Topic: Nighthawk 550 Bobber/Chopper, kinda

[Laminar]

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...

Are you saying that the rubber boots that go between the airbox and the carbs are too short?

If you unscrew the two bolts holding the top of the airbox to the frame, you can slide a screwdriver through one of the holes in the frame and use it to pry the airbox towards the carbs. The holes that the two bolts go through are oval in shape to allow for some adjustability.

[Alan F.]

In selecting a suitable replacement for a front end swap there is allot to consider, the length of the fork assembly (for correct ride height), the fork offset of the new triples, and new front wheel's size will both contribute to your new trail measurement, so keeping them close to stock will yield results nearer to stock.

But anything can be bolted up roll, you just want to have a rideable bike when it's complete. 

Spring rates and preload, fork oil viscosity and a few other factors can be altered after the front end is in place to adjust how the bike handles and to bring it more inline with your tastes and riding style.

Calculating trail is one thing, measuring trail is quite another.  If you will be making any changes to the rear suspension or wheel size or tire size or shock length...your trail will be changed.

Dual disc brakes at the front of a bike aren't the 'end-all...be-all' of motorcycle brakes.  The performance of a modern single disc brake is considerably better than a vintage single disc setup, and higher performance rotors and pads are available in the aftermarket to increase the performance of these designs also.

-Alan

[pikeymick]

The overall appeal of the new front end is as well aesthetic. In doing the mod I want to have some fun with it and learn as much as I can, especially from people like yourselves who have a wealth of knowledge and experience on the subject.

So if I was to get a CBR 1000 ('05) for with an offset of 23.75 deg, ah hell. I can't find fork lengths for this thing. What type of a range do the length of sport bikes fork vary? I would imagine it can't be more than 3-4 cm's, no? (granted that would probably be a significant difference is it not less than that, still searching for info)

But if a fork was too long it could be lowered in the triples to compensate for that difference. This is going to be an around the city bike.

I think this is the 5th edit. The CBR has a fork offset of 27.5 mm, the important numbers are fork offset, and wheel size for a front end replacement (assume rear shocks and wheels size are static)

[tomsweb1]

I love these bikes. Alot of fun to ride.

  They do have a problem, though... the con-rod bolts tend to loosen up and destroy the crankshaft.... I have personally seen this twice, and heard of it countless other times. #2 piston. YOu can relatively easily get at it by removing the exhaust and then the oil pan. Make sure they are tight. I know it sounds like a pain in the a$$, but it could save you a massive headache later. I still haven't found a good crank for mine. Most used sets out there are missing the crankshaft, and one piston rod. coincidence...? I think not.

[The_Crippler]

"These bikes" as in CBs in general, or the 550s in particular?

[Alan F.]

The overall appeal of the new front end is as well aesthetic. In doing the mod I want to have some fun with it and learn as much as I can.

So if I was to get a CBR 1000 ('05).....What type of a range do the length of sport bikes fork vary? I would imagine it can't be more than 3-4 cm's, no? (granted that would probably be a significant difference is it not less than that, still searching for info)

But if a fork was too long it could be lowered in the triples to compensate for that difference. This is going to be an around the city bike.

The CBR has a fork offset of 27.5 mm, the important numbers are fork offset, and wheel size for a front end replacement (assume rear shocks and wheels size are static)

Your frame neck is at 29 degrees and with the stock front end you've got 4.2"(106.68mm)of trail with a 100/90-19 wheel/tire. That's quite a bit, but then it's a cruiser.

A 2005 CBR1000RR has 23.45 degrees of rake at the steering head, and a trail of 4.015" (or 102mm) trail with a 120/70-17 wheel/tire.

http://www.hondanighthawks.net/550.htm
http://www.motorbikes.be/en/Honda/2005/CBR%201000%20RR%20Fireblade/

[pikeymick]

Yeah that's where I had pulled my data from. I think with any form off of a sport bike I'll be ok. The angles on this thing are so slack.

[Alan F.]

Your frame neck is at 29 degrees and with the stock front end you've got 4.2"(106.68mm)of trail with a 100/90-19 wheel/tire. That's quite a bit, but then it's a cruiser.

