Topic: '76 400 four engine parts

[StewJ]

Hello All.
I am a 'newbie' to the site and I have to say there is a huge amount of usefull info available.

I have recently embarked on a Cafe style project based on a 50k 400 four. I will post some project pictures etc. in the near future but firstly I could use some advice with the motor.
It ran OK (no smoke or rattles) but was very oily around the head gasket and in general the engine needed tidying. Upon closer inspection and a top end teardown there is damage / breakages to pistons, rings, bores, valves and cyl head. it looks like a few of the rings have let go and ate their way through the piston crowns.....Not pretty! I am amazed it even ran

My question is, what options are available for oversize pistons and rings? They don't have to be OEM parts. Any info would be greatly appreciated.

Cheers
Stew
P.S. I am in the UK.

[gerryw]

David Silver spares.

Gerry

[Doctorlumen]

The 400 four is pretty in vogue right now, and there are quite a few NOS and modern parts available online for this little bike. David Silver and CMSNL are two good options for OEM. Bike bandit as well. Rick Denoon makes some trick parts for these bikes as well as TTR-400 out of South Africa.

I've heard really good things about the big bore kits on ebay...they are for sure the cheapest. If you wanna pay, I think Yoshimura still makes a kit as well, as well as a tried and true performance exhaust.

At 50k, you should strongly consider a bottom-end tear down as well. Inspect the cam chain tensioner as well as the threads on the adjustment screw. Bearings should be replaced with new as a matter of course. If that cam chain tensioner is shot, look into one from TTR400, and never worry about it again.

If you want a step-by-step rebuild story to follow, RickB's 400 rebuild on this site is bar none.

[bryanj]

You have to get 400 specific stuff (or 400 big bore kit) as the 400 has a smaller wrist pin diameter than the other 4's('cept the 350 of course)

[Stev-o]

Ozzy sells em down under.....


http://www.ebay.com/itm/HONDA-CB400F-466cc-BIG-BORE-PISTON-KIT-NOS-NEW-CB-400-RINGS-GASKET-CB400-4-FOUR-/271049988231?hash=item3f1bd69887&item=271049988231&pt=Motorcycles_Parts_Accessories&vxp=mtr

[Tim2005]

Ah, that sounds like the fairly common 400f disintegrating top rings problem .. not unusual on high milers. If you wish to stick with around stock CCs there is not much available at the minute, David Silvers haven't any kits in any oversize, though CMSNL do have pattern kits for about €200. If you want to go bigger, these kits seem to attract very good reviews from people, and are well priced indeed, though you will need to factor in the extra cost of boring the cylinders by 3mm+. 

http://www.ebay.co.uk/itm/75-77-HONDA-CB400F-PISTON-BIGBORE-54-5mm-SET-WITH-GASKET-/160823345986?pt=Motorcycles_Parts_Accessories&hash=item2571d18342

You are also going to need to check out what damage has been done to the cylinder head- sometimes that can be quite nasty indeed with very deep gouges, others it will smooth back with a little emery. It is a bit alarming that you mention valve damage though, I haven't managed that before. Then as others suggest, a quick overhaul with camchain, tensioner blade (at least) and primary chain will be likely to be essential at those miles too. And have a good look at 6th gear on the output shaft for any pitting, otherwise the bottom ends are pretty long lasting.

[StewJ]

Thanks guys for all your replies. It's good to know that this is a can be a problem with the 400 motor.

I have torn down the whole motor now. Bottom end is obviously showing signs of wear but luckily there doesn't appear to be any unexpected nastiness within. Main bearing shells will need replacing but this is just because of wear and not damage.

The damage to the head is in only one combustion chamber and it's associated valves, it looks a like a build up,welded mess of piston and ring material rather than chunks missing. I'm going to try removing the material before looking into tracking down a replacement head (nothing to loose, right). The offending valves will be replaced.
All the seats are un damaged, so a grind should freshen them up I hope.

As I say my main concern is the damage to the bores and the availability of suitable pistons........The big bore kits are looking more attractive by the minute!

Thanks again for all your advice, I'll keep you posted.
Cheers
Stew