CBX 82 project

[Theggi]

Little crack in the rear upper engine mount

[NobleHops]

NOW it’s an adventure, but we always knew it would be. That is 100% weldable by a very good TIG welder, that’s the good news. The potentially bad news is that when we had a bike where that was busted (on the other side) it was because the frame was bent and so the engine had to be forced in there, which eventually busted the aluminum mounting boss.

Since that experience we made it standard to check bikes for straightness with a laser level before we got in deep, by leveling the frame at the seat and then putting a vertical laser line down the steering head and front wheel. When they’re bent, this makes it immediately obvious. I respectfully advise you to put the fork and wheel back on and do the same.

P.S. A bent frame is fixable where I am, but I don’t know where that might be done near you.

N.

[NobleHops]

Like so. Thought I had a better photo, but when this line was extended down to the tire it was very obvious that the bike was bent, which was confirmed at the frame straightening shop in Phoenix. You do this with the frame shimmed to be dead level at the seat.

1400C76A-73B2-40B5-A938-14668E3205CA.jpeg

N.

[Theggi]

NOW it’s an adventure, but we always knew it would be. That is 100% weldable by a very good TIG welder, that’s the good news. The potentially bad news is that when we had a bike where that was busted (on the other side) it was because the frame was bent and so the engine had to be forced in there, which eventually busted the aluminum mounting boss.

Since that experience we made it standard to check bikes for straightness with a laser level before we got in deep, by leveling the frame at the seat and then putting a vertical laser line down the steering head and front wheel. When they’re bent, this makes it immediately obvious. I respectfully advise you to put the fork and wheel back on and do the same.

P.S. A bent frame is fixable where I am, but I don’t know where that might be done near you.

N.

The bike is old, so anything could have happened. But it just seems to be very solid and maybe a collision or so is needed for the frame to be bent? or maybe too much torque on the bolts.. I will try your lazer trick ;) My neighbour is a welder, so i will let him take a look on it.

[Syscrush]

aaah, i didnt even thought of that. Good tip. I already ordered a new upper triple from top yoke. But i will try to find a calculator like you are speaking about and look into it. Thanks :)

Let me know if you have any problems finding a calculator or figuring out what's good for your setup. In general, the shorter forks will mean less rake and less trail, but the reduced offset will mean more trail, so you may end up with more or less trail than stock depending on how all of the numbers work out. IMO it's worth running the numbers and setting reasonable targets, so you have an idea of what to expect.

For reference:
A stock CBX has 27.5° of rake and 120mm of trail.
A (modern) CB1100 has 27° / 114mm.
A CB550 has 26° / 105 mm.
A Bandit 1200 has 25.2°/ 104mm.
A Hayabusa has 24.2° / 97mm.

Both the CB550 and Bandit 1200 are considered nimble naked bikes, and they have very similar geometry (despite being made decades apart). Based on that, I took about 1-1.5° of rake out of the bike (by raising the rear and running a slightly smaller dia front tire), and added offset to reduce the trail to about 110mm. I didn't want to go to radical sportbike geometry, or risk overwhelming the frame (which I have not braced).

With wide Superbike bend LSL bars, my bike turns in and transitions similarly to the target bikes: a Bandit, CB, or Ducati Monster. It's not nearly as aggressive as something like a CBR600RR, but it's definitely more nimble than it was before.

Custom triples are NOT NECESSARY for doing a front end swap and getting a nice, rideable bike - lots of people have proven this to be true. The shorter forks will reduce your rake quite a bit, which will mitigate the way the smaller offset increases your trail. However, I just wanted to mention it so that you're making an informed choice.

[AshishNJ]

Good knowledge here. If I may ask, with a different trail while using modern forks , how would a shorter wheelbase affect the riding ?

[Syscrush]

Shorter wheelbase doesn't affect static geometry, but it does make for faster changes in dynamic geometry as the bike will pitch forward or backwards more than a longer-wheelbase bike with the same weight and spring rates. Both the shorter wheelbase on its own, and its effect on dynamically reducing both rake and trail when braking into a turn will mean a shorter bike turns in better.

A longer bike is a bit more stable especially for 2-up highway cruising.

[bobcat]

aaah, i didnt even thought of that. Good tip. I already ordered a new upper triple from top yoke. But i will try to find a calculator like you are speaking about and look into it. Thanks :)

Let me know if you have any problems finding a calculator or figuring out what's good for your setup. In general, the shorter forks will mean less rake and less trail, but the reduced offset will mean more trail, so you may end up with more or less trail than stock depending on how all of the numbers work out. IMO it's worth running the numbers and setting reasonable targets, so you have an idea of what to expect.

For reference:
A stock CBX has 27.5° of rake and 120mm of trail.
A (modern) CB1100 has 27° / 114mm.
A CB550 has 26° / 105 mm.
A Bandit 1200 has 25.2°/ 104mm.
A Hayabusa has 24.2° / 97mm.

Both the CB550 and Bandit 1200 are considered nimble naked bikes, and they have very similar geometry (despite being made decades apart). Based on that, I took about 1-1.5° of rake out of the bike (by raising the rear and running a slightly smaller dia front tire), and added offset to reduce the trail to about 110mm. I didn't want to go to radical sportbike geometry, or risk overwhelming the frame (which I have not braced).

With wide Superbike bend LSL bars, my bike turns in and transitions similarly to the target bikes: a Bandit, CB, or Ducati Monster. It's not nearly as aggressive as something like a CBR600RR, but it's definitely more nimble than it was before.

