oil to use with the new bore kit and how many kms to run in safely
4.Does the larger rear tyre size decreases mileage coz i dnt knw abt it buyt i surely decreases acceleration
5.Wht shld be the exact Afr setting noe

Fitting K&N would have leaned out your AFR,and to compensate the AFR must have been made rich.Now that you have the stock box the AFR must be made lean...First of all ensure your patch up is not leading to air leaks in the air box..better still get a new one and fix in place.
The AFR must be adjusted for stock which I think is 2 full 360 degrees turn from fully clockwise tight condition...visit the RTR180 thread in the "owners experience" forum and it is full of helpful suggestions.
Your engine bogging down at higher RPM could be due to rich AFR which is evident from the lower FE, as also due to a tighter valve(tappet) clearance setting.. It may also be due to worn piston rings since you had been running the bike at higher RPM most of the time..
Do a compression test and if it is ok then check and adjust the AFR..if it is not then you may have to check and adjust tappet clearance to stock, and if still the compression is poor suspect valve seating and piston(and bore) ring wear.

1.check ur engine valve align properly
2.check regular d level of engine oil,,,after 100 kms..if its goin too low pls consult ur mechanic.
3.check ur jet position,,either it is running on lean or rich mixture,,,,it effects ur mileage on various speeds....

Answer to your querries:
1. If the oil leak is from upper side of head (Near Head cover) Then Head cover packing needs to be replaced. If its from anywhere else, go to SVC ASAP.

2. 11k !!! Never RedLine (If you need bike in good condition) !!

3. Check if carb is getting enough air to breath via Air Filter box.

4. NEVER mess with taped, Go to SVC and get Taped set to company stated distance.

5. Low Mileage maybe becaused you taped tightened

6. I have less knowledge about tires .

7. I think K&N won't have caused any problem.

Query approved