Author Topic: New (to me!) '77 CB400F - US model  (Read 38164 times)

Offline Nurse Julie

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Re: New (to me!) '77 CB400F - US model
« Reply #240 on: March 10, 2019, 04:18:16 PM »
How much re-tightening torque are we talking about here?
There is no torque, its automatic spring tension that enables the process of adjusting the chain. You only undo the lock nut and adjuster bolt to allow free movement of the chain tensioner adjuster bar to allow the springs to push the chain tensioner adjuster bar to be pushed down further on to the horse shoe, which in turn, pushes the tensioner slipper on to the chain to take up the slack. It's an automatic tensioner. But for the process to work and remove any cam chain rattle from a slack chain, the chain must still be within service limit, the horse shoe pivot not seized and the spring not weak. As Bryan says, worry not now, sort it out at a later date if needed.

We may be talking semantics here.  Since there is a locking nut, I figured that the adjuster wasn't relying on torque alone to hold it in place, but the manual does say to re-tighten it, and to my mind that means some kind of torque - even if the intent is only to tighten it just until resistance is felt.  The answer to "how tight should it be?" is a torque value, isn't it?  The manual reveals nothing on this score...

From Haynes - "Turn it again inwards, until slight resistance is felt, then re-tighten the locknut."
Yes, after you have released the lock nut and washer and the chain has self tensioned. You do not tighten the bolt and lick nut to achieve tension, you loosen it, which achieves tension via the springs.The tension they are talking about is the bolt on the arm.
« Last Edit: March 10, 2019, 04:21:56 PM by Nurse Julie »
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Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #241 on: March 10, 2019, 04:20:34 PM »
Yes, after you have released the lick nut and washer and the chain has self tensioned. You do not tighten the bolt and lick nut to achieve tension, you loosen it, which achieves tension via the springs.

Understood - it was the very non-specific "re-tighten" instruction in the manual that had me wondering, is all...

Offline Nurse Julie

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Re: New (to me!) '77 CB400F - US model
« Reply #242 on: March 10, 2019, 04:23:57 PM »
Yes, after you have released the lick nut and washer and the chain has self tensioned. You do not tighten the bolt and lick nut to achieve tension, you loosen it, which achieves tension via the springs.

Understood - it was the very non-specific "re-tighten" instruction in the manual that had me wondering, is all...
It doesn't need to be any more specific really, you are only doing up what you undone previously, if you get my drift.
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Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #243 on: March 30, 2019, 11:13:47 AM »
I can't be certain, but I think I may hold the record here for keeping the longest thread running without actually doing anything.  Just saying...  :-[  ::)

I do wish I had the bike in my own garage, it sure would make it easier to sort through some of these things...

I'm wondering about whether the bike was dropped, or had some sort of accident, based on the condition (three years ago) of the shift lever (bent), the left rear turn signal (bent), and the rear fender (broken). 

When I first saw the bike three years ago, it looked like this:





And the fender looked like this when it arrived, with the tail light's upper right-side mounting point broken, but that's obviously not recent, either (the rest of these pics can be zoomed in by clicking):

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That underside mounting plate is broken in two, and some of the spot welds have parted as well, so the closer portion is free to turn when you try to remove the tail light.

I can't remember if that left rear signal was bent but secure, or just loose - either way, when I got the bike, the signal was more or less straight.  When I removed it, I found an extra (locking!) washer in the stack of mounting hardware, which was cranked so tight I thought for sure I was going to break something trying to loosen it.  The fender damage seems like it could be from vibration, although I haven't heard of this problem on these bikes, or maybe the light fixture could have been struck to cause the break.  The bent shift lever speaks for itself - but there is no other sign of impact damage, and these parts show no other scuffs or scrapes which you'd expect to see.

Turn Signal:

Here's a photo I just took of the signal brackets.  You can guess which one is the left one!

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I'm hopeful that I can bend it back to "normal" and go back to the correct mounting hardware and it will be right - and that the frame at the mounting point isn't bent as well.  But in the photo you can see that even the right side bracket has a bit of a curve - did that get bent over time, or is it supposed to be that way, anybody know?

Fender:

I had to get a bit rough with the broken mounting plate, as it turned with the mounting bolt and had clear intentions of shearing the wiring.  I'm not even sure where all the broken pieces of the fender are:

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I'm keeping an eye out for a used replacement in reasonable condition - I just don't want to spend top dollar on a brand new one, which will look out of place with the rest of the bike's patina.  I've heard, I think, that a 350 fender would fit, too - there seem to be more of them on ebay, but they all have four tail light mounting points, while the 400's all seem to have three mounting points.  Some I'm seeing for sale include the tail light, so that could work - or I could just drill a hole.