A 2005 CBR1000RR has 23.45 degrees of rake at the steering head, and a trail of 4.015" (or 102mm) trail with a 120/70-17 wheel/tire.

a 100/90-19 has a radius of 331.3mm

a 120/70-17 has a radius of 299.9mm

I'm listing this info for the purpose of calculating trail with the 05 CBR1000RR gear bolted up to your 550 NH. The trail calculators I've found on the web all figure a little differently, so pretty much find one you like and stay with it for the whole project, I've got a link to one I like but it's in another computer, when I find it I'll post the link here and offer some explanation.  The reason to use a trail calculator with the stock specs of the bikes is to figure the fork offset numbers out, with those numbers missing it's tough to calculate trail with the CBR stuff on the 550 NH.  If I remember correctly I would plug in the rake, offset, wheel radius, and fork length (although it didn't change the result if I varied the length...) if I played around entering a few different values for the fork offset, I'd eventually find one that makes sense given the specified trail for the bike.   Make any sense? I'll post back when I've found the trail calc I used.
-Alan

[pikeymick]

Your frame neck is at 29 degrees and with the stock front end you've got 4.2"(106.68mm)of trail with a 100/90-19 wheel/tire. That's quite a bit, but then it's a cruiser.

A 2005 CBR1000RR has 23.45 degrees of rake at the steering head, and a trail of 4.015" (or 102mm) trail with a 120/70-17 wheel/tire.

a 100/90-19 has a radius of 331.3mm

a 120/70-17 has a radius of 299.9mm

I'm listing this info for the purpose of calculating trail with the 05 CBR1000RR gear bolted up to your 550 NH. The trail calculators I've found on the web all figure a little differently, so pretty much find one you like and stay with it for the whole project, I've got a link to one I like but it's in another computer, when I find it I'll post the link here and offer some explanation.  The reason to use a trail calculator with the stock specs of the bikes is to figure the fork offset numbers out, with those numbers missing it's tough to calculate trail with the CBR stuff on the 550 NH.  If I remember correctly I would plug in the rake, offset, wheel radius, and fork length (although it didn't change the result if I varied the length...) if I played around entering a few different values for the fork offset, I'd eventually find one that makes sense given the specified trail for the bike.   Make any sense? I'll post back when I've found the trail calc I used.
-Alan

Ahhhh now I get ya!

[pikeymick]

http://www.kogswell.com/geo.php

I found this one, and I get what it's doing, but I'm missing data... I have head angle, and tire diameter, but I can't for the life of me find fork offset information.

[Alan F.]

I calculate the 550 NH has a 67.5mm fork offset...

And the 05 CBR1000rr has an offset of 25.75mm


With these numbers, if you're able to bolt the 05 CBR front end to the 550NH, you'd get 136.8mm of trail.
Maybe a front tire size change will be in order, maybe a rear size change too to get it back in the 104mm range.

I've got a few files that I'm unable to post here on the forums, the trail calculator I use, a tire size comparison spreadsheet, and a few others.
If anyone wants these files send me a PM and I'll try to send them out in the morning.  I'm heading off for the night.
-Alan

[tomsweb1]

"These bikes" as in CBs in general, or the 550s in particular?

I meant the 550 nighthawk. Never ridden any other, so I really can't say. The 550 was nimble, and very quick. I don't know how many times I pulled up the front wheel unintentionally in 2nd.
  Just wish it was still running.

[pikeymick]

I calculate the 550 NH has a 67.5mm fork offset...

And the 05 CBR1000rr has an offset of 25.75mm


With these numbers, if you're able to bolt the 05 CBR front end to the 550NH, you'd get 136.8mm of trail.
Maybe a front tire size change will be in order, maybe a rear size change too to get it back in the 104mm range.

I've got a few files that I'm unable to post here on the forums, the trail calculator I use, a tire size comparison spreadsheet, and a few others.
If anyone wants these files send me a PM and I'll try to send them out in the morning.  I'm heading off for the night.
-Alan

When you calculate the fork offset is it measured the same as the picture above this? 67.5mm seems really high. Roughing it with a tape measure on my bike its closer to 31.75... I wonder if we're measuring the same thing.

[Alan F.]

Fork offset is the distance between the centerlines of the fork tubes to the centerline of the steering stem bolt.

If I've calculated inaccurately it's because I used a program to do the work, instead of actually measuring the parts (which I don't have access to)

31.75mm offset on a 550NH?  my CB750K3 measures 1.805" (45.847mm) offset.  

(77-78 CB750's had a greater offset as well as the change from an 18" to a 17" rear wheel.)

EDIT: Things are a little different because you have 'LEADING AXLE FORKS', I was looking at the diagram below and this measurement will also come into play.
The diagram lists triple clamp offset and fork offset, I think you need to add these two up and maybe they'll be closer to 67.5mm.
-Alan

[Alan F.]

I've made a web page to allow access to the files and documents I've found useful in figuring out swaps like these.

Have a look and download whatever you like, or you can even run them online.

If anyone's got other files that would complement this collection, by all means send them to me and I'll add them asap.

http://sites.google.com/site/alansdocuments/

Cheers!
-Alan

[pikeymick]

Fork offset is the distance between the centerlines of the fork tubes to the centerline of the steering stem bolt.

