[1982 Honda CB125s]Camchain tightening procedure - need advice


2010 Royal Enfield Bullet 500 - 1982 Honda CB125s
Hi to all,

I have a CB125s and recently while riding I noticed a lot of noise coming from the head and determined that the cam chain might be a bit loose causing the sound. I know the valves are alright as those were tightened to spec recently.

I have a Clymer manual and it specifically indicates that there is a different procedure for the 1970s CB125s and for the 1976 onwards CB125s.

The pre 76 ones can be adjusted cold, you just remove the plastic cover from the bolt, remove the top plug bolt and then loosen then re-tighten the adjustment bolt. However for the 76+ models it asks that you turn on the bike, let it get warm, get to idle at 1300 and then do the adjustment while the engine runs and to not remove the plug bolt completely as oil will spurt out.

Here's the problem : The 1982 CB125S does not have a tachometer and so the manual says you should use a portable tach to set it to 1300 idle.

I am trying to figure out if I can adjust the cam chain exactly as done in this video:

I want to avoid buying a portable tach (they seem to be 100-125 dollars for wireless ones that sense the pulse from the coil) to do this adjustment...

I figure it should be possible if done like in the video but I don't want to make the situation worse....

Thanks for reading.


2010 Royal Enfield Bullet 500 - 1982 Honda CB125s
Hmmm well I wasn't able to get some advice elsewhere or here which is fine so I guess I will attempt to adjust it by ear.

I figured it would be horribly inaccurate but I have no hope of installing a tach so I will find the best youtube vid of a similar bike idling at 1300 and try to match it with mine then do the cam chain adjustment.



No Custom Title
I put one of these on my 72 CL100. Not great, but it will get you in the ballpark of 1300rpm.
Its got a battery built in. So just wrap the single wire around the plug wire about 5 wraps close to the coil. Secure w a piece of tape.



where does this go?
You should be fine following the video, assuming your bike is like the one shown. The exact rpm used in the manual is not that critical. The engine just needs to be running slow, but fast enough to be running smoothly. The reason is to allow the side of the chain where the tensioner is to be as slack as possible so that all of the slack can be taken up when you adjust the tensioner. In the video, this is achieved by having the cam positioned where the valves are not pushing back on the cam and creating slack on the opposite side of the chain. If you want to follow the video, it would be a good idea to put a wrench on the crank and apply pressure in the direction of running to ensure the non tensioner side of the chain is tight. Hold pressure on the wrench and adjust the tensioner. There is another benefit to the video, which is manually exercising the spring loaded tensioner mechanism because they often stick. Moving it manually through its travel a few times will scrape away any varnish that may hang the mechanism up ensuring the proper tension is achieved.


2010 Royal Enfield Bullet 500 - 1982 Honda CB125s
Thank you trek97 and jpmobius, I greatly appreciate the replies.

Trek, that's a cheap piece so that's definitely an option. Since I posted a friend of mine has given me a tach but I had no idea how to install it and was beginning to look into that. I think I'll be good with your instructions.

jpmobius, yeah I was thinking of doing what he did in the video with pushing down the mechanism using a screwdriver to make sure it's not stuck. I'll do my best to get an idle close to 1300, at least my bike has no trouble idling so I won't have to fight it.

Okay I think I will be trying this on Sunday. I will try to take videos to post here of before and after so it can be more useful for people who stumble upon this thread in the future.



2010 Royal Enfield Bullet 500 - 1982 Honda CB125s
Hi everyone,

Okay so on Sunday I got to the bike, unscrewed the top cap of the adjuster nut and tried to use a screwdriver to push the mechanism down. It wasn't budging and I felt like if I pushed any harder I might do some damage so I decided to leave it. Unsure if it is stuck....

I then turned on the bike, got it warm and drove it around a little bit, came back and got it to idle no problem. Not sure if it was 1300 but it was a steady good idle you will hear it in the video.

I loosened the nut a lot...felt like it was almost about to come out of the engine so I then re-tightened it.

I have a really shitty torque bar thing that is in mKG and the cylmer manual was saying to adjust to 12 lb-ft. I did the conversion which is close to like 1.6 mKG so I torqued it to about that and it was indeed tight.

However there is no difference in sound. The engine is still making a loud chattery noise. I had previously done a valve adjustment on this bike too and it was in spec. I'm a newb so there's a chance I completely fucked it up but I made sure to check the valves 3 times in a row making damn sure the adjustment nut on the valves was fully tightened and then re-checked to ensure I didn't screw up the gap by doing that.

So yeah I'm wondering what could be causing such noise and if my engine will grenade while I'm riding because of it.

The GOOD NEWS !!!! however is that I took the bike for about 25 minutes driving around town and it did not reproduce the condition causing me to do this adjustment in the first place. I had a problem where if I was in 3rd,4th or 5th and quickly decelerated to a stop the engine would cut out. Right after the adjustment I tried to reproduce that many times and it did not stall and seemed to idle much better.

So victory?

I had promised to film a video pre-adjustment video and a post-adjustment video and did do that. I am only posting the post-adjustment video because I listened to both and I can tell you they are 100% the same in terms of sound nothing has changed.

Please remember my bike is a project and is incomplete if you're feeling the urge to point out things like a missing front fender :p

https://streamable.com/flhvi Please let me know if this link doesn't work I will re-upload if that is the case.


Books, Books, Books, knowledge is within
did you put a wrench on the crank bolt and put tension on it to take up the slack on front side of the motor to leave skack on the the tensioner side of the chain?


