Author Topic: New (to me!) '77 CB400F - US model  (Read 38179 times)

Offline taysidedragon

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Re: New (to me!) '77 CB400F - US model
« Reply #330 on: May 25, 2020, 12:04:07 AM »
The missing stud on left hand side is a worry. A bolt into a shallow threaded hole is not as strong or secure. You could possibly find yourself riding on only one shock.
A good engineering shop should be able to repair that back to standard.
The dome nuts are longer than a standard size nut, hence the spacers. David Silver sells them.
Gareth

1977 CB400F
1965 T100SS

Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #331 on: May 25, 2020, 12:12:19 AM »
The missing stud on left hand side is a worry. A bolt into a shallow threaded hole is not as strong or secure. You could possibly find yourself riding on only one shock.
A good engineering shop should be able to repair that back to standard.
The dome nuts are longer than a standard size nut, hence the spacers. David Silver sells them.

Thanks taysidedragon!

The threaded hole is 7/8" deep.  Not what I'd call shallow - I wouldn't worry about the bolt pulling out, but I do think about the possibility of the whole spindle snapping off if it's "walls" are too thin after being drilled and threaded...

Offline taysidedragon

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Re: New (to me!) '77 CB400F - US model
« Reply #332 on: May 25, 2020, 12:27:28 AM »
I didn't realise you had that much left to bolt into. I assumed it had snapped of at the frame.
It doesn't sound strong enough to me as it is. 🙁
Gareth

1977 CB400F
1965 T100SS

Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #333 on: May 25, 2020, 01:09:21 AM »
I didn't realise you had that much left to bolt into. I assumed it had snapped of at the frame.
It doesn't sound strong enough to me as it is. 🙁

No, the "spindle" that the shock bushing fits on is still there.  More like just the threaded part broke off and someone drilled and threaded it.  Here it is with the bolt partially inserted:

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How should this be repaired?  Cut the whole spindle off and weld up a new one?  Would the new one - spindle and threads - be machined from a single piece, or does a stud get threaded in, kind of like was done here?

Offline Bryanj

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Re: New (to me!) '77 CB400F - US model
« Reply #334 on: May 25, 2020, 06:12:29 AM »
Me, i would make stud with the thread on the spigot one end and long enough to bottom out fitted with the best locktite and the correct thread on the visible part.
That "stepped" nut was for a carrier of some sort

Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #335 on: June 01, 2020, 05:53:29 PM »
I'm at a bit of a standstill waiting for a few parts... I finally got the electric start up and running so I decided to cross my fingers, hold my breath, and do a compression test.  Should have done it a lot sooner, although I don't know if it would have mattered.  My results are most disappointing...

I tried it with all the plugs out, to go easy on the motor and battery - all four read only in the 72 - 78 psi range.  That's right, 100 psi less than they should be.  Next I tried it with all the plugs installed - excepting the cylinder being tested, of course - and found no change.  I added a little oil, against ring leakage, which bought them up just a few points.  I tried loosing all the tappets, against valve leaks due to bad adjustment, which brought them up to the 91 - 95 psi range... better, but still nowhere close. I pulled the head cover and tried re-torquing the head, against a leaky head gasket due to a loose head (all the head nuts were tight except for the two "pillar nuts," which moved a little bit), but this made no change.  While I had the cover off, I checked the cam timing, just in case - the marks on the sprocket are just where they should be with the "T" mark on the spark advancer aligned with the matching mark...

To rule out a faulty compression tester, I tried a borrowed one, which matched mine's readings.  I also hooked my tester up to my air compressor, and found it's readings within 5 psi of the compressor's regulator gauge.

Things aren't looking too good for our hero...

Offline Bryanj

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Re: New (to me!) '77 CB400F - US model
« Reply #336 on: June 01, 2020, 05:58:28 PM »
Its not been run for so long get it going and see what happens

Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #337 on: June 01, 2020, 06:01:04 PM »
Its not been run for so long get it going and see what happens

It's been about 2 years.

I was going to ask whether it was a good idea to try it first, before "writing it off" and opening up the engine...

Offline Bryanj

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Re: New (to me!) '77 CB400F - US model
« Reply #338 on: June 01, 2020, 06:56:59 PM »
As you can take the top off in the frame i would try and get it to run, probably bolting on the absolute minimum

Offline K2-K6

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Re: New (to me!) '77 CB400F - US model
« Reply #339 on: June 01, 2020, 10:26:05 PM »
I'm with trying to start it too,  give the little guy a chance  ;D

First it may be worth spinning it with plugs out and wd40 down the bores to help if there's any long term oil gumminess in the rings.

If it runs,  let it warm a bit, plugs out,  carbs open and retest for compression then. See what you've got as it'll tell you one way or the other if it stays low as to further decisions.

Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #340 on: June 01, 2020, 10:32:10 PM »
I'll probably do that... put it together enough to run it and give it a chance... just to satisfy my curiosity, if nothing else!

Offline Lobo

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Re: New (to me!) '77 CB400F - US model
« Reply #341 on: June 01, 2020, 10:38:27 PM »
Matt - haven’t fully read the previous 23 pages of this post - ie forgive me, but are you performing the compression test correctly ie with the throttle wide open? (and plugs out). Page 1 says your bike has 22k miles (ie barely run in!) and it seems odd all 4 cylinders are ultra low .... and yet within a few psi of each other....

Simon

Addendum... and Air filter removed.
« Last Edit: June 01, 2020, 10:44:40 PM by Lobo »

Offline mattsz

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Re: New (to me!) '77 CB400F - US model
« Reply #342 on: June 01, 2020, 10:45:48 PM »
Matt - haven’t read the previous 23 pages of this post - ie forgive me, but are you performing the compression test correctly ie with the throttle wide open? (and plugs out). Page 1 says your bike has 22k miles (ie barely run in!) and it seems odd all 4 cylinders are ultra low .... and yet within a few psi of each other....

Simon

Simon - very good question!  I've actually let some of the details on this slide a bit, as my recent posts here have drawn little comment (with a few exceptions, of course - you know who you are, thank you!).  No surprise, I suppose; I've done a lot of talking, but not taken much action in the past year-and-a-half.  I'm getting bored of me!

I should have said: the carbs are currently off the bike, as is the silencer.  I have four open carb insulators, and an open exhaust collector...

Offline Lobo

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Re: New (to me!) '77 CB400F - US model
« Reply #343 on: June 02, 2020, 06:07:09 AM »
...that’s bad news; I’m no mechanic but frankly surprised all 4 readings the same given the significant loss of compression.
Hopefully this implies ‘good news’ - ie nothing mechanically buggered.

Offline Bryanj

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Re: New (to me!) '77 CB400F - US model
« Reply #344 on: June 02, 2020, 06:54:00 AM »
It could be rings stuck in grooves and in all honesty it could go either way in get it running and hot , all frees up and then runs fine OR get it running and hot they stay stuck and it runs like shite. Either way i think its worth trying

 

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