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DIY: I opened up Honda CB 350RS engine after service centre messes up

So finally that big decision of doing it all by myself popped into my head. I knew it was risky but anyway that dead mechanic inside me was eager to come back to life.

BHPian DocOn2Wheels recently shared this with other enthusiasts:

DIY with Honda CB 350RS engine.

Either this post is going to be quite long or will be followed by back to back posts. I hope the moderators approve!

Complete story of how a normal college boy ended up with doing DIY with an almost new bike's engine. In April the ASC guys called me to give them the last chance. They overhauled the entire engine with red RTV silicon gasket maker, probably Anabond, being used in surplus. That was done around 8400km on the ODO. I could see the bond oozing out from all the joints. The bike rode fine with that unrefined noise from the engine which remained but the missing problem subsided. I noticed that it was overheating a lot but then I convinced myself maybe it's my overthinking. Even short spins used to heat the engine to an extent that I could feel it inside my denim and even inside that thick viaterra grid gloves being put 5 inches away from the engine.

It was around 9600km on the ODO that the engine started missing again, losing power in the initial RPMs. As I posted earlier I was doubtful about the oil flow to the head. So I thought maybe it is a problem of inadequate oil supply to the head due to which the engine is overheating and maybe the valve seat got damaged again like the previous time as stated by them. So finally that big decision of doing it all by myself popped into my head. I knew it was risky but anyway that dead mechanic inside me was eager to come back to life. I mean it! Since my childhood I have been fascinated with mechanical stuffs, gears, pistons, tools and everything. Used to wonder how bike and cars run. While I was in 8th standard I asked my father to let me pursue mechanical engineering but without any consideration he denied and here I'm pursuing medicine.

First the work started in the parking lot in the basement. Drained the oil out, opened the clutch side case to check the oil pump and the oil strainer. The interesting bit is that the oil pump is integrated in the case unlike other bikes.

I also made a rough diagram of the RH side with bolt slots to make sure not to mismatch them because sometimes they might be of different length.

To mention my reference I've watched countless videos on Youtube about engine overhauling especially of Honda Shine and unicorn.
I couldn't find anything wrong with the oil pump on physical inspection but had to make sure. Reassembled the case, poured back in the oil and with the oil filter out cranked the engine. Oil started to rush with pressure through the opening in the oil filter chamber which confirmed that the pump is in good shape. It was both a good news and a bad news. Bad news cause now I had to open the head to clear the oil flow channels. Just by the thought of it I got terrified!

It remained as such for four days until my friend gave me the idea to bring the bike up on our floor(4th) in lift and use one vacant room of our hostel for all the work. We brought it up, cleaned the room, prepared the floor with cartoon pieces and now the real work begins.

From here onwards me and my friend worked for 5 days continuously to dismantle and reassemble the engine head.
I'll give a basic summary of the entire work done.
We followed the below mentioned steps:

1. Removed the seat and the tank by disconnecting the fuel line and the power supply to the fuel pump
2. Then removed the crankcase breather hose which connects to the rocker head cover and the air box chamber
3. Removed the fuel injector from the throttle body using 10mm socket

4. Removed both the sides throttle body covers and also disconnected the throttle cable from the throttle body and disconnected all the electrical connections around it

5. Removed the ignition coil to make way for the rocker head cover removal
6. Removed the rocker head cover
7. Removed the timing chain tensioner

8. Removed the timing chain gear from the camshaft using 8mm socket. For this I had to use a gear lock tool to keep the gear from rotating. Used it in the gear connected to the crankshaft on the RH side of the crankcase.

9. Opened the stud bolts. It was 12 or 13mm, I'm not sure. Tried to remove the rocker head but failed. Saw the studs having bolt head pattern on top. Removed the studs using 6mm socket. One point to remember is that the right side studs are taller than the left side studs and are of equal length on each side.

10. Removed the rocker head. It has two dowels on the right side front and back

11. Removed the exhaust before removing the head. First unscrew the O2 sensor then make sure to remove the earthing connection near the rider footpeg.
12. Took these two 10mm bolts from the right side of the head.

Took the head out with throttle body intact. The head has two dowels at the bottom in front.
13. The real deal. Have a loot at the head gasket!



All the holes were blocked by RTV gasket. This is the workmanship you should expect from Honda's premium offering.
So we got to the actual problem. Going further was an option and I chose to proceed. Removed the cylinder block too just to make sure there was nothing fishy down there and to my surprise here is how it was.

Removing the cylinder gasket was really tough as it was stuck firmly. Although risky I used a box cutter blade, with high precaution so as not to damage the surface, to remove that gasket. That task required a lot of patience, time and effort.

I rubbed all the joint surfaces with 1200 grit sandpaper followed by 2000 grit and cleaned it thoroughly with petrol to remove all the glue and imperfections and it worked out nicely.
Checked the valve seats and found out that the intake valve was leaking as I had doubted. So had to take it to lathe shop to get it seated properly.

There was too much dry soot deposit on the piston and the valves which flaked off easily. I know it was due to improper combustion of fuel but don't know what's causing it.

I checked the cylinder wall and it was ok. Had nothing to do with the gearbox so left it as it is. Cleaned everything with petrol and started assembling everything following the exact same steps in the reverse manner.

Fitting the cylinder back was a tough task due to lack of prior experience. One thing to mention; I always kept the timing chain tied up with a rope.

Cleaned the throttle body with petrol. Dismantled everything including the TPS

Didn't use any glue anywhere, instead changed all the gaskets to new one.

Tools used:

1. Stanley 1/2" socket set- STMT72795-8
2. Stanley 1/4" socket set- STMT72794-8
3. Nose pliers
4. Gear lock tool(optional)
5. Few open head spanners

I have the videos of dismantling the engine but those were not recorded with an intention to upload anywhere. Anyway I'll try to put it in a presentable format and if possible will share the link here.
Further updates in the coming posts.
Till then happy riding!

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