Topic: CB350F cam chain adjustment

[Hopper]

Can someone explain where I can find the "special plug bolt" referred to in the FAQ?
Is it the bolt above the tensioner adjuster lock bolt, which holds the spring in place?
But if that were the case, you would be pushing down on it, not up, as the FAQ posting states.
Is there another bolt? Where? Anyone got a pic??

From FAQs:
The 350/400 is done running, but usually requires a careful, gentle push through the plugged hole at the front lower part of the engine, While the engine is idling, loosen the tensioner locknut and bolt. Remove the special plug bolt and insert a Phillips screwdriver. Gently push upward against the tensioner mechanism while snugging the tensioner bolt, then the locknut. Be really careful. If you push on the screwdriver too hard, you can damage the tensioner.

[Kevin400F]

Text should read "push downward".

[Bodi]

The plug bolt does not hold the springs in; they are held in by a step in the hole and can only be removed after splitting the cases. The bolt just plugs the hole where it was drilled right through at the factory. You can slip a thin screwdriver or a dulled nail down and hit the top of the tensioner push rod. I remove the plug bolt, insert the nail and get something ready to push on it. Then start the (warm) engine and press down while I loosen the lock bolt. Then I press down just hard enough to quiet the camchain rattle and tighten the lock bolt. After the headers cool down I can put the plug bolt back in with some difficulty, taping it on a socket works well.
As I recall the auto tensioning system worked OK in 1978 when the engine was fairly new. Whether the springs wore out or the megacycles cam changed things I dunno... but now I have to help the springs.

[bender01]

I also found it easier to adjust with the front engine mount off the frame iff it comes to this method. Pushing down pushes it up as its a lever. You cant loossen it if you over adjust this way. So maybe a couple of times might be a suggestion. 

[fmctm1sw]

yeah, right behind the headers.  waiting to burn the hell out of you...  I had a good photo here of a chewed up tensioner here, I'll see if I can find it.  I did it with mine running...

chewed up tensioner (I've seen worse though):  http://forums.sohc4.net/index.php?action=dlattach;topic=57399.0;attach=88047;image

[Hopper]

Thanks much for all the replies, guys.
Much clearer now.
Will give it a burl on the morrow. (Recovering from Christmas today  )

[Bodi]

"I also found it easier to adjust with the front engine mount off the frame iff it comes to this method. Pushing down pushes it up as its a lever. You cant loossen it if you over adjust this way. So maybe a couple of times might be a suggestion."

Taking the engine mounts off has to be more trouble than doinf this with them on.
Pushing it down pushes it down. It is not a lever, it's a pushrod acting on the horsheshoe shaped lever that pushes up on the end of the tensioner blade, warping it.
This method is equivalent to the Honda original system, you just add a bit of force to the spring force. You can loosen the tensioner afterward exactly as normal by loosening the clamp bolt that keeps the rod immobile.
Do it whenever the cam chain starts rattling. For me that's about every 500 - 1000 miles.

You can overtension the cam chain by increasing the force on the rod this way. That will accelerate wear on the chain, tensioner blade, and slider. Use just enough force to quiet the chain rattle.  Be gentle when working with the locking bolt. It's a special bolt and is not very strong, if you break it off you're in for some major trouble.

[HondanutRider]

Instead of poking something down that hole (to apply some additional tension to the adjuster), another tip is to mount a bolt or screw (e..g. a stainless hex-head) that has the end slightly rounded off, into the hole where the plug screws in.  This replacement bolt can have a nut on it to lock it in place, once you get it set/screwed-in to the correct position.  It may be easier to apply a consistent, fine amount of tension this way, without as much risk of burning your fingers on hot exhaust.

[Hopper]

Now that sounds rather clever.
Thanks for the idea, I might see about turning something up on the lathe to do the job.

[donpark1086]

I too think that this is a wonderful idea.  And will do it.

[socalenduro]

can someone post a photo of where the plug bolt is?
I see the lock nut and adjuster bolt.....

[flybox1]

can someone post a photo of where the plug bolt is?
I see the lock nut and adjuster bolt.....

socal
locate you rlock nut and adjuster bolt.
then, look in the same area, a little higher, maybe 6" higher, right between your 2 & 3 cyl, tucked in behind your case mounts and 2/3 headers. this bold angles down and to the rear of your bike, take that out.  put on your ov-glove so you save the skin on your knuckes 
start your engine, place a small phillips in the upper bolt hole, and while depressing the phillips, you'll fee and hear the rattle of the camchain.  press down until it quiets, hold there, and then tighten the lower bold to secure the cam tensioner in place.

[vames]

can someone post a photo of where the plug bolt is?
I see the lock nut and adjuster bolt.....

No photo -- but this can give you an idea of how it looks (this is a 400f but it should be the same with the 350F). Find the regular tensioner bolt (#219 in the picture) and just follow up the tensioner rod (#55), and you'll eventually see the plug bolt (#177). You can also see in the picture how you would be able to take that plug bolt out and stick something in there to "help" the old springs tension the chain. Once the chain stops rattling, you can then tighten the old adjuster bold (#219) to hold it in place and you should be set.

[y2kc0wb0y]

I need to do this on my 350F tomorrow or the next day. I will try to take a photo of the bolt. Hopefully I can have some success with this adjustment method. :O)

[DarcyCB400F]

Here's a thread where you may find some interesting tip 'n tricks.

http://forums.sohc4.net/index.php?topic=69468.0

[77Pinto]

I found this thread, and rather than start a new one....

To recap: To adjust the chain, one needs to loosen the lower adjuster nut/bolt and remove the upper bolt, with a small blunt tool inserted into the top hole press down until the chain noise goes away, tighten/lock the adjuster nut/bolt, re-install the top bolt.

