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NC23 (re)build thread

numist

what I don't even
Joined
Oct 26, 2009
Location
Oakland
Moto(s)
SR/S, R12RLC, NC23(J)
Name
Scott
BARF perks
AMA #: 2762043
So on Tuesday I visited aram to check out the NC23 he had listed in Moto for Sale. I got there at 9pm, and everything looked like it did in his pictures, just darker. Since I don't have a cage here, I rented a truck yesterday and came back during daylight.

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aram had a whole lot of spare parts and sundry, some of which are going to be really useful (like the spare engine), and some of which were more to get them out of his garage and into a dumpster somewhere (like the wrecked Ninja (probably?) race tail and three tires). Should have charged a waste removal fee!

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Into the shop and onto a lift it went. Pictured on the left is thenewwazoo who, along with MotorToad (who took this picture and the one after), are responsible for me doing this dumb.

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The three of us swarmed the bike for half an hour inspecting, removing stuff like the race rearstand, and installing other stuff from the bins like the left rearset and kickstand. After a while it was starting to look like maybe this thing won't cost me my marriage, it's actually kinda pretty.

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As night fell and my frenemies went home to their warm dinners and beds, I started in on testing compression on the main (as opposed to spare) engine. Since it had been sitting for a time, I pulled the airbox and carbs (dirty!) to derestrict the intake and marvelled at the tiny valves.

While the wiring harness looks complete, plugging in the ignition and starter switch and hooking up a battery wasn't enough to get the starter relay to wake up. I didn't want to troubleshoot wiring all night (I've got the weekend for that!), so compression testing moved forward by applying power directly to the starter motor. Big sparks!

And bad news. Things started out strong, with cylinder 1 reporting 165psi and 2 making 185, but then 3 came in at 60 and 4 a meager 50. Drained the oil and fetched a dolly, this engine was going directly into surgery. As of this morning, the frame is looking pretty spartan. I'll probably take the opportunity to take apart the rest of the chassis and clean things up a bit while I'm rebuilding the engine on Thursdays.

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The todo and parts-to-order lists are growing. As you can see it needs a front wheel, and that 18" rear is going to be impossible to get decent shoes for, so I'm on the prowl for a set of NC29 wheels, or maybe F2 wheels (the front will fit, the rear is a possible but unproven fit). It's pretty obvious that I'm going to have to find some people with access to parts.
 
I just want to publicly state that except for making him aware of the listing, convincing him it was a good idea, and helping him get the thing home, I had nothing at all to do with this dumb idea and accept no blame.

Perhaps this will motivate me to start a build thread for my NC35. It's the season for 400 cc grey bikes!
 
I just want to publicly state that except for making him aware of the listing, convincing him it was a good idea, and helping him get the thing home, I had nothing at all to do with this dumb idea and accept no blame.

Perhaps this will motivate me to start a build thread for my NC35. It's the season for 400 cc grey bikes!

:thumbup
 
It's the season for 400 cc grey bikes!

Heck ya! I'm in the process of building an nc35 too.

Glad this bike found a good home. I was very temped to pick this up, but I need to stick with my in depth nc35 build and finish that up.
 
i'm just curious, but why did you remove the motor because of the low compression? imo the next logical step would be a leak down test to determine "why" the compression was low. i mean you could just have a couple tight valves, that could easily be adjusted in the frame :confused
 
I forgot to mention in my first post that when we removed the exhaust, a large amount of dirt came out of the headers. I'm not sure whether to :rofl, :wtf, or D:

i'm just curious, but why did you remove the motor because of the low compression? imo the next logical step would be a leak down test to determine "why" the compression was low. i mean you could just have a couple tight valves, that could easily be adjusted in the frame :confused

Good question! The bike was previously raced and I suspect that two cylinders without compression is just the beginning of its woes. I was intending on giving the lump a refresh anyway. Anything for a look at the cam geartrain!

The engine's not apart yet, so it's not too late :)

from the listing
Compression 60 & 50? Ouch. That's not good. When will you know about the spare engine?

I was thinking of sealing it, oiling it, bolting the starter on, and bench testing it tomorrow. Given I was planning on rebuilding the/an engine anyway, I'm not sure if the exercise will do anything other than keep me busy.
 
Not cheap, but a great place to find parts for your bike:
http://www.cmsnl.com/

Also a lot of the Honda items you should cross reference with bikebandit and cheapcycleparts as you may find the same thing here for much cheaper.
 
So let's start this with a question: what's this for? Pretend it's right way up, internet is hard :mad



This female blade connector is near the cooling fan motor plug (also pictured) and I can't find it in the Haynes manual. I know to take that with a grain of salt though, because the Haynes manual also says this about the side lights.



I took an EE course or two back in the day and I'm pretty sure that can't work. Any other possible references are in Japanese, though.

