'75 CB550K1 Gulf - Round...3, the fun stuff

Re: '75 CB550 Gulf - round two

Hey, that makes sense about the spring rate. I'll see about swapping springs.


Tyler, going back to your suggestion that the forks have too much damping. That got me thinking. Under 50mph, the forks like to pogo. Or I thought it was a pogo; it's more of vibration. Anyways, I've got insomnia tonight, so spent the last few hours digging up info about this, and found this interesting bit:

http://www.advrider.com/forums/showthread.php?t=609345

Exactly my situation, and post #3 really struck a chord with me.

You know how, during a ride, you can look down at the bike's shadow and watch the forks follow every little bump in the road, yet the bike stays still? Well I found myself noticing that my forks don't do that at speeds under 50. Basically I watched them not work, and remain rigid at slower speeds. It seems that I may have mistaken the harsh/bumpy ride as a lack of damping, when it was really just stiff as hell. Sound reasonable?
 
Re: '75 CB550 Gulf - round two

Well, as far as diagnosing and formulating a sensible plan, I think I've accomplished more tonight than I have in the past six months of just me half-heartedly thinking about the problem.

I owe you both both a beer or three.
 
Re: '75 CB550 Gulf - round two

Wow, very ineresting conversation, glad I read it. Makes me realize I need to be careful with what I plan to do to the front end on the GL when I rebuild it this or next year for sure.

Cheers guys and good luck figuring it out I'll be reading along.
 
Re: '75 CB550 Gulf - round two

Ringo said:
Hey, that makes sense about the spring rate. I'll see about swapping springs.


Tyler, going back to your suggestion that the forks have too much damping. That got me thinking. Under 50mph, the forks like to pogo. Or I thought it was a pogo; it's more of vibration. Anyways, I've got insomnia tonight, so spent the last few hours digging up info about this, and found this interesting bit:

http://www.advrider.com/forums/showthread.php?t=609345

Exactly my situation, and post #3 really struck a chord with me.

You know how, during a ride, you can look down at the bike's shadow and watch the forks follow every little bump in the road, yet the bike stays still? Well I found myself noticing that my forks don't do that at speeds under 50. Basically I watched them not work, and remain rigid at slower speeds. It seems that I may have mistaken the harsh/bumpy ride as a lack of damping, when it was really just stiff as hell. Sound reasonable?

That is good info, and nice to know someone else is having the same problem! I could see the really light weight of the bike coupled by the fact that you aren't a 400 pounder ( ;D) requiring a lot less for damping than a stock setup might. It might also be that RaceTech's recommendations are for a race-type application, and not as useable on the street. Either way, sounds like it might be a direction to take...
 
Re: '75 CB550 Gulf - round two

Have you tried playing with the tire pressures? Just to throw a whole 'nother wrench into the equation. From the sounds of this conversation you have the shocks too soft and the forks too stiff. I always liked a stiffer shock than forks and set my bikes up like that. I would be interested to find out what you come up with that makes this bike handle as good as should.
 
Re: '75 CB550 Gulf - round two

Yeah Travis I haven't played around too much with tire pressure. I've kept them fairly constant at the recommended pressure on the tire.

I will definitely keep a log of the changes and their effects. I think I have a pretty good baseline now.
 
Re: '75 CB550 Gulf - round two

Formulate a plan and change one thing at a time if possible - Not the way I do things, but how it's supposed to be done.

Sag and springs - rear first since that's all wrong and then forks
Fork Compression damping - oil weight and Emulators
Fork rebound damping - holes in the damper rods
Shock damping - if required
Brace swingarm to eliminate twist
Fine tune as required
Tire pressures - fine tuning to get 10-15% pressure rise from cold when ridden hard

Or go straight to 20mm cartridges from a later bike or move to R6/929/600RR forks or whichever set looks like the best fit at the best price.
 
Re: '75 CB550 Gulf - round two

If you decide on later forks, CBR F2/F3 (1994-1998) forks would be a great way to go. They're cartidge, but not USD, so they don't look out of place. They're also 41mm, so fork twist/flex wouldn't be an issue. They're also pretty resonably priced, and F2/F3 parts bikes are plentiful...
 