If I've calculated inaccurately it's because I used a program to do the work, instead of actually measuring the parts (which I don't have access to)

31.75mm offset on a 550NH?  my CB750K3 measures 1.805" (45.847mm) offset.  

(77-78 CB750's had a greater offset as well as the change from an 18" to a 17" rear wheel.)

EDIT: Things are a little different because you have 'LEADING AXLE FORKS', I was looking at the diagram below and this measurement will also come into play.
The diagram lists triple clamp offset and fork offset, I think you need to add these two up and maybe they'll be closer to 67.5mm.
-Alan

Yeah 67.5 does look right with the differences between the fork tubes and stem, added to the offset at the leading axle from the fork centerline, but that being said the stock trail is good. The variable is what the trail will be with a new front end... I couldn't use the trail calculators, only mac's on this end.

As I read more and more online about this, there are a lot of different definitions for the same thing. Some call Head Angle the same as fork tube angle, some say fork rake is all you need, but then negate the rake from the triple trees vs. that of the head. I don't think I'm going to tackle this for a couple of months, #$%* the thing doesn't run reliably yet. haha

[Alan F.]

I know what you mean, I was really weirded out the first time I saw a rake angle of 63 degrees listed somewhere, it's actually 27 degrees, you just have to realize that it's figuring the angle from the ground and not 90 degrees vertical.

I've uploaded a bunch more files to that page of mine, some are pics and measurements, some are lists of compatible parts and what bikes they came on.

EBay is actually a pretty useful tool too, you can send messages to sellers asking them to measure a part for you, as them what the size stamped on a wheel is, or whatever, the more people you ask the question of, the more you can corelate the answers you get to prove the info is correct.  It's a great way to get good info without buying anything and without going to a junkyard to measure.

Tons of part manufacturers in the aftermarket will cross reference their parts to other bikes they fit, the DennisKirk web catalog has this function too, it's very useful to find all of the bikes a part fits, then go to craigslist or eBay or a local junkyard armed with this info to get the best pricing on parts you need.

Having plenty of time is very important, wanting to ride the darn thing will only get you into trouble, it's best to have something else to ride so that your project can progress naturally as time and money allow, and to stick to the plan regardless of what parts are still needed.
-Alan

[pikeymick]

Well the jets came in tonight, and I set the carbs back up and got them on, but now have no spark.... http://forums.sohc4.net/index.php?topic=59243.0

[pikeymick]

Ok I have some catching up to do. Got the spark back, the battery was pretty low and I think the starter must have been sapping all the juice.

The gap between the carbs and the intakes boots: The airbox is mounted all the way forward that it can go... and that gap persists despite this. With the new jets in I think I still may have carb problems... It idled briefly and didn't sound much different (tapping noise was gone, thank the spaghetti monster!!)

[Laminar]

What does your air filter look like?

I'm going by memory here, but you should be able to slide the carbs out of the carb-to-engine tubes a little bit and clamp them securely. It might give you just enough that you can clamp the carb-to-airbox boots onto the carbs.

[Alan F.]

on my 92 750 nighthawk (I don't know if it's a similar setup at all) I had to take out the airbox mounting screws to slide the airbox back to the rear as far as it would go before I could remove he carbs.
To get them back in I had to push the airbox foreward well past its mounting points to seat the air tubes onto the carb inlets, then once the airbox tubes were clamped to the carbs the airbox easily settled back a bit so that I could mount it to the frame again.  That airbox has plenty of give and stretch at the air tubes, I'd guess yours will too and you can make up the gap that way.

Hope maybe it helps.

[Alan F.]

OK, yeah not too different between the two, maybe pulling the airbox mounting screws first is the trick.

[pikeymick]

Ok those are good ideas I'll give them a go! Got her running this morning, started up as soon as it turned over, but only on 1&2.... 3&4 you suck, but not hard enough because you're not getting any gas.

I have compression, spark, and air. But no gas, which means tonight I get to clean the carbs, again, whoopppiiieee! I bought a cheap gas filter at the store going to throw that on there just to eliminate variables. I really hate the petcock on this bike. The suction thing is a good preventative feature, but a PIA when trying to fill empty bowls without turning it over (or sucking on the hose).

[Laminar]

Have you pulled the carbs apart and cleaned the gasoline passages between carbs?

[pikeymick]

I didn't separate the group, but sprayed carb cleaner through it until it looked like it was draining to each carb. I confirmed that each carb had gas by cracking the overflow drain.... I need to pick up a impact driver on the way home tonight, and separate them.

There is also the other conjoining thing between all the carbs (looks like a vent), or do you guys see that as a non-issue if it was cleaned out and carb cleaner moved through all of them?