On an engine, valves are situated in the cylinder head (‘top end’) and their job is to let fuel-air mixture in to the cylinder for combustion and to let burnt exhaust gasses out. The CBF125 uses the traditional ‘tappet and lock nut’ method for setting valve clearances, which is very common, if not universal, on simple, small displacement engines. The term ‘valve clearance’ refers to the gap between the tappet and top of a valve stem. The tappet is a small part that is part of an assembly called a rocker arm and it is the part that pushes on the stem of the poppet valve to open it. That gap is there for a very good reason – as the engine heats up, these components will expand and the gap will be filled. If there is no valve clearance (gap too small), you could bend the valve or it will be forced open a little, causing poor idling, excessive fuel consumption and/or poor running (depending on which valve is the culprit). If the valve clearance is too great, with a large gap between the tappet and valve stem, then the valve stem and tappet will wear more quickly as they’d be colliding against each-other with more force. The valves may also not open fully, which will cause poorer engine performance/idling.
Before we start, this information is simply an account of my experiences. There may well be sections of it that are incorrect! I will not accept any responsibility or liability whatsoever if you damage/destroy something or injure/kill someone by following what I’ve written! YOU are entirely responsible for your own choices and actions, including the choice of following what I have written and the actions of carrying out the work. If you are not confident in following any part of this procedure, I strongly suggest you get a competent person or qualified mechanic to do the work. Please also refer to the owner’s manual as a primary source of information regarding this procedure!
Okay, let’s get on with the job! Click on the images to get nice big juicy high-resolution versions.
Honda specify that you adjust the valve clearance on the CBF125 at the 600 mile first service, then every 2’500 mile service afterwards. However, during the interim between the 600 mile service and first 2’500 mile service, things are still bedding in, so it is advisable to check them at some point in between. For me, that’s at 1’500 miles.
You will need the following tools:
- Screwdrivers – Phillips sizes 2 and 3 (as well as a short no. 2).
- Metric feeler gauges (make sure they are clean and lightly oiled – WD40 is fine).
- Tappet adjusting tool (you can get away with long nose pliers or possibly your fingers!).
- 10mm ring spanner.
- Allen sockets – 6mm and 10mm.
- Sockets – 10mm and 19mm.
- Torque wrench capable of between 10-20Nm at least.
- Socket extension bar.
- Breaker bar.
Before you start, the engine must be stone cold, ideally having sat overnight.
Firstly, we need to remove some bits and pieces in the way. Start with the passenger seat, use the key to unlock it (if you can’t do this, I highly recommend you leave the entire job to a competent mechanic!). Next, the rider’s seat, which is held in place by two screws (10mm socket needed):
Next we remove the left-hand side (from rider’s perspective) matte plastic fairing, held in place by 2 phillips no. 3 screws:
Be patient and careful as not to snap anything – the cover basically pulls forward/upward/outward – feel for lugs that are still holding it to the bike, and you’ll see what I mean.
Next, we remove the left hand side cowling, firstly the matte black cover that is held on by one phillips no. 2 screw:
Once you’ve removed the screw, carefully prise this part backwards, holding on to the front of it, near the instrument cluster. It will ‘snap’ out. Again, be careful and patient as always.
Now comes the fiddly part – removing the larger section of cowling. It is held in place by four screws (3 phillips no. 2’s and 1 phillips no. 3). Remove them. In the picture below, there are 2 screws which hold the cowling on to the front headlight fairing, one above the other, but only one is visible, the other, below it, is obscured by a wire – a magnetic screwdriver is very helpful here!
The third no. 2 phillips screw is located in the middle of the side of the cowling, towards the top of it. I couldn’t get the camera in close enough to show it here. Next, you need to pull the speedometer cable out of its holder in the cowling, which is at the bottom of it. You will also see on the other side of the cowling that there are three brackets that hold the wiring in place, one large and two smaller either side. Gently free the wiring from them, bend them a little if you have to. Finally, unplug the indicator relay and put the cowling somewhere safe:
Now all that’s out of the way, the real fun can begin! Grab your 10mm Allen socket and undo the larger alternator rotor access cap, then use the 6mm Allen socket to remove the timing access cap. A word of advice: do not be tempted to use an Allen key! Trust me, the proper tools make this job so much easier!
Make sure the o-rings come out with them.
Next, off comes the cylinder head/valve rocker cover. It’s held on by two diagonally opposed hex screws – 10mm head. Be careful as space is limited and you need to wiggle the tools around a little to get good access:
Prize away the rocker cover – it will be a little sticky so use some force, carefully. I found it quite tricky to manoeuvre it away – but try to move it towards the exhaust down pipe as there seems to be enough space there to get it out. Also make sure you get the gasket/oil seal with it – don’t leave that part on the engine as it makes re-fitting the cover difficult. You should check that there is a covering of engine oil over the top end of the engine innards. If they are completely dry, you may have an oil circulation issue or be running very low on oil. Get it investigated and sorted pronto!
