Topic: Nighthawk 550 Bobber/Chopper, kinda

[pikeymick]

Bought a 1983 CB550SC Nighthawk today, 150 bones! Overall it's in good shape (visually). I found a crack in the valve cover that someone JB welded (I hate that stuff), the forks are shot, the clutch master cylinder is toast, and the rear brake return spring is shot (if not the whole assembly). The PO said he had it running but that it ran like crap. His thought was that the carbs just needed cleaning. So first thing to get into were the carbs. I pulled them off and noticed the intake boots (from carb to engine what's the proper name for these) were cracked on 2 out of the 4. I also noticed the plug wires were labeled by cylinder, but were not hooked up to the corresponding cylinders. I'm not sure if the labels are correct.

Anyway I got the carbs off (PITA) and then started to take the bowls off. Three of the screws were stripped then got the idea to try freezing them with an airduster can turned upside down. I had bought a couple of cans to try and pop a dent on my pickup. I froze the screw then tapped it with a hammer and the damn thing came right out! All three of them! I got the bowls off and it looked like someone had scooped up some red sand, then reassembled the carbs with it in the bowls. I'm guessing it's rust mixed with varnished old gas. Some carb cleaner and a hose later I've got the guts of the carbs sparkling again. I cleaned out all the jets, and there respective orifices. The slides seem to be in good shape, the jets pass light, the alleys and pathways through the carbs are shiny again, but there is some weird corrosion on the inside of the intakes on the heads....................

The plan is to get an R6 front end and swap that on there. Fab up a glass rear fender, do something for the tank, rear suspension, and rear brake and have some fun with her. Tomorrow I'll finish up cleaning out the carbs, and reassemble, and take some pics to add to this... not sure if the o-rings on the bowl's are any good anymore... also need to replace those stripped screws.

Someone already did a round light conversion on it.

Shopping list:

R6 front end-
Clutch master cylinder- (will most mc's bolt right up? would be nice to just use the one on the R6 front end)
Intake manifold boots- (at least 2)
Battery-
Tank cleaner and sealant-
Reshape/Reupholster seat-
Rear shocks-
Rear brakes- (pads, return spring, grease up joints?)
Check lights/wiring-
Pod air filters-

[pikeymick]

Got some pictures today.




The intake manifolds ending up not being bad after all. There were hairline cracks in the rubber at the base where it meets the engine, but upon taking them off it looked like there was a metal sleeve that would keep the rubber crack from causing any problems. I cleaned the corrosion up with a wire wheel and then put them back on.


Here is the crack in the valve cover (on the left)


I got the carbs all cleaned up. Then put them back on. Going to stray to get it started tomorrow.

[Alan F.]

Good project!  I've been thinking about one of these for a long time, but I think you've beaten me to it.  Good luck with your build, I'll keep reading.
Honda built it as a bit of a cruiser, but the neck rake isn't bad at 29 degrees for a sportier front end.  It's already got good wheels, and sportier shocks are out there, maybe a Kawa ZRX?  I dunno what the tire sizes are, but something sticky must be out there, I have a 400T project that uses a 16" rear and a 19" front, everyone says bridgestone spitfire S11 is a very good tire and it comes in those sizes.  Will you be dropping any weight? plastic fenders are an easy one, you might have to keep the airbox though just to keep it running right without a hassle (I will be on my 400) Lightweight motocross bars are out there too, and there are tons of other little things that you can trim off or swap out for liter parts. 
Best of luck.
-Alan

[pikeymick]

Thanks Alan! Yeah that's the fonrt end I've been looking for, well any of the 600's. But I'm on a tough budget so I've got to do a lot of searching for parts for the right price.

For weight I'm going to drop as much as I can. Get rid of the whole @ss assembly. I pulled the sissy bar and rear stuff off tonight. But I'm trying to find a balance between being able to drive it as I go, and doing everything that I want to get done. I was hoping to drop the airbox as well, throw some pods on and richen up the mixture (once I get it running), but you think that'll be tough?

Where did you find the head angle information?

[Alan F.]

To keep the cost down could you just slip the fork tubes up in the trees an inch or two and install progressive springs and new fork oil?  You could run clip-ons  at the top of the tubes too, that'd look pretty cool, but drag bars are cheap.

When I got the airbox out of my 400 I was surprised at how light it was, not really a big deal keeping it at that point, plus I probably won't have much trouble jetting it for whichever exhaust I wind up with, and rain won't bother it.  I don't want to reinvent the air intake system, too much time involved.