2010 Royal Enfield Bullet 500 - 1982 Honda CB125s

I did not...I only followed the clymer manual instructions which doesn't require you to remove the cover or keep torque on the crank bolt. I thought I would get lucky but you're right I need to do it again and remove the cover to see if I have actually adjusted anything.

I was weary of opening that side of the engine again but now remember that it can be done without losing much oil so it shouldn't be a problem. I will do it again and take a video again and see if I can actually get it to adjust.



2010 Royal Enfield Bullet 500 - 1982 Honda CB125s
Just to make sure I don't newb out and screw it all up.

I assume by crank bolt you mean this bolt here right ? (Not my engine just a pic from the internet) https://imgur.com/a/N7ZZFvr


2010 Royal Enfield Bullet 500 - 1982 Honda CB125s
Okay so I am at a loss.

I took off the covers on the alternator side and inspected it and took some photos to show you what I can see. It appears I have the same cam chain tensioner as in the video from my first post.

I did my best to get the light in there: https://imgur.com/a/GwolWrk

So I don't know what is up but I once again put a screwdriver down the plug bolt hole and pressed against the mechanism and it would not budge. I then completely removed the adjustment bolt to see what was down the hole and it seems to be some sort of plastic rod/plunger coated in oil. I was able to push down on that one though so I did a few times. I also put the adjustment bolt back in and torqued it loose and tight to see if it affected the cam chain at all and from what I could see nothing happened at all.

I took a screwdriver and pushed on the cam chain to see if it was taut and indeed it was...it is no way shape or form loose and it does move a bit so not over tightened either.

Put it all back together and turned the bike on, let it idle to warm up, attempted to adjust it both ways to see if it affected the sound and nothing happened whatsoever.

I simply retightened it according to torque spec and put the rubber boot back on.

Took it for a ride....bike rides fine, my original problem that I started this whole process for IS gone which is a relief (stall when stopping for a red light/stop sign from 3rd, 4th, or 5th would cause the bike to stall once stopped. That no longer happens)

But when I got home the bike just reeks of burnt something. Burnt fuel/chemical smell it just don't smell good. It really smells near the exhaust pipe entering the engine so it seems I have some sort of exhaust leak.

In my search for more info to try and determine if this is really a loose cam chain noise or valve out of spec noise I discovered this :

Someone mentioned that sometimes exhausts crack and somehow the inner wall of the exhaust rattles against the outter wall of the exhaust? and that the sound would go away as you reach high rev on the road but as you slow down it starts to chatter again....

I wonder if it could be that? my pipes are 36 years old idk....

But why I don't think it's that is when I am at high rev on a higher gear and clutch in and begin to brake hard the engine makes this super loud winding down noise.....idk if the exhaust rattling would do that sort of noise.

I'm sorry guys I am super stumped....I just have no idea what's wrong and I feel like if I keep ridding my bike is going to grenade despite it riding better than ever and idling better than ever....


2010 Royal Enfield Bullet 500 - 1982 Honda CB125s
Hmmm I think you missed my latest reply but yeah it had no effect.

I'm now wondering if I'm crazy and the sound is normal or w/e idk. I went looking on youtube for 1981/82 CB125S idle sounds and some sound very thumpy with a lower speed idle of like 1000-1100 and this one at 1300 or so idle sounds identical to my bike...


Not 81/82 but similar sound : https://www.youtube.com/watch?v=hq5nnDZuAQM

This one especially sounds similar : https://www.youtube.com/watch?v=mwAKF_vDeMM

Maybe they just sound this way? Idk my bike runs better than ever so I feel like if the cam chain was loose or if my valves were screwed up the performance would be way down.

I'm thinking maybe since I stage'd 1 my carb and am getting way more power than stock the bike just makes more noise as it is working harder idk.

Going to try and post my idle vid to a cb125s specific forum and see what other owners can say about the sound.

Thanks for all the help.


Found another video of an 81/82 CB125s idling and it sounds very much like my bike so IDK maybe I don't have a problem after all and am going crazy :


2010 Royal Enfield Bullet 500 - 1982 Honda CB125s
Okay I think I have the final piece of info I need now.

So we can disregard the videos I posted above re: sound. Most of those bikes are out of spec too.

I contacted someone I knew had a lot of experience with CB125s as he has been selling 125cc bikes in the UK for over 30 years and has personally owned many CB125s. He owns like 12 different motorcycles or something so I trust his judgement.

He told me this :

"First things first - camchain adjustment is entirely manual on these things, and is counter-intuitive. You have to turn the adjuster bolt (on top of the cases, behind the block) anti-clockwise to tighten the chain. I assume you have a workshop manual?

A few years ago, I bought a 'restored' CB125S that was making a noise like yours, cheap, because although it had had a new camchain it was still sounding horrible. I tried adjusting the camchain (see above) and it made no difference, so I reckoned I'd look at the arm that attaches to the tensioner. There's a pivot pin and it's secured in place with a little clip washer.

Sure enough, no clip and the adjuster arm was just dangling, useless. I re-connected it, and fitted a new spring clip (I have a box of the things). One lovely quiet engine.

Check yours. If it's detached, you do have to remove the alternator stator (three bolts, I think) but you can leave the rotor in place: if you have a pair of long needle nosed pliers, there's just enough space to do it."

I find it very interesting that the clymer manual is incorrect. I did some googling and it appears it is also incorrect for the Honda C100 as well.

Now that I have this info I am going to pull the rotor and hopefully repair the chain adjuster.

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