How-to: Check and adjust valve clearances on the CBF125

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!
Job jobbed!
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.

24 thoughts on “How-to: Check and adjust valve clearances on the CBF125

  1. Thanks for a great how to!

    I’m picking up my CBF 125 tomorrow evening. It was first registered September 2009 but has only done 900 miles. So a change of fluids is a definite first!

    This is all new to me so your blog is great source of information. I think that I better get myself the workshop manual.


  2. HI,

    I recently checked my valves and my bike is the same as yours with regards to the timing ‘o’, mine sits below the horizontal line on the right hand side as you look at it so i guess it may be a typo in your manual. I must say the fairings on the bike are a pain when doing any work they feel very flimsy but i suppose they look the part. I am very impressed with the bikes economy i have had over 150miles to the gallon, i had to check this 3 times as i didn’t beleive it could be so high!! How do you find the bikes handling in wind mine seems very sketchy at times , i don;t think the fairings help in side winds.
    Thanks for all the information in this blog



    • Hi Mark,

      Thank you so much for confirming this, must be an error in the Workhop Manual. The Owner’s Manual does not mention anything about marks on that sprocket, but only tells you to check for free play in the rockers/followers to ascertain whether the piston is at TDC on the compression stroke.

      • Hi,

        I just wanted to further confirm that the markings you have observed were the same on my CBF125 (i.e. ‘o’ below right horizontal line). I also found the exhaust valve clearance to be too small and the inlet valve clearance to be too large. Since you haven’t seen any further movement since you adjusted yours originally it makes me wonder whether the factory configure them slightly different.


      • Hi All, and especially CBF125 Rider for this excellent site!

        I would like to also confirm the same on my ’09: the ‘o‘ mark is on the right, below the horizontal line when the piston is at TDC. I confirmed this by jiggling the rockers a bit. Also, the ‘o‘ mark can’t be on the left and above the line with the ‘T’ mark simultaneously visible on the timing indicator. Must be a workshop manual error as expected!

        FYI I have 8,000 kilometres (5000 miles) on the clock and have just checked the valves for the first time (I know – a little late, but better late than never)! The exhaust valve clearance was just slightly loose (high) by 0.01 (at about 0.13). The intake valve was actually just slightly tight (low) by 0.01 (at about 0.07).

        – Brett

  3. Hi Mark,

    Thanks very much for this. Your instructions inspired me to tackle the 600mile service myself. I’ve done 730miles on my lovely white CBF125M 2010, but I’m a fine-weather learner rider and don’t thrash it, so the extra 130 miles won’t matter.

    I checked the clearances and they were bang on the correct settings of 0.08mm intake and 0.12mm exhaust, so thankfully I didn’t need to adjust them.

    However, I ran into a problem when I was putting the cylinder head cover back on. I’d manoeuvred the cover back on and was about to tighten the bolts, when I noticed a piece from the bike on the blanket I was kneeling on. Oh bugger! It was a metal tube, about 20mm long and 5mm diameter, with a rubber 0-ring exactly in the middle. I reasoned that it must have come from the cylinder head cover, so I took the cylinder head cover back off and looked on the inside of it. I soon figured out the recess in the inside of the cylinder head cover where this tube & O-ring thingamajig came from, and pushed it back in place.
    (I’ve since googled and found a diagram which shows the thingamajig as parts 3 & 8 in the picture at
    I think its purpose is to help transmit pumped oil to the top of the cylinder head cover, which squirts over the workings to keep them oiled (and possibly cooled?). However, every time I turned the cylinder head cover over to put it back on the bike, the thingamajig kept falling out of its recess, onto the floor. I decided instead to put the thingamajig with the O-ring positioned in the middle (the O-ring can slide up and down the metal tube), into the recess it fits into on the actual engine, and them put the cylinder head cover on over the top. However, during my first aborted attempt to put the cylinder head cover on, the edge of the cover knocked and pushed the thingamajig tube down further into the recess so that the O-ring was no longer in the middle of it. I pulled the thingamajig out of the engine, slid the O-ring back into the middle of the tube and tried again. Eventually I got everything back together.

