Big Bore install Part 1 of 2

Since everything is here in theory and the barrel is sprayed its all go!

Removing the engine is a fairly straight procedure especially when the engine of a single cylinder isn’t to heavy and can be lifted by yourself with some effort. You start by:

1. Removing fuel tank
2. Remove carb
3. Remove side panels
4. Drain oil
5. Unlink the clutch, chain and gear lever

This should leave you with the engine exposed, now its a case of getting some spanners ready, 10mm, 12mm, 13mm, 14mm and 16mm. The smaller bolts are at the front end and easily undone. However at the back of the engine sit two colossal bolts and nuts at 14mm and 16mm, even with a big torque wrench I struggled to no end and ended up sheering one nut. In the end I had to borrow my neighbours van and take it to my friends garage to borrow his pneumatic gun to undo the bolts with an aid of the smaller socket and some heat for the sheered one. It seems the Chinese have only two torque settings unlike the torque settings listed in an earlier post. Which are tight and very tight!

Once bolts are undone, gently push them out and support the engine, the engine will then come out. Take it to your allocated area of work.

For the big bore kit you want to have the official marking tool to mark things up, or as mechanics call it “tipex”, I know many mechanics that use this for marking up timings, in and on and engine without any problems, and I use it as well. Now what you want to do is remove cam cover at the top of the engine along with the two inspection caps at the bottom end (they look like they can easily be undone with a coin rather than a screw driver). Turn the engine over with a 14mm socket anticlockwise and mark things up to anything and everything timing wise.

Once done, you have 4 head bolts at the top (12mm from memory) followed by another bolt just below the cam sprocket with a phillips head (10mm), undo them. The next step is removing the starter motor and undo the tensioner with allen keys (the starter motor gets in the way). The next step involves you holding the bottom end with a spanner (where you turn the engine over) and undoing the two bolts of the timing sprocket off the cams. Once undone take the sprocket out slowly and gently and slip the chain off and keep it tensioned, the last thing you want to do is drop the chain and unset the timings completely! Heed this warning! – However should you loose timings I will explain in the second part to this install!

 Now you can take the valve head off and the barrel off slowly whilst keeping the chain tensioned! Once off, support the chain as not to loose timing, you will end up with something like this.

Undo the two clips around the piston and push the wrist pin out, the piston will then just come off, now this is where problems start with the CB150 kits.

My CB150 kit came with everything required, the ceramic coated piston, barrel etc… but there’s some issues, the wrist pin on the CB150 kit (156cc) is bigger, you have two options:

• Use the stock pin and make spacers (very good idea)
  OR
• Bore the stock rod to around 15mm at the top end

The only problem with the second option is if it’s a good idea to begin with, as I’m not sure if boring out will make the rod to weak and no longer durable long term, but I’m going to guinea pig it and give people feedback providing its successful or not. Boring out the rod is extremely slow and requires some tools, I used a drill press and a 15mm blacksmith drill bit, not cheap and boring (-literally boring as in boredom) as it takes a lot of time with continuous oil lubrication to aid cutting and cooling.

Once done you can use a piston compressor and lightly tap in the new piston into the bigger barrel for assembly, whilst the valve head is off you can easily adjust clearances as well. But this is merely the start of the install as there’s another issue which I will discuss in part 2. The issue being the new piston sits considerably higher around nearly 3mm, meaning it will and does hit the valves, but this will be discussed in part 2!

On top of this………. I decided I wanted to also throw in a 163FML camshaft which has 1mm more lift, however getting the cams out is a very difficult task. The top of the engine isn’t very user friendly, no rocker cover. So instead the camshafts are hydraulically pressed in, which causes many issues as you can’t get anything in like a hub puller in, due to the lack of room, alternatively wedging a screw driver does not exert enough force for it to come out either. Sadly I do not know anyone with a reversed hydraulic press nor have I ever seen one, as usually presses are used on wheel bearings, press old one out one side, followed by pressing a new one in.

So what do you do??? Well my honest answer is, no idea? However my friend decided to come out with a daft, yet brilliant idea that did work for your entertainment, I do strongly advise against it though, but enjoy.

🙂