Author Topic: CB400f motor needs rebuild  (Read 1681 times)

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Offline danbar

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CB400f motor needs rebuild
« on: July 17, 2011, 03:31:00 PM »
Hi everyone,

So after years of on and off searching for a 400 I finally took the plunge and picked up a nice little project.  The bike is in really clean shape but the supposedly "rebuilt" motor bolted into it turned out to be junk.  I've been taking it apart and it's scary, several missing nuts and bolts inside, nothing torqued, there was no compression to speak of, I even found a ring bent up around one of the rods.

I was hoping to find a motor out there that will pass a leak down test and bolt that in for the time being.  That is proving a bit harder than I hoped it would be.  So now I'm thinking of biting the bullet and getting a full rebuild.  I can turn a wrench or two and have been working on my own cars for years but I'm not sure that I trust myself with the kind of perfection required to build a motor myself. That, and I would really like to ride this bike at some point sooner than later and if I tackle this myself then there will be quite the learning curve that will eat up more time.  As I'm a new member of the vintage Honda scene I'm not really sure where to turn.  I'm in Seattle and was wondering who might be good to talk to about having the motor rebuilt locally or if there is somewhere else worth looking into.  I'm sure it's not cheap and that may prevent me from going this route for the time being but I need to do something as this bike is calling to me day and night from my garage.  Thanks for any advice.

Offline davesee

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Re: CB400f motor needs rebuild
« Reply #1 on: July 17, 2011, 04:36:52 PM »
my dad and i are rebuilding my 650 right now. we don't have much experience, but it doesn't seem too hard, just frustrating, taking 5 times as long and costing three times as much as we expected. that said, it's fun.

of course, we don't have it back together yet.

if you can find a machine shop to do the measuring and honing (or god forbid boring) then there isn't much else to it but being organized and turning wrenches.

good luck!
1980 honda cb650 with many weekends worth of modifications.

Offline camelman

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Re: CB400f motor needs rebuild
« Reply #2 on: July 17, 2011, 07:38:02 PM »
Pretty bike... too bad about the engine.  If you can turn a wrench, and are patient, then you should be able to rebuild that bike without an issue.  If you are going to do it, then here's a decent set of steps to get you there.

1) Check the bores to see if they are within spec.  If they are, then buy standard bore rings, have the cylinders honed, and you'll be ready to reassemble.
2) If the cylinders are not within spec, then decide how big you want to go and send them off to be bored.
     a) Bob Hamilton (I can give you his number) in Virginia can do this for under $200.
     b) a 466 kit off eBay is only $135 shipped, and I highly recommend it.  Other overbores can be found on eBay too.
3) Buy a gasket kit for the upper and lower seals in the engine and replace them all (ask for more detail before you do this)
4) Check the timing chain components and replace whatever is worn.

It sounds like the first thing you should do it check the bore on the cylinders.  The next thing is to check your timing chain components.  Replacing the timing chain really isn't bad, and gives you an opportunity to replace all of the seals in the bottom of the engine and replace any roller bearings that might be worn out.

Once you decide your route, we can help you find parts and lay out a plan.  I'm rebuilding another 400F engine right now, and can walk you through it pretty easily if you want.

Camelman
1972 350f rider: sold
1972 350f/466f cafe: for sale
1977 CB400f cafe:sold
1975 CB400f rider: sold
1970 CB750 K0 complete bike: sold
2005 Triumph Sprint ST 1050 rider

We've got to cut it off... and then come down on rockets.  (quoted from: seven minutes of terror)

Offline camelman

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Re: CB400f motor needs rebuild
« Reply #3 on: July 17, 2011, 07:45:08 PM »
Check out the San Francisco Craigslist ads.  There are a couple CB400F engines listed.  I don't know what shape they are in though.

Camelman
1972 350f rider: sold
1972 350f/466f cafe: for sale
1977 CB400f cafe:sold
1975 CB400f rider: sold
1970 CB750 K0 complete bike: sold
2005 Triumph Sprint ST 1050 rider

We've got to cut it off... and then come down on rockets.  (quoted from: seven minutes of terror)

Offline Mars

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Re: CB400f motor needs rebuild
« Reply #4 on: July 18, 2011, 01:10:34 AM »
Jeremiah at North City Vintage Honda is a really cool dude, and has lots of experience with these fours. You'll probably get to know him well if you need stuff. It's great to support a local business too!

Also, myself and Rat400f have 400f's and are in Seattle, so you could PM us from time to time.

Offline danbar

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Re: CB400f motor needs rebuild
« Reply #5 on: July 18, 2011, 09:54:37 AM »
Thanks guys,

I'm thinking of tackling this more and more.  I've got the top end apart and after seeing the crap I came across there I would definitely want someone that knows what to look for and check to take a look at the bottom end.  I've been hesitant to crack the case though,  I guess I'm afraid all the little pieces will explode out and I won't know where everything goes or something.

As for pistons and rings, I want to replace those.  Where is a good source for these?  I'm fine with stock displacement.  Also what do I need to check for to see if I need to bore or just hone the cylinders?  I don't know the specs.

Finally is there a way to tell if the case halves are a matching set?  The top and bottom are slightly different colors and that worried me but then I noticed the same thing on another 400 I looked at this week so maybe that's normal?

Sorry for the million questions, I'm just antsy to ride this thing. Thanks again!

Offline camelman

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Re: CB400f motor needs rebuild
« Reply #6 on: July 18, 2011, 02:21:06 PM »
Hmm, that's not where that ring goes. ;-)

Check eBay for pistons and rings they have been showing up there pretty cheap from a guy in japan. They are good quality and he supplies a head gasket too.
1972 350f rider: sold
1972 350f/466f cafe: for sale
1977 CB400f cafe:sold
1975 CB400f rider: sold
1970 CB750 K0 complete bike: sold
2005 Triumph Sprint ST 1050 rider

We've got to cut it off... and then come down on rockets.  (quoted from: seven minutes of terror)

Offline Ernest T

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Re: CB400f motor needs rebuild
« Reply #7 on: July 18, 2011, 05:53:16 PM »
A good machine shop makes this easier on you.  I use a shop here in San Antonio that is old school and actually has a guy that only does motorcycles.  I take him the head, cylinder and crank and he measures everything and tells me what parts I need.  He rebuilds the head and does all the measurements for things like valve spring length and crank play.  Find one of those in your neighborhood and half the battle is won before you even start.

Offline Kwality

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Re: CB400f motor needs rebuild
« Reply #8 on: July 18, 2011, 06:02:30 PM »
Twinline in Seattle also know their way around a 400f. 

[url]http://new.twinlinemotorcycles.com/]http://new.twinlinemotorcycles.com/