Anyway, during this process I did manage to find the main ground, but it looks like I should replace it.



I also found the likely reason why the bike wouldn't power up last Thursday; the main fuse at the starter relay was in place and good, but the other fuses weren't connected to the harness. Nice to have some closure on that one.

Along with the ground wire there's a few other things that should get some love, including this home repair to the rear subframe that's started to rust.



Here's a shot of all the electronics (minus the engine bits) plugged in. Other than the speedometer and that one wire, everything is present and accounted for, which is a relief.



One exception to that relief is the left side switch pod. There are two, an old one with dodgy switches (this is why you test!), and a newer one with the horn wire cut to a separate harness, likely for a lap timer. So that's going to have to get fixed back up. Are the housings on the wiring bundle just a flexible heat shrink, or something more fancy?



I looked through all the parts today, and there are a few other unexpected hiccups. The front brakes are frozen and the radiator has a broken mounting tab among some other problems. It's definitely labelled improperly:


(if you flip it upside-down, it says MEN, which is much more apt)

On the other side of things, I found two parts new in their Honda parts bag!



According to Partzilla, they're both PLATE, FR. FENDER for the CBR900RR, which doesn't actually seem very useful.

On to the next system, the carbs looked pretty dirty on the outside when I pulled them, so I wanted to get a look at their insides.



I was planning on taking pictures of disassembly and then posting a picture of a clean set of carbs, but something didn't seem right when I looked at the spare set I was going to use to fool you folks; the new set didn't have the mounts for the airbox and velocity stacks! The joke was on me.



In fact, if any of you know where these carbs came from, I'm pretty curious now. Other than this, they look exactly the same.

With the aid of a hammer and a manual impact driver, the carbs came apart pretty easily other than one screw that's now a flathead.



The slides all came out without too much drama, aided by some B-12 chemtool judiciously applied by thenewwazoo.



On the float side, carbs 1-3 are varnished and all barnacled as you'd expect, but carb 4 is incredibly clean looking. Looks like the insides aren't as scary as the outsides led me to believe. Now to find a kit of new seals for a JDM-only bike from the 80s :party

Finally, for akasha, here are the exhaust components laid over the mostly-swept away dirt from last time I was in the shop.



The 4-2-1 rustpipe isn't really usable, though it's the only part that fits—the 4-1 header isn't aligned right and it doesn't look like it should fit in the engine (though I haven't measured, I did try). I'd really like to use the collector-midpipe-can piece, but haven't yet figured out how to connect it to the engine.
 
The female connector plugs into the fan switch that's screwed into the radiator. At a certain temp, the switch changes state and either completes the circuit to ground through the radiator, or opens; I'm not sure which.
 
On the other side of things, I found two parts new in their Honda parts bag!


According to Partzilla, they're both PLATE, FR. FENDER for the CBR900RR, which doesn't actually seem very useful.


Honda is very good at using the same part for multiple bikes. The 900RR would be the first bike that part was used on, and your NC isn't listed (most likely) because it's not a US bike.

If you understand how to read Honda part numbers, and look at something like say, a CB550, you'll see that it has parts from CB350's, CB125's, etc. :laughing
 
The female connector plugs into the fan switch that's screwed into the radiator. At a certain temp, the switch changes state and either completes the circuit to ground through the radiator, or opens; I'm not sure which.

It completes the circuit. I just had to test and replace the one on my nc30 a few days ago. If you touch that plug to the frame, the fan should start up. If not then you have a bad fan, connection, or fuse.
 
It completes the circuit. I just had to test and replace the one on my nc30 a few days ago. If you touch that plug to the frame, the fan should start up. If not then you have a bad fan, connection, or fuse.

Great! In that case I can happily claim an entirely unmodified stock wiring harness. What a relief.
 
Actually, scratch that. Crom, if you have an NC30 fan switch handy, could you measure the threads? The NC35 one is too big for my (cheap, from-China, NC30) radiator.
 
That's common with those Chinese rads. You think it wouldn't be that hard to use the correct size in the first place. I'm out of town right now and don't have it around but I'm 99.5% sure it's an M16 1.5 pitch

I ordered part #37760-mt2-003 which is the part number for the NC35 (as well as a bunch of other Hondas) and it works. The parts manual on the NC30 have the fan switch labeled as part #37760-mr1-003. The only difference I noticed is the latter (MR1) is brass and the MT2 is plated. As long as it fits and turns on at 100C (there's a "100" stamped on the part) than I think your ok. You might want to figure out the size your of chinese rad has and just go to an auto parts store or on the internet to see if they have one. It's common for them to fail from what I've gathered.
 
Subscribing. Can't wait to see this come together. I want to do this at some point with a bike, just haven't found the right one yet. Well, actually I have, but don't have the money right now. But someday, it will happen.
 
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