    However, since “completing” the job, I’m concerned I’ve made a mistake. In putting the thingamajig into the recess on the actual engine and dropping the cylinder head cover over it, it will have been easy for part of the cylinder head cover to have pushed the thingamajig tube down into the recess in the engine so that the tube might be less than half inside the recess in the cylinder head cover. I’m not sure, but if this happened (as it did on my previous aborted attempt to fit the cylinder head cover over the top) it might affect the efficiency of the flow of oil pumped to the top of the cylinder head cover. What I think I need to do is to find some way to fit the cylinder head cover with the thingamajig in place in its recess in the cylinder head cover, without it dropping out. That way, if the thingamajig tube makes contact with part of the engine when I’m putting the cover on, it will remain in place because it can only go so far (half its length) into the recess in the cover. I’m considering either a using a small dab of rubber glue from an inner-tube repair kit to hold the rubber O-ring (and hence the tube) in place in the cover, or a dab of sticky grease might do equally do the trick.

    Any further advice will be appreciated and I’ll come back to let you know how it goes when I’ve done it at the weekend.

    Kind regards,
    Simon S.
    South Yorkshire, UK

    • Hey Simon,

      (my name isn’t Mark, in case you were thanking me – apologies if you weren’t! 😉 )

      It’s just an ‘oil through’, as you suspected. My understanding is that when everything is reassembled, the o-ring will be compressed against its internal recess in the cylinder head and the recess in the cylinder head cover. I have always left it and its o-ring in the engine rather than the cover and never suffered any issues. The o-ring seals the link between the cylinder head and cover anyway – that’s more of a spacer to hold the o-ring in place. No need to worry!

  4. Thanks for your quick reply ‘CBF125 Rider’, and sorry for calling you ‘Mark’ – it’s a fine name but it belongs to someone else on the forum I mistook for you, my bad 😉

    You’re probably right about the fitting being OK the way we’ve both done it, but for peace of mind I’ll do it again with the tube and O-ring thingamajig in place in the cylinder head cover. I’ve had another idea how to do it. I might be able to use an old credit card or similar piece of plastic to hold the tube place so it doesn’t drop out as I lower it down, then slide the plastic out. when its nearly lowered into position the last centimeter or so.

    • There’s really no need to go through all that hassle – it’s literally a dowel that keeps the o-ring lined up where it should be and to make sure the cover’s oil ways that feed oil to the valve gear line up correctly when re-fitting, that’s all. It makes absolutely no difference if you try and hold it in the cover whilst you refit it or leave it in the cylinder head. Gravity will make it fall to the bottom of the recess in the cylinder head regardless.

      The recess isn’t deep enough for it to be lost – it will protrude by a few mm which is fine. Even with it just poking out by a few mm, you’d know if it wasn’t slotting back into the cover’s hole when trying to refit as the cover would not line up or seat correctly until it did fit, so there’s absolutely no danger of what you’ve described happening.

      The o-ring compresses between the surfaces of the cylinder head and cover and that’s what makes the seal, and the o-ring is the only component that, if missing, would affect oil flow. I’ve never had an issue and have done this job on this particular bike 3 times now.

  5. Hey ‘CBF125 Rider’ (again),

    You’re probably right. It just seemed significant to me that when I found that thingamajig on the floor when it fell out of the cylinder head cover, the O-ring (or ‘Gasket B, Head Cover’ to give it the name on the diagram) was exactly half-way along the tube (or “Dowel Pin, 8×14′ – why do they call it a dowel pin when it’s not solid?). This seems to be how it would be when the top half is fully inserted into the recess in the cyclinder head cover as far as it will go, and the bottom half goes down into the recess in the cylinder head. I’m also surmising that when the cylinder head cover is tightened down, the pressure on the O-ring/Gasket B that squeezes it to form the seal will ALSO grip the tube/Dowel Pin tightly and hold it in that position (the position I found it in when it dropped out).