Please tell me if this is correct or not, and I do not have a manual on this bike.

Now for my issue: I noticed that the adjuster nut/bolt on mine is doing nothing but plugging the hole.  If I back off the locknut I can turn the bolt into the engine all the way to the collar on the bolt where the larger nut threads start.  I verified this by inserting a small torx screwdriver to see how far in it will go (lightly pressing into the lower hole with the same screwdriver while the bike is running made no noise difference).  As of right now I have not attempted to remove the upper bolt or press down on anything there, and I will try, but the lower bolt holding nothing has me concerned.

My 350f had been sitting for an unknown amount of time, and I just got it running today.  I have yet to do the carb. sync, so some of my noise might go away with that, but I don't have much anyway.


BTW: I can see why people have the lower engine holes stripped out, as people might just crank down on the bolt thinking if they twist it 'just a little more' the chain will stop making noise.


Thanks in advance,
Bill

[HondanutRider]

From your description, I assume you are referring to part 219 in the previous diagram when you describe the "adjuster nut/bolt".  This bolt is supposed to lock down the rod number 55 which is tensioned by the springs 52 and 53, and what is supposed to provide the pressure to adjust the cam chain slack though one of the slippers 54 by leveraging the u-yoke 49.  It's a convoluted arrangement and with rather feeble springs 52 and 53 being relied upon to provide the right amount of tension, you are best to open the top with bolt 177 and press down on the rod 55 yourself.  If your bolt 219 doesn't hit anything to lock down, then maybe you have no rod 55.

[77Pinto]

..... If your bolt 219 doesn't hit anything to lock down, then maybe you have no rod 55....

Or maybe its bent? 

Thanks for the info, as being not what I expected I did not want to mess with it until I got more details

I will see what I can do with it tomorrow.



Bill

[hoodellyhoo]

I would remove your "219" and make sure it's the correct stepped bolt. Maybe someone unknowingly replaced it with a shorter bolt and it's no longer contacting "55"

If that checks out okay, somewhere here there's a thread here that talks about replacing "177" with a modified/longer bolt and lock nut so that all you have to do is crank on that to adjust your cam chain tension.

[77Pinto]

I would remove your "219" and make sure it's the correct stepped bolt. Maybe someone unknowingly replaced it with a shorter bolt and it's no longer contacting "55"

If that checks out okay, somewhere here there's a thread here that talks about replacing "177" with a modified/longer bolt and lock nut so that all you have to do is crank on that to adjust your cam chain tension.

The "219" is correct as mentioned in my other post.  It appears not to be modified either.

That said, my issue seems to have resolved itself.  I removed the 177, loosened the 219, and with the bike running I lightly pushed in the hole for the 177 and the chain noise went away, lightly tighened the 219 and its locknut; done.  The 219 no longer FULLY rests on the part between the two size threads like it did before, but due to it being close, I did NOT crank down on it.  It might have bent or distorted the rod, or worn a spot into it, or something (??).

Thanks again for the tips!  I would not have known where to press without this site and its members.


Bill

[Dos]

I have a cb350f as well and my cam chain really rattles around.. I snapped off the adjuster nut. Am I screwed?

[jpschroeder]

Resurrecting this ancient thread since it has great reference material. I went to tension the cam chain today (my first time) I watched this video too:

which lines up pretty well with the info in here. I tried it, I heard no “noise” when loosening the adjuster. So I opened the bolt above it and tried to push down and it didn’t seem to budge. I did it when the engine was running and I couldn’t really tell a difference.

I also am not sure if the cam chain is noisy or not - I’ve never had a classic Honda so I don’t know what I’m listening to. If the chain was already tensioned when I bought it, would I expect movement?

[bryanj]

Chances are if you can not push the tensioner down the whole unit is damaged and locked up, unfortunately this means removing the lower crankcase after engine out to fix.
A UK firm knocksnrattles does a very nice repair kit for the tensioner lockbolt in stainless should you need it

[jpschroeder]

@bryanj how far down is the thing you have to push on? I’m only able to put something in about an inch and a half or so. Maybe I’m not all the way?

I don’t want to take it all apart 😭

[jpschroeder]

Let me ask my question more clearly, I can see washer #255 - how far under that would I expect to hit rod #55? And how hard do i need to push on it?

also attached is a video of the cam chain sound. is that higher pitch rattle the sound of the chain or are these normal engine sounds?

[bryanj]

You should not need to push hard at all, it is just a plunger that pushes on the horseshoe th increase the bend on the tensioner.
What happens is a loose chain batters the pivot of the horsehoe siezing the pivot so the shoe wont move no matter how hard you push the rod.

Look at the parts diagram to see what happens.

To fix it means removing the horseshoe and that requires the crankcases to be split

[jpschroeder]

You think it’s ok to ride the bike some (<1000mi) and crack the case over the winter? Or is that a super bad idea?

[jonda500]

Back in the eighties I rode my 400-4 for years with the adjuster bolt snapped off in the hole and an ezy-out snapped off inside the broken adjuster bolt (it was like that when I bought it). I had to order a new adjuster bolt and lock nut, split the cases and got the bolt disintegrated out. My horse shoe pivot/hinge did get damaged quite a bit from running with a lose chain for so long but it was still movable.
I always had to push hardish on the phillips head to get the rod to move - but it would always easily loosen if I reduced the amount of push - important not to push so much that it slows down the idling engine, you want the rattle to only just barely go quiet, no tighter!
John

[jpschroeder]

Ok little update. I did push hard. I couldn’t tell if it was really moving but with the engine running it actually really quieted up the chain. I was able to tighten it like that too. That’ll have to do till this winter when I’ll do a rebuild. Wish me luck, it’s my first