Looks like a cases of bad workmanship, which generally plagues the 2-wheeler service centres across India. Moreover, I am sure they haven't used the correct grade engine oil. Basically the requirements of bigger engine are better engine oil & more than just regular checks, as the bigger vehicles are exposed to harsher driving conditions overall as compared to smaller displacement bikes... you can't just feed the same food to a horse & a donkey.

I feel these A.S.S buy bulk engine oil generally of single (lower) grade for cheap bucks & top it up (& not replace) it in all bikes. And on the top of it they charge you full for engine oil change. IMO they should replace the engine oil everytime the bike is serviced, & if they don't do the same, you should get it done from outside.

If you follow this simple procedure your bike will last longer .

The same Engine now at 76000 odo reading, the oil leak just does nt seem to stop.
after service at castrol bike zone (ramamurthynagar bangalore) the first two months the leak was minimal, just as the third month began the leaks seems to have really increased.
No mechanic is able to give a solution to this problem. My rides are usually only 20 km a day at an average 40km/hr speed.

Will I have to go in for an engine overhaul? If yes which would be a genuine place to do it in Bangalore?
Kindly help

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As per my understanding and information, there is one sealing (O-ring) which fits in between exhaust outlet and at the muffler inlet to make the system fully leak proof.

Have you ever changed the sealing ? if not try changing the sealing. No need to go for entire engine overhaul IMO. HMSI's engines are really good, my sister's aviator has clocked more then 83K on the ODO and still going very strong.

I remember when the unicorn launched, with in few months Honda received so many complaints about the oil leakages from engine head and also from exhaust side areas. The culprit was poor quality of sealing, so they voluntary replaced the O-ring seal from the exhaust muffler side and the customer whose oil leakages are quite saviour from engine head side they have replaced the head gasket as well. Usually this happens due to excessive heating of the engine. I hope this help.

anyway you will be visiting to mechanic right ? so please do write up what is the actual issue.

arjun_b2

Your photos show oil is on the fins of the cylinder head as well as some, higher on the rocker arm covers (the smooth covers on top of the cylinder head).

This leads me to believe the problem is with the gasket between the rocker arm covers and the cylinder head. Possibly some oil is leaking out of the joints between the bolts that hold the rocker arm covers in place.

I haven't worked on a Unicorn but generally speaking, the rocker arm covers are designed to be easily removed by unscrewing the bolts on the top.

The gasket(s) between the rocker arm covers and the cylinder head could be replaced to stop the leakage but perhaps a better solution is to take the covers and gasket(s) off and throughly clean them. Pay special attention to the surfaces which mate with the gasket. Also, clean off the gasket surface on the cylinder head.

Buy some oil resistant Silicone gasket sealer.
This is similar to the Silicone RTV sealer used to seal joints on sinks and plumbing but unlike the common RTV which works poorly around motor oil, a automotive grade gasket sealer is resistant to oil. A few brand names are Permatex Ultra Black, Permatex Ultra Gray, Permatex Ultra Copper and Loctite RTV 598.
I'm sure if one of these isn't available there are other brands of oil resistant gasket sealers available in India. Be sure to make sure whatever you use is oil resistant.
Also, do not use one of the non-silicone rubber gasket sealers that harden. If you do, removing the rocker arm covers in the future may be very difficult.

When you put the covers back on, be sure to apply a good coating to both surfaces of the gaskets and also do not forget to seal the surfaces under the bolt heads where the bolts tighten against the covers using the same RTV sealer. That should prevent oil from leaking out from under the bolt heads.

When you have finished sealing the covers, clean off the oil residue on the cylinder head fins and the cylinder fins. I would use a disk brake cleaner but if you don't have any of that, mix up some dish washing detergent with a little water and use it along with a stiff bristled brush to scour the fins. The detergent will cut thru the oil and wash it off.

As for the exhaust seal, IMO the only thing inside the pipe in the area of the joint between the cylinder head and the exhaust pipe is exhaust.
Unless the engine is burning oil and leaving huge clouds of smoke behind you, there will not be any oil in the exhaust.

