Honda-SOHC

SOHC.co.uk Forums => CB350/400 => Topic started by: mattsz on August 31, 2020, 06:58:10 PM

Title: '77 CB400F - it runs!
Post by: mattsz on August 31, 2020, 06:58:10 PM
See subject heading...

First start - fired right up on the second button press, with a barely-there puff of smoke - not surprising, as there was oil in the cylinders.  All 4 cylinders heated up quickly and uniformly.  No obvious oil leaks, yet.  With a bit of juggling choke lever and idle screw, I quickly got it down to a steady 1200 rpm idle with the choke off.

The front end sounds very rattly - is this a loose timing chain?  I know it's hard to hear sometimes on a video, but I've posted a couple.  Would you guys check them out and give me some opinions?

The first one is the start video (because I had to!), just over 1 minute long.  It ran until I shut off the choke and it stalled:

 https://youtu.be/PoMMEqoxnK0  (https://youtu.be/PoMMEqoxnK0)

The second video is a shorter (about 25 second) "running" video to highlight the noise. It's running without the choke at this point:

https://youtu.be/fzLM4dWA_lE  (https://youtu.be/fzLM4dWA_lE)
Title: Re: '77 CB400F - it runs!
Post by: Nurse Julie on August 31, 2020, 07:23:09 PM
Sounds like cam chain rattle. Well done for all your work so far, it's great to hear it running.
Title: Re: '77 CB400F - it runs!
Post by: mattsz on August 31, 2020, 07:27:58 PM
Sounds like cam chain rattle. Well done for all your work so far, it's great to hear it running.

To be honest, I'm shocked it went so smoothly!  But I'm not there yet!

I tried to adjust the cam chain tension using Bryanj's method of "putting pressure on the [crank] so that the engine is just about to turn but not quite turning."  I don't know if I did it right, or if the adjuster isn't working correctly.  Any advice on how to proceed?  Dare I follow Honda's recommendation and let it adjust itself while the engine is running?
Title: Re: '77 CB400F - it runs!
Post by: Nurse Julie on August 31, 2020, 07:48:26 PM
Sounds like cam chain rattle. Well done for all your work so far, it's great to hear it running.

To be honest, I'm shocked it went so smoothly!  But I'm not there yet!

I tried to adjust the cam chain tension using Bryanj's method of "putting pressure on the [crank] so that the engine is just about to turn but not quite turning."  I don't know if I did it right, or if the adjuster isn't working correctly.  Any advice on how to proceed?  Dare I follow Honda's recommendation and let it adjust itself while the engine is running?
Yes, I would have a go Hondas way. If it doesn't make any difference to the rattle, it would diagnose either a cam chain stretched well beyond spec or a seized horse shoe pivot, or even both.
Title: Re: '77 CB400F - it runs!
Post by: mattsz on August 31, 2020, 07:53:55 PM
Thanks Julie!

I did investigate the function of the tensioner based on the advice of another forum member.  I did get some results, but I never got an answer as to whether my results were normal.  If you wouldn't mind, would you take a few minutes and read this short post and the three which follow it to see what was suggested, and my results?

http://www.sohc.co.uk/index.php/topic,17461.msg205855.html#msg205855 (http://www.sohc.co.uk/index.php/topic,17461.msg205855.html#msg205855)
Title: Re: '77 CB400F - it runs!
Post by: Nurse Julie on August 31, 2020, 08:02:47 PM
Nigels method and your result proves there is a little movement but it does not prove if the chain is beyond spec, or if the horse shoe has minimal movement before it seizes.
Title: Re: '77 CB400F - it runs!
Post by: mattsz on August 31, 2020, 08:17:19 PM
Nigels method and your result proves there is a little movement but it does not prove if the chain is beyond spec, or if the horse shoe has minimal movement before it seizes.

True.  I was hoping to hear from Nigel about whether he thought the amount of movement I discovered was ok or not.  No matter now... my attempts at Bryanj's adjustment method didn't have a satisfactory result, and I just tried Honda's simple "idle the engine and loosen the adjustment bolt" technique which didn't change anything.

Worth trying to adjust the tension by removing the upper bolt and pushing on the plunger by hand?
Title: Re: '77 CB400F - it runs!
Post by: mattsz on August 31, 2020, 08:21:03 PM
When I ran it again just now, it still started and ran well, but I had some steady whitish smoke out the exhaust this time... and a surprising amount of water dripping out of the joint between the silencer and header collector - no wonder they rust out!

Should I not take it out on the road with that rattle?

Title: Re: '77 CB400F - it runs!
Post by: Nurse Julie on August 31, 2020, 08:36:26 PM
You will get condensation unless you ride the bike and get it hot enough to dry the steam out. My personal view, others may disagree, I wouldn't ride the bike with the chain rattling like that. Others may take a risk at a ride up the road but whether you choose to or not, that chain and adjuster need replacing.
Title: Re: '77 CB400F - it runs!
Post by: mattsz on August 31, 2020, 09:10:49 PM
You will get condensation unless you ride the bike and get it hot enough to dry the steam out. My personal view, others may disagree, I wouldn't ride the bike with the chain rattling like that. Others may take a risk at a ride up the road but whether you choose to or not, that chain and adjuster need replacing.