If I can't find a replacement, I may just knock out a new mounting plate, wide enough for a couple of extra bolts to hold the tail light to the fender - four in line instead of just the two at the top of the tail light bracket...
« Last Edit: March 30, 2019, 11:15:27 AM by mattsz »

Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #244 on: April 03, 2019, 03:10:26 PM »
No takers on the turn signal brackets?

Online K2-K6

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Re: New (to me!) '77 CB400F - US model
« Reply #245 on: April 03, 2019, 03:32:24 PM »
It looks consistent with just falling over onto the floor while stationary to me. If the gear lever is not ground away underside of tip,  it would verify this. Perhaps fallen off its side stand.

Signal brackets,  I'd bend them back again either by supporting with something like a socket on the back/frame side of the bracket and tapping the face with a hammer to bring them back to flat.

If the frame ends have also twisted,  you can use an adjustable spanner on them to gently twist back to vertical to maintain alignment once the signals are mounted.

Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #246 on: April 03, 2019, 05:05:15 PM »
It looks consistent with just falling over onto the floor while stationary to me. If the gear lever is not ground away underside of tip,  it would verify this. Perhaps fallen off its side stand.

Signal brackets,  I'd bend them back again either by supporting with something like a socket on the back/frame side of the bracket and tapping the face with a hammer to bring them back to flat.

If the frame ends have also twisted,  you can use an adjustable spanner on them to gently twist back to vertical to maintain alignment once the signals are mounted.

Thanks K2-K6 - based on my brief investigations thus far, I'm thinking that "tapping" might be underselling somewhat the effort that will be needed... but I'm at work this week, where there's access to a decent vice and lots of tools, including a wide variety of hammers...


Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #247 on: June 25, 2019, 12:59:44 PM »
How much play should the side stand have?  Mine seems loose, whether its up or deployed.  A very short video:

https://youtu.be/2w5YY23Uh40

I take it we can't embed youtube videos here?

Offline kent400

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Re: New (to me!) '77 CB400F - US model
« Reply #248 on: June 25, 2019, 05:59:03 PM »
Well that side stand is too loose wrong bolt maybe securing it to the frame

Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #249 on: June 25, 2019, 08:53:08 PM »
Well that side stand is too loose wrong bolt maybe securing it to the frame

Cool!  Another thing to add to the list!  ;D

Easy enough to check that, anyway... thanks!!

Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #250 on: July 19, 2019, 02:20:04 PM »
I'm reading some recent posts about cam chain tension and other engine specifics.  Waaaaay back at the distant beginning of this thread, I posted an "engine run" video - it didn't garner any attention, which I'll assume is a good thing!

Anyone want to check it out again, with an ear towards whether there's anything that sounds amiss?  Any red-flag rumbles or rattles or what have you?  I know, a crappy video is a difficult diagnostic tool...

https://youtu.be/Szxke8bD_dg

Although I made that video almost exactly four years ago, the previous owner only put about 300 further miles on the bike before I got it, so it's likely still representative of the engine condition...

Offline Nurse Julie

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Re: New (to me!) '77 CB400F - US model
« Reply #251 on: July 19, 2019, 02:47:51 PM »
Impossible to tell anything with it idling far too high. But, like you say, videos are difficult to hear anything on. It sounds like there is a rattle there somewhere, which would not be expected with the revs that high. Also, running quite poorly by the sounds of it, sounds like it needs a good service and basic maintenance before any real diagnostics can take place.
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Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #252 on: July 19, 2019, 03:13:03 PM »
Impossible to tell anything with it idling far too high. But, like you say, videos are difficult to hear anything on. It sounds like there is a rattle there somewhere, which would not be expected with the revs that high. Also, running quite poorly by the sounds of it, sounds like it needs a good service and basic maintenance before any real diagnostics can take place.

Yes - it was running very poorly at that time - and probably would be now, too... ;D

Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #253 on: July 19, 2019, 08:35:26 PM »
Well that side stand is too loose wrong bolt maybe securing it to the frame

Not sure if it's the wrong bolt, but I don't think so.  The non-threaded portion of the bolt is an ever-so-slightly loose fit in the frame bracket - I think the problem is that the stand is bent.  Observe how the outside tang splays out at the top, and the resulting gap where the bolt's head doesn't touch as a result:

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Evidence is stacking up that this thing was dropped on the left side, or in some kind of accident.  The bent side-stand (although I would think the "inside" tang would be bent if the stand got pushed inwards somehow), and also the gear lever...

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... and the rear turn signal, of course...

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Offline Bryanj

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Re: New (to me!) '77 CB400F - US model
« Reply #254 on: July 19, 2019, 10:31:27 PM »
The "Opening Up" of the slot is a fairly common thing to see but with that and wear on the frame lug you get too much "slop" I have before now carefully straightened the stand for and put a shim washer under the bolt head to keep it tighter.

 

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