Topic: Bore out a cb400F?

[krksquared]

I'm aware that there sources for parts to take the 400 from 51mm to 54mm. Does this usually require sleeving or can the cylinders be bored that much (assuming cylinders otherwise in good shape)? What about balancing?

[robvangulik]

Just bore it, with as small as possible clearance.

[krksquared]

Ok. Thanks for the pic. Didn't even know it had liners already. So the technique is to pull my existing liners and have them bored? According to the shop manual, the piston to cylinder clearance should be 0.001 inches or .020 to .030mm. Seems kinda tight but I certainly trust the Honda engineers. Never done a motorcycle engine but i have done a number of V8's (Chevy & Ford). How are these Hondas balanced?

[bryanj]

NO, the liners stay in the block and you use a proper boring table. 1 thou is a max clearance on these and you will need to find somebody used to boring Hondas not just bikes to get it done right plus the bore size is smaller than the "standard" boring bars can do.
Unless you are racing is it worth it? Lot of cash , no more oversizes for not much more go As to balance you dont Honda got it right first time and the pistons should be matched by supplier

[Mark1976]

   Best 'bang for your buck ' investment is a cam and head recondition. If you want to, go to the next o/s piston, it leaves you room to grow should you need too. Either way you're going to spend a few bucks so find a reputable machinist as well, then determine whether you're going to use Honda or aftermarket parts. Do it right the 1st time, if ya don't, your wasting your time and your money. Plenty of stories on here of not getting these small bore engines put back together right the 1st time.

[krksquared]

Miles on my 75 are 27406. The bike paint, chrome and seat look great - like new. It runs fine & doesn't smoke. Clutch & brakes are fine, too. I sometimes have to pinch myself when I realize it's a 47 year old bike. I guess I just find it a little difficult comparing it to my CBX & Buell. Maybe I should just enjoy it for what it is & not try to make it what it's not. Sorry, it's the hot rodder instinct in me 

[krksquared]

Then again, maybe a turbocharger would be cool. Sorry...

[bryanj]

Dont forget these tiddlers need to be at the red line before you change up, they love revs and hate lugging

[krksquared]

I have noticed that. It starts to come alive above 5000. My Buell comes alive right off idle up to around 7000. I kinda raced a Porsche 911 S the other day with my CBX  & kept right up with him. 

[bryanj]

Cbx shoulda stomped all over it!

[krksquared]

Well I didn't know he was getting on it so I had to react to his run. We quickly ran out of room so I didn't pass him. Dang red lights...

[grcamna2]

I agree with looking carefully before choosing a qualified machinist who wants to follow The Book's correct specs.
I have heard some on here had trouble with Cruizin Image piston/ringsets:excessive smoking after rebuild.
I'm not sure whether that was because the piston to cylinder specs were ignored,etc. or whether it was the rings?

[Rick4004]

There are probably hundreds of 400's out there running the 458cc overbore kits with good results. The liners are pretty thin once bored, but they don't seem to cause a problem.

-Balancing, or re-balancing is not required.
-The specified clearances are TIGHT, and a shop that is not experienced with these engines might put up a fight when you tell them what clearances you want. Find a shop that will give you what you want.
-Run a big oil cooler to help keep temps in check.

I ran a set of Cruizin Image 1st over pistons and rings last summer that did about 7000km, on my turbocharged 400F. I had the engine apart this winter and the piston/rings were fine. I suspect that the problems that people have with smoking are issued with the boring, probably too much clearance.

[dave500]

talk to a couple of machine shops and see if they really take an interest in your small motor,luckily i have a good friend with an engine rebuild shop,he measured each of my 1st oversize 550 pistons and bored and honed each one individually!

[Bodi]

Never going to pull like a CBX or Buell.
The 458 still has one overboard to 466. When Yoshimura sold piston kits, the 466 kit outsold the 458 a lot.
In 2022 it's unlikely a 400 with a fresh 458 or 466 kit will be ridden enough to wear out the rebuild.
I used Yoshimura and can't comment on the CI kits.
The 466 kit plus a street cam made a definite increase 8n mid and high rpm power and it idles with just a hint of cam roughness.