Author Topic: CB400 Four - a long-overdue completion  (Read 1166 times)

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Offline Nerdos

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CB400 Four - a long-overdue completion
« on: September 29, 2018, 08:27:46 AM »
Hello fellow SOHC chums

This is just to introduce my project and give some backstory (if it is of any interest).

The backstory
I am almost 50 years old now.  I have owned my 1976 CB400 Four since June 1988.  When I bought the bike it was fairly standard except for a reverse cone megaphone exhaust, no mirrors, one missing side panel and the remaining panel and tank were finished in matt black.  This was my first 'big' bike after the delights of a CG125. The PO's mother sold me the bike for £300 while her son was at university.  He was from the year above me at school and I neved did find out if the sale had his blessing.  The bike was reliable and fun and I repaid that reliability and fun by despatching the arse off it.  I would rag the poor thing up to London from the south coast and back with barely any thought for any sort of maintenance apart from when bits fell off (like the gearshift on the M1 at Teddington).  A while later I became aware that these bikes were being considered 'classic' and so I started trying to look after it a little more.  I had quit despatching (and my deluded notion that I was Ron Haslam in a dayglo bib) while I still lived.  This was the pre-internet age and finding parts or advice was pretty hard so not a lot of progress was made.
Fast forward to university and I had another go at making the bike better but there is only so much you can do with no money and good intentions: degreasing components in the bath, rebuilding carbs in your bedroom. 
Now let's move to 2005 when I had a proper job and almost a proper salary.  I also, crucially, had a garage.  The bike was stripped and an attempt at a grown up restoration started.  NOS front and rear mudguards/fenders were obtained.  A NOS complete exhaust was also purchased.  The frame was powder coated.  The fork stanchions were rechromed.  I rebuilt the wheels with new spokes and rims.  Then came child one and a move of house.  I had not done anything with the engine but I had a spare (and indeed a whole other 400 four basket case) so I threw that into the frame to get the bike going and to avoid losing parts in the move.  It did run  for a while and then fell into disuse in a neglected corner of the garage, its puny 37BHP being no match for the other bikes with which it now shared space.  Now its time has come and so I aim to properly rebuild the engine that goes with the frame.  The engine has 51,000 miles on it and looks pretty skanky.  I stole the rear light for my CB750K3 (elsewhere on this site), the seat has some inexplicable resin-type deposit on the back and the tank and side panels were sprayed using aerosols in the back garden of my student digs in about 1993.  So the bike is half there with some of the more difficult-to-source items already accounted for.

I will post some pictures of what the bike looks like shortly but this is the poor, decrepit engine.  Bless it.

Offline Nerdos

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Re: CB400 Four - a long-overdue completion
« Reply #1 on: September 29, 2018, 09:25:12 AM »
Got the head off this afternoon.  It was an embarrassing reminder to my previous bodging.  Of the 17 or so holding the rocker cover on, only three were the correct type.  There are four stripped threads in the head.  I have a thread repair kit but have never used it so that could be fun.

What is the opinion on the state of the head where the cam runs.  It looks superficial to me but I am open to more learned opinions.

Offline MoMo

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Re: CB400 Four - a long-overdue completion
« Reply #2 on: September 29, 2018, 02:34:58 PM »
can you feel any ridges or is it smooth?  Looks scored to me....Larry

Offline Nerdos

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Re: CB400 Four - a long-overdue completion
« Reply #3 on: September 30, 2018, 04:46:38 AM »
The bearing faces don't feel scored to the touch but I agree that they don't look to be in optimum condition.
Fortunately I have another spare engine.  It came from a bike with a twisted frame and CB400N forks and wheels.  The engine, tank and carbs were the only things potentially worth saving.  As you can see it has a nice patina of filth on it.  I will disassemble this engine too, marking the parts  as I go to be able to identify them later.  I believe you should not put the camshaft from one bike into the head of another.  Happy to be corrected though.
I took the rocker cover off and it looks marginally better although I cannot get the head off to inspect the piston side of it as the flanged nut that holds the head down next to the spark plug - one of the two nuts exposed to the weather - will not budge.  I have treated it to a good roasting with a hot air gun and it is currently soaking in plusgas.  I have a feeling that something will give if I persist with it.  Either the socket will split, the nut will round off or the stud will snap.  Thankfully I am in no rush so the plusgas can have a chance to work its magic.
This head has seen some bodging too.  There is a snapped bolt in it, a helicoil plus - and this is a first - I found the remains of a used wooden matchstick under the camshaft.
« Last Edit: September 30, 2018, 06:27:59 AM by Nerdos »

Offline MoMo

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Re: CB400 Four - a long-overdue completion
« Reply #4 on: September 30, 2018, 02:21:13 PM »
shouldn't be a problem swapping cams...Larry

Online Don R

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Re: CB400 Four - a long-overdue completion
« Reply #5 on: October 26, 2018, 07:11:28 AM »
 I wouldn't be afraid to swap cams to a different head, keeping the same rocker arms with the cam would be a plus since they already have an established wear pattern. I'd use a little assembly lube so the moving parts have plenty of protection until the oil gets there. 
No matter how many times you paint over a shadow, it's still there.
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