I think the trick to being able to ride while you work on it is to make changes that won't affect reliability, like keeping the wiring stock, airbox, suspension stock, etc...
just making subtle (and cheap) changes that'll gradually transform it into a sportier ride without ever even hitting the ATM or PayPal.

Asking around toyour local members and friends for plastic or fiberglass fenders is a good start.  Grind the rivets off the front fender, keep the under bracket and pop-rivet on the lighter fender in place of the heavy steel one, same in the rear, you might have to get creative with tail light mounting though.  Lighter directionals are available everywhere, used ones will be cheaper. Center stand is easy to lose, and you can bolt it up for maintenance.
That's all I can think of for now, here's where I got the specs  http://www.hondanighthawks.net/550.htm

Have a good week and good luck.
-Alan

[pikeymick]

Anyone know what the damned socket size is for the spark plugs on these things?

[Alan F.]

Isn't it 18mm like other Honda bikes?  Maybe 5/8" if you have american plugs in there.
-Alan

[pikeymick]

Yeah going to pick up a 18mm plug socket on the way home. Should work.

[pikeymick]

Anyone know what kind of cross tank compatibility the CB's have? I remember reading that there wasn't much, but the mounts look like they are relatively in the same position. I wonder how much work it would be to get one on, I would think it would just be moving the gas tank mounting points, the ones with the rubber grommets on them.

[pikeymick]

Ok it lives. But barely... I think cylinders 3 & 4 aren't firing. Spark is there (perhaps weak), air is there, which only leaves fuel...

Backed out overflow screws on 3&4 and fuel came out. Really don't want to pull the carbs again, especially now that they're filled with gas....

When it runs its backfiring from what sounds like 3&4. I tried riding it but it stalls under power. My concern is that 3&4 have bad rings, or maybe other's do to. Hmmmmm.  Here's some video of it running, the knocking noise is that a rod bearing? Any ideas? I also sprayed WD-40 on the isolators while it was running to no effect, so I think I'm good for leaks there.
[youtube=425,350]<object width="425" height="344"><param name="movie" value="

name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="

type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="425" height="344"></embed></object>[/youtube]

[pikeymick]

Pulled the carbs back off. The fast jet (small one) on #3 & #4 were clogged... again. The weird part was after sitting for 30 mins while I cleaned out the breathers on the carbs, the jets magically unclogged themselves. Not to believe chance occurrences like that I start cleaning them with carb cleaner, again, and held them up and after soaking in carb cleaner they appeared clogged again! WTF. I rememberred a post about someone boiling carb stuff in lemon water so I gave that a go, and pulled them out to check after two minutes, and sure as #$%* they were open. Put em back in and checked them again another five minutes later, and I'll be a friggin dwarf at the pound with a raw steak around my neck they were clogged again! I've passed wire through them, I've soaked them in every solvent I can think of. I think it might be time to just buy two new fast jets...

[Alan F.]

Anyone know what kind of cross tank compatibility the CB's have? I remember reading that there wasn't much, but the mounts look like they are relatively in the same position. I wonder how much work it would be to get one on, I would think it would just be moving the gas tank mounting points, the ones with the rubber grommets on them.

Yeah, somewhere in these forums I can remember a pic of a frame that had those points removed and replaced with bolt-on plates that relocated the front mounts higher.  A larger tank on that bike would be killer, I was thinking of a Valkyrie tank for my CM400 project, but prices are still too high for that low budget build to justify.  I saw one go for around $100 on eBay, it had one scratch, no dents, cap, key, petcock and factory paint too. They're about 6 gallons I think, would give your bike a nice range between fill ups.  I don't know what other bikes had high capacity, but my 92 750 Nighthawk holds 4.7 gallons and those tanks can be had for cheap sometimes, I've seen one on someones 650 bobber around the forums too.
-Alan

[Alan F.]

Ok it lives. But barely... I think cylinders 3 & 4 aren't firing. Spark is there (perhaps weak), air is there, which only leaves fuel...

Backed out overflow screws on 3&4 and fuel came out. Really don't want to pull the carbs again, especially now that they're filled with gas....

When it runs its backfiring from what sounds like 3&4. I tried riding it but it stalls under power. My concern is that 3&4 have bad rings, or maybe other's do to. Hmmmmm.  Here's some video of it running, the knocking noise is that a rod bearing? Any ideas? I also sprayed WD-40 on the isolators while it was running to no effect, so I think I'm good for leaks there.
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name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="

type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="425" height="344"></embed></object>[/youtube]

Yeah I'd call that clogged jets too, but not on all 4. Good find.

[Alan F.]