Custom triples are NOT NECESSARY for doing a front end swap and getting a nice, rideable bike - lots of people have proven this to be true. The shorter forks will reduce your rake quite a bit, which will mitigate the way the smaller offset increases your trail. However, I just wanted to mention it so that you're making an informed choice.

I'm reading this with a great deal of interest ! I am using a complete front suspension from
an 04 CBR1000RR. The triples have very little offset compared to the 81 Pro Link and I'm not
sure what I'll end up with. (17" wheels).

[wyly]

Shorter wheelbase doesn't affect static geometry, but it does make for faster changes in dynamic geometry as the bike will pitch forward or backwards more than a longer-wheelbase bike with the same weight and spring rates. Both the shorter wheelbase on its own, and its effect on dynamically reducing both rake and trail when braking into a turn will mean a shorter bike turns in better.

A longer bike is a bit more stable especially for 2-up highway cruising.

My longer GS1000 swing-arm gave me a more stable ride, the smaller Bol d'Or 18" front wheel may have countered some of that. Feels okay for my riding style and was given the thumbs up by my WSBK mechanic on a test ride. My suspensions modifications were mild, I'd be much more cautious if I went with 17' wheels, inverted forks and single sided swing arm, I'd let the WSBK tuner handle those calculations.

[Theggi]

aaah, i didnt even thought of that. Good tip. I already ordered a new upper triple from top yoke. But i will try to find a calculator like you are speaking about and look into it. Thanks :)

Let me know if you have any problems finding a calculator or figuring out what's good for your setup. In general, the shorter forks will mean less rake and less trail, but the reduced offset will mean more trail, so you may end up with more or less trail than stock depending on how all of the numbers work out. IMO it's worth running the numbers and setting reasonable targets, so you have an idea of what to expect.

For reference:
A stock CBX has 27.5° of rake and 120mm of trail.
A (modern) CB1100 has 27° / 114mm.
A CB550 has 26° / 105 mm.
A Bandit 1200 has 25.2°/ 104mm.
A Hayabusa has 24.2° / 97mm.

Both the CB550 and Bandit 1200 are considered nimble naked bikes, and they have very similar geometry (despite being made decades apart). Based on that, I took about 1-1.5° of rake out of the bike (by raising the rear and running a slightly smaller dia front tire), and added offset to reduce the trail to about 110mm. I didn't want to go to radical sportbike geometry, or risk overwhelming the frame (which I have not braced).

With wide Superbike bend LSL bars, my bike turns in and transitions similarly to the target bikes: a Bandit, CB, or Ducati Monster. It's not nearly as aggressive as something like a CBR600RR, but it's definitely more nimble than it was before.

Custom triples are NOT NECESSARY for doing a front end swap and getting a nice, rideable bike - lots of people have proven this to be true. The shorter forks will reduce your rake quite a bit, which will mitigate the way the smaller offset increases your trail. However, I just wanted to mention it so that you're making an informed choice.

I see. Thanks for this good info. I havent been thinking of this for a second, but i understand what you are saying. I see they take alot of money for those triple trees with custom offset. With your numbers my wheel now comes nearer to the engine and that can me the steering more quicker and unstable with sharper response? I look up my previous bike, a BMW s1000r and see it got almost the same numbers as the Hayabusa. Since a havent ride this CBX at all i cant compare it from how it was when im finish But a steering damper would seem to be a smart thing.

[wyly]

Steering damper is probably a good idea. I don't know if "82 had a high speed wobble but I experienced it on the '79 before I made modifications.

[NobleHops]

I’ve never experienced a hint of bad behavior along those lines from my own ‘82, although it has an aftermaket (Ikon) shock in the rear and RaceTech stuff up front. The only oddness is a wallow at fairly high (80ish) speed turns that, while annoying, never increases. Different than head shake.

[bikeymikey748]

I’ve got GSXR 1000 forks and swingarm (same bits as on ‘Busas I believe). Forks are much shorter though solutions exist if you determine that to be an issue for you
http://www.extremecreations.com.au/fork ... -50mm-75mm
In my own case, I have to be mindful of dragging my exhaust collector if I get frisky in RH turns.
The swing arm is longer than the Pro-Link bit, and acts to slow the steering down.
Sorry, I didn’t take notes so I can’t tell you the actual differences lengthwise.
I’ve a steering damper installed, but figure it’s a superfluous addition.
I have never ridden a more stable and forgiving bike. Road irregularities that would have induced all manner of weave/wobble in my Ducati/CBR/SR pass all but unnoticed under the wheels of the Blob. It can’t be made to misbehave no matter how fast you ride either. As well, it can be hustled through corners without working up a sweat, it’s not like you’re on a barge.
I think you will be happy with the results when all is said and done.

[Syscrush]

The only oddness is a wallow at fairly high (80ish) speed turns that, while annoying, never increases. Different than head shake.

I suspect that has much more to do with spring rates and damping than with geometry.

[Syscrush]

I have never ridden a more stable and forgiving bike. Road irregularities that would have induced all manner of weave/wobble in my Ducati/CBR/SR pass all but unnoticed under the wheels of the Blob. It can’t be made to misbehave no matter how fast you ride either. As well, it can be hustled through corners without working up a sweat, it’s not like you’re on a barge.
I think you will be happy with the results when all is said and done.

Your experience is why I always add an asterisk when advising people to consider custom triples to dial in the geometry.