If you manage to get the Permatex Ultra Copper or one of the Red silicone sealers that is resistant to oil, either one of them is made for high temperatures so they will work to seal the exhaust if they are applied between the end of the pipe and the cylinder head.

Although the above may seem to be a daunting job, it actually isn't.
Anyone who knows how to loosen and tighten the bolts should be able to do the job without any problems.

I have a hands on experience with what you are going through in my karizma. While i was in pune, i had to change the block as i was using my bike on the highways travelling from goa to pune and back almost every week.
My bike went to one of the well known mechs in pune who replaced the block and from there on my oil leakage saga started, hardly a few kilometers from his shop, i noticed oil leak so i went back, he again re-opened it and did the job, again when i collected the bike i had oil leakage after 20kms. I went back, mind you this guy was very genuine and had not come across something like this which required opening and re fixing twice, he re-did the job the third time and i never had oil leakage.
I wanted to know what the issue was and he explained that it was due to high points in the mating surface of two side which allowed oil to leak.He re surfaced both side and using the factory gasket was able to get perfect mating of both sides.
You could try the same or else as Arizonajim has suggested that would work as well.

Yes, I have given my bike to Dream machine mechanic Shop in RMV 2nd stage Sanjaynagar Bangalore.
Will know the result tomorrow.

Hi,
I had visited both authorized Honda service center and the local good mechanics.

The sealing (o ring) has been changed many times.
They (at honda service centre feel the noise coming from engine especially in 3rd gear suggests something is wrong within the engine.
Anyways has not opted for engine overhaul.
Riding only within city with speed lower than 50kmph.
The leak is minimal now especially after the service from Haiku honda at OMR (Indiranagar).

Shaking up a very old thread!

My Honda Unicorn is used quite sparingly and only runs around 250 to 300 kms a month. I use Shell semi-synthetic oil and change it during every service once in 9 or 10 months.

Just had the front shock springs and oil replaced and the service guy said the engine oil seems to be burnt. But when I asked him if I need to change it immediately, he said it is fine "you can change in the next service".

Is this fine to do? Or do engine oils lose their viscosity after few months and need a change irrespective of the kms done?

A bike like Honda Unicorn doesn't need a semi-synthetic oil TBH. And yes, oils tend to lose viscosity when left un-used for a long period of time. As a fellow Unicorn owner, I would suggest changing to a mineral oil (20w40 grade from Motul, Valvoline or Veedol) for better performance. Change every 2000kms and it'll be just fine. Unicorn isn't too power heavy to be a semi-synth. There's not much difference between mineral and SS oil on a 2V 150cc motor.

Hi All Honda Unicorn owners need your help!

I am using a second hand Unicorn 2013 model that I purchased through my friends referral. When I purchased the odometer reading was around 9000 Km. But ever since I had purchased it I had frequent breakdowns. I have spent around 25K with four different mechanics. I have replaced valve and entire clutch assembly twice, also replaced new bore kit and reworked crank shaft for connecting rod shaking issue. All these work had been done was just in my 10000 km of riding. I take good care of bikes I dont ride it hard nor knock the engine dead slow. The last mechanic after taking 1 week of time finally tells me that the carb has some issue with TPS so it will not fire and the timing will also change which makes the bike have no good response to throttle. Even the Honda service guys could not identify the correct problem. Can any one of you please suggest me a method to find out the real problem? My engine is almost new the only thing left out as old is the carb and the electricals. Since I have spent a lot I dint want to sell it. In a way I like this bike as its heavy like a bullet and smooth and sturdy. Please help me out with your experience.

I am not a Unicorn owner but just wanted to know what exactly are the problems with the bike?.

A local garage wallah has messed up some tube connections to carburetor of my Unicorn 150. The tube marked in red in attached picture (Above air screw and sensor) is completely missing and looks lost.

I will get a new tube but need help on how the tube is routed and where will the other end of the tube go.

You don't have to worry. The other end of the tube is not connected anywhere. It's simply routed towards the rear of the bike through the top side of the airbox(close to the frame).

That's the answer I was looking for and I could reconfirm that from the workshop manual . thank you.