Best deal for jets I know of: http://www.chaparral-racing.com/Chaparral/dept.asp?dept%5Fid=3381&gift=False&0=assets%2Fhtml%2Fd%5Fstreet%2Easp%2CnavId%3Dd%5Fstreet%2A0%26menu%5Fid%3D%26Tree%3D%2CStreet&1=dept%2Easp%2Cdept%5Fid%3D3316%26menu%5Fid%3D%26Tree%3D0%2CStreet%20Fuel%20%26%20Air&mscssid=9F2F1026F7A9476CB7C63B7D8F5EB515

[Alan F.]

I just looked up the fuel capacity for the CB900-1000C's from the early 80's, seems they held 3.6 with a .8 reserve, so 4.4 gallons there if you can find a good one cheap it may be a workable solution.

[pikeymick]

I just looked up the fuel capacity for the CB900-1000C's from the early 80's, seems they held 3.6 with a .8 reserve, so 4.4 gallons there if you can find a good one cheap it may be a workable solution.

Check out this bad boy! http://cgi.ebay.com/ebaymotors/1981-Honda-CB900C-CB900-Custom-CB-900-Gas-Fuel-Tank_W0QQcmdZViewItemQQ_trksidZp3286Q2ec0Q2em14QQhashZitem2a014bb192QQitemZ180410364306QQptZMotorcyclesQ5fPartsQ5fAccessories#ht_634wt_941

I wish this thing was up and running and I could justify body upgrades! That paint job is sick! Albeit beat up...

[Alan F.]

I just looked up the fuel capacity for the CB900-1000C's from the early 80's, seems they held 3.6 with a .8 reserve, so 4.4 gallons there if you can find a good one cheap it may be a workable solution.

Check out this bad boy! http://cgi.ebay.com/ebaymotors/1981-Honda-CB900C-CB900-Custom-CB-900-Gas-Fuel-Tank_W0QQcmdZViewItemQQ_trksidZp3286Q2ec0Q2em14QQhashZitem2a014bb192QQitemZ180410364306QQptZMotorcyclesQ5fPartsQ5fAccessories#ht_634wt_941

I wish this thing was up and running and I could justify body upgrades! That paint job is sick! Albeit beat up...

That's cool, I wonder how much for a cap and petcock?

[Laminar]

I'll be keeping an eye on this with some interest.

One thing about the pods - I've heard that trying to tune CV carbs with pods can be a bear. I'd stick with the airbox.

Why the R6 front end? If you just want dual discs, the '83-~'85 Nighthawk 650 had dual discs and most of those components will be a direct swap, and probably loads cheaper.

That tapping doesn't sound good - it could just be a tappet pumping up, but that's supposed to go away after a few seconds.

A few questions:
1. Have you changed the oil/filter yet?
2. Have you done a compression test?
3. How is the bike getting fuel while it's sitting there with the tank off?
4. Did you cap the petcock vacuum line or just leave it open?

If you're putting new, clean gas through clean lines into clean carbs, then your jets shouldn't be clogging. Somewhere along the line your gas is getting dirty.

[pikeymick]

I'll be keeping an eye on this with some interest.

One thing about the pods - I've heard that trying to tune CV carbs with pods can be a bear. I'd stick with the airbox.

Why the R6 front end? If you just want dual discs, the '83-~'85 Nighthawk 650 had dual discs and most of those components will be a direct swap, and probably loads cheaper.

That tapping doesn't sound good - it could just be a tappet pumping up, but that's supposed to go away after a few seconds.

A few questions:
1. Have you changed the oil/filter yet?
2. Have you done a compression test?
3. How is the bike getting fuel while it's sitting there with the tank off?
4. Did you cap the petcock vacuum line or just leave it open?

If you're putting new, clean gas through clean lines into clean carbs, then your jets shouldn't be clogging. Somewhere along the line your gas is getting dirty.

1)The oil and filter was changed by the PO, and he never had it running (oil still looks new)

2)I haven't done a compression test yet, I need to get some cash together to get one.

3)I took the tank off just prior to taking that video.

4)For the petcock vacuum line was open. I'll post one with it closed at the end. But I was getting similar response with it capped, but at a lower RPM.

And for the gas I cleaned out the tank as well, and put in a clear fuel line, only clean gas getting through. The two jets that are clogging are snafu'd. They appear open one second closed the next, but it seems to be dependent on moisture of some sort. It could be an organic blockage that is swelling with the moisture. The tapping noise does get better as it idles more. It went completely away at one point.

