Strange Engine Problem - (Temporally solved). Review on Honda Unicorn 150 cc

My Unicorn is just 8 months old and 5500 kilometers. The bike was very smooth and silent except some small issues like rear break.

But I recently had a very bad experience twice with unicorn engine. It suddenly stopped and not starting even through self starter or kick starter. Kick starter seemed to be moving freely and no pressure!!. Later I had to take it to Service center to repair it!!.

First time it happened when I was coming back from Mysore to Bangalore. It suddenly stopped in the middle after some 130 kilometers near Bangalore city outer ring road. Second time, when I was on the way to Mysore, at Mandya, after some 100 Kms.

Both times the vehicle had traveled more than 100 kms but absolutely was not giving any indication of an engine problem. It was quiet smooth and average hot. Even second time it happened in the evening when I tried to start the bike after a 30-45 minuted halt for dinner.

Now, lets say about Service center guys, they took the vehicle for service after first engine stop, repaired and gave back to me. But did not tell anything much about the cause except like some valve issues. They did not charge also for any replacement but engine oil. Second time I had to take it to some bike repair shop in Mandya and did open the engine head cover (given photograph) for repairing it. They fixed the problem very quickly and told me to tell about "the freely moving kicker" when I go to service center for identifying the problem. Also I got a new information from them, the valve might have bent inside the engine. I could only see they rotating the crank wheel using hand and positioning the rocker arms.

And now (also), the bike is running even more smoothly and silently. I want to take it to Service center and complain about this. Before that, I would like to have an idea, how it could happen on Unicorn engine. Anybody aware of such kind of an issue?? I will be thankful if you can share your information here.

---Temporally solved----

I approached the Service Center through Honda customer care, and now got a solution which seems not bad. I could meet with a senior service manager and technician there and they really supported me solving this problem. I will brief out the findings and solution here:

Findings:

a) Engine was heating up than normal; Exhaust valve misbehaved at this over hot condition.

b) Oil pump was not functioning well inside the engine and this caused insufficient oil circulation and again led to overheat and friction.

c) Valve clearance adjustments were needed. Gradual changes to this clearance gap also produced less mechanical and more heat energy.

d) Engine head cover rubber gasket was cut due to which oil leak happened.

e) Clutch lift plate had bent which formed after trying so many kicks while not starting.

Solution:

a) Rubber mounts replaced on top of both exhaust and intake valves.

b) Oil pump motor unit replaced under warranty.

c) Proper valve clearance done for now. No guarantee it will retain. Needs to check periodically based on use.

d) Engine head cover rubber gasket replaced. Oil leak stopped.

e) Clutch lift plate replaced under warranty.

I had a long discussion with both Service manager and Senior Technician. They have shown and explained all the replaced parts to me. I will conclude what I could observe all about:

Expansion happened to exhaust valve due to overheat and it hesitated to open and close properly. Exhaust outlet remain closed and air block happened at the time of exhaust stroke. So piston became engaged and this led to an engine firing failure.

Service center guys had no clear answer about the kicker free phenomenon. (The true relation between piston engage and kicker free is depending upon the Honda engineering. I have no much idea. A kicker could be free because it is detached from other stuck units.)

And I believe there could be either a leak or block of gas to and from combustion chamber, but mostly it can be a block (of either burned gas to go out of the chamber or new fuel air mixture to come inside the chamber) because the mechanic could start the engine easily after he open the head cover and manually rotated the crank along with moving rocker arms and camshaft. This could release the blocked gas or blocked valve. I conclude it was an engine breathing problem caused by mis-positioned valve(s).

Anyways, the service center guys found no worn to any metallic parts inside head including bore and thus not changed.

And now,

The Service was done properly and I can realize the change in engine sound and response in terms of performance. It’s going smoothly and will update soon after my next long trip.

Thanks,

Meharo

Bangalore