    You say I should avoid the hassle of taking the cylinder head cover off again and refitting. As I said above, you’re probably correct. However, I’m going to do the oil change this weekend (I didn’t have a suitable 12mm socket to fit my 3/8” sq. drive torque wrench last weekend) so will be working on the bike anyway. I’m also fuss-pot, almost to the the point of OCD, and these things bother me if I’m not 100% confident I’ve done the job exactly right. Now that I’m familiar with taking the left side cover and cowling off and putting it back on again, it should only take me a small fraction of the time I spent last weekend.

  6. I took the cylinder head cover off again to inspect the ‘Dowel Pin, 8×14’ and found it remained in place on the cylinder head (not in the cylinder head cover) with only about 4mm proud that had protruded into the cylinder head cover recess. To refit the cylinder head cover I used a blob of Castrol general purpose grease to hold the ‘Dowel Pin, 8×14’ and ‘Gasket B’ (O-ring) in place in the recess in the cylinder head cover, without it dropping out when upturned (shook and tapped the cover to make sure it didn’t fallout), and then refitted the cover.

    I also did the oil change with Castrol Power 1 4T 10W/30 Motorcycle Engine Oil – 1ltr ( . The old oil wasn’t too bad after 736miles – a dark brown with a tinge of red (the new oil is a clear red colour) so the Castrol 10W30 I’ve used is probably very similar to what was originally put in. I didn’t find any metal fragments either, so conclude the bike has run-in well.

    After a long test ride I found the engined sounded somewhat smoother and quieter, especially in 3rd gear. I’m well pleased.

    Thanks for your help.

  7. Pingback: honda stunner mileage prob :( Help required - Page 3

  8. Today i tackle this myself, my bike is approaching 7500 miles so decided to go for it!

    So i followed all the instructions and everything, checked it, and put it all back together. I have started the bike up and noticed straight away something was wrong. it wont start without throttle and even when it does theres a small amount of smoke! when its started, and i let go of the throttle it cuts out. now im guessing this is something to do with the intake valve, something i havent done right?

    Please help!

    Kind regards, tom.

  9. I come off my bike the other day and my neck has been clicking ever since I’m just wondering if anyone else has this problem

    • I know when I get clicking in audio I’m working on (I’m a sound engineer), I draw the clicks out with the Pencil tool or use a plugin like Waves X-Click.

      In all seriousness, if this isn’t a troll, go and see a doctors about it and I hope it isn’t anything really bad.

  10. Hi

    Im looking to buy a honda bike cb unicorn. What should I look for. What’s the compression?

    Also to do the adjustment do I use the same parameters you have use for the cbr 125

    Thank you

  11. Can any one help me with some advice? I’m new to bikes and my cbf has developed an oil leak from the head gasket. So far I’ve managed to follow Haynes to where I need to remove the camshaft but it appears to be stuck. Have I done something wrong?

  12. Pingback: How To Adjust Engine Valve Clearances | Information

  13. Hey guys, I need your advice: I’ve wanted to check the valve clearances today.. First I didn’t feel any movement on the exhaust valve nor on the intake valve but then I cranked the engine until I could see the T marker again and I could feel a little play on the intake valve. But I couldn’t move the exhaust valve – the intake valve was fine.. The intake valve had a play of ~0,15mm and the exhaust valve was below 0,10mm (this was the smallest unit I had). The engine was at the TDC because I saw the T index marker and the lines on the camshaft sprocket were aligned parallel to the cylinder head also. But why couldn’t I feel any movement on the exhaust valve?

    Kind regards.

  14. Great write up, thank you for keeping this information going.

    Just for info the specs pdf hosted here has the inlet & exhaust figures the opposite way round to the above write up? I’m guessing it’s the larger clearance on the the exhaust side is the correct figure.

    Thanks again


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s