Now we have to get the piston sitting at Top Dead Centre (TDC) on the compression stroke. In order to do this, we crank the engine over manually via the alternator rotor – use the 19mm socket on an extension bar to do this, and turn it ANTI-CLOCKWISE! That’s VERY important. DO NOT TURN IT CLOCKWISE, EVER, because you can cause the cam-chain to skip a tooth and do some serious resultant damage.
Whilst slowly turning the engine over, look carefully into the timing inspection hole until you see the T (on its side) marker line up with the index line, exactly like the picture below (be extremely careful not to mistake it for the F (ignition firing) marker, which comes just before you get to the T marker):
Also look at the camshaft sprocket (the big gear with a chain going around it!). There should be two lines, either side, aligned horizontally, parallel to the cylinder head (see the second photograph below). Now, this is a confusing bit – the workshop manual says that when the piston is at TDC on the compression stroke an ‘o‘ mark should be above the horizontal line on the left on the camshaft sprocket. BUT in my case the opposite is true – the ‘o‘ mark is on the right, below the horizontal line! Either the manual is wrong or my camshaft sprocket was installed the wrong way around…
To be 100% sure that the piston is at TDC on the compression stroke, grab the exhaust rocker arm (towards the front of the engine) and push/pull it gently up/down. You should feel a little movement (play). If you do not feel any movement, the engine is not at TDC on the compression stroke, and the exhaust valve is being pushed open by the tappet/rocker arm (which is why it can’t be moved by hand!). If this is the case, crank the engine through one more rotation until you see the T mark again, and give it another try. You should now feel some play on both rocker arms, and we’re ready to begin checking/adjusting the valve clearance:
Specified clearances are:
- Exhaust valve: 0.12mm.
- Intake valve: 0.08mm.
The exhaust valve is on the front of the engine (next to the exhaust down pipe, funnily enough!) and the intake valve is on the back, near the throttle body, where the air/fuel comes from!
Get hold of your feeler gauge and find strip that corresponds to the gap you want to measure. If you don’t have a 0.12mm strip, like me, you can add others together, in my case 0.08mm and 0.04mm. Now pull the rocker arm up and try to slide the feeler gauge in under the tappet, where it meets the valve stem, as shown (you can slide the strip in via its side if you want):
You should be able to slide the feeler gauge under the tappet and feel some drag/resistance. A gauge of the next size above should not fit, and one a size below should easily fit. If that’s the case for both valves, then congratulations! You’re done!
If not, you need to adjust them. In my case the intake valve had a clearance that was too large and the exhaust valve clearance was too small. Now, this part is very fiddly and often takes a few attempts to get right. Grab your 10mm ring spanner and undo the locknut of the tappet you wish to adjust. Leave the spanner in place and use either the tappet adjusting tool or pliers to turn the square end of it until you feel a bite on the feeler gauge strip:
Now, hold the tappet in place and tighten the locknut with the ring spanner, but not too tight. Remove the feeler gauge and torque up the locknut to 14Nm. Now, slide the feeler gauge under the tappet again and check that it’s a firm sliding fit, in order to check that the torquing up the locknut did not disturb the adjustment (in my case it did a couple of times and I had to repeat the procedure). It’s fiddly, so be very patient with it. After you’re successful, turn the engine over a few times with your 19mm socket/bar assembly and find TDC on the compression stroke again. Now check the valve clearances again and they should be okay. If not, you have to readjust!
If you’ve got this far, I can gladly say you’re done! Oops, you need to put it all back together again! Now, with the rocker cover, give the oil seal a nice smearing of engine oil and push it into the underside of the cover before you put it back on the cylinder head. Carefully manoeuvre it back over the cylinder head, via the other side of the exhaust down pipe and make sure the seal stays in place as you do so. Be careful with the screws that hold on the rocker cover as I have been told tales of people stripping threads or breaking them. I used my torque wrench with a setting of 10Nm and had no problems or leaks. I used a setting of 15Nm to tighten up the crankshaft cover cap and 10Nm for the timing inspection cap – don’t forget to smear some oil over the o-rings and grease the crankshaft cover cap threads (LM grease is fine). Note: the workshop manual actually recommends replacing o-rings every time (Honda are covering themselves probably), but in all honesty, my experience has been that I have never had any leaks or other issues whatsoever by reusing them, also on the YBR. Do check them though to make sure they’re not perished, damaged, split etc. If they are, then definitely replace them.
Fitting the cowling/fairing back is a case of reversing the removal procedure. I would assume that if you have got this far, you know what you’re doing and don’t need to be told to be careful when lining up the various lugs etc to avoid snapping anything!
As a side note, in comparison to the YBR, I found it a little more time consuming to do this on the CBF, mostly due to the plastic fairing parts having to be removed first. I also found the lack of space around the cylinder head to be annoying – the YBR has just two smaller access caps – one covering each rocker arm, but the disadvantage to this is that you need to bend the feeler gauge slightly when using it, as the tappets are slightly recessed. The access caps on the side of the engine use a slot instead of a hex hole, which is more difficult to undo, with more chance of damaging the slot if you’re not careful with the screwdriver. The CBF does better in that regard.