Topic: CB400F top end assembly

[Big Bob]

Some time in the next few days I'll be assembling a CB400F top end.

I've done several CB750 top ends.

The cam chain tensioners and oiling system are obviously different.  Any "gotchas" I need to look out for as I put this thing together?  Any words of wisdom?  Any exciting new profanity that I'm not already familiar with?

Gotta say these are some cute little parts in this thing.  I'm thinking of having the holes in some extra pistons welded up so I can use them as shot glasses.

[jessezm]

On the cam chain tensioner parts, careful of two things--one, when you are taking out the two bolts that hold the tensioner arm in place, careful because it will pop out and those bolts can fall down into the motor.  Second, when pulling out the tensioner itself, there are rubber cushes both on the top and bottom that may come out with the tensioner, or may stay in their respective housing.  What you don't want is for one to drop down into the motor.  Just be gentle, and they should stay put.

On reassembly, I've been told to put a thin film of grey hondabond or similar product around the two o-ringed oil passages between the jugs and heads on both ends of the cylinders to prevent a post-assembly oil weep.  Twice I have done this and twice I have had a leak there nonetheless!!!  I got the heads decked, but not the jugs, so there may just be a slight warpage issue, I dunno...

Other than that, it's pretty straight-forward!  Oh, if you've bored it out to 466cc, getting the cylinders over the pistons is a pain in the butt since there's little if any taper left in the sleeves.  If you think those 400 pistons are cute, you should see the 350's!!!

[DarcyCB400F]

Lots of trouble with the cam chain tensioner "holding" bolt... the one in the front of the motor that locks the adjuster once adjusted. This threaded hole is stripped out on most and is very weak. Assuming the motor is sitting on your bench and not mounted in the bike, you may want to weld an external nut on the front of the motor now that it's out and apart. Your choice for sure, but at least be darn sure the threads in the block are in great condition. You would hate to have to heli coil or time-cert it after installing the motor.

Jessezm has some great advice too! One thing I would do is "exercise" the cam chain tensioner by inserting a screw driver in the the blind hole above the locking bolt to push down the adjuster. This will push the shoe that supports the chain on the bottom up. Push the shoe back down and repeat a few times to ensure the adjuster bolt and spring setup is moving freely. The spring and adjuster parts are only accessable to replace with engine on bench and bottom end torn apart.

You can also perform this exercise once the head is on but before you cap the tensioner that Jessezm refers to.

Have a shot for me too!

[Big Bob]

http://www.servicehondapsn.com/fiche_image_popup.asp?fveh=2911&section=121649&year=1975&make=HONDA&category=MOTORCYCLES&dc=5924&name=CYLINDER+HEAD

Wow.  Those copper washers are expensive!  $2.84 each.  M8x17, about 2.5mm thick.  Anybody got a cheaper option?  The seal washers are $4.81 each but at least there's only 2 of them.

[faux fiddy]

I have opened up a couple three fifties, and the ones I worked on without fail  seem to have seized up in a position where a cam sprocket bolt  is  inaccesible.  Two of them I was able to grind away a bit of casting under the cam tower and slip a very thin wrench on.

I would think of taking away this bit of this  metal opposite the camsprocket while it is off the motor.

[Big Bob]

Spoke to a very knowledgeable friend.  Ordered new seal washers.  Annealed the copper ones.  Amazing the difference pre and post annealing.

Did a dry assembly of the cylinders, head, and cam chain tensioners to get a feel for how thing go together before doing the actual assembly.  Notice that the cam chain slipper in the front is just slightly "proud" of the slot in the head.  It looks like it's intended to be held down by the valve cover.

The Clymer manual that I have is a comprehensive CB350/400/500/550 book.  It lacks detail about the 400.  Anybody got a line on a better one?

[RickB]

The Hanyes manual is pretty good for assembly stuff. The first half of the book is for the engine basically. Lots of photos rather than the illustrations of the Clymer manual. I haven't seen the Honda shop manual, but it's supposedly very good.

[Big Bob]

Man.  This thing is TINY.  Anybody know where I can get some really small piston ring compressors?

[jessezm]

I ended up using metal hose clamps from the auto parts store on mine, and custom cut wood blocks under the pistons about 7/8" high.  Do the inner two, then remove the blocks and clamps and rotate the engine to bring up pistons 1 and 4, rinse and repeat.  Because of the 54.5mm pistons, it was a REAL pain.  But if you still have a standard bore it should be easy.