Understood.  By way of investigation, I'm tempted to try manually adjusting the tension by accessing the pushrod through the opening just above the proper adjustment bolts.  If I do, can I try it with the engine running, or will removing that upper bolt spray oil out?  It looks to me like that's open to the unpressurized crank case, so oil shouldn't be a concern...
Title: Re: '77 CB400F - it runs!
Post by: Bryanj on August 31, 2020, 11:40:05 PM
I admit my method takes practice but it does work, oil will not spray out of that plug you talk about but i will lay odd you will burn several bits of yourself on the exhaust
Title: Re: '77 CB400F - it runs!
Post by: mattsz on September 01, 2020, 12:35:17 AM
I admit my method takes practice but it does work, oil will not spray out of that plug you talk about but i will lay odd you will burn several bits of yourself on the exhaust

I will not take that bet...  ;)
Title: Re: '77 CB400F - it runs!
Post by: taysidedragon on September 03, 2020, 01:14:07 PM
Wear protective gloves if working near hot exhaust headers. The one time I didn't bother, "I'll be careful,  it'll be fine" , i thought, and ........

Title: Re: '77 CB400F - it runs!
Post by: mattsz on September 03, 2020, 01:28:57 PM
Ouch!  thanks for the reminder...
Title: Re: '77 CB400F - it runs!
Post by: AndyD on September 03, 2020, 02:57:18 PM
Gareth,
Looks familiar!!!
When I finally got the 400 running the other week I was so keen to just sit on it I forgot that wearing shorts isn't a great idea near a piping hot exhaust - nice burn to remind me next time!
Cheers,
Andy
Title: Re: '77 CB400F - it runs!
Post by: SeanFD on September 03, 2020, 03:25:38 PM
I’m jealous; you are where I want to be, without the cam chain problem of course. Well done.

I read somewhere that it is possible to “fix” a non-functioning adjuster by, essentially, doing just what you said.

You plug off the adjuster bolt and use a longer bolt with a locknut in the oil cap channel to push down on top of the adjuster rod until the noise goes away. The tighten up the locknut.

So I guess it wold be safe enough to try. It won’t work if the horseshoe is seized or if the chain is over-stretched, as Julie says, I suppose, but it might work if the horseshoe is just a bit sticky.

Oh and no, I didn’t try it. I fixed the adjuster bolt etc.
Title: Re: '77 CB400F - it runs!
Post by: taysidedragon on September 03, 2020, 03:49:23 PM
Gareth,
Looks familiar!!!
When I finally got the 400 running the other week I was so keen to just sit on it I forgot that wearing shorts isn't a great idea near a piping hot exhaust - nice burn to remind me next time!
Cheers,
Andy

Ouchy! Stings doesn't it. 😯
Title: Re: '77 CB400F - it runs!
Post by: mattsz on September 03, 2020, 04:06:21 PM
I’m jealous; you are where I want to be, without the cam chain problem of course. Well done.

I read somewhere that it is possible to “fix” a non-functioning adjuster by, essentially, doing just what you said.

You plug off the adjuster bolt and use a longer bolt with a locknut in the oil cap channel to push down on top of the adjuster rod until the noise goes away. The tighten up the locknut.

So I guess it wold be safe enough to try. It won’t work if the horseshoe is seized or if the chain is over-stretched, as Julie says, I suppose, but it might work if the horseshoe is just a bit sticky.

Oh and no, I didn’t try it. I fixed the adjuster bolt etc.

Certainly worth a try... to that end, I took a chance and ordered this "manual cam chain adjuster" bolt, made by our friend Kevin from TTR400.  It basically does the job you describe above, and is much more controllable than just inserting some kind of rod down into the opening and just pushing by hand.  As long as I can maneuver my tools in between the header pipes and frame openings...

Worst that can happen, I guess, is that it won't work and I'm out $20.  Or is it?  ;)  At least it will help me diagnose the issue...
Title: Re: '77 CB400F - it runs!
Post by: Johnny4428 on September 03, 2020, 04:37:30 PM
That is not good! OUCH!
Title: Re: '77 CB400F - it runs!
Post by: mattsz on September 04, 2020, 08:35:29 PM
Update - the manual adjustment bolt came last night.  It was a bit fiddly, but today I was able to get it installed and found a way to get some tools on it without burning myself.  It seems to have worked quite well - I slowly tightened down on the adjustment screw and the rattle slowly quieted down:

https://youtu.be/GEFcueAWPXM (https://youtu.be/GEFcueAWPXM)

I'm not sure if this is where it really wants to be, but it's so much quieter after tightening just a bit that I'm going to ride it a few miles and see what happens...
Title: Re: '77 CB400F - it runs!
Post by: McCabe-Thiele (Ted) on September 06, 2020, 09:55:05 AM
So pleased for you that its running.  :) :)

I plan to be where you are by the end of this month.
I know I bought mine with a declared cam chain rattle - I just don't want any other nasty sounds.
When the frame is being powder coated I will then sort out the cam rattle, take the head off, check piston tops etc.
Title: Re: '77 CB400F - it runs!
Post by: mattsz on September 06, 2020, 11:35:13 AM
So pleased for you that its running.  :) :)

I plan to be where you are by the end of this month.
I know I bought mine with a declared cam chain rattle - I just don't want any other nasty sounds.
When the frame is being powder coated I will then sort out the cam rattle, take the head off, check piston tops etc.

Thanks Macabethiele!  And, sorry for cluttering up your shiny new project thread with all that petcock talk, we really should have moved it somewhere else!  :-[

My time-frame has been a bit longer than yours... I got the bike almost 2 years ago!  And I haven't done any major work on the engine, it's just been puttering with many, many odds and ends just to get the bike road-worthy to see if the engine works...
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