In this video I pulled the 4th cylinder plug off and you can see no change in engine tone, that was my test to see if they were firing.
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name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="

type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="425" height="344"></embed></object>[/youtube]

[pikeymick]

One thing about the pods - I've heard that trying to tune CV carbs with pods can be a bear. I'd stick with the airbox.

Why the R6 front end?

That's a bummer to hear... the stock intake doesn't fit between the airbox and the carbs, it's about 3mm's too short... And I really like the look of the open frame. The sport forks I want to do for the suspension upgrade. These forks are completely shot, they were full of water. The first time I compressed them two streams of water shot into the air through teh forks seals, haha, no joke! I've rebuilt forks before... I'd rather spend the money on upgrading the front end. Give it a more aggressive/modern look. I really liked the look on the other project threads of the new forks on older bikes.

But I'm not stuck on the R6. I'd go with any reasonable front end. It'll be a balance of price, a complete front end, and availability.

[The_Crippler]

That's a bummer to hear... the stock intake doesn't fit between the airbox and the carbs, it's about 3mm's too short... And I really like the look of the open frame.

I was in the same boat as you...but the more I read and the more people in the know I talked to, and I decided that it was outside of both my desire and knowledge to have hope of making it work.

But I'm not stuck on the R6. I'd go with any reasonable front end. It'll be a balance of price, a complete front end, and availability.

I'm interested in learned more about both the R6 front ends and the dual disc swap.  I also like the look of the new frontends and was thinking about swapping the one on my 650C...how does one go about figuring out which modles are compatable?

I might just swap components to get the dual brakes...certainly a lot easier to do.  Can that be done with mag wheels?  I know that some 1980 CB650Cs had the duallies, but mine does not.

Sorry for the threadjack, but I figured someone might be able to help both of us.

[pikeymick]

I'm interested in learned more about both the R6 front ends and the dual disc swap.  I also like the look of the new frontends and was thinking about swapping the one on my 650C...how does one go about figuring out which modles are compatable?

I might just swap components to get the dual brakes...certainly a lot easier to do.  Can that be done with mag wheels?  I know that some 1980 CB650Cs had the duallies, but mine does not.

Sorry for the threadjack, but I figured someone might be able to help both of us.

From what I've read it's a matter of getting the bearings to fit, as this is a complete front end swap. Forks, stem, triple crowns, bars, calipers, and wheel. But the bearings would be the bottle neck. I guess the best next step would be to know the diameter of the stem on these Nighthawks, if they're "modern" enough to match modern front ends, well that'd be something to dance about.

[The_Crippler]

The 550 Interceptor thread has a lot of info about what he did...I'm also wondering about other years and models as well.  I know that the bearings are a bottleneck - but what about the angle/height/etc of the frontend?  I'm sure that factors in as well, too - right?  (Again, this is in cases that one isn't using an R6 on a 550)

[pikeymick]

Yeah it definitely does. But at the same time with this bike I'm not expecting a transformation of how it drives. Too steep would be bad because it wouldn't be stable, but I have a feeling it's more likely to become more slack with a newer front end. Especially of a sport bike. However my assumptions could be off.

The biggest problem I anticipate is the (I don't know if these terms are technically accurate) the spring rate, compression, and rebound. If I was so put a front end from a much heavier bike it could create a hazard when cornering, or under heavy braking (I could be totally off on this) because the front wheel would be more prone to locking up, but at the same time I don't plan on dragging knees haha, but in an emergency or something, I would be concerned.

[pikeymick]

First I should start this with I am not an engineer, nor have I ever played one on TV.

Trail is a function of head angle, fork offset or rake, and wheel size. Their relationship can be described by this formula:

where Rw is wheel radius, Ah is the head angle measured clock-wise from the horizontal and Of is the fork offset or rake. Trail can be increased by increasing the wheel size, decreasing or slackening the head angle, or decreasing the fork rake.
The more trail a bike has, the more stable it feels. Bikes with negative trail (where the contact patch is actually in front of where the steering axis intersects the ground), while still ridable, feel very unstable. Bikes with too much trail feel difficult to steer. Normally, road racing bicycles have more trail than mountain bikes or touring bikes. In the case of mountain bikes, less trail allows more accurate path selection off-road, and also allows the rider to recover from obstacles on the trail which might knock the front wheel off course. Touring bikes are built with small trail to allow the rider to control a bike weighed down with baggage. As a consequence, an unloaded touring bike can feel unstable. In bicycles, fork rake, often a curve in the fork blades forward of the steering axis, is used to diminish trail.[18] In motorcycles, rake refers to the head angle instead, and offset created by the triple tree is used to diminish trail.[19]


(pilfered from the wiki gods)