Re: '75 CB550 Gulf - round two

Thanks guys, I'll be staying with the original forks. This is a 37 year old bike, and despite all the stylization, I'd like it to still feel look firmly planted in the 70s.

As far as the plan is concerned, I'm going to drill another low-speed damping hole in each emulator and back out some preload on the valve springs. Keeping the 10w oil in the forks for now. For the rear, I'm going to call Dave Quinn up and ask about swapping springs...sounds like he might do it for free, or very little.
 
Re: '75 CB550 Gulf - round two

teazer said:
One trick I learned years ago to see if the suspension is balanced: Press down firmly and quickly above the center of gravity ie the rear of the tank. Both ends should dive and return at more or less the same rate. Often one end is more damped in compression or rebound or one end is sprung too hard. If that's the case, one end will drop or return faster than the other end.
Thank you for that ;)
 
Re: '75 CB550 Gulf - round two

Frustrating past couple of days. Two members on SOHC4 that I need parts from have gone awol. One guy makes a speedometer drive adapter plate that allows the use of the stock drive with a dual disc setup. Without his plate, I'll have to run an electronic speedo. Not thrilled. The other guy makes a phenolic brake piston...much lighter than stock. I have one already, but again for the dual disc setup, I'd like to keep the same type on the second disc. I finally have all the parts for a dual disc setup except these two.

Besides the useless complaining, I don't have much else to report. The belly pan plug is coming along, and parts are starting to show up...
 
Re: '75 CB550 Gulf - round two

Hey Ringo,
Been reading along as I also needed to change my suspension due to a Brembo Goldline 320 brake mod on my build.
I have real good feeling with a 15W oil and just 10cc more than advised.

Any comments on why to put the brace on top instead of at the bottom of the swingarm ?
I wan't to brace my CB500 as well, ( http://www.dotheton.com/forum/index.php?topic=33182.0 )

REAL BRACE
Foto-MH4JP7EU-D.jpg

SUBTILE BRACE
Foto-SPJGZXBP-D.jpg
 
Re: '75 CB550 Gulf - round two

Thanks yawlright.

Tetter, having the brace on the top or bottom doesn't seem to matter to me. However you can work it to clear the chain... Some benefits for a top mounted brace include easier mono-shock swap and the ability to easily mount a fender, which is why I was thinking of going that route.
 
Re: '75 CB550 Gulf - round two

I got a hold of Dave Quinn today and inquired about a spring swap for the Hagons. They'll do it for free if they can come up with a solution I'm happy with. I gave then the info from teazer about too soft/too much preload, and they seemed to think they gave me shocks with a heavy damping body, not the medium that they were supposed to come with. Either way, the length can't be reduced on the springs, but they do have stiffer. We will see.

So that's the good(ish) news, the bad news is I messed up my back pretty bad lifting the bike to swap shocks. And I'm not in the slightest bit surprised; it's what I get for being in a hurry. ::) I can hardly move now! At least it's a strain, not a sprain though.
 
Re: '75 CB550 Gulf - round two

Another twist: I decided to take the shocks apart before I send them to DQ, and found that one of them isn't working properly. Awful hard to compress and really slow to rebound, compared to the other. That might be my sag problem right there. The springs don't seem overly preloaded; they're about a half inch longer than when on the shock, and with my weight I can compress them about an inch, maybe less. So they're still fairly stiff...

With the shocks assembled, I still can't compress them that much, off the bike. I can live with stiff shocks...if they function properly. I actually prefer stiffness.
 
Re: '75 CB550 Gulf - round two

One last little bit for the day...

Besides some very modest dabbling in welding mild steel, I don't work with metal. I needed a few heavy steel axle and engine mount spacers recreated in aluminum, along with some lightening of my top triple and sprocket cover. Naturally, I chose a highly talented machinist and forum member to work his magic: Swagger. He's been sending me regular updates, and I have to say I'm more giddy than a horny Asian school girl at a Justin Bieber concert. Stay tuned for some seriously cool, completely one-of-a-kind work!
 
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