Query Approved.

That's surprising
I too have a 2007 unicorn which has till date clocked 54k, including my Leh trip , and it's still giving a economy of 48 at 70-90 speeds , and it's still running on the original clutch plates .

So it's surprising that something like this is happening to a Honda and that too only after 40k .

Whenever I felt the engine getting rough, I'd just change the oil -- that worked for me (by the way, I ride almost 90 kms every day, so I needed to change the oil more often)

I too had to replace my bore set at 20k,on top of that at one point of time my engine lost compression.

How much has the new bore-kit done?

Shocking to know you needed a bore change in a HONDA Bike at 40 k Kms.Do you rip the bike often ? why did you change the bore ?....Ok here is something you can check out:
1.Have you changed the Spark Plugs after every 10K Kms ? Take out the Spark Plug and Check for wear and damage . The center white Silica Insulator should have a Tan appearance.If it is on the white side,your bike is running very lean AF mix.Check for air leaks ,or punctured Air Filter.If everything is ok ,then Adjust it towards richer AF mix.
2.If you have changed the bore and Piston you must drive the bike within 4000 RPM for the first 1000 Kms,to allow the engine to set in properly.
3. Have you checked and cleaned your engine oil filter..if not do it.If the oil is dirty ,dark in color,change it with recommended grade oil of required quantity..do not over fill...more is not better.
3. Get your engine timing checked with the help of a knowledgeable Mechanic or with the A.S.S.If it is not as per spec.,Check and change the Ignitor.
4. Check and clean the Air filter.

total cost rounded to 2500 rs for block and piston.
@to all how my block went kaput
I was riding at around 90km/hr speed at the kandivli flyover,suddenly my bike shuts down.Tried the self first,but the self motor was sounding funny,as if it was cranking the engine too fast.then tried the kick starter,shocked to find it going down freely.I had to push the bike all the way from thakur complex to malad.At that pont of time i met a mechanic who managed to free one of the valves after which the engine gained compression.
Took the bike to ass .The svc engg incharge told me that the valves got stuck due to excess carbon deposit.Got the engine decarbonised.Km the bike had done 19500km.
After a week when i had gone to attend a g2g,at that point of time i saw bluish smoke coming out of the exhaust.took it to ass,the svc engg said that i will have to replace the block and piston.

I had followed the run in strictly with regular oil changes and all services upto date

Velociraptor I think your problem is due to heavy carbon deposits in your engine..First the Valves..then I think your RINGS froze due to carbon deposit...this is what I could judge from what you have said.
The white smoke came all of a sudden ,or progressively over a period of time say over a few thousand Kilometers ?If it happened quickly it indicates stuck piston rings,and if it happened over a few thousand kilometers it is normal wear out ....but how within 20 K kms is still a mystery..

My guess is your Valve's stem seals have failed and leaked oil in to the chamber,thus causing excessive carbon build up.

ROSH please give more details otherwise how do you expect people here to give you a probable reason when Honda service center could not after seeing your bike.

1. By replacing bore set did you mean rebore and new piston. If yes who did it. How many KMs have you after that and do you see any improvements at all if any after the job.

2. Have you done any modifications to stock bike like airfilter, exhaust , Carb.

3. How did this problem start. Do you get too much smoke if yes what colour.

4. Any thing else you can think of.

Try and give maximum information if you want people to give you good solutions.

Exactly,I used to use petronas fullsyn oil.Mysteriously the levels used to go down,atleast 200ml in one week,that too when i used to never drive above 80.When i replaced the bore,i did notice some scratches on the piston skirt and the bore
The failed compression was definitely due to one of the valves getting stuck.
Ps-i had got the stem seals replaced when i took the bike to the svc after the failed compression and had got the engine decarbonized.

Full synth oils contain esters that sometime causes the rubber to contract ,leading to leaks.It happens when you switch oils..200ml a week is high by any standards.Like I said your engine valve stem seals must have leaked and led to oil being burnt in the chamber leading to carbon formation. The piston rings must have seized also due to high carbon deposit and your engine started consuming oil.Ultimately leading to total bore change.Please use the recommended oil of correct viscosity index and type,to avoid these types of early engine problems.

Oil has much less octane than petrol. When it burns it leads to detonation which results in overheating of the pistons. As the piston overheats more heat is transferred to the skirts which results in skirts expanding and scuffing the bore. Scuffed bore by piston skirt is a classical example of detonation and overheating. Other signs of detonation is pitting on the piston in areas far from the spark plug. Had read about it but noticed all this when I opened up my bullet engine after increasing compression which led to severe detonation.