Frame/chassis.

[MEHall]

I've heard here it says the frame/chassis is poor/weak but in what way is it poor/weak?
If it is so I have an idea to get a better frame/chassis, so therefore I wonder what frame/chassis is the easiest to use for some customisation so the engine can fit.
In other words what frames/ chassis can hold the cb650 engine without to much customisation?
Any ideas and information is greatly appreciated.

[Volker_P]

I've heard here it says the frame/chassis is poor/weak but in what way is it poor/weak?

- fork tube diameter too small
- fork springs too soft
- steering angle too flat
- frame too weak (poor stiffness)
- rear suspension too soft
- poor declination angle
- long wheelbase

probably still incomplete.

The correct procedure is called "Buber tuning"

[MEHall]

That the springs are to soft I've noticed so my idea was to use a better frame/chassis. What I need to know then, is what frame/chassis I can use instead without to much modification.

[Volker_P]

Well, for a reasonable chassis you would need some mid 90's bike.
This bike will typically come with a reasonable stock engine with more power and a better low rpm torque characteristics than a CB650 engine.

So no real reason to try that and so you might be the first one.

Which again might be a reason to try it.

[MEHall]

Sorry, but in economical aspect younger than 80's bikes is no option to me as you need to pay taxes every year for them. Bikes older than 1980 is free from motor vehicle tax. And I believe the insurance may be to high for me also. Sweden is a bit expensive country to own big cc bikes and the rate goes up with higher effect also. The 650cc engine is as, I think, just the right size, maybe not the best engine though but It dont matter to much for me.
The idea I got is to find any frame that could use the 650cc engine without to much modification and be old enough to be free from vehicle tax.
The only dilemma I have is that I dont know what can fit where when it comes to this.
It's not to important tho but it would be fun to know.

[Volker_P]

Now I see your reasons and boundary conditions.
I really doubt that one finds anything before 1980 that can carry a CB650 engine and has significant better stock chassis properties. After the CB750 shock of 1969 one could think they just developed engines and build "something" around them for some time. At least for the heavier bikes.

So this is what I have done:
- Progressive fork springs (rated 10% stronger)
- 15W fork oil. (ATF is supposed to be about 7.5W)
- Stainless steel braid brake lines.
- About 7mm support rings for about 2 steps more precompression on the stock rear shocks. I was told Konis don't make a real difference but did not try it our myself.
- Modern type tyres. Especially rear makes the difference.

All this is quite cheap and in summary gives a considerable improvement.

A bracer connecting the fork legs might be still worth a try, too.
For now I don't see any further, cheap options beyond that.

And: after all it is the rider, not the bike!

[MEHall]

Ok I see. It was just an idea I had, not that I think the cb650 is to bad as I dont drive it too hard. I'll try with something else instead.

[MiGhost]

If I am understanding you correctly. You are trying to fit the 650 engine into some frame before 1980.

The 650 engine is a direct bolt in on the pre '78 cb550 frame, but once again you will be looking at renforcing the frame for better strength. Better springs for the suspension. A fork brace to stiffen up the front end. Most of the typical modifications that are made when a bike is built up as a cafe racer style bike.

Ghost