So, took my NC 23 to teretonga raceway today for testing. first time its been to the track.

short version, heard a bang, rattle, clunkaclunkaclunka halfway round a lap during session 2.

The bottom half of the spark plug has dissappeared. Ill post a photo later. Im yet to pull the engine, but I wanted to check how much these can be bored out? are they nikasil coated bores, or can I just bore away?

Im open to suggestions on what work to do while I have the engine out, as Im going to have to remove the head and assess the damage, so it will be part anyway.

I will probably get the valve seats re-cut, and clearances reset at a minimum, and depending on damage to the piston, and the bore, I might go up a size in piston and rings, and skim the head. Thought Id run this by you guys and see what this model does, or does not respond well to.

 

Hi ,the cylinder barrels are steel, hopefully can be rehoned cylinder head can be skimmed by 0.5mm see below
400GreyBike ? View topic - Skimming head with gear driven cams

 

Thanks for the reply!.

Its a bit worse than I thought. The bottom 1/3 of the spark plug has disintegrated, there's a hole in the piston I can poke two fingers through, the cylinder barrels are damaged badly, and the head is stuffed - two valved are destroyed, and I think its probably beyond repair.

Nc23 engines are not easy to come by over here, what other engines fit right in easily with minimum effort?

 

Sorry to hear that, and not sure of your racing class or how it works, but there is a swap cbr600 engine, never done it myself but there's a lot of info about it.Have a look here.
NC23 CBR400 Bottom end blown - 600 Replacement? [VIDEO] - Honda Motorcycles - FireBlades.org
and
http://www.400greybike.com/forum/vie...p?f=28&t=25212

 

thanks. I will definitely look into that. Though my mind wanders back to the nc29 engine I know of not too far from here - I had a thread about this a little while ago.

I can get an nc29 engine with all the electrics, carbs and ecu. Im wondering if thats easier than the 600 swap. The biggest issue is the availability of the engines, so I am kind of limited by what I can find out there.

is the exhaust a direct bolt up nc23 - nc29?.

 

See here for exhaust
400GreyBike ? View topic - NC23 - NC29 full exhaust system compatability

and the framewill need some cutting/welding

 

hmmm, dont really want to start cutting into the frame, I dont have the tools for it here.

The top of the barrel on #4 is damaged, in a couple of spots around the lip. Im wondering if it would be salvageable? Ill post a photo, and perhaps you could tell me what you think?

its possible I could remove barrel, replace piston and rings, remove debris thats fallen into the motor, and stick a new head on it

 

ok heres some photos of the damage.
I have found a complete head, waiting on a price though. MIGHT have found a set of cylinders as well, but not sure if he still has them.

Im hoping I can get away with perhaps going 0.5mm oversize (was still on stock 55mm piston and rings) with a new head. any thoughts on whether I should reuse the cylinders?

 

few more

 

and does anyone have advice on where to find head and base gaskets for the nc23? few places I have looked just list it as 'obsolete'